nbd_aio_cache - send cache (prefetch) command to the NBD server
#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
);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.
This call returns the 64 bit cookie of the command. The cookie is ≥ 1. Cookies are unique (per libnbd handle, not globally).
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_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 │
└─────────────────────────────────────┴─────────────────────────┘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 1nbd_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).
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.
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