nbd_add_meta_context - ask server to negotiate metadata context
#include <libnbd.h> int nbd_add_meta_context (struct nbd_handle *h, const char *name);
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.
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:..." for qemu-nbd (see qemu-nbd -B option).
If the call is successful the function returns
-1 is returned.
Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.
The handle must be newly created, 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:
#define LIBNBD_HAVE_NBD_ADD_META_CONTEXT 1
nbd_block_status(3), nbd_can_meta_context(3), nbd_create(3), libnbd(3).
Richard W.M. Jones
Copyright (C) 2019-2020 Red Hat Inc.
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