1nbd_zero(3)                         LIBNBD                         nbd_zero(3)
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NAME

6       nbd_zero - send write zeroes command to the NBD server
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SYNOPSIS

9        #include <libnbd.h>
10
11        int nbd_zero (struct nbd_handle *h, uint64_t count,
12                      uint64_t offset, uint32_t flags);
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DESCRIPTION

15       Issue a write zeroes command to the NBD server, which if supported by
16       the server causes a zeroes to be written efficiently starting at
17       "offset" and ending at "offset" + "count" - 1.  The call returns when
18       the command has been acknowledged by the server, or there is an error.
19       Note this will generally return an error if nbd_can_zero(3) is false or
20       nbd_is_read_only(3) is true.
21
22       Note that not all servers can support a "count" of 4GiB or larger.  The
23       NBD protocol does not yet have a way for a client to learn if the
24       server will enforce an even smaller maximum zero size, although a
25       future extension may add a constraint visible in nbd_get_block_size(3).
26       Also, some servers may permit a larger zero request only when the
27       "LIBNBD_CMD_FLAG_FAST_ZERO" is in use.
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29       The "flags" parameter may be 0 for no flags, or may contain
30       "LIBNBD_CMD_FLAG_FUA" meaning that the server should not return until
31       the data has been committed to permanent storage (if that is supported
32       - some servers cannot do this, see nbd_can_fua(3)),
33       "LIBNBD_CMD_FLAG_NO_HOLE" meaning that the server should favor writing
34       actual allocated zeroes over punching a hole, and/or
35       "LIBNBD_CMD_FLAG_FAST_ZERO" meaning that the server must fail quickly
36       if writing zeroes is no faster than a normal write (if that is
37       supported - some servers cannot do this, see nbd_can_fast_zero(3)).
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39       By default, libnbd will reject attempts to use this function with
40       parameters that are likely to result in server failure, such as
41       requesting an unknown command flag.  The nbd_set_strict_mode(3)
42       function can be used to alter which scenarios should await a server
43       reply rather than failing fast.
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RETURN VALUE

46       If the call is successful the function returns 0.
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ERRORS

49       On error "-1" is returned.
50
51       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
52       of the error.
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HANDLE STATE

55       The handle must be connected with the server, otherwise this call will
56       return an error.
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VERSION

59       This function first appeared in libnbd 1.0.
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61       If you need to test if this function is available at compile time check
62       if the following macro is defined:
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64        #define LIBNBD_HAVE_NBD_ZERO 1
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SEE ALSO

67       nbd_aio_zero(3), nbd_can_fast_zero(3), nbd_can_fua(3), nbd_can_zero(3),
68       nbd_create(3), nbd_get_block_size(3), nbd_is_read_only(3),
69       nbd_set_strict_mode(3), libnbd(3).
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AUTHORS

72       Eric Blake
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74       Richard W.M. Jones
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77       Copyright (C) 2019-2021 Red Hat Inc.
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LICENSE

80       This library is free software; you can redistribute it and/or modify it
81       under the terms of the GNU Lesser General Public License as published
82       by the Free Software Foundation; either version 2 of the License, or
83       (at your option) any later version.
84
85       This library is distributed in the hope that it will be useful, but
86       WITHOUT ANY WARRANTY; without even the implied warranty of
87       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
88       Lesser General Public License for more details.
89
90       You should have received a copy of the GNU Lesser General Public
91       License along with this library; if not, write to the Free Software
92       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
93       02110-1301 USA
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97libnbd-1.12.5                     2022-07-10                       nbd_zero(3)
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