Man page - nbd_aio_block_status(3)

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nbd_aio_block_status(3) LIBNBD nbd_aio_block_status(3)

nbd_aio_block_status - send block status command, with 32-bit callback

 #include <libnbd.h>
 typedef struct {
   int (*callback) (void *user_data,
                    const char *metacontext,
                    uint64_t offset, uint32_t *entries,
                    size_t nr_entries, int *error);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_extent_callback;
 typedef struct {
   int (*callback) (void *user_data, int *error);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_completion_callback;
 int64_t nbd_aio_block_status (
           struct nbd_handle *h, uint64_t count,
           uint64_t offset,
           nbd_extent_callback extent_callback,
           nbd_completion_callback completion_callback,
           uint32_t flags
         );

Send the block status command to the NBD server.

To check if the command completed, call nbd_aio_command_completed(3). Or supply the optional "completion_callback" which will be invoked as described in "Completion callbacks" in libnbd(3).

Other parameters behave as documented in nbd_block_status(3).

This function is inherently limited to 32-bit values. If the server replies with a larger extent, the length of that extent will be truncated to just below 32 bits and any further extents from the server will be ignored. If the server replies with a status value larger than 32 bits (only possible when extended headers are in use), the callback function will be passed an "EOVERFLOW" error. To get the full extent information from a server that supports 64-bit extents, you must use nbd_aio_block_status_64(3).

By default, libnbd will reject attempts to use this function with parameters that are likely to result in server failure, such as requesting an unknown command flag. The nbd_set_strict_mode(3) function can be used to alter which scenarios should await a server reply rather than failing fast.

This call returns the 64 bit cookie of the command. The cookie is ≥ 1. Cookies are unique (per libnbd handle, not globally).

On error -1 is returned.

Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

The following parameters must not be NULL: "h". For more information see "Non-NULL parameters" in libnbd(3).

nbd_aio_block_status can be called when the handle is in the following state:

 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ❌ error                │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ❌ error                │
 │ Connected to the server             │ ✅ allowed              │
 │ Connection shut down                │ ❌ error                │
 │ Handle dead                         │ ❌ error                │
 └─────────────────────────────────────┴─────────────────────────┘

This function first appeared in libnbd 1.0.

If you need to test if this function is available at compile time check if the following macro is defined:

 #define LIBNBD_HAVE_NBD_AIO_BLOCK_STATUS 1

nbd_aio_block_status_64(3), nbd_aio_command_completed(3), nbd_block_status(3), nbd_can_meta_context(3), nbd_create(3), nbd_set_strict_mode(3), "Issuing asynchronous commands" in libnbd(3), libnbd(3).

Eric Blake

Richard W.M. Jones

Copyright Red Hat

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

2025-06-14 libnbd-1.22.2