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 2018-04-30 "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.
87 shared file data extents will be made private to the file to guarantee
88 that a subsequent write will not fail due to lack of space.
89 Typically, this will be done by performing a copy-on-write operation on
90 all shared data in the file.
91 This flag may not be supported by all filesystems.
93 Because allocation is done in block size chunks,
95 may allocate a larger range of disk space than was specified.
96 .SS Deallocating file space
98 .BR FALLOC_FL_PUNCH_HOLE
99 flag (available since Linux 2.6.38) in
101 deallocates space (i.e., creates a hole)
102 in the byte range starting at
107 Within the specified range, partial filesystem blocks are zeroed,
108 and whole filesystem blocks are removed from the file.
109 After a successful call,
110 subsequent reads from this range will return zeros.
113 .BR FALLOC_FL_PUNCH_HOLE
114 flag must be ORed with
115 .BR FALLOC_FL_KEEP_SIZE
118 in other words, even when punching off the end of the file, the file size
123 Not all filesystems support
124 .BR FALLOC_FL_PUNCH_HOLE ;
125 if a filesystem doesn't support the operation, an error is returned.
126 The operation is supported on at least the following filesystems:
128 XFS (since Linux 2.6.38)
130 ext4 (since Linux 3.0)
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133 Btrfs (since Linux 3.7)
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138 .SS Collapsing file space
139 .\" commit 00f5e61998dd17f5375d9dfc01331f104b83f841
141 .BR FALLOC_FL_COLLAPSE_RANGE
142 flag (available since Linux 3.15) in
144 removes a byte range from a file, without leaving a hole.
145 The byte range to be collapsed starts at
150 At the completion of the operation,
151 the contents of the file starting at the location
153 will be appended at the location
159 A filesystem may place limitations on the granularity of the operation,
160 in order to ensure efficient implementation.
165 must be a multiple of the filesystem logical block size,
166 which varies according to the filesystem type and configuration.
167 If a filesystem has such a requirement,
171 if this requirement is violated.
173 If the region specified by
177 reaches or passes the end of file, an error is returned;
182 No other flags may be specified in
185 .BR FALLOC_FL_COLLAPSE_RANGE .
188 .B FALLOC_FL_COLLAPSE_RANGE
190 ext4 (only for extent-based files)
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193 .\" commit e1d8fb88a64c1f8094b9f6c3b6d2d9e6719c970d
194 .SS Zeroing file space
196 .BR FALLOC_FL_ZERO_RANGE
197 flag (available since Linux 3.15)
198 .\" commit 409332b65d3ed8cfa7a8030f1e9d52f372219642
201 zeros space in the byte range starting at
206 Within the specified range, blocks are preallocated for the regions
207 that span the holes in the file.
208 After a successful call, subsequent
209 reads from this range will return zeros.
211 Zeroing is done within the filesystem preferably by converting the range into
213 This approach means that the specified range will not be physically zeroed
214 out on the device (except for partial blocks at the either end of the range),
215 and I/O is (otherwise) required only to update metadata.
218 .B FALLOC_FL_KEEP_SIZE
219 flag is additionally specified in
221 the behavior of the call is similar,
222 but the file size will not be changed even if
224 is greater than the file size.
225 This behavior is the same as when preallocating space with
226 .B FALLOC_FL_KEEP_SIZE
229 Not all filesystems support
230 .BR FALLOC_FL_ZERO_RANGE ;
231 if a filesystem doesn't support the operation, an error is returned.
232 The operation is supported on at least the following filesystems:
234 XFS (since Linux 3.15)
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237 ext4, for extent-based files (since Linux 3.15)
238 .\" commit b8a8684502a0fc852afa0056c6bb2a9273f6fcc0
240 SMB3 (since Linux 3.17)
241 .\" commit 30175628bf7f521e9ee31ac98fa6d6fe7441a556
243 Btrfs (since Linux 4.16)
244 .\" commit f27451f229966874a8793995b8e6b74326d125df
245 .SS Increasing file space
247 .BR FALLOC_FL_INSERT_RANGE
249 (available since Linux 4.1)
250 .\" commit dd46c787788d5bf5b974729d43e4c405814a4c7d
253 increases the file space by inserting a hole within the file size without
254 overwriting any existing data.
255 The hole will start at
260 When inserting the hole inside file, the contents of the file starting at
262 will be shifted upward (i.e., to a higher file offset) by
265 Inserting a hole inside a file increases the file size by
269 This mode has the same limitations as
270 .BR FALLOC_FL_COLLAPSE_RANGE
271 regarding the granularity of the operation.
