Librados (C)

Librados (C)

librados provides low-level access to the RADOS service. For anoverview of RADOS, see Architecture.

Example: connecting and writing an object

To use Librados, you instantiate a rados_t variable (a cluster handle) andcall rados_create() with a pointer to it:

int err;
rados_t cluster;
 
err = rados_create(&cluster, NULL);
if (err < 0) {
        fprintf(stderr, "%s: cannot create a cluster handle: %s\n", argv[0], strerror(-err));
        exit(1);
}

Then you configure your rados_t to connect to your cluster,either by setting individual values (rados_conf_set()),using a configuration file (rados_conf_read_file()), usingcommand line options (rados_conf_parse_argv()), or anenvironment variable (rados_conf_parse_env()):

err = rados_conf_read_file(cluster, "/path/to/myceph.conf");
if (err < 0) {
        fprintf(stderr, "%s: cannot read config file: %s\n", argv[0], strerror(-err));
        exit(1);
}

Once the cluster handle is configured, you can connect to the cluster with rados_connect():

err = rados_connect(cluster);
if (err < 0) {
        fprintf(stderr, "%s: cannot connect to cluster: %s\n", argv[0], strerror(-err));
        exit(1);
}

Then you open an “IO context”, a rados_ioctx_t, with rados_ioctx_create():

rados_ioctx_t io;
char *poolname = "mypool";
 
err = rados_ioctx_create(cluster, poolname, &io);
if (err < 0) {
        fprintf(stderr, "%s: cannot open rados pool %s: %s\n", argv[0], poolname, strerror(-err));
        rados_shutdown(cluster);
        exit(1);
}

Note that the pool you try to access must exist.

Then you can use the RADOS data manipulation functions, for examplewrite into an object called greeting withrados_write_full():

err = rados_write_full(io, "greeting", "hello", 5);
if (err < 0) {
        fprintf(stderr, "%s: cannot write pool %s: %s\n", argv[0], poolname, strerror(-err));
        rados_ioctx_destroy(io);
        rados_shutdown(cluster);
        exit(1);
}

In the end, you will want to close your IO context and connection to RADOS with rados_ioctx_destroy() and rados_shutdown():

rados_ioctx_destroy(io);
rados_shutdown(cluster);

Asynchronous IO

When doing lots of IO, you often don’t need to wait for one operationto complete before starting the next one. Librados providesasynchronous versions of several operations:

For each operation, you must first create arados_completion_t that represents what to do when theoperation is safe or complete by callingrados_aio_create_completion(). If you don’t need anythingspecial to happen, you can pass NULL:

rados_completion_t comp;
err = rados_aio_create_completion(NULL, NULL, NULL, &comp);
if (err < 0) {
        fprintf(stderr, "%s: could not create aio completion: %s\n", argv[0], strerror(-err));
        rados_ioctx_destroy(io);
        rados_shutdown(cluster);
        exit(1);
}

Now you can call any of the aio operations, and wait for it tobe in memory or on disk on all replicas:

err = rados_aio_write(io, "foo", comp, "bar", 3, 0);
if (err < 0) {
        fprintf(stderr, "%s: could not schedule aio write: %s\n", argv[0], strerror(-err));
        rados_aio_release(comp);
        rados_ioctx_destroy(io);
        rados_shutdown(cluster);
        exit(1);
}
rados_aio_wait_for_complete(comp); // in memory
rados_aio_wait_for_safe(comp); // on disk

Finally, we need to free the memory used by the completion with rados_aio_release():

rados_aio_release(comp);

You can use the callbacks to tell your application when writes aredurable, or when read buffers are full. For example, if you wanted tomeasure the latency of each operation when appending to severalobjects, you could schedule several writes and store the ack andcommit time in the corresponding callback, then wait for all of themto complete using rados_aio_flush() before analyzing thelatencies:

typedef struct {
        struct timeval start;
        struct timeval ack_end;
        struct timeval commit_end;
} req_duration;
 
void ack_callback(rados_completion_t comp, void *arg) {
        req_duration *dur = (req_duration *) arg;
        gettimeofday(&dur->ack_end, NULL);
}
 
void commit_callback(rados_completion_t comp, void *arg) {
        req_duration *dur = (req_duration *) arg;
        gettimeofday(&dur->commit_end, NULL);
}
 
int output_append_latency(rados_ioctx_t io, const char *data, size_t len, size_t num_writes) {
        req_duration times[num_writes];
        rados_completion_t comps[num_writes];
        for (size_t i = 0; i < num_writes; ++i) {
                gettimeofday(&times[i].start, NULL);
                int err = rados_aio_create_completion((void*) &times[i], ack_callback, commit_callback, &comps[i]);
                if (err < 0) {
                        fprintf(stderr, "Error creating rados completion: %s\n", strerror(-err));
                        return err;
                }
                char obj_name[100];
                snprintf(obj_name, sizeof(obj_name), "foo%ld", (unsigned long)i);
                err = rados_aio_append(io, obj_name, comps[i], data, len);
                if (err < 0) {
                        fprintf(stderr, "Error from rados_aio_append: %s", strerror(-err));
                        return err;
                }
        }
        // wait until all requests finish *and* the callbacks complete
        rados_aio_flush(io);
        // the latencies can now be analyzed
        printf("Request # | Ack latency (s) | Commit latency (s)\n");
        for (size_t i = 0; i < num_writes; ++i) {
                // don't forget to free the completions
                rados_aio_release(comps[i]);
                struct timeval ack_lat, commit_lat;
                timersub(&times[i].ack_end, &times[i].start, &ack_lat);
                timersub(&times[i].commit_end, &times[i].start, &commit_lat);
                printf("%9ld | %8ld.%06ld | %10ld.%06ld\n", (unsigned long) i, ack_lat.tv_sec, ack_lat.tv_usec, commit_lat.tv_sec, commit_lat.tv_usec);
        }
        return 0;
}

Note that all the rados_completion_t must be freed with rados_aio_release() to avoid leaking memory.

