nbd_set_request_meta_context - control whether connect automatically requests meta contexts
#include <libnbd.h>
int nbd_set_request_meta_context (
struct nbd_handle *h, bool request
);This function controls whether the act of connecting to an export (all nbd_connect_* calls when nbd_set_opt_mode(3) is false, or nbd_opt_go(3) and nbd_opt_info(3) when option mode is enabled) will also try to issue NBD_OPT_SET_META_CONTEXT when the server supports structured replies or extended headers and any contexts were registered by nbd_add_meta_context(3). The default setting is true; however the extra step of negotiating meta contexts is not always desirable: performing both info and go on the same export works without needing to re-negotiate contexts on the second call; integration testing of other servers may benefit from manual invocation of nbd_opt_set_meta_context(3) at other times in the negotiation sequence; and even when using just nbd_opt_info(3), it can be faster to collect the server's results by relying on the callback function passed to nbd_opt_list_meta_context(3) than a series of post-process calls to nbd_can_meta_context(3).
Note that this control has no effect if the server does not negotiate structured replies or extended headers, or if the client did not request any contexts via nbd_add_meta_context(3). Setting this control to false may cause nbd_block_status(3) to fail.
If the call is successful the function returns 0.
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).
nbd_set_request_meta_context can be called when the handle is in the following states:
┌─────────────────────────────────────┬─────────────────────────┐
│ Handle created, before connecting │ ✅ allowed │
│ Connecting │ ❌ error │
│ Connecting & handshaking (opt_mode) │ ✅ allowed │
│ Connected to the server │ ❌ error │
│ Connection shut down │ ❌ error │
│ Handle dead │ ❌ error │
└─────────────────────────────────────┴─────────────────────────┘This function first appeared in libnbd 1.16.
If you need to test if this function is available at compile time check if the following macro is defined:
#define LIBNBD_HAVE_NBD_SET_REQUEST_META_CONTEXT 1nbd_add_meta_context(3), nbd_block_status(3), nbd_can_meta_context(3), nbd_create(3), nbd_get_request_meta_context(3), nbd_get_structured_replies_negotiated(3), nbd_opt_go(3), nbd_opt_info(3), nbd_opt_list_meta_context(3), nbd_opt_set_meta_context(3), nbd_set_opt_mode(3), libnbd(3).
Eric Blake
Richard W.M. Jones
Copyright Red Hat
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.
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