nbd_aio_block_status - Man Page

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.

Return Value

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).

Handle State

The handle must be connected with the server, otherwise this call will return an 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:


See Also

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


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

Referenced By

libnbd(3), nbd_aio_block_status_64(3), nbd_block_status(3).

2023-09-08 libnbd-1.17.5