API calls

Defines
LIBRADOSALL_NSPACES
Pass as nspace argument to rados_ioctx_set_namespace() before calling rados_nobjects_list_open() to return all objects in all namespaces.
struct obj_watch_t
#include <rados_types.h>
One item from list_watchers
Public Members
char obj_watch_t::addr[256]
Address of the Watcher.
int64_t watcher_id
Watcher ID.
uint64_t cookie
Cookie.
uint32_t timeout_seconds
Timeout in Seconds.
xattr comparison operations
Operators for comparing xattrs on objects, and aborting the rados_read_op or rados_write_op transaction if the comparison fails.
@anon_1
Values:
1
2
3
4
5
6
Operation Flags
Flags for rados_read_op_operate(), rados_write_op_operate(), rados_aio_read_op_operate(), and rados_aio_write_op_operate(). See librados.hpp for details.
@anon_2
Values:
0
1
2
4
8
16
32
64
128
256
512
1024
Alloc hint flags
Flags for rados_write_op_alloc_hint2() and rados_set_alloc_hint2() indicating future IO patterns.
@anon_3
Values:
1
2
4
8
16
32
64
128
256
512
Asynchronous I/O
Read and write to objects without blocking.
typedef rados_callback_t
Callbacks for asynchrous operations take two parameters:
cb the completion that has finished
arg application defined data made available to the callback function
CEPH_RADOS_API int rados_aio_create_completion(void cb_arg, rados_callback_t cb_complete, rados_callback_t cb_safe, rados_completion_t pc)
Constructs a completion to use with asynchronous operations
The complete and safe callbacks correspond to operations being acked and committed, respectively. The callbacks are called in order of receipt, so the safe callback may be triggered before the complete callback, and vice versa. This is affected by journalling on the OSDs.
TODO: more complete documentation of this elsewhere (in the RADOS docs?)
Note
Read operations only get a complete callback.
Note
BUG: this should check for ENOMEM instead of throwing an exception
Return
0
Parameters
cb_arg: application-defined data passed to the callback functions
cb_complete: the function to be called when the operation is in memory on all replicas
cb_safe: the function to be called when the operation is on stable storage on all replicas
pc: where to store the completion
CEPH_RADOS_API int rados_aio_create_completion2(void cb_arg, rados_callback_t cb_complete, rados_completion_t pc)
Constructs a completion to use with asynchronous operations
The complete callback corresponds to operation being acked.
Note
BUG: this should check for ENOMEM instead of throwing an exception
Return
0
Parameters
cb_arg: application-defined data passed to the callback functions
cb_complete: the function to be called when the operation is committed on all replicas
pc: where to store the completion
CEPH_RADOS_API int rados_aio_wait_for_complete(rados_completion_t c)
Block until an operation completes
This means it is in memory on all replicas.
Note
BUG: this should be void
Return
0
Parameters
c: operation to wait for
CEPH_RADOS_API int rados_aio_wait_for_safe(rados_completion_t c)
Block until an operation is safe
This means it is on stable storage on all replicas.
Note
BUG: this should be void
Return
0
Parameters
c: operation to wait for
CEPH_RADOS_API int rados_aio_is_complete(rados_completion_t c)
Has an asynchronous operation completed?
Warning
This does not imply that the complete callback has finished
Return
whether c is complete
Parameters
c: async operation to inspect
CEPH_RADOS_API int rados_aio_is_safe(rados_completion_t c)
Is an asynchronous operation safe?
Warning
This does not imply that the safe callback has finished
Return
whether c is safe
Parameters
c: async operation to inspect
CEPH_RADOS_API int rados_aio_wait_for_complete_and_cb(rados_completion_t c)
Block until an operation completes and callback completes
This means it is in memory on all replicas and can be read.
Note
BUG: this should be void
Return
0
Parameters
c: operation to wait for
CEPH_RADOS_API int rados_aio_wait_for_safe_and_cb(rados_completion_t c)
Block until an operation is safe and callback has completed
This means it is on stable storage on all replicas.
Note
BUG: this should be void
Return
0
Parameters
c: operation to wait for
CEPH_RADOS_API int rados_aio_is_complete_and_cb(rados_completion_t c)
Has an asynchronous operation and callback completed
Return
whether c is complete
Parameters
c: async operation to inspect
CEPH_RADOS_API int rados_aio_is_safe_and_cb(rados_completion_t c)
Is an asynchronous operation safe and has the callback completed
Return
whether c is safe
Parameters
c: async operation to inspect
CEPH_RADOS_API int rados_aio_get_return_value(rados_completion_t c)
Get the return value of an asychronous operation
The return value is set when the operation is complete or safe, whichever comes first.
Pre
The operation is safe or complete
Note
BUG: complete callback may never be called when the safe message is received before the complete message
Return
return value of the operation
Parameters
c: async operation to inspect
CEPH_RADOS_API uint64_t rados_aio_get_version(rados_completion_t c)
Get the internal object version of the target of an asychronous operation
The return value is set when the operation is complete or safe, whichever comes first.
Pre
The operation is safe or complete
Note
BUG: complete callback may never be called when the safe message is received before the complete message
Return
version number of the asychronous operation’s target
Parameters
c: async operation to inspect
CEPH_RADOS_API void rados_aio_release(rados_completion_t c)
Release a completion
Call this when you no longer need the completion. It may not be freed immediately if the operation is not acked and committed.
Parameters
c: completion to release
CEPH_RADOS_API int rados_aio_write(rados_ioctx_t io, const char oid, rados_completion_t completion, const char buf, size_t len, uint64_t off)
Write data to an object asynchronously
Queues the write and returns. The return value of the completion will be 0 on success, negative error code on failure.
Return
0 on success, -EROFS if the io context specifies a snap_seq other than LIBRADOS_SNAP_HEAD
Parameters
io: the context in which the write will occur
oid: name of the object
completion: what to do when the write is safe and complete
buf: data to write
len: length of the data, in bytes
off: byte offset in the object to begin writing at
CEPH_RADOS_API int rados_aio_append(rados_ioctx_t io, const char oid, rados_completion_t completion, const char buf, size_t len)
Asynchronously append data to an object
Queues the append and returns.
The return value of the completion will be 0 on success, negative error code on failure.
Return
0 on success, -EROFS if the io context specifies a snap_seq other than LIBRADOS_SNAP_HEAD
Parameters
io: the context to operate in
oid: the name of the object
completion: what to do when the append is safe and complete
buf: the data to append
len: length of buf (in bytes)
CEPH_RADOS_API int rados_aio_write_full(rados_ioctx_t io, const char oid, rados_completion_t completion, const char buf, size_t len)
Asynchronously write an entire object
The object is filled with the provided data. If the object exists, it is atomically truncated and then written. Queues the write_full and returns.
The return value of the completion will be 0 on success, negative error code on failure.
Return
0 on success, -EROFS if the io context specifies a snap_seq other than LIBRADOS_SNAP_HEAD
Parameters
io: the io context in which the write will occur
oid: name of the object
completion: what to do when the write_full is safe and complete
buf: data to write
len: length of the data, in bytes
CEPH_RADOS_API int rados_aio_writesame(rados_ioctx_t io, const char oid, rados_completion_t completion, const char buf, size_t data_len, size_t write_len, uint64_t off)
Asynchronously write the same buffer multiple times
Queues the writesame and returns.
The return value of the completion will be 0 on success, negative error code on failure.
Return
0 on success, -EROFS if the io context specifies a snap_seq other than LIBRADOS_SNAP_HEAD
Parameters
io: the io context in which the write will occur
oid: name of the object
completion: what to do when the writesame is safe and complete
buf: data to write
data_len: length of the data, in bytes
write_len: the total number of bytes to write
off: byte offset in the object to begin writing at
CEPH_RADOS_API int rados_aio_remove(rados_ioctx_t io, const char oid, rados_completion_t completion)
Asynchronously remove an object
Queues the remove and returns.
The return value of the completion will be 0 on success, negative error code on failure.
Return
0 on success, -EROFS if the io context specifies a snap_seq other than LIBRADOS_SNAP_HEAD
Parameters
io: the context to operate in
oid: the name of the object
completion: what to do when the remove is safe and complete
CEPH_RADOS_API int rados_aio_read(rados_ioctx_t io, const char oid, rados_completion_t completion, char buf, size_t len, uint64_t off)
Asynchronously read data from an object
The io context determines the snapshot to read from, if any was set by rados_ioctx_snap_set_read().
The return value of the completion will be number of bytes read on success, negative error code on failure.
Note
only the ‘complete’ callback of the completion will be called.
Return
0 on success, negative error code on failure
Parameters
io: the context in which to perform the read
oid: the name of the object to read from
completion: what to do when the read is complete
buf: where to store the results
len: the number of bytes to read
off: the offset to start reading from in the object
CEPH_RADOS_API int rados_aio_flush(rados_ioctx_t io)
Block until all pending writes in an io context are safe
This is not equivalent to calling rados_aio_wait_for_safe() on all write completions, since this waits for the associated callbacks to complete as well.
Note
BUG: always returns 0, should be void or accept a timeout
Return
0 on success, negative error code on failure
Parameters
io: the context to flush
CEPH_RADOS_API int rados_aio_flush_async(rados_ioctx_t io, rados_completion_t completion)
Schedule a callback for when all currently pending aio writes are safe. This is a non-blocking version of rados_aio_flush().
Return
0 on success, negative error code on failure
Parameters
io: the context to flush
completion: what to do when the writes are safe
CEPH_RADOS_API int rados_aio_stat(rados_ioctx_t io, const char o, rados_completion_t completion, uint64_t psize, time_t pmtime)
Asynchronously get object stats (size/mtime)
Return
0 on success, negative error code on failure
Parameters
io: ioctx
o: object name
completion: what to do when the stat is complete
psize: where to store object size
pmtime: where to store modification time
CEPH_RADOS_API int rados_aio_cmpext(rados_ioctx_t io, const char o, rados_completion_t completion, const char cmp_buf, size_t cmp_len, uint64_t off)
Asynchronously compare an on-disk object range with a buffer
Return
0 on success, negative error code on failure, (-MAX_ERRNO - mismatch_off) on mismatch
Parameters
io: the context in which to perform the comparison
o: the name of the object to compare with
completion: what to do when the comparison is complete
cmp_buf: buffer containing bytes to be compared with object contents
cmp_len: length to compare and size of cmp_buf in bytes
off: object byte offset at which to start the comparison
CEPH_RADOS_API int rados_aio_cancel(rados_ioctx_t io, rados_completion_t completion)
Cancel async operation
Return
0 on success, negative error code on failure
Parameters
io: ioctx
completion: completion handle
CEPH_RADOS_API int rados_aio_exec(rados_ioctx_t io, const char o, rados_completion_t completion, const char cls, const char method, const char in_buf, size_t in_len, char buf, size_t out_len)
Asynchronously execute an OSD class method on an object
The OSD has a plugin mechanism for performing complicated operations on an object atomically. These plugins are called classes. This function allows librados users to call the custom methods. The input and output formats are defined by the class. Classes in ceph.git can be found in src/cls subdirectories
Return
0 on success, negative error code on failure
Parameters
io: the context in which to call the method
o: name of the object
completion: what to do when the exec completes
cls: the name of the class
method: the name of the method
in_buf: where to find input
in_len: length of in_buf in bytes
buf: where to store output
out_len: length of buf in bytes
Watch/Notify
Watch/notify is a protocol to help communicate among clients. It can be used to sychronize client state. All that’s needed is a well-known object name (for example, rbd uses the header object of an image).
Watchers register an interest in an object, and receive all notifies on that object. A notify attempts to communicate with all clients watching an object, and blocks on the notifier until each client responds or a timeout is reached.
See rados_watch() and rados_notify() for more details.
typedef rados_watchcb_t
Callback activated when a notify is received on a watched object.
Note
BUG: opcode is an internal detail that shouldn’t be exposed
Note
BUG: ver is unused
Parameters
opcode: undefined
ver: version of the watched object
arg: application-specific data
typedef rados_watchcb2_t
Callback activated when a notify is received on a watched object.
Parameters
arg: opaque user-defined value provided to rados_watch2()
notify_id: an id for this notify event
handle: the watcher handle we are notifying
notifier_id: the unique client id for the notifier
data: payload from the notifier
datalen: length of payload buffer
typedef rados_watcherrcb_t
Callback activated when we encounter an error with the watch session. This can happen when the location of the objects moves within the cluster and we fail to register our watch with the new object location, or when our connection with the object OSD is otherwise interrupted and we may have missed notify events.
Parameters
pre: opaque user-defined value provided to rados_watch2()
err: error code
CEPH_RADOS_API int rados_watch(rados_ioctx_t io, const char o, uint64_t ver, uint64_t cookie, rados_watchcb_t watchcb, void arg)
Register an interest in an object
A watch operation registers the client as being interested in notifications on an object. OSDs keep track of watches on persistent storage, so they are preserved across cluster changes by the normal recovery process. If the client loses its connection to the primary OSD for a watched object, the watch will be removed after 30 seconds. Watches are automatically reestablished when a new connection is made, or a placement group switches OSDs.
Note
BUG: librados should provide a way for watchers to notice connection resets
Note
BUG: the ver parameter does not work, and -ERANGE will never be returned (See URL tracker.ceph.com/issues/2592)
Return
0 on success, negative error code on failure
Return
-ERANGE if the version of the object is greater than ver
Parameters
io: the pool the object is in
o: the object to watch
ver: expected version of the object
cookie: where to store the internal id assigned to this watch
watchcb: what to do when a notify is received on this object
arg: application defined data to pass when watchcb is called
CEPH_RADOS_API int rados_watch2(rados_ioctx_t io, const char o, uint64_t cookie, rados_watchcb2_t watchcb, rados_watcherrcb_t watcherrcb, void arg)
Register an interest in an object
A watch operation registers the client as being interested in notifications on an object. OSDs keep track of watches on persistent storage, so they are preserved across cluster changes by the normal recovery process. If the client loses its connection to the primary OSD for a watched object, the watch will be removed after a timeout configured with osd_client_watch_timeout. Watches are automatically reestablished when a new connection is made, or a placement group switches OSDs.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the object to watch
cookie: where to store the internal id assigned to this watch
watchcb: what to do when a notify is received on this object
watcherrcb: what to do when the watch session encounters an error
arg: opaque value to pass to the callback
CEPH_RADOS_API int rados_watch3(rados_ioctx_t io, const char o, uint64_t cookie, rados_watchcb2_t watchcb, rados_watcherrcb_t watcherrcb, uint32_t timeout, void arg)
Register an interest in an object
A watch operation registers the client as being interested in notifications on an object. OSDs keep track of watches on persistent storage, so they are preserved across cluster changes by the normal recovery process. Watches are automatically reestablished when a new connection is made, or a placement group switches OSDs.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the object to watch
cookie: where to store the internal id assigned to this watch
watchcb: what to do when a notify is received on this object
watcherrcb: what to do when the watch session encounters an error
timeout: how many seconds the connection will keep after disconnection
arg: opaque value to pass to the callback
CEPH_RADOS_API int rados_aio_watch(rados_ioctx_t io, const char o, rados_completion_t completion, uint64_t handle, rados_watchcb2_t watchcb, rados_watcherrcb_t watcherrcb, void arg)
Asynchronous register an interest in an object
A watch operation registers the client as being interested in notifications on an object. OSDs keep track of watches on persistent storage, so they are preserved across cluster changes by the normal recovery process. If the client loses its connection to the primary OSD for a watched object, the watch will be removed after 30 seconds. Watches are automatically reestablished when a new connection is made, or a placement group switches OSDs.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the object to watch
completion: what to do when operation has been attempted
handle: where to store the internal id assigned to this watch
watchcb: what to do when a notify is received on this object
watcherrcb: what to do when the watch session encounters an error
arg: opaque value to pass to the callback
CEPH_RADOS_API int rados_aio_watch2(rados_ioctx_t io, const char o, rados_completion_t completion, uint64_t handle, rados_watchcb2_t watchcb, rados_watcherrcb_t watcherrcb, uint32_t timeout, void arg)
Asynchronous register an interest in an object
A watch operation registers the client as being interested in notifications on an object. OSDs keep track of watches on persistent storage, so they are preserved across cluster changes by the normal recovery process. If the client loses its connection to the primary OSD for a watched object, the watch will be removed after the number of seconds that configured in timeout parameter. Watches are automatically reestablished when a new connection is made, or a placement group switches OSDs.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the object to watch
completion: what to do when operation has been attempted
handle: where to store the internal id assigned to this watch
watchcb: what to do when a notify is received on this object
watcherrcb: what to do when the watch session encounters an error
timeout: how many seconds the connection will keep after disconnection
arg: opaque value to pass to the callback
CEPH_RADOS_API int rados_watch_check(rados_ioctx_t io, uint64_t cookie)
Check on the status of a watch
Return the number of milliseconds since the watch was last confirmed. Or, if there has been an error, return that.
If there is an error, the watch is no longer valid, and should be destroyed with rados_unwatch2(). The the user is still interested in the object, a new watch should be created with rados_watch2().
Return
ms since last confirmed on success, negative error code on failure
Parameters
io: the pool the object is in
cookie: the watch handle
CEPH_RADOS_API int rados_unwatch(rados_ioctx_t io, const char o, uint64_t cookie)
Unregister an interest in an object
Once this completes, no more notifies will be sent to us for this watch. This should be called to clean up unneeded watchers.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the name of the watched object (ignored)
cookie: which watch to unregister
CEPH_RADOS_API int rados_unwatch2(rados_ioctx_t io, uint64_t cookie)
Unregister an interest in an object
Once this completes, no more notifies will be sent to us for this watch. This should be called to clean up unneeded watchers.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
cookie: which watch to unregister
CEPH_RADOS_API int rados_aio_unwatch(rados_ioctx_t io, uint64_t cookie, rados_completion_t completion)
Asynchronous unregister an interest in an object
Once this completes, no more notifies will be sent to us for this watch. This should be called to clean up unneeded watchers.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
completion: what to do when operation has been attempted
cookie: which watch to unregister
CEPH_RADOS_API int rados_notify(rados_ioctx_t io, const char o, uint64_t ver, const char buf, int buf_len)
Sychronously notify watchers of an object
This blocks until all watchers of the object have received and reacted to the notify, or a timeout is reached.
Note
BUG: the timeout is not changeable via the C API
Note
BUG: the bufferlist is inaccessible in a rados_watchcb_t
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the name of the object
ver: obsolete - just pass zero
buf: data to send to watchers
buf_len: length of buf in bytes
CEPH_RADOS_API int rados_aio_notify(rados_ioctx_t io, const char o, rados_completion_t completion, const char buf, int buf_len, uint64_t timeout_ms, char ** reply_buffer, size_t reply_buffer_len)
Sychronously notify watchers of an object
This blocks until all watchers of the object have received and reacted to the notify, or a timeout is reached.
The reply buffer is optional. If specified, the client will get back an encoded buffer that includes the ids of the clients that acknowledged the notify as well as their notify ack payloads (if any). Clients that timed out are not included. Even clients that do not include a notify ack payload are included in the list but have a 0-length payload associated with them. The format:
le32 num_acks { le64 gid global id for the client (for client.1234 that’s 1234) le64 cookie cookie for the client le32 buflen length of reply message buffer u8 buflen payload } num_acks le32 num_timeouts { le64 gid global id for the client le64 cookie cookie for the client } num_timeouts
Note: There may be multiple instances of the same gid if there are multiple watchers registered via the same client.
Note: The buffer must be released with rados_buffer_free() when the user is done with it.
Note: Since the result buffer includes clients that time out, it will be set even when rados_notify() returns an error code (like -ETIMEDOUT).
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
completion: what to do when operation has been attempted
o: the name of the object
buf: data to send to watchers
buf_len: length of buf in bytes
timeout_ms: notify timeout (in ms)
reply_buffer: pointer to reply buffer pointer (free with rados_buffer_free)
reply_buffer_len: pointer to size of reply buffer
CEPH_RADOS_API int rados_notify2(rados_ioctx_t io, const char o, const char buf, int buf_len, uint64_t timeout_ms, char ** reply_buffer, size_t reply_buffer_len)
CEPH_RADOS_API int rados_notify_ack(rados_ioctx_t io, const char o, uint64_t notify_id, uint64_t cookie, const char buf, int buf_len)
Acknolwedge receipt of a notify
Return
0 on success
Parameters
io: the pool the object is in
o: the name of the object
notify_id: the notify_id we got on the watchcb2_t callback
cookie: the watcher handle
buf: payload to return to notifier (optional)
buf_len: payload length
CEPH_RADOS_API int rados_watch_flush(rados_t cluster)
Flush watch/notify callbacks
This call will block until all pending watch/notify callbacks have been executed and the queue is empty. It should usually be called after shutting down any watches before shutting down the ioctx or librados to ensure that any callbacks do not misuse the ioctx (for example by calling rados_notify_ack after the ioctx has been destroyed).
Parameters
cluster: the cluster handle
CEPH_RADOS_API int rados_aio_watch_flush(rados_t cluster, rados_completion_t completion)
Flush watch/notify callbacks
This call will be nonblock, and the completion will be called until all pending watch/notify callbacks have been executed and the queue is empty. It should usually be called after shutting down any watches before shutting down the ioctx or librados to ensure that any callbacks do not misuse the ioctx (for example by calling rados_notify_ack after the ioctx has been destroyed).
Parameters
cluster: the cluster handle
completion: what to do when operation has been attempted
Mon/OSD/PG Commands
These interfaces send commands relating to the monitor, OSD, or PGs.
typedef void( rados_log_callback_t)(void arg, const char line, const char who, uint64_t sec, uint64_t nsec, uint64_t seq, const char level, const char msg)
typedef void( rados_log_callback2_t)(void arg, const char line, const char channel, const char who, const char name, uint64_t sec, uint64_t nsec, uint64_t seq, const char level, const char msg)
CEPH_RADOS_API int rados_mon_command(rados_t cluster, const char cmd, size_t cmdlen, const char * inbuf, size_t inbuflen, char outbuf, size_t outbuflen, char ** outs, size_t outslen)
Send monitor command.
The result buffers are allocated on the heap; the caller is expected to release that memory with rados_buffer_free(). The buffer and length pointers can all be NULL, in which case they are not filled in.
Note
Takes command string in carefully-formatted JSON; must match defined commands, types, etc.
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle
cmd: an array of char ’s representing the command
cmdlen: count of valid entries in cmd
inbuf: any bulk input data (crush map, etc.)
inbuflen: input buffer length
outbuf: double pointer to output buffer
outbuflen: pointer to output buffer length
outs: double pointer to status string
outslen: pointer to status string length

