nbd_zero(3)                         LIBNBD                         nbd_zero(3)


NAME
       nbd_zero - send write zeroes command to the NBD server

SYNOPSIS
        #include <libnbd.h>

        int nbd_zero (
              struct nbd_handle *h, uint64_t count,
              uint64_t offset, uint32_t flags
            );

DESCRIPTION
       Issue a write zeroes command to the NBD server, which if supported by
       the server causes a zeroes to be written efficiently starting at
       "offset" and ending at "offset" + "count" - 1.  The call returns when
       the command has been acknowledged by the server, or there is an error.
       Note this will generally return an error if nbd_can_zero(3) is false or
       nbd_is_read_only(3) is true.

       Note that not all servers can support a "count" of 4GiB or larger;
       nbd_get_extended_headers_negotiated(3) indicates which servers will
       parse a request larger than 32 bits.  The NBD protocol does not yet
       have a way for a client to learn if the server will enforce an even
       smaller maximum zero size, although a future extension may add a
       constraint visible in nbd_get_block_size(3).  Also, some servers may
       permit a larger zero request only when the "LIBNBD_CMD_FLAG_FAST_ZERO"
       is in use.

       The "flags" parameter may be 0 for no flags, or may contain
       "LIBNBD_CMD_FLAG_FUA" meaning that the server should not return until
       the data has been committed to permanent storage (if that is supported
       - some servers cannot do this, see nbd_can_fua(3)),
       "LIBNBD_CMD_FLAG_NO_HOLE" meaning that the server should favor writing
       actual allocated zeroes over punching a hole, and/or
       "LIBNBD_CMD_FLAG_FAST_ZERO" meaning that the server must fail quickly
       if writing zeroes is no faster than a normal write (if that is
       supported - some servers cannot do this, see nbd_can_fast_zero(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
       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_zero 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_ZERO 1

SEE ALSO
       nbd_aio_zero(3), nbd_can_fast_zero(3), nbd_can_fua(3), nbd_can_zero(3),
       nbd_create(3), nbd_get_block_size(3),
       nbd_get_extended_headers_negotiated(3), nbd_is_read_only(3),
       nbd_set_strict_mode(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

libnbd-1.20.0                     2024-05-31                       nbd_zero(3)