| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | SEE ALSO | COLOPHON | The Linux Programming Interface |
FALLOCATE(2) Linux Programmer's Manual FALLOCATE(2)
fallocate - manipulate file space
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <fcntl.h>
int fallocate(int fd, int mode, off_t offset, off_t len);
This is a nonportable, Linux-specific system call. For the portable,
POSIX.1-specified method of ensuring that space is allocated for a file, see
posix_fallocate().
fallocate() allows the caller to directly manipulate the allocated disk space
for the file referred to by fd for the byte range starting at offset and
continuing for len bytes.
The mode argument determines the operation to be performed on the given range.
Currently only one flag is supported for mode:
FALLOC_FL_KEEP_SIZE
This flag allocates and initializes to zero the disk space within the
range specified by offset and len. After a successful call, subsequent
writes into this range are guaranteed not to fail because of lack of
disk space. Preallocating zeroed blocks beyond the end of the file is
useful for optimizing append workloads. Preallocating blocks does not
change the file size (as reported by stat(2)) even if it is less than
offset+len.
If FALLOC_FL_KEEP_SIZE flag is not specified in mode, the default behavior is
almost same as when this flag is specified. The only difference is that on
success, the file size will be changed if offset + len is greater than the
file size. This default behavior closely resembles the behavior of the
posix_fallocate(3) library function, and is intended as a method of optimally
implementing that function.
Because allocation is done in block size chunks, fallocate() may allocate a
larger range than that which was specified.
fallocate() returns zero on success, and -1 on failure.
EBADF fd is not a valid file descriptor, or is not opened for writing.
EFBIG offset+len exceeds the maximum file size.
EINTR A signal was caught during execution.
EINVAL offset was less than 0, or len was less than or equal to 0.
EIO An I/O error occurred while reading from or writing to a file system.
ENODEV fd does not refer to a regular file or a directory. (If fd is a pipe
or FIFO, a different error results.)
ENOSPC There is not enough space left on the device containing the file
referred to by fd.
ENOSYS The file system containing the file referred to by fd does not support
this operation.
EOPNOTSUPP
The mode is not supported by the file system containing the file
referred to by fd.
fallocate() is available on Linux since kernel 2.6.23. Support is provided by
glibc since version 2.10.
fallocate() is Linux-specific.
ftruncate(2), posix_fadvise(3), posix_fallocate(3)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2010-09-10 FALLOCATE(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface