nbd_block_status_filter - send filtered block status command, with 64-bit callback


 #include <libnbd.h>

 typedef struct {
   int (*callback) (void *user_data,
                    const char *metacontext,
                    uint64_t offset, nbd_extent *entries,
                    size_t nr_entries, int *error);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_extent64_callback;

 int nbd_block_status_filter (
       struct nbd_handle *h, uint64_t count,
       uint64_t offset, char **contexts,
       nbd_extent64_callback extent64_callback,
       uint32_t flags


Issue a filtered block status command to the NBD server. If supported by the server (see nbd_can_block_status_payload(3)), this causes metadata context information about blocks beginning from the specified offset to be returned, and with the result limited to just the contexts specified in filter. Note that all strings in filter must be supported by nbd_can_meta_context(3).

All other parameters to this function have the same semantics as in nbd_block_status_64(3); except that for convenience, unless <nbd_set_strict_flags(3)> was used to disable LIBNBD_STRICT_AUTO_FLAG, libnbd ignores the presence or absence of the flag LIBNBD_CMD_FLAG_PAYLOAD_LEN in flags, while correctly using the flag over the wire.

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.


If the call is successful the function returns 0.


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, contexts. For more information see "Non-NULL parameters" in libnbd(3).


nbd_block_status_filter 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 1.18.

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



nbd_aio_block_status_filter(3), nbd_block_status_64(3), nbd_can_block_status_payload(3), nbd_can_meta_context(3), nbd_create(3), nbd_set_strict_mode(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