1 .\" Copyright (c) 2007 Silicon Graphics, Inc. All Rights Reserved
2 .\" Written by Dave Chinner <dgc@sgi.com>
4 .\" %%%LICENSE_START(GPLv2_ONELINE)
5 .\" May be distributed as per GNU General Public License version 2.
8 .\" 2011-09-19: Added FALLOC_FL_PUNCH_HOLE
9 .\" 2011-09-19: Substantial restructuring of the page
11 .TH FALLOCATE 2 2014-01-24 "Linux" "Linux Programmer's Manual"
13 fallocate \- manipulate file space
16 .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
19 .BI "int fallocate(int " fd ", int " mode ", off_t " offset \
23 This is a nonportable, Linux-specific system call.
24 For the portable, POSIX.1-specified method of ensuring that space
25 is allocated for a file, see
26 .BR posix_fallocate (3).
29 allows the caller to directly manipulate the allocated disk space
30 for the file referred to by
32 for the byte range starting at
40 argument determines the operation to be performed on the given range.
41 Details of the supported operations are given in the subsections below.
42 .SS Allocating disk space
43 The default operation (i.e.,
47 allocates the disk space within the range specified by
51 The file size (as reported by
55 is greater than the file size.
56 Any subregion within the range specified by
60 that did not contain data before the call will be initialized to zero.
61 This default behavior closely resembles the behavior of the
62 .BR posix_fallocate (3)
64 and is intended as a method of optimally implementing that function.
66 After a successful call, subsequent writes into the range specified by
70 are guaranteed not to fail because of lack of disk space.
73 .B FALLOC_FL_KEEP_SIZE
76 the behavior of the call is similar,
77 but the file size will not be changed even if
79 is greater than the file size.
80 Preallocating zeroed blocks beyond the end of the file in this manner
81 is useful for optimizing append workloads.
83 Because allocation is done in block size chunks,
85 may allocate a larger range of disk space than was specified.
86 .SS Deallocating file space
88 .BR FALLOC_FL_PUNCH_HOLE
89 flag (available since Linux 2.6.38) in
91 deallocates space (i.e., creates a hole)
92 in the byte range starting at
97 Within the specified range, partial filesystem blocks are zeroed,
98 and whole filesystem blocks are removed from the file.
99 After a successful call,
100 subsequent reads from this range will return zeroes.
103 .BR FALLOC_FL_PUNCH_HOLE
104 flag must be ORed with
105 .BR FALLOC_FL_KEEP_SIZE
108 in other words, even when punching off the end of the file, the file size
113 Not all filesystems support
114 .BR FALLOC_FL_PUNCH_HOLE ;
115 if a filesystem doesn't support the operation, an error is returned.
116 The operation is supported on at least the following filesystems
118 XFS (since Linux 2.6.38)
120 ext4 (since Linux 3.0)
121 .\" commit a4bb6b64e39abc0e41ca077725f2a72c868e7622
123 Btrfs (since Linux 3.7)
125 tmpfs (since Linux 3.5)
126 .\" commit 83e4fa9c16e4af7122e31be3eca5d57881d236fe
131 On error, \-1 is returned and
133 is set to indicate the error.
138 is not a valid file descriptor, or is not opened for writing.
142 exceeds the maximum file size.
145 A signal was caught during execution.
151 .\" FIXME (raise a kernel bug) Probably the len==0 case should be
152 .\" a no-op, rather than an error. That would be consistent with
153 .\" similar APIs for the len==0 case.
154 .\" See "Re: [PATCH] fallocate.2: add FALLOC_FL_PUNCH_HOLE flag definition"
156 .\" http://thread.gmane.org/gmane.linux.file-systems/48331/focus=1193526
157 was less than or equal to 0.
160 An I/O error occurred while reading from or writing to a filesystem.
164 does not refer to a regular file or a directory.
167 is a pipe or FIFO, a different error results.)
170 There is not enough space left on the device containing the file
175 This kernel does not implement
179 The filesystem containing the file referred to by
181 does not support this operation;
184 is not supported by the filesystem containing the file referred to by
188 The file referred to by
190 is marked immutable (see
195 .BR FALLOC_FL_PUNCH_HOLE
197 the file referred to by
199 is marked append-only
205 refers to a pipe or FIFO.
208 is available on Linux since kernel 2.6.23.
209 Support is provided by glibc since version 2.10.
212 flags are defined in glibc headers only since version 2.18.
213 .\" See http://sourceware.org/bugzilla/show_bug.cgi?id=14964
220 .BR posix_fadvise (3),
221 .BR posix_fallocate (3)
223 This page is part of release 3.64 of the Linux
226 A description of the project,
227 and information about reporting bugs,
229 \%http://www.kernel.org/doc/man\-pages/.