272 If the granularity requirements are not met,
278 is equal to or greater than the end of file, an error is returned.
279 For such operations (i.e., inserting a hole at the end of file),
283 No other flags may be specified in
286 .BR FALLOC_FL_INSERT_RANGE .
288 .B FALLOC_FL_INSERT_RANGE
289 requires filesystem support.
290 Filesystems that support this operation include
291 XFS (since Linux 4.1)
292 .\" commit a904b1ca5751faf5ece8600e18cd3b674afcca1b
293 and ext4 (since Linux 4.2).
294 .\" commit 331573febb6a224bc50322e3670da326cb7f4cfc
295 .\" f2fs also has support since Linux 4.2
296 .\" commit f62185d0e283e9d311e3ac1020f159d95f0aab39
301 On error, \-1 is returned and
303 is set to indicate the error.
308 is not a valid file descriptor, or is not opened for writing.
312 exceeds the maximum file size.
317 .BR FALLOC_FL_INSERT_RANGE ,
318 and the current file size+\fIlen\fP exceeds the maximum file size.
321 A signal was caught during execution; see
328 .\" FIXME . (raise a kernel bug) Probably the len==0 case should be
329 .\" a no-op, rather than an error. That would be consistent with
330 .\" similar APIs for the len==0 case.
331 .\" See "Re: [PATCH] fallocate.2: add FALLOC_FL_PUNCH_HOLE flag definition"
333 .\" http://thread.gmane.org/gmane.linux.file-systems/48331/focus=1193526
334 was less than or equal to 0.
339 .BR FALLOC_FL_COLLAPSE_RANGE
340 and the range specified by
344 reaches or passes the end of the file.
349 .BR FALLOC_FL_INSERT_RANGE
350 and the range specified by
352 reaches or passes the end of the file.
357 .BR FALLOC_FL_COLLAPSE_RANGE
359 .BR FALLOC_FL_INSERT_RANGE ,
364 is not a multiple of the filesystem block size.
369 .B FALLOC_FL_COLLAPSE_RANGE
371 .B FALLOC_FL_INSERT_RANGE
372 and also other flags;
373 no other flags are permitted with
374 .BR FALLOC_FL_COLLAPSE_RANGE
376 .BR FALLOC_FL_INSERT_RANGE .
381 .BR FALLOC_FL_COLLAPSE_RANGE
383 .BR FALLOC_FL_ZERO_RANGE
385 .BR FALLOC_FL_INSERT_RANGE ,
386 but the file referred to by
388 is not a regular file.
389 .\" There was an inconsistency in 3.15-rc1, that should be resolved so that all
390 .\" filesystems use this error for this case. (Tytso says ex4 will change.)
391 .\" http://thread.gmane.org/gmane.comp.file-systems.xfs.general/60485/focus=5521
392 .\" From: Michael Kerrisk (man-pages <mtk.manpages@...>
393 .\" Subject: Re: [PATCH v5 10/10] manpage: update FALLOC_FL_COLLAPSE_RANGE flag in fallocate
394 .\" Newsgroups: gmane.linux.man, gmane.linux.file-systems
395 .\" Date: 2014-04-17 13:40:05 GMT
398 An I/O error occurred while reading from or writing to a filesystem.
402 does not refer to a regular file or a directory.
405 is a pipe or FIFO, a different error results.)
408 There is not enough space left on the device containing the file
413 This kernel does not implement
417 The filesystem containing the file referred to by
419 does not support this operation;
422 is not supported by the filesystem containing the file referred to by
426 The file referred to by
428 is marked immutable (see
434 .BR FALLOC_FL_PUNCH_HOLE
436 .BR FALLOC_FL_COLLAPSE_RANGE
438 .BR FALLOC_FL_INSERT_RANGE
440 the file referred to by
442 is marked append-only
447 The operation was prevented by a file seal; see
452 refers to a pipe or FIFO.
457 .BR FALLOC_FL_COLLAPSE_RANGE
459 .BR FALLOC_FL_INSERT_RANGE ,
460 but the file referred to by
462 is currently being executed.
465 is available on Linux since kernel 2.6.23.
466 Support is provided by glibc since version 2.10.
469 flags are defined in glibc headers only since version 2.18.
470 .\" See http://sourceware.org/bugzilla/show_bug.cgi?id=14964
477 .BR posix_fadvise (3),
478 .BR posix_fallocate (3)