Librados (C)¶

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

Example: connecting and writing an object¶

To use Librados, you instantiate a rados_t variable (a cluster handle) and call 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()), using command line options (rados_conf_parse_argv()), or an environment 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 example write into an object called greeting with rados_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’ll want to close your IO context and connection to RADOS with rados_ioctx_destroy() and rados_shutdown():

rados_ioctx_destroy(io);
rados_shutdown(cluster);

Asychronous IO¶

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

rados_aio_write()
rados_aio_append()
rados_aio_write_full()
rados_aio_read()

For each operation, you must first create a rados_completion_t that represents what to do when the operation is safe or complete by calling rados_aio_create_completion(). If you don’t need anything special 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 to be 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_wait_for_complete(comp); // in memory
rados_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 are durable, or when read buffers are full. For example, if you wanted to measure the latency of each operation when appending to several objects, you could schedule several writes and store the ack and commit time in the corresponding callback, then wait for all of them to complete using rados_aio_flush() before analyzing the latencies:

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

LIBRADOS_ALL_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 addr[256]¶

int64_t watcher_id¶

uint64_t cookie¶

uint32_t timeout_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.

enum [anonymous]¶

Values:

LIBRADOS_CMPXATTR_OP_EQ = 1¶

LIBRADOS_CMPXATTR_OP_NE = 2¶

LIBRADOS_CMPXATTR_OP_GT = 3¶

LIBRADOS_CMPXATTR_OP_GTE = 4¶

LIBRADOS_CMPXATTR_OP_LT = 5¶

LIBRADOS_CMPXATTR_OP_LTE = 6¶

Operation Flags

Flags for rados_read_op_opeprate(), rados_write_op_operate(), rados_aio_read_op_operate(), and rados_aio_write_op_operate(). See librados.hpp for details.

enum [anonymous]¶

Values:

LIBRADOS_OPERATION_NOFLAG = 0¶

LIBRADOS_OPERATION_BALANCE_READS = 1¶

LIBRADOS_OPERATION_LOCALIZE_READS = 2¶

LIBRADOS_OPERATION_ORDER_READS_WRITES = 4¶

LIBRADOS_OPERATION_IGNORE_CACHE = 8¶

LIBRADOS_OPERATION_SKIPRWLOCKS = 16¶

LIBRADOS_OPERATION_IGNORE_OVERLAY = 32¶

Asynchronous I/O

Read and write to objects without blocking.

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.

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.

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 relpicas

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_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 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)

Asychronously 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)

Asychronously 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_remove(rados_ioctx_t io, const char * oid, rados_completion_t completion)

Asychronously 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)

Asychronously 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

psize -
where to store object size

pmtime -
where to store modification time

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

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

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: watch timeout should be configurable

BUG: librados should provide a way for watchers to notice connection resets

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

-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 30 seconds. Watches are automatically reestablished when a new connection is made, or a placement group switches OSDs.

Note

BUG: watch timeout should be configurable

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_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_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

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_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)

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

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_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

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)

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.)

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.)

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)

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

mon_id -
ID of the monitor to ping

outstr -
double pointer with the resulting reply

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 sucess, 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.

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

All possible options can be found in src/common/config_opts.h in ceph.git

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

-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

-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.

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 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_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.

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 hadnle 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

-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 owner is the admin user (auid 0). 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

The auid is the authenticated user id to give ownership of the pool. TODO: document auid and the rest of the auth system

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

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

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.”

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

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 uint64_t rados_ioctx_pool_required_alignment(rados_ioctx_t io)

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.

This is useful if you need to do clone_range operations, which must be done with the source and destination objects 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

New 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 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_objects_list_*

Return

0 on success, negative error code on failure

-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)

CEPH_RADOS_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

Deprecated Listing Objects

Older listing objects interface. Please use the new interface.

CEPH_RADOS_API int rados_objects_list_open(rados_ioctx_t io, rados_list_ctx_t * ctx)

Warning

Deprecated: Use rados_nobjects_list_open() instead

CEPH_RADOS_API uint32_t rados_objects_list_get_pg_hash_position(rados_list_ctx_t ctx)

Warning

Deprecated: Use rados_nobjects_list_get_pg_hash_position() instead

CEPH_RADOS_API uint32_t rados_objects_list_seek(rados_list_ctx_t ctx, uint32_t pos)

Warning

Deprecated: Use rados_nobjects_list_seek() instead

CEPH_RADOS_API int rados_objects_list_next(rados_list_ctx_t ctx, const char ** entry, const char ** key)

Warning

Deprecated: Use rados_nobjects_list_next() instead

CEPH_RADOS_API void rados_objects_list_close(rados_list_ctx_t ctx)

Warning

Deprecated: Use rados_nobjects_list_close() instead

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 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 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

-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

-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

-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_clone_range(rados_ioctx_t io, const char * dst, uint64_t dst_off, const char * src, uint64_t src_off, size_t len)

Efficiently copy a portion of one object to another

If the underlying filesystem on the OSD supports it, this will be a copy-on-write clone.

