NAME

       nbd_add_meta_context - ask server to negotiate metadata context

SYNOPSIS

        #include <libnbd.h>

        int nbd_add_meta_context (
              struct nbd_handle *h, const char *name
            );

DESCRIPTION

       During connection libnbd can negotiate zero or more metadata contexts with the server.
       Metadata contexts are features (such as "base:allocation") which describe information
       returned by the nbd_block_status(3) command (for "base:allocation" this is whether blocks
       of data are allocated, zero or sparse).

       This call adds one metadata context to the list to be negotiated.  You can call it as many
       times as needed.  The list is initially empty when the handle is created; you can check
       the contents of the list with nbd_get_nr_meta_contexts(3) and nbd_get_meta_context(3), or
       clear it with nbd_clear_meta_contexts(3).

       The NBD protocol limits meta context names to 4096 bytes, but servers may not support the
       full length.  The encoding of meta context names is always UTF-8.

       Not all servers support all metadata contexts.  To learn if a context was actually
       negotiated, call nbd_can_meta_context(3) after connecting.

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

       Other metadata contexts are server-specific, but include "qemu:dirty-bitmap:..." and
       "qemu:allocation-depth" for qemu-nbd (see qemu-nbd -B and -A options).

RETURN VALUE

       If the call is successful the function returns 0.

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

HANDLE STATE

       The handle must be newly created, or negotiating, otherwise this call will return an
       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_ADD_META_CONTEXT 1

SEE ALSO

       nbd_block_status(3), nbd_can_meta_context(3), nbd_clear_meta_contexts(3), nbd_create(3),
       nbd_get_meta_context(3), nbd_get_nr_meta_contexts(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