CEPH_RADOS_API int rados_mgr_command(rados_t cluster, const char ** cmd, size_t cmdlen, const char inbuf, size_t inbuflen, char outbuf, size_t * outbuflen, char outs, size_t outslen)
Send ceph-mgr command.
The result buffers are allocated on the heap; the caller is expected to release that memory with rados_buffer_free(). The buffer and length pointers can all be NULL, in which case they are not filled in.
Note
Takes command string in carefully-formatted JSON; must match defined commands, types, etc.
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle
cmd: an array of char ’s representing the command
cmdlen: count of valid entries in cmd
inbuf: any bulk input data (crush map, etc.)
inbuflen: input buffer length
outbuf: double pointer to output buffer
outbuflen: pointer to output buffer length
outs: double pointer to status string
outslen: pointer to status string length
CEPH_RADOS_API int rados_mgr_command_target(rados_t cluster, const char name, const char ** cmd, size_t cmdlen, const char inbuf, size_t inbuflen, char outbuf, size_t * outbuflen, char outs, size_t outslen)
Send ceph-mgr tell command.
The result buffers are allocated on the heap; the caller is expected to release that memory with rados_buffer_free(). The buffer and length pointers can all be NULL, in which case they are not filled in.
Note
Takes command string in carefully-formatted JSON; must match defined commands, types, etc.
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle
name: mgr name to target
cmd: an array of char ’s representing the command
cmdlen: count of valid entries in cmd
inbuf: any bulk input data (crush map, etc.)
inbuflen: input buffer length
outbuf: double pointer to output buffer
outbuflen: pointer to output buffer length
outs: double pointer to status string
outslen: pointer to status string length
CEPH_RADOS_API int rados_mon_command_target(rados_t cluster, const char name, const char ** cmd, size_t cmdlen, const char inbuf, size_t inbuflen, char outbuf, size_t * outbuflen, char outs, size_t outslen)
Send monitor command to a specific monitor.
The result buffers are allocated on the heap; the caller is expected to release that memory with rados_buffer_free(). The buffer and length pointers can all be NULL, in which case they are not filled in.
Note
Takes command string in carefully-formatted JSON; must match defined commands, types, etc.
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle
name: target monitor’s name
cmd: an array of char ’s representing the command
cmdlen: count of valid entries in cmd
inbuf: any bulk input data (crush map, etc.)
inbuflen: input buffer length
outbuf: double pointer to output buffer
outbuflen: pointer to output buffer length
outs: double pointer to status string
outslen: pointer to status string length
CEPH_RADOS_API void rados_buffer_free(char buf)
free a rados-allocated buffer
Release memory allocated by librados calls like rados_mon_command().
Parameters
buf: buffer pointer
CEPH_RADOS_API int rados_osd_command(rados_t cluster, int osdid, const char ** cmd, size_t cmdlen, const char inbuf, size_t inbuflen, char outbuf, size_t * outbuflen, char outs, size_t outslen)

CEPH_RADOS_API int rados_pg_command(rados_t cluster, const char pgstr, const char cmd, size_t cmdlen, const char * inbuf, size_t inbuflen, char outbuf, size_t outbuflen, char ** outs, size_t outslen)
CEPH_RADOS_API int rados_monitor_log(rados_t cluster, const char level, rados_log_callback_t cb, void arg)
CEPH_RADOS_API int rados_monitor_log2(rados_t cluster, const char level, rados_log_callback2_t cb, void arg)
CEPH_RADOS_API int rados_service_register(rados_t cluster, const char service, const char daemon, const char metadata_dict)
register daemon instance for a service
Register us as a daemon providing a particular service. We identify the service (e.g., ‘rgw’) and our instance name (e.g., ‘rgw.$hostname’). The metadata is a map of keys and values with arbitrary static metdata for this instance. The encoding is a series of NULL-terminated strings, alternating key names and values, terminating with an empty key name. For example, “foo\0bar\0this\0that\0\0” is the dict {foo=bar,this=that}.
For the lifetime of the librados instance, regular beacons will be sent to the cluster to maintain our registration in the service map.
Parameters
cluster: handle
service: service name
daemon: daemon instance name
metadata_dict: static daemon metadata dict
CEPH_RADOS_API int rados_service_update_status(rados_t cluster, const char status_dict)
update daemon status
Update our mutable status information in the service map.
The status dict is encoded the same way the daemon metadata is encoded for rados_service_register. For example, “foo\0bar\0this\0that\0\0” is {foo=bar,this=that}.
Parameters
cluster: rados cluster handle
status_dict: status dict
Setup and Teardown
These are the first and last functions to that should be called when using librados.
CEPH_RADOS_API int rados_create(rados_t cluster, const char const id)
Create a handle for communicating with a RADOS cluster.
Ceph environment variables are read when this is called, so if $CEPH_ARGS specifies everything you need to connect, no further configuration is necessary.
Return
0 on success, negative error code on failure
Parameters
cluster: where to store the handle
id: the user to connect as (i.e. admin, not client.admin)
CEPH_RADOS_API int rados_create2(rados_t pcluster, const char const clustername, const char const name, uint64_t flags)
Extended version of rados_create.
Like rados_create, but 1) don’t assume ‘client.’+id; allow full specification of name 2) allow specification of cluster name 3) flags for future expansion
CEPH_RADOS_API int rados_create_with_context(rados_t cluster, rados_config_t cct)
Initialize a cluster handle from an existing configuration.
Share configuration state with another rados_t instance.
Return
0 on success, negative error code on failure
Parameters
cluster: where to store the handle
cct: the existing configuration to use
CEPH_RADOS_API int rados_ping_monitor(rados_t cluster, const char mon_id, char ** outstr, size_t outstrlen)
Ping the monitor with ID mon_id, storing the resulting reply in buf (if specified) with a maximum size of len.
The result buffer is allocated on the heap; the caller is expected to release that memory with rados_buffer_free(). The buffer and length pointers can be NULL, in which case they are not filled in.
Parameters
cluster: cluster handle
[in] mon_id: ID of the monitor to ping
[out] outstr: double pointer with the resulting reply
[out] outstrlen: pointer with the size of the reply in outstr
CEPH_RADOS_API int rados_connect(rados_t cluster)
Connect to the cluster.
Note
BUG: Before calling this, calling a function that communicates with the cluster will crash.
Pre
The cluster handle is configured with at least a monitor address. If cephx is enabled, a client name and secret must also be set.
Post
If this succeeds, any function in librados may be used
Return
0 on success, negative error code on failure
Parameters
cluster: The cluster to connect to.
CEPH_RADOS_API void rados_shutdown(rados_t cluster)
Disconnects from the cluster.
For clean up, this is only necessary after rados_connect() has succeeded.
Warning
This does not guarantee any asynchronous writes have completed. To do that, you must call rados_aio_flush() on all open io contexts.
Warning
We implicitly call rados_watch_flush() on shutdown. If there are watches being used, this should be done explicitly before destroying the relevant IoCtx. We do it here as a safety measure.
Post
the cluster handle cannot be used again
Parameters
cluster: the cluster to shutdown
Configuration
These functions read and update Ceph configuration for a cluster handle. Any configuration changes must be done before connecting to the cluster.
Options that librados users might want to set include:
mon_host
auth_supported
key, keyfile, or keyring when using cephx
log_file, log_to_stderr, err_to_stderr, and log_to_syslog
debug_rados, debug_objecter, debug_monc, debug_auth, or debug_ms
See docs.ceph.com for information about available configuration options`
CEPH_RADOS_API int rados_conf_read_file(rados_t cluster, const char path)
Configure the cluster handle using a Ceph config file
If path is NULL, the default locations are searched, and the first found is used. The locations are:
$CEPH_CONF (environment variable)
/etc/ceph/ceph.conf
~/.ceph/config
ceph.conf (in the current working directory)
Pre
rados_connect() has not been called on the cluster handle
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle to configure
path: path to a Ceph configuration file
CEPH_RADOS_API int rados_conf_parse_argv(rados_t cluster, int argc, const char argv)
Configure the cluster handle with command line arguments
argv can contain any common Ceph command line option, including any configuration parameter prefixed by ‘’ and replacing spaces with dashes or underscores. For example, the following options are equivalent:
mon-host 10.0.0.1:6789
mon_host 10.0.0.1:6789
-m 10.0.0.1:6789
Pre
rados_connect() has not been called on the cluster handle
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle to configure
argc: number of arguments in argv
argv: arguments to parse
CEPH_RADOS_API int rados_conf_parse_argv_remainder(rados_t cluster, int argc, const char argv, const char ** remargv)
Configure the cluster handle with command line arguments, returning any remainders. Same rados_conf_parse_argv, except for extra remargv argument to hold returns unrecognized arguments.
Pre
rados_connect() has not been called on the cluster handle
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle to configure
argc: number of arguments in argv
argv: arguments to parse
remargv: char array for returned unrecognized arguments
CEPH_RADOS_API int rados_conf_parse_env(rados_t cluster, const char var)
Configure the cluster handle based on an environment variable
The contents of the environment variable are parsed as if they were Ceph command line options. If var is NULL, the CEPH_ARGS environment variable is used.
Pre
rados_connect() has not been called on the cluster handle
Note
BUG: this is not threadsafe - it uses a static buffer
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle to configure
var: name of the environment variable to read
CEPH_RADOS_API int rados_conf_set(rados_t cluster, const char option, const char value)
Set a configuration option
Pre
rados_connect() has not been called on the cluster handle
Return
0 on success, negative error code on failure
Return
-ENOENT when the option is not a Ceph configuration option
Parameters
cluster: cluster handle to configure
option: option to set
value: value of the option
CEPH_RADOS_API int rados_conf_get(rados_t cluster, const char option, char buf, size_t len)
Get the value of a configuration option
Return
0 on success, negative error code on failure
Return
-ENAMETOOLONG if the buffer is too short to contain the requested value
Parameters
cluster: configuration to read
option: which option to read
buf: where to write the configuration value
len: the size of buf in bytes
Pools
RADOS pools are separate namespaces for objects. Pools may have different crush rules associated with them, so they could have differing replication levels or placement strategies. RADOS permissions are also tied to pools - users can have different read, write, and execute permissions on a per-pool basis.
CEPH_RADOS_API int rados_pool_list(rados_t cluster, char buf, size_t len)
List pools
Gets a list of pool names as NULL-terminated strings. The pool names will be placed in the supplied buffer one after another. After the last pool name, there will be two 0 bytes in a row.
If len is too short to fit all the pool name entries we need, we will fill as much as we can.
Buf may be null to determine the buffer size needed to list all pools.
Return
length of the buffer we would need to list all pools
Parameters
cluster: cluster handle
buf: output buffer
len: output buffer length
CEPH_RADOS_API int rados_inconsistent_pg_list(rados_t cluster, int64_t pool, char buf, size_t len)
List inconsistent placement groups of the given pool
Gets a list of inconsistent placement groups as NULL-terminated strings. The placement group names will be placed in the supplied buffer one after another. After the last name, there will be two 0 types in a row.
If len is too short to fit all the placement group entries we need, we will fill as much as we can.
Return
length of the buffer we would need to list all pools
Parameters
cluster: cluster handle
pool: pool ID
buf: output buffer
len: output buffer length
CEPH_RADOS_API rados_config_t rados_cct(rados_t cluster)
Get a configuration handle for a rados cluster handle
This handle is valid only as long as the cluster handle is valid.
Return
config handle for this cluster
Parameters
cluster: cluster handle
CEPH_RADOS_API uint64_t rados_get_instance_id(rados_t cluster)
Get a global id for current instance
This id is a unique representation of current connection to the cluster
Return
instance global id
Parameters
cluster: cluster handle
CEPH_RADOS_API int rados_get_min_compatible_osd(rados_t cluster, int8_t require_osd_release)
Gets the minimum compatible OSD version
Return
0 on sucess, negative error code on failure
Parameters
cluster: cluster handle
[out] require_osd_release: minimum compatible OSD version based upon the current features
CEPH_RADOS_API int rados_get_min_compatible_client(rados_t cluster, int8_t min_compat_client, int8_t require_min_compat_client)
Gets the minimum compatible client version
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle
[out] min_compat_client: minimum compatible client version based upon the current features
[out] require_min_compat_client: required minimum client version based upon explicit setting
CEPH_RADOS_API int rados_ioctx_create(rados_t cluster, const char pool_name, rados_ioctx_t ioctx)
Create an io context
The io context allows you to perform operations within a particular pool. For more details see rados_ioctx_t.
Return
0 on success, negative error code on failure
Parameters
cluster: which cluster the pool is in
pool_name: name of the pool
ioctx: where to store the io context
CEPH_RADOS_API int rados_ioctx_create2(rados_t cluster, int64_t pool_id, rados_ioctx_t ioctx)

