Section (3) posix_fallocate
Name
posix_fallocate — allocate file space
Synopsis
#include <fcntl.h>
int
posix_fallocate( |
int fd, |
off_t offset, | |
off_t len) ; |
![]() |
Note | ||
---|---|---|---|
|
DESCRIPTION
The function posix_fallocate
() ensures that disk space
is allocated for the file referred to by the file descriptor
fd
for the bytes in
the range starting at offset
and continuing for
len
bytes. After a
successful call to posix_fallocate
(), subsequent writes to
bytes in the specified range are guaranteed not to fail
because of lack of disk space.
If the size of the file is less than offset
+len
, then the file is increased
to this size; otherwise the file size is left unchanged.
RETURN VALUE
posix_fallocate
() returns
zero on success, or an error number on failure. Note that
errno
is not set.
ERRORS
- 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, orlen
was less than or equal to 0, or the underlying filesystem does not support the operation. - ENODEV
-
fd
does not refer to a regular file. - ENOSPC
-
There is not enough space left on the device containing the file referred to by
fd
. - ESPIPE
-
fd
refers to a pipe.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value |
posix_fallocate () |
Thread safety | MT-Safe (but see NOTES) |
CONFORMING TO
POSIX.1-2001.
POSIX.1-2008 says that an implementation shall
give the EINVAL error if len
was 0, or offset
was less than 0.
POSIX.1-2001 says that an implementation shall
give the EINVAL error if len
is less than 0, or
offset
was less than
0, and may
give the error if
len
equals zero.
NOTES
In the glibc implementation, posix_fallocate
() is implemented using the
fallocate(2) system call,
which is MT-safe. If the underlying filesystem does not
support fallocate(2), then the
operation is emulated with the following caveats:
-
The emulation is inefficient.
-
There is a race condition where concurrent writes from another thread or process could be overwritten with null bytes.
-
There is a race condition where concurrent file size increases by another thread or process could result in a file whose size is smaller than expected.
-
If
fd
has been opened with theO_APPEND
orO_WRONLY
flags, the function fails with the error EBADF.
In general, the emulation is not MT-safe. On Linux, applications may use fallocate(2) if they cannot tolerate the emulation caveats. In general, this is only recommended if the application plans to terminate the operation if EOPNOTSUPP is returned, otherwise the application itself will need to implement a fallback with all the same problems as the emulation provided by glibc.
COLOPHON
This page is part of release 4.16 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
Copyright (c) 2006, Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |