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nbd_get_extended_headers_negotiated - Man Page

see if extended headers are in use


 #include <libnbd.h>

 int nbd_get_extended_headers_negotiated (
       struct nbd_handle *h


After connecting you may call this to find out if the connection is using extended headers.  Note that this setting is sticky; this can return true even after a second nbd_opt_extended_headers(3) returns false because the server detected a duplicate request.

When extended headers are not in use, commands are limited to a 32-bit length, even when the libnbd API uses a 64-bit parameter to express the length.  But even when extended headers are supported, the server may enforce other limits, visible through nbd_get_block_size(3).

Note that when extended headers are negotiated, you should prefer the use of nbd_block_status_64(3) instead of nbd_block_status(3) if any of the meta contexts you requested via nbd_add_meta_context(3) might return 64-bit status values; however, all of the well-known meta contexts covered by current LIBNBD_CONTEXT_* constants only return 32-bit status.

Return Value

This call returns a boolean value.


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

Handle State

nbd_get_extended_headers_negotiated 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                │


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:


See Also

nbd_add_meta_context(3), nbd_block_status(3), nbd_block_status_64(3), nbd_cache(3), nbd_create(3), nbd_get_block_size(3), nbd_get_protocol(3), nbd_get_request_extended_headers(3), nbd_get_structured_replies_negotiated(3), nbd_opt_extended_headers(3), nbd_set_request_extended_headers(3), nbd_trim(3), nbd_zero(3), libnbd(3).


Eric Blake

Richard W.M. Jones


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

Referenced By

libnbd(3), libnbd-release-notes-1.18(1), NBD(3), nbd_block_status(3), nbd_block_status_64(3), nbd_cache(3), nbd_can_block_status_payload(3), nbd_get_request_extended_headers(3), nbd_get_structured_replies_negotiated(3), nbdinfo(1), nbd_opt_extended_headers(3), nbd_set_request_extended_headers(3), nbd_trim(3), nbd_zero(3).

2024-06-25 libnbd-1.21.1