CEPH_RADOS_API void rados_ioctx_destroy(rados_ioctx_t io)
The opposite of rados_ioctx_create
This just tells librados that you no longer need to use the io context. It may not be freed immediately if there are pending asynchronous requests on it, but you should not use an io context again after calling this function on it.
Warning
This does not guarantee any asynchronous writes have completed. You must call rados_aio_flush() on the io context before destroying it to do that.
Warning
If this ioctx is used by rados_watch, the caller needs to be sure that all registered watches are disconnected via rados_unwatch() and that rados_watch_flush() is called. This ensures that a racing watch callback does not make use of a destroyed ioctx.
Parameters
io: the io context to dispose of
CEPH_RADOS_API rados_config_t rados_ioctx_cct(rados_ioctx_t io)
Get configuration handle for a pool handle
Return
rados_config_t for this cluster
Parameters
io: pool handle
CEPH_RADOS_API rados_t rados_ioctx_get_cluster(rados_ioctx_t io)
Get the cluster handle used by this rados_ioctx_t Note that this is a weak reference, and should not be destroyed via rados_shutdown().
Return
the cluster handle for this io context
Parameters
io: the io context
CEPH_RADOS_API int rados_ioctx_pool_stat(rados_ioctx_t io, struct rados_pool_stat_t stats)
Get pool usage statistics
Fills in a rados_pool_stat_t after querying the cluster.
Return
0 on success, negative error code on failure
Parameters
io: determines which pool to query
stats: where to store the results
CEPH_RADOS_API int64_t rados_pool_lookup(rados_t cluster, const char pool_name)
Get the id of a pool
Return
id of the pool
Return
-ENOENT if the pool is not found
Parameters
cluster: which cluster the pool is in
pool_name: which pool to look up
CEPH_RADOS_API int rados_pool_reverse_lookup(rados_t cluster, int64_t id, char buf, size_t maxlen)
Get the name of a pool
Return
length of string stored, or -ERANGE if buffer too small
Parameters
cluster: which cluster the pool is in
id: the id of the pool
buf: where to store the pool name
maxlen: size of buffer where name will be stored
CEPH_RADOS_API int rados_pool_create(rados_t cluster, const char pool_name)
Create a pool with default settings
The default crush rule is rule 0.
Return
0 on success, negative error code on failure
Parameters
cluster: the cluster in which the pool will be created
pool_name: the name of the new pool
CEPH_RADOS_API int rados_pool_create_with_auid(rados_t cluster, const char pool_name, uint64_t auid)
Create a pool owned by a specific auid.
DEPRECATED: auid support has been removed, and this call will be removed in a future release.
Return
0 on success, negative error code on failure
Parameters
cluster: the cluster in which the pool will be created
pool_name: the name of the new pool
auid: the id of the owner of the new pool
CEPH_RADOS_API int rados_pool_create_with_crush_rule(rados_t cluster, const char pool_name, uint8_t crush_rule_num)
Create a pool with a specific CRUSH rule
Return
0 on success, negative error code on failure
Parameters
cluster: the cluster in which the pool will be created
pool_name: the name of the new pool
crush_rule_num: which rule to use for placement in the new pool1
CEPH_RADOS_API int rados_pool_create_with_all(rados_t cluster, const char pool_name, uint64_t auid, uint8_t crush_rule_num)
Create a pool with a specific CRUSH rule and auid
DEPRECATED: auid support has been removed and this call will be removed in a future release.
This is a combination of rados_pool_create_with_crush_rule() and rados_pool_create_with_auid().
Return
0 on success, negative error code on failure
Parameters
cluster: the cluster in which the pool will be created
pool_name: the name of the new pool
crush_rule_num: which rule to use for placement in the new pool2
auid: the id of the owner of the new pool
CEPH_RADOS_API int rados_pool_get_base_tier(rados_t cluster, int64_t pool, int64_t base_tier)
Returns the pool that is the base tier for this pool.
The return value is the ID of the pool that should be used to read from/write to. If tiering is not set up for the pool, returns pool.
Return
0 on success, negative error code on failure
Parameters
cluster: the cluster the pool is in
pool: ID of the pool to query
[out] base_tier: base tier, or pool if tiering is not configured
CEPH_RADOS_API int rados_pool_delete(rados_t cluster, const char pool_name)
Delete a pool and all data inside it
The pool is removed from the cluster immediately, but the actual data is deleted in the background.
Return
0 on success, negative error code on failure
Parameters
cluster: the cluster the pool is in
pool_name: which pool to delete
CEPH_RADOS_API int rados_ioctx_pool_set_auid(rados_ioctx_t io, uint64_t auid)
Attempt to change an io context’s associated auid “owner”
DEPRECATED: auid support has been removed and this call has no effect.
Requires that you have write permission on both the current and new auid.
Return
0 on success, negative error code on failure
Parameters
io: reference to the pool to change.
auid: the auid you wish the io to have.
CEPH_RADOS_API int rados_ioctx_pool_get_auid(rados_ioctx_t io, uint64_t auid)
Get the auid of a pool
DEPRECATED: auid support has been removed and this call always reports CEPH_AUTH_UID_DEFAULT (-1).
Return
0 on success, negative error code on failure
Parameters
io: pool to query
auid: where to store the auid
CEPH_RADOS_API int rados_ioctx_pool_requires_alignment(rados_ioctx_t io)
CEPH_RADOS_API int rados_ioctx_pool_requires_alignment2(rados_ioctx_t io, int req)
Test whether the specified pool requires alignment or not.
Return
0 on success, negative error code on failure
Parameters
io: pool to query
req: 1 if alignment is supported, 0 if not.
CEPH_RADOS_API uint64_t rados_ioctx_pool_required_alignment(rados_ioctx_t io)
CEPH_RADOS_API int rados_ioctx_pool_required_alignment2(rados_ioctx_t io, uint64_t alignment)
Get the alignment flavor of a pool
Return
0 on success, negative error code on failure
Parameters
io: pool to query
alignment: where to store the alignment flavor
CEPH_RADOS_API int64_t rados_ioctx_get_id(rados_ioctx_t io)
Get the pool id of the io context
Return
the id of the pool the io context uses
Parameters
io: the io context to query
CEPH_RADOS_API int rados_ioctx_get_pool_name(rados_ioctx_t io, char buf, unsigned maxlen)
Get the pool name of the io context
Return
length of string stored, or -ERANGE if buffer too small
Parameters
io: the io context to query
buf: pointer to buffer where name will be stored
maxlen: size of buffer where name will be stored
Object Locators
CEPH_RADOS_API void rados_ioctx_locator_set_key(rados_ioctx_t io, const char key)
Set the key for mapping objects to pgs within an io context.
The key is used instead of the object name to determine which placement groups an object is put in. This affects all subsequent operations of the io context - until a different locator key is set, all objects in this io context will be placed in the same pg.
Parameters
io: the io context to change
key: the key to use as the object locator, or NULL to discard any previously set key
CEPH_RADOS_API void rados_ioctx_set_namespace(rados_ioctx_t io, const char nspace)
Set the namespace for objects within an io context
The namespace specification further refines a pool into different domains. The mapping of objects to pgs is also based on this value.
Parameters
io: the io context to change
nspace: the name to use as the namespace, or NULL use the default namespace
CEPH_RADOS_API int rados_ioctx_get_namespace(rados_ioctx_t io, char buf, unsigned maxlen)
Get the namespace for objects within the io context
Return
length of string stored, or -ERANGE if buffer too small
Parameters
io: the io context to query
buf: pointer to buffer where name will be stored
maxlen: size of buffer where name will be stored
Listing Objects
CEPH_RADOS_API int rados_nobjects_list_open(rados_ioctx_t io, rados_list_ctx_t ctx)
Start listing objects in a pool
Return
0 on success, negative error code on failure
Parameters
io: the pool to list from
ctx: the handle to store list context in
CEPH_RADOS_API uint32_t rados_nobjects_list_get_pg_hash_position(rados_list_ctx_t ctx)
Return hash position of iterator, rounded to the current PG
Return
current hash position, rounded to the current pg
Parameters
ctx: iterator marking where you are in the listing
CEPH_RADOS_API uint32_t rados_nobjects_list_seek(rados_list_ctx_t ctx, uint32_t pos)
Reposition object iterator to a different hash position
Return
actual (rounded) position we moved to
Parameters
ctx: iterator marking where you are in the listing
pos: hash position to move to
CEPH_RADOS_API uint32_t rados_nobjects_list_seek_cursor(rados_list_ctx_t ctx, rados_object_list_cursor cursor)
Reposition object iterator to a different position
Return
rounded position we moved to
Parameters
ctx: iterator marking where you are in the listing
cursor: position to move to
CEPH_RADOS_API int rados_nobjects_list_get_cursor(rados_list_ctx_t ctx, rados_object_list_cursor cursor)
Reposition object iterator to a different position
The returned handle must be released with rados_object_list_cursor_free().
Return
0 on success, negative error code on failure
Parameters
ctx: iterator marking where you are in the listing
cursor: where to store cursor
CEPH_RADOS_API int rados_nobjects_list_next(rados_list_ctx_t ctx, const char entry, const char key, const char ** nspace)
Get the next object name and locator in the pool
entry and key are valid until next call to rados_nobjects_list
Return
0 on success, negative error code on failure
Return
-ENOENT when there are no more objects to list
Parameters
ctx: iterator marking where you are in the listing
entry: where to store the name of the entry
key: where to store the object locator (set to NULL to ignore)
nspace: where to store the object namespace (set to NULL to ignore)
CEPHRADOS_API void rados_nobjects_list_close(rados_list_ctx_t ctx)
Close the object listing handle.
This should be called when the handle is no longer needed. The handle should not be used after it has been closed.
Parameters
ctx: the handle to close
CEPH_RADOS_API rados_object_list_cursor rados_object_list_begin(rados_ioctx_t io)
Get cursor handle pointing to the beginning of a pool.
This is an opaque handle pointing to the start of a pool. It must be released with rados_object_list_cursor_free().
Return
handle for the pool, NULL on error (pool does not exist)
Parameters
io: ioctx for the pool
CEPH_RADOS_API rados_object_list_cursor rados_object_list_end(rados_ioctx_t io)
Get cursor handle pointing to the end of a pool.
This is an opaque handle pointing to the start of a pool. It must be released with rados_object_list_cursor_free().
Return
handle for the pool, NULL on error (pool does not exist)
Parameters
io: ioctx for the pool
CEPH_RADOS_API int rados_object_list_is_end(rados_ioctx_t io, rados_object_list_cursor cur)
Check if a cursor has reached the end of a pool
Return
1 if the cursor has reached the end of the pool, 0 otherwise
Parameters
io: ioctx
cur: cursor
CEPH_RADOS_API void rados_object_list_cursor_free(rados_ioctx_t io, rados_object_list_cursor cur)
Release a cursor
Release a cursor. The handle may not be used after this point.
Parameters
io: ioctx
cur: cursor
CEPH_RADOS_API int rados_object_list_cursor_cmp(rados_ioctx_t io, rados_object_list_cursor lhs, rados_object_list_cursor rhs)
Compare two cursor positions
Compare two cursors, and indicate whether the first cursor precedes, matches, or follows the second.
Return
-1, 0, or 1 for lhs < rhs, lhs == rhs, or lhs > rhs
Parameters
io: ioctx
lhs: first cursor
rhs: second cursor
CEPH_RADOS_API int rados_object_list(rados_ioctx_t io, const rados_object_list_cursor start, const rados_object_list_cursor finish, const size_t result_size, const char filter_buf, const size_t filter_buf_len, rados_object_list_item results, rados_object_list_cursor next)

