#include <linux/falloc.h>long fallocate(int fd, int mode, loff_t offset, loff_t len);
DESCRIPTION
This is a non-portable, 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.
RETURN VALUE
fallocate()
returns zero on success, and -1 on failure.
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.
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.
VERSIONS
fallocate()
is available on Linux since kernel 2.6.23.
CONFORMING TO
fallocate()
is Linux-specific.
NOTES
Glibc does not provide a wrapper for this system call; call it using
syscall(2).
This page is part of release 3.14 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/.
