1nbd_zero(3) LIBNBD nbd_zero(3)
2
6 nbd_zero - send write zeroes command to the NBD server
7
9 #include <libnbd.h>
10 int nbd_zero (struct nbd_handle *h, uint64_t count,
12 uint64_t offset, uint32_t flags);
13
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 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.
28 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)).
38 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.
44
46 If the call is successful the function returns 0.
47
49 On error "-1" is returned.
50 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
52 of the error.
53 The following parameters must not be NULL: "h". For more information
55 see "Non-NULL parameters" in libnbd(3).
56
58 The handle must be connected with the server, otherwise this call will
59 return an error.
60
62 This function first appeared in libnbd 1.0.
63 If you need to test if this function is available at compile time check
65 if the following macro is defined:
66 #define LIBNBD_HAVE_NBD_ZERO 1
68
70 nbd_aio_zero(3), nbd_can_fast_zero(3), nbd_can_fua(3), nbd_can_zero(3),
71 nbd_create(3), nbd_get_block_size(3), nbd_is_read_only(3),
72 nbd_set_strict_mode(3), libnbd(3).
73
75 Eric Blake
76 Richard W.M. Jones
78
80 Copyright (C) 2019-2021 Red Hat Inc.
81
83 This library is free software; you can redistribute it and/or modify it
84 under the terms of the GNU Lesser General Public License as published
85 by the Free Software Foundation; either version 2 of the License, or
86 (at your option) any later version.
87 This library is distributed in the hope that it will be useful, but
89 WITHOUT ANY WARRANTY; without even the implied warranty of
90 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
91 Lesser General Public License for more details.
92 You should have received a copy of the GNU Lesser General Public
94 License along with this library; if not, write to the Free Software
95 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
96 02110-1301 USA
97libnbd-1.14.2 2023-01-03 nbd_zero(3)