Return
the number of items set in the results array
CEPH_RADOS_API void rados_object_list_free(const size_t result_size, rados_object_list_item results)
CEPH_RADOS_API void rados_object_list_slice(rados_ioctx_t io, const rados_object_list_cursor start, const rados_object_list_cursor finish, const size_t n, const size_t m, rados_object_list_cursor split_start, rados_object_list_cursor split_finish)
Obtain cursors delineating a subset of a range. Use this when you want to split up the work of iterating over the global namespace. Expected use case is when you are iterating in parallel, with m workers, and each worker taking an id n.
Parameters
io: ioctx
start: start of the range to be sliced up (inclusive)
finish: end of the range to be sliced up (exclusive)
n: which of the m chunks you would like to get cursors for
m: how many chunks to divide start-finish into
split_start: cursor populated with start of the subrange (inclusive)
split_finish: cursor populated with end of the subrange (exclusive)
Snapshots
RADOS snapshots are based upon sequence numbers that form a snapshot context. They are pool-specific. The snapshot context consists of the current snapshot sequence number for a pool, and an array of sequence numbers at which snapshots were taken, in descending order. Whenever a snapshot is created or deleted, the snapshot sequence number for the pool is increased. To add a new snapshot, the new snapshot sequence number must be increased and added to the snapshot context.
There are two ways to manage these snapshot contexts:
within the RADOS cluster These are called pool snapshots, and store the snapshot context in the OSDMap. These represent a snapshot of all the objects in a pool.
within the RADOS clients These are called self-managed snapshots, and push the responsibility for keeping track of the snapshot context to the clients. For every write, the client must send the snapshot context. In librados, this is accomplished with rados_selfmanaged_snap_set_write_ctx(). These are more difficult to manage, but are restricted to specific objects instead of applying to an entire pool.
CEPH_RADOS_API int rados_ioctx_snap_create(rados_ioctx_t io, const char snapname)
Create a pool-wide snapshot
Return
0 on success, negative error code on failure
Parameters
io: the pool to snapshot
snapname: the name of the snapshot
CEPH_RADOS_API int rados_ioctx_snap_remove(rados_ioctx_t io, const char snapname)
Delete a pool snapshot
Return
0 on success, negative error code on failure
Parameters
io: the pool to delete the snapshot from
snapname: which snapshot to delete
CEPH_RADOS_API int rados_ioctx_snap_rollback(rados_ioctx_t io, const char oid, const char snapname)
Rollback an object to a pool snapshot
The contents of the object will be the same as when the snapshot was taken.
Return
0 on success, negative error code on failure
Parameters
io: the pool in which the object is stored
oid: the name of the object to rollback
snapname: which snapshot to rollback to
CEPH_RADOS_API int rados_rollback(rados_ioctx_t io, const char oid, const char snapname)
Warning
Deprecated: Use rados_ioctx_snap_rollback() instead
CEPH_RADOS_API void rados_ioctx_snap_set_read(rados_ioctx_t io, rados_snap_t snap)
Set the snapshot from which reads are performed.
Subsequent reads will return data as it was at the time of that snapshot.
Parameters
io: the io context to change
snap: the id of the snapshot to set, or LIBRADOS_SNAP_HEAD for no snapshot (i.e. normal operation)
CEPH_RADOS_API int rados_ioctx_selfmanaged_snap_create(rados_ioctx_t io, rados_snap_t snapid)
Allocate an ID for a self-managed snapshot
Get a unique ID to put in the snaphot context to create a snapshot. A clone of an object is not created until a write with the new snapshot context is completed.
Return
0 on success, negative error code on failure
Parameters
io: the pool in which the snapshot will exist
snapid: where to store the newly allocated snapshot ID
CEPH_RADOS_API void rados_aio_ioctx_selfmanaged_snap_create(rados_ioctx_t io, rados_snap_t snapid, rados_completion_t completion)
CEPH_RADOS_API int rados_ioctx_selfmanaged_snap_remove(rados_ioctx_t io, rados_snap_t snapid)
Remove a self-managed snapshot
This increases the snapshot sequence number, which will cause snapshots to be removed lazily.
Return
0 on success, negative error code on failure
Parameters
io: the pool in which the snapshot will exist
snapid: where to store the newly allocated snapshot ID
CEPH_RADOS_API void rados_aio_ioctx_selfmanaged_snap_remove(rados_ioctx_t io, rados_snap_t snapid, rados_completion_t completion)
CEPH_RADOS_API int rados_ioctx_selfmanaged_snap_rollback(rados_ioctx_t io, const char oid, rados_snap_t snapid)
Rollback an object to a self-managed snapshot
The contents of the object will be the same as when the snapshot was taken.
Return
0 on success, negative error code on failure
Parameters
io: the pool in which the object is stored
oid: the name of the object to rollback
snapid: which snapshot to rollback to
CEPH_RADOS_API int rados_ioctx_selfmanaged_snap_set_write_ctx(rados_ioctx_t io, rados_snap_t seq, rados_snap_t snaps, int num_snaps)
Set the snapshot context for use when writing to objects
This is stored in the io context, and applies to all future writes.
Return
0 on success, negative error code on failure
Return
-EINVAL if snaps are not in descending order
Parameters
io: the io context to change
seq: the newest snapshot sequence number for the pool
snaps: array of snapshots in sorted by descending id
num_snaps: how many snaphosts are in the snaps array
CEPH_RADOS_API int rados_ioctx_snap_list(rados_ioctx_t io, rados_snap_t snaps, int maxlen)
List all the ids of pool snapshots
If the output array does not have enough space to fit all the snapshots, -ERANGE is returned and the caller should retry with a larger array.
Return
number of snapshots on success, negative error code on failure
Return
-ERANGE is returned if the snaps array is too short
Parameters
io: the pool to read from
snaps: where to store the results
maxlen: the number of rados_snap_t that fit in the snaps array
CEPH_RADOS_API int rados_ioctx_snap_lookup(rados_ioctx_t io, const char name, rados_snap_t id)
Get the id of a pool snapshot
Return
0 on success, negative error code on failure
Parameters
io: the pool to read from
name: the snapshot to find
id: where to store the result
CEPH_RADOS_API int rados_ioctx_snap_get_name(rados_ioctx_t io, rados_snap_t id, char name, int maxlen)
Get the name of a pool snapshot
Return
0 on success, negative error code on failure
Return
-ERANGE if the name array is too small
Parameters
io: the pool to read from
id: the snapshot to find
name: where to store the result
maxlen: the size of the name array
CEPH_RADOS_API int rados_ioctx_snap_get_stamp(rados_ioctx_t io, rados_snap_t id, time_t t)
Find when a pool snapshot occurred
Return
0 on success, negative error code on failure
Parameters
io: the pool the snapshot was taken in
id: the snapshot to lookup
t: where to store the result
Synchronous I/O
Writes are replicated to a number of OSDs based on the configuration of the pool they are in. These write functions block until data is in memory on all replicas of the object they’re writing to - they are equivalent to doing the corresponding asynchronous write, and the calling rados_ioctx_wait_for_complete(). For greater data safety, use the asynchronous functions and rados_aio_wait_for_safe().
CEPH_RADOS_API uint64_t rados_get_last_version(rados_ioctx_t io)
Return the version of the last object read or written to.
This exposes the internal version number of the last object read or written via this io context
Return
last read or written object version
Parameters
io: the io context to check
CEPH_RADOS_API int rados_write(rados_ioctx_t io, const char oid, const char buf, size_t len, uint64_t off)
Write len bytes from buf into the oid object, starting at offset off. The value of len must be <= UINT_MAX/2.
Note
This will never return a positive value not equal to len.
Return
0 on success, negative error code on failure
Parameters
io: the io context in which the write will occur
oid: name of the object
buf: data to write
len: length of the data, in bytes
off: byte offset in the object to begin writing at
CEPH_RADOS_API int rados_write_full(rados_ioctx_t io, const char oid, const char buf, size_t len)
Write len bytes from buf into the oid object. The value of len must be <= UINT_MAX/2.
The object is filled with the provided data. If the object exists, it is atomically truncated and then written.
Return
0 on success, negative error code on failure
Parameters
io: the io context in which the write will occur
oid: name of the object
buf: data to write
len: length of the data, in bytes
CEPH_RADOS_API int rados_writesame(rados_ioctx_t io, const char oid, const char buf, size_t data_len, size_t write_len, uint64_t off)
Write the same data_len bytes from buf multiple times into the oid object. write_len bytes are written in total, which must be a multiple of data_len. The value of write_len and data_len must be <= UINT_MAX/2.
Return
0 on success, negative error code on failure
Parameters
io: the io context in which the write will occur
oid: name of the object
buf: data to write
data_len: length of the data, in bytes
write_len: the total number of bytes to write
off: byte offset in the object to begin writing at
CEPH_RADOS_API int rados_append(rados_ioctx_t io, const char oid, const char buf, size_t len)
Append len bytes from buf into the oid object. The value of len must be <= UINT_MAX/2.
Return
0 on success, negative error code on failure
Parameters
io: the context to operate in
oid: the name of the object
buf: the data to append
len: length of buf (in bytes)
CEPH_RADOS_API int rados_read(rados_ioctx_t io, const char oid, char buf, size_t len, uint64_t off)
Read data from an object
The io context determines the snapshot to read from, if any was set by rados_ioctx_snap_set_read().
Return
number of bytes read on success, negative error code on failure
Parameters
io: the context in which to perform the read
oid: the name of the object to read from
buf: where to store the results
len: the number of bytes to read
off: the offset to start reading from in the object
CEPH_RADOS_API int rados_checksum(rados_ioctx_t io, const char oid, rados_checksum_type_t type, const char init_value, size_t init_value_len, size_t len, uint64_t off, size_t chunk_size, char pchecksum, size_t checksum_len)
Compute checksum from object data
The io context determines the snapshot to checksum, if any was set by rados_ioctx_snap_set_read(). The length of the init_value and resulting checksum are dependent upon the checksum type:
XXHASH64: le64 XXHASH32: le32 CRC32C: le32
The checksum result is encoded the following manner:
le32 num_checksum_chunks { leXX checksum for chunk (where XX = appropriate size for the checksum type) } num_checksum_chunks

