nbd_set_request_meta_context3

Usage

 #include <libnbd.h>
 int nbd_set_request_meta_context (
       struct nbd_handle *h, bool request
     );

Overview

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.

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

Handle state

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                │
 └─────────────────────────────────────┴─────────────────────────┘

Version

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 1