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 (
12 struct nbd_handle *h, uint64_t count,
13 uint64_t offset, uint32_t flags
14 );
15
17 Issue a write zeroes command to the NBD server, which if supported by
18 the server causes a zeroes to be written efficiently starting at
19 "offset" and ending at "offset" + "count" - 1. The call returns when
20 the command has been acknowledged by the server, or there is an error.
21 Note this will generally return an error if nbd_can_zero(3) is false or
22 nbd_is_read_only(3) is true.
23 Note that not all servers can support a "count" of 4GiB or larger;
25 nbd_get_extended_headers_negotiated(3) indicates which servers will
26 parse a request larger than 32 bits. The NBD protocol does not yet
27 have a way for a client to learn if the server will enforce an even
28 smaller maximum zero size, although a future extension may add a
29 constraint visible in nbd_get_block_size(3). Also, some servers may
30 permit a larger zero request only when the "LIBNBD_CMD_FLAG_FAST_ZERO"
31 is in use.
32 The "flags" parameter may be 0 for no flags, or may contain
34 "LIBNBD_CMD_FLAG_FUA" meaning that the server should not return until
35 the data has been committed to permanent storage (if that is supported
36 - some servers cannot do this, see nbd_can_fua(3)),
37 "LIBNBD_CMD_FLAG_NO_HOLE" meaning that the server should favor writing
38 actual allocated zeroes over punching a hole, and/or
39 "LIBNBD_CMD_FLAG_FAST_ZERO" meaning that the server must fail quickly
40 if writing zeroes is no faster than a normal write (if that is
41 supported - some servers cannot do this, see nbd_can_fast_zero(3)).
42 By default, libnbd will reject attempts to use this function with
44 parameters that are likely to result in server failure, such as
45 requesting an unknown command flag. The nbd_set_strict_mode(3)
46 function can be used to alter which scenarios should await a server
47 reply rather than failing fast.
48
50 If the call is successful the function returns 0.
51
53 On error -1 is returned.
54 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
56 of the error.
57 The following parameters must not be NULL: "h". For more information
59 see "Non-NULL parameters" in libnbd(3).
60
62 The handle must be connected with the server, otherwise this call will
63 return an error.
64
66 This function first appeared in libnbd 1.0.
67 If you need to test if this function is available at compile time check
69 if the following macro is defined:
70 #define LIBNBD_HAVE_NBD_ZERO 1
72
74 nbd_aio_zero(3), nbd_can_fast_zero(3), nbd_can_fua(3), nbd_can_zero(3),
75 nbd_create(3), nbd_get_block_size(3),
76 nbd_get_extended_headers_negotiated(3), nbd_is_read_only(3),
77 nbd_set_strict_mode(3), libnbd(3).
78
80 Eric Blake
81 Richard W.M. Jones
83
85 Copyright Red Hat
86
88 This library is free software; you can redistribute it and/or modify it
89 under the terms of the GNU Lesser General Public License as published
90 by the Free Software Foundation; either version 2 of the License, or
91 (at your option) any later version.
92 This library is distributed in the hope that it will be useful, but
94 WITHOUT ANY WARRANTY; without even the implied warranty of
95 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
96 Lesser General Public License for more details.
97 You should have received a copy of the GNU Lesser General Public
99 License along with this library; if not, write to the Free Software
100 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
101 02110-1301 USA
102libnbd-1.18.1 2023-10-31 nbd_zero(3)