nbd_aio_opt_set_meta_context3

Usage

 #include <libnbd.h>
 typedef struct {
   int (*callback) (void *user_data, const char *name);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_context_callback;
 typedef struct {
   int (*callback) (void *user_data, int *error);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_completion_callback;
 int nbd_aio_opt_set_meta_context (
       struct nbd_handle *h,
       nbd_context_callback context_callback,
       nbd_completion_callback completion_callback
     );

Overview

Request that the server supply all recognized meta contexts registered through prior calls to nbd_add_meta_context(3), in conjunction with the export previously specified by the most recent nbd_set_export_name(3) or nbd_connect_uri(3). This can only be used if nbd_set_opt_mode(3) enabled option mode. Normally, this function is redundant, as nbd_opt_go(3) automatically does the same task if structured replies or extended headers have already been negotiated. But manual control over meta context requests can be useful for fine-grained testing of how a server handles unusual negotiation sequences. Often, use of this function is coupled with nbd_set_request_meta_context(3) to bypass the automatic context request normally performed by nbd_opt_go(3).

To determine when the request completes, wait for nbd_aio_is_connecting(3) to return false. Or supply the optional "completion_callback" which will be invoked as described in "Completion callbacks" in libnbd(3), except that it is automatically retired regardless of return value. Note that detecting whether the server returns an error (as is done by the return value of the synchronous counterpart) is only possible with a completion callback.

Return value

This call returns an integer ≥ 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_aio_opt_set_meta_context can be called when the handle is in the following state:

 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ❌ error                │
 │ 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_AIO_OPT_SET_META_CONTEXT 1