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.\"
.IX Title "nbd_can_meta_context 3"
.TH nbd_can_meta_context 3 2024-05-08 libnbd-1.20.1 LIBNBD
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH NAME
nbd_can_meta_context \- does the server support a specific meta context?
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <libnbd.h>
\&
\& int nbd_can_meta_context (
\&       struct nbd_handle *h, const char *metacontext
\&     );
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Returns true if the server supports the given meta context
(see \fBnbd_add_meta_context\fR\|(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.
.PP
If the server supports block status filtering (see
\&\fBnbd_can_block_status_payload\fR\|(3), this function must return
true for any filter name passed to \fBnbd_block_status_filter\fR\|(3).
.PP
The single parameter is the name of the metadata context,
for example \f(CW\*(C`LIBNBD_CONTEXT_BASE_ALLOCATION\*(C'\fR.
\&\fB<libnbd.h>\fR includes defined constants for well-known
namespace contexts beginning with \f(CW\*(C`LIBNBD_CONTEXT_\*(C'\fR, but you
are free to pass in other contexts.
.PP
This call does not block, because it returns data that is saved in
the handle from the NBD protocol handshake.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
This call returns a boolean value.
.SH ERRORS
.IX Header "ERRORS"
On error \f(CW\-1\fR is returned.
.PP
Refer to "ERROR HANDLING" in \fBlibnbd\fR\|(3)
for how to get further details of the error.
.PP
The following parameters must not be NULL: \f(CW\*(C`h\*(C'\fR, \f(CW\*(C`metacontext\*(C'\fR.
For more information see "Non-NULL parameters" in \fBlibnbd\fR\|(3).
.SH "HANDLE STATE"
.IX Header "HANDLE STATE"
nbd_can_meta_context
can be called when the handle is in the following states:
.PP
.Vb 8
\& ┌─────────────────────────────────────┬─────────────────────────┐
\& │ Handle created, before connecting   │ ❌ error                │
\& │ Connecting                          │ ❌ error                │
\& │ Connecting & handshaking (opt_mode) │ ✅ allowed              │
\& │ Connected to the server             │ ✅ allowed              │
\& │ Connection shut down                │ ✅ allowed              │
\& │ Handle dead                         │ ❌ error                │
\& └─────────────────────────────────────┴─────────────────────────┘
.Ve
.SH VERSION
.IX Header "VERSION"
This function first appeared in libnbd 1.0.
.PP
If you need to test if this function is available at compile time
check if the following macro is defined:
.PP
.Vb 1
\& #define LIBNBD_HAVE_NBD_CAN_META_CONTEXT 1
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbd_add_meta_context\fR\|(3),
\&\fBnbd_aio_block_status_64\fR\|(3),
\&\fBnbd_block_status_64\fR\|(3),
\&\fBnbd_block_status_filter\fR\|(3),
\&\fBnbd_can_block_status_payload\fR\|(3),
\&\fBnbd_create\fR\|(3),
\&\fBnbd_opt_info\fR\|(3),
\&\fBnbd_opt_set_meta_context\fR\|(3),
\&\fBnbd_set_request_meta_context\fR\|(3),
"Flag calls" in \fBlibnbd\fR\|(3),
\&\fBlibnbd\fR\|(3).
.SH AUTHORS
.IX Header "AUTHORS"
Eric Blake
.PP
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "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.
.PP
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.
.PP
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