POSIX_FALLOCATE
Section: Linux Programmer's Manual (3)
Updated: 2021-03-22
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NAME
posix_fallocate - allocate file space
SYNOPSIS
#include <fcntl.h>
int posix_fallocate(int fd, off_t offset, off_t len);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
posix_fallocate():
_POSIX_C_SOURCE >= 200112L
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, or
len
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.
- EOPNOTSUPP
-
The filesystem containing the file referred to by
fd
does not support this operation.
This error code can be returned by C libraries that don't perform the
emulation shown in NOTES, such as musl libc.
- ESPIPE
-
fd
refers to a pipe.
VERSIONS
posix_fallocate()
is available since glibc 2.1.94.
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 the
O_APPEND
or
O_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.
SEE ALSO
fallocate(1),
fallocate(2),
lseek(2),
posix_fadvise(2)
COLOPHON
This page is part of release 5.11 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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Time: 06:22:44 GMT, May 09, 2021