Return
negative error code on failure
Parameters
io: the context in which to perform the checksum
oid: the name of the object to checksum
type: the checksum algorithm to utilize
init_value: the init value for the algorithm
init_value_len: the length of the init value
len: the number of bytes to checksum
off: the offset to start checksumming in the object
chunk_size: optional length-aligned chunk size for checksums
pchecksum: where to store the checksum result
checksum_len: the number of bytes available for the result
CEPH_RADOS_API int rados_remove(rados_ioctx_t io, const char oid)
Delete an object
Note
This does not delete any snapshots of the object.
Return
0 on success, negative error code on failure
Parameters
io: the pool to delete the object from
oid: the name of the object to delete
CEPH_RADOS_API int rados_trunc(rados_ioctx_t io, const char oid, uint64_t size)
Resize an object
If this enlarges the object, the new area is logically filled with zeroes. If this shrinks the object, the excess data is removed.
Return
0 on success, negative error code on failure
Parameters
io: the context in which to truncate
oid: the name of the object
size: the new size of the object in bytes
CEPH_RADOS_API int rados_cmpext(rados_ioctx_t io, const char o, const char cmp_buf, size_t cmp_len, uint64_t off)
Compare an on-disk object range with a buffer
Return
0 on success, negative error code on failure, (-MAX_ERRNO - mismatch_off) on mismatch
Parameters
io: the context in which to perform the comparison
o: name of the object
cmp_buf: buffer containing bytes to be compared with object contents
cmp_len: length to compare and size of cmp_buf in bytes
off: object byte offset at which to start the comparison
Xattrs
Extended attributes are stored as extended attributes on the files representing an object on the OSDs. Thus, they have the same limitations as the underlying filesystem. On ext4, this means that the total data stored in xattrs cannot exceed 4KB.
CEPH_RADOS_API int rados_getxattr(rados_ioctx_t io, const char o, const char name, char buf, size_t len)
Get the value of an extended attribute on an object.
Return
length of xattr value on success, negative error code on failure
Parameters
io: the context in which the attribute is read
o: name of the object
name: which extended attribute to read
buf: where to store the result
len: size of buf in bytes
CEPH_RADOS_API int rados_setxattr(rados_ioctx_t io, const char o, const char name, const char buf, size_t len)
Set an extended attribute on an object.
Return
0 on success, negative error code on failure
Parameters
io: the context in which xattr is set
o: name of the object
name: which extended attribute to set
buf: what to store in the xattr
len: the number of bytes in buf
CEPH_RADOS_API int rados_rmxattr(rados_ioctx_t io, const char o, const char name)
Delete an extended attribute from an object.
Return
0 on success, negative error code on failure
Parameters
io: the context in which to delete the xattr
o: the name of the object
name: which xattr to delete
CEPH_RADOS_API int rados_getxattrs(rados_ioctx_t io, const char oid, rados_xattrs_iter_t iter)
Start iterating over xattrs on an object.
Post
iter is a valid iterator
Return
0 on success, negative error code on failure
Parameters
io: the context in which to list xattrs
oid: name of the object
iter: where to store the iterator
CEPH_RADOS_API int rados_getxattrs_next(rados_xattrs_iter_t iter, const char name, const char val, size_t len)
Get the next xattr on the object
Pre
iter is a valid iterator
Post
name is the NULL-terminated name of the next xattr, and val contains the value of the xattr, which is of length len. If the end of the list has been reached, name and val are NULL, and len is 0.
Return
0 on success, negative error code on failure
Parameters
iter: iterator to advance
name: where to store the name of the next xattr
val: where to store the value of the next xattr
len: the number of bytes in val
CEPH_RADOS_API void rados_getxattrs_end(rados_xattrs_iter_t iter)
Close the xattr iterator.
iter should not be used after this is called.
Parameters
iter: the iterator to close
Asynchronous Xattrs
Extended attributes are stored as extended attributes on the files representing an object on the OSDs. Thus, they have the same limitations as the underlying filesystem. On ext4, this means that the total data stored in xattrs cannot exceed 4KB.
CEPH_RADOS_API int rados_aio_getxattr(rados_ioctx_t io, const char o, rados_completion_t completion, const char name, char buf, size_t len)
Asynchronously get the value of an extended attribute on an object.
Return
length of xattr value on success, negative error code on failure
Parameters
io: the context in which the attribute is read
o: name of the object
completion: what to do when the getxattr completes
name: which extended attribute to read
buf: where to store the result
len: size of buf in bytes
CEPH_RADOS_API int rados_aio_setxattr(rados_ioctx_t io, const char o, rados_completion_t completion, const char name, const char buf, size_t len)
Asynchronously set an extended attribute on an object.
Return
0 on success, negative error code on failure
Parameters
io: the context in which xattr is set
o: name of the object
completion: what to do when the setxattr completes
name: which extended attribute to set
buf: what to store in the xattr
len: the number of bytes in buf
CEPH_RADOS_API int rados_aio_rmxattr(rados_ioctx_t io, const char o, rados_completion_t completion, const char name)
Asynchronously delete an extended attribute from an object.
Return
0 on success, negative error code on failure
Parameters
io: the context in which to delete the xattr
o: the name of the object
completion: what to do when the rmxattr completes
name: which xattr to delete
CEPH_RADOS_API int rados_aio_getxattrs(rados_ioctx_t io, const char oid, rados_completion_t completion, rados_xattrs_iter_t iter)
Asynchronously start iterating over xattrs on an object.
Post
iter is a valid iterator
Return
0 on success, negative error code on failure
Parameters
io: the context in which to list xattrs
oid: name of the object
completion: what to do when the getxattrs completes
iter: where to store the iterator
Hints
CEPH_RADOS_API int rados_set_alloc_hint(rados_ioctx_t io, const char o, uint64_t expected_object_size, uint64_t expected_write_size)
Set allocation hint for an object
This is an advisory operation, it will always succeed (as if it was submitted with a LIBRADOS_OP_FLAG_FAILOK flag set) and is not guaranteed to do anything on the backend.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the name of the object
expected_object_size: expected size of the object, in bytes
expected_write_size: expected size of writes to the object, in bytes
CEPH_RADOS_API int rados_set_alloc_hint2(rados_ioctx_t io, const char o, uint64_t expected_object_size, uint64_t expected_write_size, uint32_t flags)
Set allocation hint for an object
This is an advisory operation, it will always succeed (as if it was submitted with a LIBRADOS_OP_FLAG_FAILOK flag set) and is not guaranteed to do anything on the backend.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the name of the object
expected_object_size: expected size of the object, in bytes
expected_write_size: expected size of writes to the object, in bytes
flags: hints about future IO patterns
Object Operations
A single rados operation can do multiple operations on one object atomically. The whole operation will succeed or fail, and no partial results will be visible.
Operations may be either reads, which can return data, or writes, which cannot. The effects of writes are applied and visible all at once, so an operation that sets an xattr and then checks its value will not see the updated value.
CEPH_RADOS_API rados_write_op_t rados_create_write_op(void)
Create a new rados_write_op_t write operation. This will store all actions to be performed atomically. You must call rados_release_write_op when you are finished with it.
Return
non-NULL on success, NULL on memory allocation error.
CEPH_RADOS_API void rados_release_write_op(rados_write_op_t write_op)
Free a rados_write_op_t, must be called when you’re done with it.
Parameters
write_op: operation to deallocate, created with rados_create_write_op
CEPH_RADOS_API void rados_write_op_set_flags(rados_write_op_t write_op, int flags)
Set flags for the last operation added to this write_op. At least one op must have been added to the write_op.
Parameters
write_op: operation to add this action to
flags: see librados.h constants beginning with LIBRADOS_OP_FLAG
CEPH_RADOS_API void rados_write_op_assert_exists(rados_write_op_t write_op)
Ensure that the object exists before writing
Parameters
write_op: operation to add this action to
CEPH_RADOS_API void rados_write_op_assert_version(rados_write_op_t write_op, uint64_t ver)
Ensure that the object exists and that its internal version number is equal to “ver” before writing. “ver” should be a version number previously obtained with rados_get_last_version().
If the object’s version is greater than the asserted version then rados_write_op_operate will return -ERANGE instead of executing the op.
If the object’s version is less than the asserted version then rados_write_op_operate will return -EOVERFLOW instead of executing the op.
Parameters
write_op: operation to add this action to
ver: object version number
CEPH_RADOS_API void rados_write_op_cmpext(rados_write_op_t write_op, const char cmp_buf, size_t cmp_len, uint64_t off, int prval)
Ensure that given object range (extent) satisfies comparison.
Parameters
write_op: operation to add this action to
cmp_buf: buffer containing bytes to be compared with object contents
cmp_len: length to compare and size of cmp_buf in bytes
off: object byte offset at which to start the comparison
prval: returned result of comparison, 0 on success, negative error code on failure, (-MAX_ERRNO - mismatch_off) on mismatch
CEPH_RADOS_API void rados_write_op_cmpxattr(rados_write_op_t write_op, const char name, uint8_t comparison_operator, const char value, size_t value_len)
Ensure that given xattr satisfies comparison. If the comparison is not satisfied, the return code of the operation will be -ECANCELED
Parameters
write_op: operation to add this action to
name: name of the xattr to look up
comparison_operator: currently undocumented, look for LIBRADOS_CMPXATTR_OP_EQ in librados.h
value: buffer to compare actual xattr value to
value_len: length of buffer to compare actual xattr value to
CEPH_RADOS_API void rados_write_op_omap_cmp(rados_write_op_t write_op, const char key, uint8_t comparison_operator, const char val, size_t val_len, int prval)
Ensure that the an omap value satisfies a comparison, with the supplied value on the right hand side (i.e. for OP_LT, the comparison is actual_value < value.
Parameters
write_op: operation to add this action to
key: which omap value to compare
comparison_operator: one of LIBRADOS_CMPXATTR_OP_EQ, LIBRADOS_CMPXATTR_OP_LT, or LIBRADOS_CMPXATTR_OP_GT
val: value to compare with
val_len: length of value in bytes
prval: where to store the return value from this action
CEPH_RADOS_API void rados_write_op_omap_cmp2(rados_write_op_t write_op, const char key, uint8_t comparison_operator, const char val, size_t key_len, size_t val_len, int prval)
Ensure that the an omap value satisfies a comparison, with the supplied value on the right hand side (i.e. for OP_LT, the comparison is actual_value < value.
Parameters
write_op: operation to add this action to
key: which omap value to compare
comparison_operator: one of LIBRADOS_CMPXATTR_OP_EQ, LIBRADOS_CMPXATTR_OP_LT, or LIBRADOS_CMPXATTR_OP_GT
val: value to compare with
key_len: length of key in bytes
val_len: length of value in bytes
prval: where to store the return value from this action
CEPH_RADOS_API void rados_write_op_setxattr(rados_write_op_t write_op, const char name, const char value, size_t value_len)
Set an xattr
Parameters
write_op: operation to add this action to
name: name of the xattr
value: buffer to set xattr to
value_len: length of buffer to set xattr to
CEPH_RADOS_API void rados_write_op_rmxattr(rados_write_op_t write_op, const char name)
Remove an xattr
Parameters
write_op: operation to add this action to
name: name of the xattr to remove
CEPH_RADOS_API void rados_write_op_create(rados_write_op_t write_op, int exclusive, const char category)
Create the object
Parameters
write_op: operation to add this action to
exclusive: set to either LIBRADOS_CREATE_EXCLUSIVE or LIBRADOS_CREATE_IDEMPOTENT will error if the object already exists.
category: category string (DEPRECATED, HAS NO EFFECT)
CEPH_RADOS_API void rados_write_op_write(rados_write_op_t write_op, const char buffer, size_t len, uint64_t offset)
Write to offset
Parameters
write_op: operation to add this action to
offset: offset to write to
buffer: bytes to write
len: length of buffer
CEPH_RADOS_API void rados_write_op_write_full(rados_write_op_t write_op, const char buffer, size_t len)
Write whole object, atomically replacing it.
Parameters
write_op: operation to add this action to
buffer: bytes to write
len: length of buffer
CEPH_RADOS_API void rados_write_op_writesame(rados_write_op_t write_op, const char buffer, size_t data_len, size_t write_len, uint64_t offset)
Write the same buffer multiple times
Parameters
write_op: operation to add this action to
buffer: bytes to write
data_len: length of buffer
write_len: total number of bytes to write, as a multiple of data_len
offset: offset to write to
CEPH_RADOS_API void rados_write_op_append(rados_write_op_t write_op, const char buffer, size_t len)
Append to end of object.
Parameters
write_op: operation to add this action to
buffer: bytes to write
len: length of buffer
CEPH_RADOS_API void rados_write_op_remove(rados_write_op_t write_op)
Remove object
Parameters
write_op: operation to add this action to
CEPH_RADOS_API void rados_write_op_truncate(rados_write_op_t write_op, uint64_t offset)
Truncate an object
Parameters
write_op: operation to add this action to
offset: Offset to truncate to
CEPH_RADOS_API void rados_write_op_zero(rados_write_op_t write_op, uint64_t offset, uint64_t len)
Zero part of an object
Parameters
write_op: operation to add this action to
offset: Offset to zero
len: length to zero
CEPH_RADOS_API void rados_write_op_exec(rados_write_op_t write_op, const char cls, const char method, const char in_buf, size_t in_len, int prval)
Execute an OSD class method on an object See rados_exec() for general description.
Parameters
write_op: operation to add this action to
cls: the name of the class
method: the name of the method
in_buf: where to find input
in_len: length of in_buf in bytes
prval: where to store the return value from the method
CEPH_RADOS_API void rados_write_op_omap_set(rados_write_op_t write_op, char const const keys, char const const vals, const size_t lens, size_t num)
Set key/value pairs on an object
Parameters
write_op: operation to add this action to
keys: array of null-terminated char arrays representing keys to set
vals: array of pointers to values to set
lens: array of lengths corresponding to each value
num: number of key/value pairs to set
CEPH_RADOS_API void rados_write_op_omap_set2(rados_write_op_t write_op, char const const keys, char const const vals, const size_t key_lens, const size_t val_lens, size_t num)
Set key/value pairs on an object
Parameters
write_op: operation to add this action to
keys: array of null-terminated char arrays representing keys to set
vals: array of pointers to values to set
key_lens: array of lengths corresponding to each key
val_lens: array of lengths corresponding to each value
num: number of key/value pairs to set
CEPH_RADOS_API void rados_write_op_omap_rm_keys(rados_write_op_t write_op, char const const keys, size_t keys_len)
Remove key/value pairs from an object
Parameters
write_op: operation to add this action to
keys: array of null-terminated char arrays representing keys to remove
keys_len: number of key/value pairs to remove
CEPH_RADOS_API void rados_write_op_omap_rm_keys2(rados_write_op_t write_op, char const const keys, const size_t key_lens, size_t keys_len)
Remove key/value pairs from an object
Parameters
write_op: operation to add this action to
keys: array of char arrays representing keys to remove
key_lens: array of size_t values representing length of each key
keys_len: number of key/value pairs to remove
CEPH_RADOS_API void rados_write_op_omap_rm_range2(rados_write_op_t write_op, const char key_begin, size_t key_begin_len, const char key_end, size_t key_end_len)
Remove key/value pairs from an object whose keys are in the range [key_begin, key_end)
Parameters
write_op: operation to add this action to
key_begin: the lower bound of the key range to remove
key_begin_len: length of key_begin
key_end: the upper bound of the key range to remove
key_end_len: length of key_end
CEPH_RADOS_API void rados_write_op_omap_clear(rados_write_op_t write_op)
Remove all key/value pairs from an object
Parameters
write_op: operation to add this action to
CEPH_RADOS_API void rados_write_op_set_alloc_hint(rados_write_op_t write_op, uint64_t expected_object_size, uint64_t expected_write_size)
Set allocation hint for an object
Parameters
write_op: operation to add this action to
expected_object_size: expected size of the object, in bytes
expected_write_size: expected size of writes to the object, in bytes
CEPH_RADOS_API void rados_write_op_set_alloc_hint2(rados_write_op_t write_op, uint64_t expected_object_size, uint64_t expected_write_size, uint32_t flags)
Set allocation hint for an object
Parameters
write_op: operation to add this action to
expected_object_size: expected size of the object, in bytes
expected_write_size: expected size of writes to the object, in bytes
flags: hints about future IO patterns
CEPH_RADOS_API int rados_write_op_operate(rados_write_op_t write_op, rados_ioctx_t io, const char oid, time_t mtime, int flags)
Perform a write operation synchronously
Parameters
write_op: operation to perform
io: the ioctx that the object is in
oid: the object id
mtime: the time to set the mtime to, NULL for the current time
flags: flags to apply to the entire operation (LIBRADOS_OPERATION)

CEPH_RADOS_API int rados_write_op_operate2(rados_write_op_t write_op, rados_ioctx_t io, const char oid, struct timespec mtime, int flags)
Perform a write operation synchronously
Parameters
writeop: operation to perform
io: the ioctx that the object is in
oid: the object id
mtime: the time to set the mtime to, NULL for the current time
flags: flags to apply to the entire operation (LIBRADOS_OPERATION)
CEPHRADOS_API int rados_aio_write_op_operate(rados_write_op_t write_op, rados_ioctx_t io, rados_completion_t completion, const char oid, time_t mtime, int flags)
Perform a write operation asynchronously
Parameters
write_op: operation to perform
io: the ioctx that the object is in
completion: what to do when operation has been attempted
oid: the object id
mtime: the time to set the mtime to, NULL for the current time
flags: flags to apply to the entire operation (LIBRADOS_OPERATION)

CEPH_RADOS_API rados_read_op_t rados_create_read_op(void)
Create a new rados_read_op_t write operation. This will store all actions to be performed atomically. You must call rados_release_read_op when you are finished with it (after it completes, or you decide not to send it in the first place).
Return
non-NULL on success, NULL on memory allocation error.
CEPH_RADOS_API void rados_release_read_op(rados_read_op_t read_op)
Free a rados_read_op_t, must be called when you’re done with it.
Parameters
read_op: operation to deallocate, created with rados_create_read_op
CEPH_RADOS_API void rados_read_op_set_flags(rados_read_op_t read_op, int flags)
Set flags for the last operation added to this read_op. At least one op must have been added to the read_op.
Parameters
read_op: operation to add this action to
flags: see librados.h constants beginning with LIBRADOS_OP_FLAG
CEPH_RADOS_API void rados_read_op_assert_exists(rados_read_op_t read_op)
Ensure that the object exists before reading
Parameters
read_op: operation to add this action to
CEPH_RADOS_API void rados_read_op_assert_version(rados_read_op_t read_op, uint64_t ver)
Ensure that the object exists and that its internal version number is equal to “ver” before reading. “ver” should be a version number previously obtained with rados_get_last_version().
If the object’s version is greater than the asserted version then rados_read_op_operate will return -ERANGE instead of executing the op.
If the object’s version is less than the asserted version then rados_read_op_operate will return -EOVERFLOW instead of executing the op.
Parameters
read_op: operation to add this action to
ver: object version number
CEPH_RADOS_API void rados_read_op_cmpext(rados_read_op_t read_op, const char cmpbuf, size_t cmp_len, uint64_t off, int prval)
Ensure that given object range (extent) satisfies comparison.
Parameters
read_op: operation to add this action to
cmp_buf: buffer containing bytes to be compared with object contents
cmp_len: length to compare and size of cmp_buf in bytes
off: object byte offset at which to start the comparison
prval: returned result of comparison, 0 on success, negative error code on failure, (-MAX_ERRNO - mismatch_off) on mismatch
CEPH_RADOS_API void rados_read_op_cmpxattr(rados_read_op_t read_op, const char name, uint8_t comparison_operator, const char value, size_t value_len)
Ensure that the an xattr satisfies a comparison If the comparison is not satisfied, the return code of the operation will be -ECANCELED
Parameters
read_op: operation to add this action to
name: name of the xattr to look up
comparison_operator: currently undocumented, look for LIBRADOS_CMPXATTR_OP_EQ in librados.h
value: buffer to compare actual xattr value to
value_len: length of buffer to compare actual xattr value to
CEPH_RADOS_API void rados_read_op_getxattrs(rados_read_op_t read_op, rados_xattrs_iter_t iter, int prval)
Start iterating over xattrs on an object.
Parameters
read_op: operation to add this action to
iter: where to store the iterator
prval: where to store the return value of this action
CEPH_RADOS_API void rados_read_op_omap_cmp(rados_read_op_t read_op, const char key, uint8_t comparison_operator, const char val, size_t val_len, int prval)
Ensure that the an omap value satisfies a comparison, with the supplied value on the right hand side (i.e. for OP_LT, the comparison is actual_value < value.
Parameters
read_op: operation to add this action to
key: which omap value to compare
comparison_operator: one of LIBRADOS_CMPXATTR_OP_EQ, LIBRADOS_CMPXATTR_OP_LT, or LIBRADOS_CMPXATTR_OP_GT
val: value to compare with
val_len: length of value in bytes
prval: where to store the return value from this action
CEPH_RADOS_API void rados_read_op_omap_cmp2(rados_read_op_t read_op, const char key, uint8_t comparison_operator, const char val, size_t key_len, size_t val_len, int prval)
Ensure that the an omap value satisfies a comparison, with the supplied value on the right hand side (i.e. for OP_LT, the comparison is actual_value < value.
Parameters
read_op: operation to add this action to
key: which omap value to compare
comparison_operator: one of LIBRADOS_CMPXATTR_OP_EQ, LIBRADOS_CMPXATTR_OP_LT, or LIBRADOS_CMPXATTR_OP_GT
val: value to compare with
key_len: length of key in bytes
val_len: length of value in bytes
prval: where to store the return value from this action
CEPH_RADOS_API void rados_read_op_stat(rados_read_op_t read_op, uint64_t psize, time_t pmtime, int prval)
Get object size and mtime
Parameters
read_op: operation to add this action to
psize: where to store object size
pmtime: where to store modification time
prval: where to store the return value of this action
CEPH_RADOS_API void rados_read_op_read(rados_read_op_t read_op, uint64_t offset, size_t len, char buffer, size_t bytes_read, int prval)
Read bytes from offset into buffer.
prlen will be filled with the number of bytes read if successful. A short read can only occur if the read reaches the end of the object.
Parameters
read_op: operation to add this action to
offset: offset to read from
len: length of buffer
buffer: where to put the data
bytes_read: where to store the number of bytes read by this action
prval: where to store the return value of this action
CEPH_RADOS_API void rados_read_op_checksum(rados_read_op_t read_op, rados_checksum_type_t type, const char init_value, size_t init_value_len, uint64_t offset, size_t len, size_t chunk_size, char pchecksum, size_t checksum_len, int prval)
Compute checksum from object data
Parameters
read_op: operation to add this action to
type: the checksum algorithm to utilize
init_value: the init value for the algorithm
init_value_len: the length of the init value
offset: the offset to start checksumming in the object
len: the number of bytes to checksum
chunk_size: optional length-aligned chunk size for checksums
pchecksum: where to store the checksum result for this action
checksum_len: the number of bytes available for the result
prval: where to store the return value for this action
CEPH_RADOS_API void rados_read_op_exec(rados_read_op_t read_op, const char cls, const char method, const char in_buf, size_t in_len, char ** out_buf, size_t out_len, int prval)
Execute an OSD class method on an object See rados_exec() for general description.
The output buffer is allocated on the heap; the caller is expected to release that memory with rados_buffer_free(). The buffer and length pointers can all be NULL, in which case they are not filled in.
Parameters
read_op: operation to add this action to
cls: the name of the class
method: the name of the method
in_buf: where to find input
in_len: length of in_buf in bytes
out_buf: where to put librados-allocated output buffer
out_len: length of out_buf in bytes
prval: where to store the return value from the method
CEPH_RADOS_API void rados_read_op_exec_user_buf(rados_read_op_t read_op, const char cls, const char method, const char in_buf, size_t in_len, char out_buf, size_t out_len, size_t used_len, int prval)
Execute an OSD class method on an object See rados_exec() for general description.
If the output buffer is too small, prval will be set to -ERANGE and used_len will be 0.
Parameters
read_op: operation to add this action to
cls: the name of the class
method: the name of the method
in_buf: where to find input
in_len: length of in_buf in bytes
out_buf: user-provided buffer to read into
out_len: length of out_buf in bytes
used_len: where to store the number of bytes read into out_buf
prval: where to store the return value from the method
CEPH_RADOS_API void rados_read_op_omap_get_vals(rados_read_op_t read_op, const char start_after, const char filter_prefix, uint64_t max_return, rados_omap_iter_t iter, int prval)
Start iterating over key/value pairs on an object.
They will be returned sorted by key.
Parameters
read_op: operation to add this action to
start_after: list keys starting after start_after
filter_prefix: list only keys beginning with filter_prefix
max_return: list no more than max_return key/value pairs
iter: where to store the iterator
prval: where to store the return value from this action
CEPH_RADOS_API void rados_read_op_omap_get_vals2(rados_read_op_t read_op, const char start_after, const char filter_prefix, uint64_t max_return, rados_omap_iter_t iter, unsigned char pmore, int prval)
Start iterating over key/value pairs on an object.
They will be returned sorted by key.
Parameters
read_op: operation to add this action to
start_after: list keys starting after start_after
filter_prefix: list only keys beginning with filter_prefix
max_return: list no more than max_return key/value pairs
iter: where to store the iterator
pmore: flag indicating whether there are more keys to fetch
prval: where to store the return value from this action
CEPH_RADOS_API void rados_read_op_omap_get_keys(rados_read_op_t read_op, const char start_after, uint64_t max_return, rados_omap_iter_t iter, int prval)
Start iterating over keys on an object.
They will be returned sorted by key, and the iterator will fill in NULL for all values if specified.
Parameters
read_op: operation to add this action to
start_after: list keys starting after start_after
max_return: list no more than max_return keys
iter: where to store the iterator
prval: where to store the return value from this action
CEPH_RADOS_API void rados_read_op_omap_get_keys2(rados_read_op_t read_op, const char start_after, uint64_t max_return, rados_omap_iter_t iter, unsigned char pmore, int prval)
Start iterating over keys on an object.
They will be returned sorted by key, and the iterator will fill in NULL for all values if specified.
Parameters
read_op: operation to add this action to
start_after: list keys starting after start_after
max_return: list no more than max_return keys
iter: where to store the iterator
pmore: flag indicating whether there are more keys to fetch
prval: where to store the return value from this action
CEPH_RADOS_API void rados_read_op_omap_get_vals_by_keys(rados_read_op_t read_op, char const const keys, size_t keys_len, rados_omap_iter_t iter, int prval)
Start iterating over specific key/value pairs
They will be returned sorted by key.
Parameters
read_op: operation to add this action to
keys: array of pointers to null-terminated keys to get
keys_len: the number of strings in keys
iter: where to store the iterator
prval: where to store the return value from this action
CEPH_RADOS_API void rados_read_op_omap_get_vals_by_keys2(rados_read_op_t read_op, char const const keys, size_t num_keys, const size_t key_lens, rados_omap_iter_t iter, int prval)
Start iterating over specific key/value pairs
They will be returned sorted by key.
Parameters
read_op: operation to add this action to
keys: array of pointers to keys to get
num_keys: the number of strings in keys
key_lens: array of size_t’s describing each key len (in bytes)
iter: where to store the iterator
prval: where to store the return value from this action
CEPH_RADOS_API int rados_read_op_operate(rados_read_op_t read_op, rados_ioctx_t io, const char * oid, int flags)
Perform a read operation synchronously
Parameters
read_op: operation to perform
io: the ioctx that the object is in
oid: the object id
flags: flags to apply to the entire operation (LIBRADOS_OPERATION)

CEPH_RADOS_API int rados_aio_read_op_operate(rados_read_op_t read_op, rados_ioctx_t io, rados_completion_t completion, const char oid, int flags)
Perform a read operation asynchronously
Parameters
readop: operation to perform
io: the ioctx that the object is in
completion: what to do when operation has been attempted
oid: the object id
flags: flags to apply to the entire operation (LIBRADOS_OPERATION)

