NAME

nbd_can_meta_context - does the server support a specific meta context?

SYNOPSIS

 #include <libnbd.h>

 int nbd_can_meta_context (
       struct nbd_handle *h, const char *metacontext
     );

DESCRIPTION

Returns true if the server supports the given meta context (see nbd_add_meta_context(3)). Returns false if the server does not. It is possible for this command to fail if meta contexts were requested but there is a missing or failed attempt at NBD_OPT_SET_META_CONTEXT during option negotiation.

If the server supports block status filtering (see nbd_can_block_status_payload(3), this function must return true for any filter name passed to nbd_block_status_filter(3).

The single parameter is the name of the metadata context, for example LIBNBD_CONTEXT_BASE_ALLOCATION. <libnbd.h> includes defined constants for well-known namespace contexts beginning with LIBNBD_CONTEXT_, but you are free to pass in other contexts.

RETURN VALUE

This call returns a boolean value.

ERRORS

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

NOTES

Non-blocking call

This call does not block, because it returns data that is saved in the handle from the NBD protocol handshake.

HANDLE STATE

nbd_can_meta_context can be called when the handle is in the following states:

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

VERSION

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_CAN_META_CONTEXT 1

SEE ALSO

nbd_add_meta_context(3), nbd_aio_block_status_64(3), nbd_block_status_64(3), nbd_block_status_filter(3), nbd_can_block_status_payload(3), nbd_create(3), nbd_opt_info(3), nbd_opt_set_meta_context(3), nbd_set_request_meta_context(3), "Flag calls" in libnbd(3), libnbd(3).

AUTHORS

Eric Blake

Richard W.M. Jones

COPYRIGHT

Copyright Red Hat

LICENSE

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