The src and dest objects must be in the same pg. To ensure this, the io context should have a locator key set (see rados_ioctx_locator_set_key()).

Return

0 on success, negative error code on failure

Parameters

io -
the context in which the data is cloned

dst -
the name of the destination object

dst_off -
the offset within the destination object (in bytes)

src -
the name of the source object

src_off -
the offset within the source object (in bytes)

len -
how much data to copy

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_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

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

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

Object Operations

A single rados operation can do multiple operations on one object atomicly. The whole operation will suceed 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

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_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_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_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_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_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 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_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

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_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_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_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_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_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 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

read_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

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_LOCK_FLAG_RENEW¶

LIBRADOS_CREATE_EXCLUSIVE¶

LIBRADOS_CREATE_IDEMPOTENT¶

CEPH_RADOS_API¶

LIBRADOS_SNAP_HEAD¶

LIBRADOS_SNAP_DIR¶

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 void* rados_config_t¶

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_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_remove, rados_write_op_truncate(), rados_write_op_zero()

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()

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()

Enums

enum [anonymous]¶

Values:

LIBRADOS_OP_FLAG_EXCL = 0x1¶

LIBRADOS_OP_FLAG_FAILOK = 0x2¶

LIBRADOS_OP_FLAG_FADVISE_RANDOM = 0x4¶

LIBRADOS_OP_FLAG_FADVISE_SEQUENTIAL = 0x8¶

LIBRADOS_OP_FLAG_FADVISE_WILLNEED = 0x10¶

LIBRADOS_OP_FLAG_FADVISE_DONTNEED = 0x20¶

LIBRADOS_OP_FLAG_FADVISE_NOCACHE = 0x40¶

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

-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 sucess, 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 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_tmap_update(rados_ioctx_t io, const char * o, const char * cmdbuf, size_t cmdbuflen)

Update tmap (trivial map)

Do compound update to a tmap object, inserting or deleting some number of records. cmdbuf is a series of operation byte codes, following by command payload. Each command is a single-byte command code, whose value is one of CEPH_OSD_TMAP_*.

update tmap ‘header’

1 byte = CEPH_OSD_TMAP_HDR

4 bytes = data length (little endian)

N bytes = data

insert/update one key/value pair

1 byte = CEPH_OSD_TMAP_SET

4 bytes = key name length (little endian)

N bytes = key name

4 bytes = data length (little endian)

M bytes = data

insert one key/value pair; return -EEXIST if it already exists.

1 byte = CEPH_OSD_TMAP_CREATE

4 bytes = key name length (little endian)

N bytes = key name

4 bytes = data length (little endian)

M bytes = data

remove one key/value pair

1 byte = CEPH_OSD_TMAP_RM

4 bytes = key name length (little endian)

N bytes = key name

Restrictions:

The HDR update must preceed any key/value updates.

All key/value updates must be in lexicographically sorted order in cmdbuf.

You can read/write to a tmap object via the regular APIs, but you should be careful not to corrupt it. Also be aware that the object format may change without notice.

Return

0 on success, negative error code on failure

Parameters

io -
ioctx

o -
object name

cmdbuf -
command buffer

cmdbuflen -
command buffer length in bytes

CEPH_RADOS_API int rados_tmap_put(rados_ioctx_t io, const char * o, const char * buf, size_t buflen)

Store complete tmap (trivial map) object

Put a full tmap object into the store, replacing what was there.

The format of buf is:

4 bytes - length of header (little endian)

N bytes - header data

4 bytes - number of keys (little endian)

and for each key,

4 bytes - key name length (little endian)

N bytes - key name

4 bytes - value length (little endian)

M bytes - value data

Return

0 on success, negative error code on failure

Parameters

io -
ioctx

o -
object name

buf -
buffer

buflen -
buffer length in bytes

CEPH_RADOS_API int rados_tmap_get(rados_ioctx_t io, const char * o, char * buf, size_t buflen)

Fetch complete tmap (trivial map) object

Read a full tmap object. See rados_tmap_put() for the format the data is returned in.

Return

0 on success, negative error code on failure

-ERANGE if buf isn’t big enough

Parameters

io -
ioctx

o -
object name

buf -
buffer

buflen -
buffer length in bytes

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_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

-EBUSY if the lock is already held by another (client, cookie) pair

-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

-EBUSY if the lock is already held by another (client, cookie) pair

-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

-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 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

-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

-ENOENT if the lock is not held by the specified (client, cookie) pair

-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)

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¶

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¶

uint64_t num_rd_kb¶

uint64_t num_wr¶

uint64_t num_wr_kb¶

struct rados_cluster_stat_t¶

#include <librados.h>
Cluster-wide usage information

Public Members

uint64_t kb¶

uint64_t kb_used¶

uint64_t kb_avail¶

uint64_t num_objects¶

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