Defines
CEPH_OSD_TMAP_HDR
CEPH_OSD_TMAP_SET
CEPH_OSD_TMAP_CREATE
CEPH_OSD_TMAP_RM
LIBRADOS_VER_MAJOR
LIBRADOS_VER_MINOR
LIBRADOS_VER_EXTRA
LIBRADOS_VERSION(maj, min, extra)
LIBRADOS_VERSION_CODE
LIBRADOS_SUPPORTS_WATCH
LIBRADOS_SUPPORTS_SERVICES
LIBRADOS_SUPPORTS_APP_METADATA
LIBRADOS_LOCK_FLAG_RENEW
LIBRADOS_CREATE_EXCLUSIVE
LIBRADOS_CREATE_IDEMPOTENT
CEPH_RADOS_API
LIBRADOS_SNAP_HEAD
LIBRADOS_SNAP_DIR
VOIDPTR_RADOS_T
Typedefs
typedef rados_t
A handle for interacting with a RADOS cluster. It encapsulates all RADOS client configuration, including username, key for authentication, logging, and debugging. Talking different clusters or to the same cluster with different users requires different cluster handles.
typedef rados_config_t
A handle for the ceph configuration context for the rados_t cluster instance. This can be used to share configuration context/state (e.g., logging configuration) between librados instance.
Warning
The config context does not have independent reference counting. As such, a rados_config_t handle retrieved from a given rados_t is only valid as long as that rados_t.
typedef rados_ioctx_t
An io context encapsulates a few settings for all I/O operations done on it:
pool - set when the io context is created (see rados_ioctx_create())
snapshot context for writes (see rados_ioctx_selfmanaged_snap_set_write_ctx())
snapshot id to read from (see rados_ioctx_snap_set_read())
object locator for all single-object operations (see rados_ioctx_locator_set_key())
namespace for all single-object operations (see rados_ioctx_set_namespace()). Set to LIBRADOS_ALL_NSPACES before rados_nobjects_list_open() will list all objects in all namespaces.
Warning
Changing any of these settings is not thread-safe - librados users must synchronize any of these changes on their own, or use separate io contexts for each thread
typedef rados_list_ctx_t
An iterator for listing the objects in a pool. Used with rados_nobjects_list_open(), rados_nobjects_list_next(), and rados_nobjects_list_close().
typedef rados_object_list_cursor
The cursor used with rados_enumerate_objects and accompanying methods.
typedef struct rados_object_list_item rados_object_list_item
typedef rados_snap_t
The id of a snapshot.
typedef rados_xattrs_iter_t
An iterator for listing extended attrbutes on an object. Used with rados_getxattrs(), rados_getxattrs_next(), and rados_getxattrs_end().
typedef rados_omap_iter_t
An iterator for listing omap key/value pairs on an object. Used with rados_read_op_omap_get_keys(), rados_read_op_omap_get_vals(), rados_read_op_omap_get_vals_by_keys(), rados_omap_get_next(), and rados_omap_get_end().
typedef rados_write_op_t
An object write operation stores a number of operations which can be executed atomically. For usage, see:
Creation and deletion: rados_create_write_op() rados_release_write_op()
Extended attribute manipulation: rados_write_op_cmpxattr() rados_write_op_cmpxattr(), rados_write_op_setxattr(), rados_write_op_rmxattr()
Object map key/value pairs: rados_write_op_omap_set(), rados_write_op_omap_rm_keys(), rados_write_op_omap_clear(), rados_write_op_omap_cmp()
Object properties: rados_write_op_assert_exists(), rados_write_op_assert_version()
Creating objects: rados_write_op_create()
IO on objects: rados_write_op_append(), rados_write_op_write(), rados_write_op_zero rados_write_op_write_full(), rados_write_op_writesame(), rados_write_op_remove, rados_write_op_truncate(), rados_write_op_zero(), rados_write_op_cmpext()
Hints: rados_write_op_set_alloc_hint()
Performing the operation: rados_write_op_operate(), rados_aio_write_op_operate()
typedef rados_read_op_t
An object read operation stores a number of operations which can be executed atomically. For usage, see:
Creation and deletion: rados_create_read_op() rados_release_read_op()
Extended attribute manipulation: rados_read_op_cmpxattr(), rados_read_op_getxattr(), rados_read_op_getxattrs()
Object map key/value pairs: rados_read_op_omap_get_vals(), rados_read_op_omap_get_keys(), rados_read_op_omap_get_vals_by_keys(), rados_read_op_omap_cmp()
Object properties: rados_read_op_stat(), rados_read_op_assert_exists(), rados_read_op_assert_version()
IO on objects: rados_read_op_read(), rados_read_op_checksum(), rados_read_op_cmpext()
Custom operations: rados_read_op_exec(), rados_read_op_exec_user_buf()
Request properties: rados_read_op_set_flags()
Performing the operation: rados_read_op_operate(), rados_aio_read_op_operate()
typedef rados_completion_t
Represents the state of an asynchronous operation - it contains the return value once the operation completes, and can be used to block until the operation is complete or safe.
Enums
@anon_0
Values:
0x1
0x2
0x4
0x8
0x10
0x20
0x40
0x80
rados_checksum_type_t
Values:
0
1
2
Functions
CEPH_RADOS_API void rados_version(int major, int minor, int extra)
Get the version of librados.
The version number is major.minor.extra. Note that this is unrelated to the Ceph version number.
TODO: define version semantics, i.e.:
incrementing major is for backwards-incompatible changes
incrementing minor is for backwards-compatible changes
incrementing extra is for bug fixes
Parameters
major: where to store the major version number
minor: where to store the minor version number
extra: where to store the extra version number
CEPH_RADOS_API int rados_cluster_stat(rados_t cluster, struct rados_cluster_stat_t result)
Read usage info about the cluster
This tells you total space, space used, space available, and number of objects. These are not updated immediately when data is written, they are eventually consistent.
Return
0 on success, negative error code on failure
Parameters
cluster: cluster to query
result: where to store the results
CEPH_RADOS_API int rados_cluster_fsid(rados_t cluster, char buf, size_t len)
Get the fsid of the cluster as a hexadecimal string.
The fsid is a unique id of an entire Ceph cluster.
Return
0 on success, negative error code on failure
Return
-ERANGE if the buffer is too short to contain the fsid
Parameters
cluster: where to get the fsid
buf: where to write the fsid
len: the size of buf in bytes (should be 37)
CEPH_RADOS_API int rados_wait_for_latest_osdmap(rados_t cluster)
Get/wait for the most recent osdmap
Return
0 on success, negative error code on failure
Parameters
cluster: the cluster to shutdown
CEPH_RADOS_API int rados_omap_get_next(rados_omap_iter_t iter, char key, char val, size_t len)
Get the next omap key/value pair on the object
Pre
iter is a valid iterator
Post
key and val are the next key/value pair. key is null-terminated, and val has length len. If the end of the list has been reached, key and val are NULL, and len is 0. key and val will not be accessible after rados_omap_get_end() is called on iter, so if they are needed after that they should be copied.
Return
0 on success, negative error code on failure
Parameters
iter: iterator to advance
key: where to store the key of the next omap entry
val: where to store the value of the next omap entry
len: where to store the number of bytes in val
CEPH_RADOS_API int rados_omap_get_next2(rados_omap_iter_t iter, char key, char val, size_t key_len, size_t val_len)
Get the next omap key/value pair on the object. Note that it’s perfectly safe to mix calls to rados_omap_get_next and rados_omap_get_next2.
Pre
iter is a valid iterator
Post
key and val are the next key/value pair. key has length keylen and val has length vallen. If the end of the list has been reached, key and val are NULL, and keylen and vallen is 0. key and val will not be accessible after rados_omap_get_end() is called on iter, so if they are needed after that they should be copied.
Return
0 on success, negative error code on failure
Parameters
iter: iterator to advance
key: where to store the key of the next omap entry
val: where to store the value of the next omap entry
key_len: where to store the number of bytes in key
val_len: where to store the number of bytes in val
CEPH_RADOS_API unsigned int rados_omap_iter_size(rados_omap_iter_t iter)
Return number of elements in the iterator
Parameters
iter: the iterator of which to return the size
CEPH_RADOS_API void rados_omap_get_end(rados_omap_iter_t iter)
Close the omap iterator.
iter should not be used after this is called.
Parameters
iter: the iterator to close
CEPH_RADOS_API int rados_stat(rados_ioctx_t io, const char o, uint64_t psize, time_t pmtime)
Get object stats (size/mtime)
TODO: when are these set, and by whom? can they be out of date?
Return
0 on success, negative error code on failure
Parameters
io: ioctx
o: object name
psize: where to store object size
pmtime: where to store modification time
CEPH_RADOS_API int rados_exec(rados_ioctx_t io, const char oid, const char cls, const char method, const char in_buf, size_t in_len, char buf, size_t out_len)
Execute an OSD class method on an object
The OSD has a plugin mechanism for performing complicated operations on an object atomically. These plugins are called classes. This function allows librados users to call the custom methods. The input and output formats are defined by the class. Classes in ceph.git can be found in src/cls subdirectories
Return
the length of the output, or -ERANGE if out_buf does not have enough space to store it (For methods that return data). For methods that don’t return data, the return value is method-specific.
Parameters
io: the context in which to call the method
oid: the object to call the method on
cls: the name of the class
method: the name of the method
in_buf: where to find input
in_len: length of in_buf in bytes
buf: where to store output
out_len: length of buf in bytes
CEPH_RADOS_API int rados_cache_pin(rados_ioctx_t io, const char o)
Pin an object in the cache tier
When an object is pinned in the cache tier, it stays in the cache tier, and won’t be flushed out.
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the object id
CEPH_RADOS_API int rados_cache_unpin(rados_ioctx_t io, const char o)
Unpin an object in the cache tier
After an object is unpinned in the cache tier, it can be flushed out
Return
0 on success, negative error code on failure
Parameters
io: the pool the object is in
o: the object id
CEPH_RADOS_API int rados_lock_exclusive(rados_ioctx_t io, const char oid, const char name, const char cookie, const char desc, struct timeval duration, uint8_t flags)
Take an exclusive lock on an object.
Return
0 on success, negative error code on failure
Return
-EBUSY if the lock is already held by another (client, cookie) pair
Return
-EEXIST if the lock is already held by the same (client, cookie) pair
Parameters
io: the context to operate in
oid: the name of the object
name: the name of the lock
cookie: user-defined identifier for this instance of the lock
desc: user-defined lock description
duration: the duration of the lock. Set to NULL for infinite duration.
flags: lock flags
CEPH_RADOS_API int rados_lock_shared(rados_ioctx_t io, const char o, const char name, const char cookie, const char tag, const char desc, struct timeval duration, uint8_t flags)
Take a shared lock on an object.
Return
0 on success, negative error code on failure
Return
-EBUSY if the lock is already held by another (client, cookie) pair
Return
-EEXIST if the lock is already held by the same (client, cookie) pair
Parameters
io: the context to operate in
o: the name of the object
name: the name of the lock
cookie: user-defined identifier for this instance of the lock
tag: The tag of the lock
desc: user-defined lock description
duration: the duration of the lock. Set to NULL for infinite duration.
flags: lock flags
CEPH_RADOS_API int rados_unlock(rados_ioctx_t io, const char o, const char name, const char cookie)
Release a shared or exclusive lock on an object.
Return
0 on success, negative error code on failure
Return
-ENOENT if the lock is not held by the specified (client, cookie) pair
Parameters
io: the context to operate in
o: the name of the object
name: the name of the lock
cookie: user-defined identifier for the instance of the lock
CEPH_RADOS_API int rados_aio_unlock(rados_ioctx_t io, const char o, const char name, const char cookie, rados_completion_t completion)
Asynchronous release a shared or exclusive lock on an object.
Return
0 on success, negative error code on failure
Parameters
io: the context to operate in
o: the name of the object
name: the name of the lock
cookie: user-defined identifier for the instance of the lock
completion: what to do when operation has been attempted
CEPH_RADOS_API ssize_t rados_list_lockers(rados_ioctx_t io, const char o, const char name, int exclusive, char tag, size_t tag_len, char clients, size_t clients_len, char cookies, size_t cookies_len, char addrs, size_t addrs_len)
List clients that have locked the named object lock and information about the lock.
The number of bytes required in each buffer is put in the corresponding size out parameter. If any of the provided buffers are too short, -ERANGE is returned after these sizes are filled in.
Return
number of lockers on success, negative error code on failure
Return
-ERANGE if any of the buffers are too short
Parameters
io: the context to operate in
o: the name of the object
name: the name of the lock
exclusive: where to store whether the lock is exclusive (1) or shared (0)
tag: where to store the tag associated with the object lock
tag_len: number of bytes in tag buffer
clients: buffer in which locker clients are stored, separated by ‘\0’
clients_len: number of bytes in the clients buffer
cookies: buffer in which locker cookies are stored, separated by ‘\0’
cookies_len: number of bytes in the cookies buffer
addrs: buffer in which locker addresses are stored, separated by ‘\0’
addrs_len: number of bytes in the clients buffer
CEPH_RADOS_API int rados_break_lock(rados_ioctx_t io, const char o, const char name, const char client, const char cookie)
Releases a shared or exclusive lock on an object, which was taken by the specified client.
Return
0 on success, negative error code on failure
Return
-ENOENT if the lock is not held by the specified (client, cookie) pair
Return
-EINVAL if the client cannot be parsed
Parameters
io: the context to operate in
o: the name of the object
name: the name of the lock
client: the client currently holding the lock
cookie: user-defined identifier for the instance of the lock
CEPH_RADOS_API int rados_blacklist_add(rados_t cluster, char client_address, uint32_t expire_seconds)
Blacklists the specified client from the OSDs
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle
client_address: client address
expire_seconds: number of seconds to blacklist (0 for default)
CEPH_RADOS_API int rados_getaddrs(rados_t cluster, char addrs)
Gets addresses of the RADOS session, suitable for blacklisting.
Return
0 on success, negative error code on failure
Parameters
cluster: cluster handle
addrs: the output string.
CEPH_RADOS_API void rados_set_osdmap_full_try(rados_ioctx_t io)
CEPH_RADOS_API void rados_unset_osdmap_full_try(rados_ioctx_t io)
CEPH_RADOS_API void rados_set_pool_full_try(rados_ioctx_t io)
CEPH_RADOS_API void rados_unset_pool_full_try(rados_ioctx_t io)
CEPH_RADOS_API int rados_application_enable(rados_ioctx_t io, const char app_name, int force)
Enable an application on a pool
Return
0 on success, negative error code on failure
Parameters
io: pool ioctx
app_name: application name
force: 0 if only single application per pool
CEPH_RADOS_API int rados_application_list(rados_ioctx_t io, char values, size_t values_len)
List all enabled applications
If the provided buffer is too short, the required length is filled in and -ERANGE is returned. Otherwise, the buffers are filled with the application names, with a ‘\0’ after each.
Return
0 on success, negative error code on failure
Return
-ERANGE if either buffer is too short
Parameters
io: pool ioctx
values: buffer in which to store application names
values_len: number of bytes in values buffer
CEPH_RADOS_API int rados_application_metadata_get(rados_ioctx_t io, const char app_name, const char key, char value, size_t value_len)
Get application metadata value from pool
Return
0 on success, negative error code on failure
Parameters
io: pool ioctx
app_name: application name
key: metadata key
value: result buffer
value_len: maximum len of value
CEPH_RADOS_API int rados_application_metadata_set(rados_ioctx_t io, const char app_name, const char key, const char value)
Set application metadata on a pool
Return
0 on success, negative error code on failure
Parameters
io: pool ioctx
app_name: application name
key: metadata key
value: metadata key
CEPH_RADOS_API int rados_application_metadata_remove(rados_ioctx_t io, const char app_name, const char key)
Remove application metadata from a pool
Return
0 on success, negative error code on failure
Parameters
io: pool ioctx
app_name: application name
key: metadata key
CEPH_RADOS_API int rados_application_metadata_list(rados_ioctx_t io, const char app_name, char keys, size_t key_len, char values, size_t vals_len)
List all metadata key/value pairs associated with an application.
This iterates over all metadata, key_len and val_len are filled in with the number of bytes put into the keys and values buffers.
If the provided buffers are too short, the required lengths are filled in and -ERANGE is returned. Otherwise, the buffers are filled with the keys and values of the metadata, with a ‘\0’ after each.
Return
0 on success, negative error code on failure
Return
-ERANGE if either buffer is too short
Parameters
io: pool ioctx
app_name: application name
keys: buffer in which to store key names
key_len: number of bytes in keys buffer
values: buffer in which to store values
vals_len: number of bytes in values buffer
CEPH_RADOS_API int rados_objects_list_open(rados_ioctx_t io, rados_list_ctx_t ctx)
CEPH_RADOS_API uint32_t rados_objects_list_get_pg_hash_position(rados_list_ctx_t ctx)
CEPH_RADOS_API uint32_t rados_objects_list_seek(rados_list_ctx_t ctx, uint32_t pos)
CEPH_RADOS_API int rados_objects_list_next(rados_list_ctx_t ctx, const char entry, const char * key)

CEPH_RADOS_API void rados_objects_list_close(rados_list_ctx_t ctx)
struct rados_object_list_item
#include <librados.h>
The item populated by rados_object_list in the results array.
Public Members
size_t oid_length
oid length
char oid
name of the object
size_t nspace_length
namespace length
char nspace
the object namespace
size_t locator_length
locator length
char locator
object locator
struct rados_pool_stat_t
#include <librados.h>
Usage information for a pool.
Public Members
uint64_t num_bytes
space used in bytes
uint64_t num_kb
space used in KB
uint64_t num_objects
number of objects in the pool
uint64_t num_object_clones
number of clones of objects
uint64_t num_object_copies
num_objects * num_replicas
uint64_t num_objects_missing_on_primary
number of objects missing on primary
uint64_t num_objects_unfound
number of objects found on no OSDs
uint64_t num_objects_degraded
number of objects replicated fewer times than they should be (but found on at least one OSD)
uint64_t num_rd
number of objects read
uint64_t num_rd_kb
objects read in KB
uint64_t num_wr
number of objects written
uint64_t num_wr_kb
objects written in KB
uint64_t num_user_bytes
bytes originally provided by user
uint64_t compressed_bytes_orig
bytes passed compression
uint64_t compressed_bytes
bytes resulted after compression
uint64_t compressed_bytes_alloc
bytes allocated at storage
struct rados_cluster_stat_t
#include <librados.h>
Cluster-wide usage information
Public Members
uint64_t kb
total device size
uint64_t kb_used
total used
uint64_t kb_avail
total available/free
uint64_t num_objects
number of objects

librados (C)

Librados (C)

Example: connecting and writing an object

Asynchronous IO

API calls