NAME

nbd_aio_cache - send cache (prefetch) command to the NBD server

SYNOPSIS

#include <libnbd.h>
typedef struct {
  int (*callback) (void *user_data, int *error);
  void *user_data;
  void (*free) (void *user_data);
} nbd_completion_callback;
int64_t nbd_aio_cache (
          struct nbd_handle *h, uint64_t count,
          uint64_t offset,
          nbd_completion_callback completion_callback,
          uint32_t flags
        );

DESCRIPTION

Issue the cache (prefetch) command to the NBD server.

To check if the command completed, call nbd_aio_command_completed(3). Or supply the optional "completion_callback" which will be invoked as described in "Completion callbacks" in libnbd(3).

Other parameters behave as documented in nbd_cache(3).

By default, libnbd will reject attempts to use this function with parameters that are likely to result in server failure, such as requesting an unknown command flag. The nbd_set_strict_mode(3) function can be used to alter which scenarios should await a server reply rather than failing fast.

RETURN VALUE

This call returns the 64 bit cookie of the command. The cookie is ≥ 1. Cookies are unique (per libnbd handle, not globally).

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_cache can be called when the handle is in the following state:

┌─────────────────────────────────────┬─────────────────────────┐
│ Handle created, before connecting   │ ❌ error                │
│ Connecting                          │ ❌ error                │
│ Connecting & handshaking (opt_mode) │ ❌ error                │
│ Connected to the server             │ ✅ allowed              │
│ Connection shut down                │ ❌ error                │
│ Handle dead                         │ ❌ error                │
└─────────────────────────────────────┴─────────────────────────┘

VERSION

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_AIO_CACHE 1

SEE ALSO

nbd_aio_command_completed(3), nbd_cache(3), nbd_can_cache(3), nbd_create(3), nbd_set_strict_mode(3), "Issuing asynchronous commands" in libnbd(3), libnbd(3).

AUTHORS

Eric Blake

Richard W.M. Jones

COPYRIGHT

Copyright Red Hat

LICENSE

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