NAME¶

nbd_aio_pread_structured - read from the NBD server

SYNOPSIS¶

 #include <libnbd.h>
 typedef struct {
   int (*callback) (void *user_data, const void *subbuf,
                    size_t count, uint64_t offset,
                    unsigned status, int *error);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_chunk_callback;
 typedef struct {
   int (*callback) (void *user_data, int *error);
   void *user_data;
   void (*free) (void *user_data);
 } nbd_completion_callback;
 int64_t nbd_aio_pread_structured (struct nbd_handle *h,
                                   void *buf, size_t count,
                                   uint64_t offset,
                                   nbd_chunk_callback chunk_callback,
                                   nbd_completion_callback completion_callback,
                                   uint32_t flags);

DESCRIPTION¶

Issue a read 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_pread_structured(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.

HANDLE STATE¶

The handle must be connected with the server, otherwise this call will return an 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_PREAD_STRUCTURED 1

SEE ALSO¶

nbd_aio_command_completed(3), nbd_aio_pread(3), nbd_create(3), nbd_pread_structured(3), nbd_set_strict_mode(3), "Issuing asynchronous commands" in libnbd(3), libnbd(3).

AUTHORS¶

Eric Blake

Richard W.M. Jones

COPYRIGHT¶

Copyright (C) 2019-2020 Red Hat Inc.

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