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>
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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.
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22       The "flags" parameter may be 0 for no flags, or may contain
23       "LIBNBD_CMD_FLAG_FUA" meaning that the server should not return until
24       the data has been committed to permanent storage (if that is supported
25       - some servers cannot do this, see nbd_can_fua(3)),
26       "LIBNBD_CMD_FLAG_NO_HOLE" meaning that the server should favor writing
27       actual allocated zeroes over punching a hole, and/or
28       "LIBNBD_CMD_FLAG_FAST_ZERO" meaning that the server must fail quickly
29       if writing zeroes is no faster than a normal write (if that is
30       supported - some servers cannot do this, see nbd_can_fast_zero(3)).
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32       By default, libnbd will reject attempts to use this function with
33       parameters that are likely to result in server failure, such as
34       requesting an unknown command flag.  The nbd_set_strict_mode(3)
35       function can be used to alter which scenarios should await a server
36       reply rather than failing fast.
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RETURN VALUE

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

42       On error "-1" is returned.
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44       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
45       of the error.
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HANDLE STATE

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

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

60       nbd_aio_zero(3), nbd_can_fast_zero(3), nbd_can_fua(3), nbd_can_zero(3),
61       nbd_create(3), nbd_is_read_only(3), nbd_set_strict_mode(3), libnbd(3).
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AUTHORS

64       Eric Blake
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66       Richard W.M. Jones
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69       Copyright (C) 2019-2021 Red Hat Inc.
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LICENSE

72       This library is free software; you can redistribute it and/or modify it
73       under the terms of the GNU Lesser General Public License as published
74       by the Free Software Foundation; either version 2 of the License, or
75       (at your option) any later version.
76
77       This library is distributed in the hope that it will be useful, but
78       WITHOUT ANY WARRANTY; without even the implied warranty of
79       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
80       Lesser General Public License for more details.
81
82       You should have received a copy of the GNU Lesser General Public
83       License along with this library; if not, write to the Free Software
84       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
85       02110-1301 USA
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89libnbd-1.10.1                     2021-10-25                       nbd_zero(3)
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