POSIX_FALLOCATE(2)

NAME
posix_fallocate - pre-allocate storage for a range in a file

LIBRARY
libc

SYNOPSIS
#include <fcntl.h>
int
posix_fallocate(int fd, off_t offset, off_t len);

DESCRIPTION
Required storage for the range offset to offset + len in the file referenced by fd is guaranteed to be allocated upon successful return. That is, if posix_fallocate() returns successfully, subsequent writes to the specified file data will not fail due to lack of free space on the file system storage media. Any existing file data in the specified range is unmodified. If offset + len is beyond the current file size, then posix_fallocate() will adjust the file size to offset + len. Otherwise, the file size will not be changed.

Space allocated by posix_fallocate() will be freed by a successful call to creat(3) or open(2) that truncates the size of the file. Space allocated via posix_fallocate() may be freed by a successful call to ftruncate(2) that reduces the file size to a size smaller than offset + len.

RETURN VALUES
If successful, posix_fallocate() returns zero. It returns an error on failure, without setting errno.

ERRORS
Possible failure conditions:

[EBADF]
    The fd argument is not a valid file descriptor.

[EBADF]
    The fd argument references a file that was opened without write permission.

[EFBIG]
    The value of offset + len is greater than the maximum file size.

[EINTR]
    A signal was caught during execution.

[EINVAL]
    The len argument was less than or equal to zero, the offset argument was less than zero, or the operation is not supported by the file system.

[EIO]
    An I/O error occurred while reading from or writing to a file system.

[ENODEV]
    The fd argument does not refer to a file that supports posix_fallocate.

[ENOSPC]
    There is insufficient free space remaining on the file system storage media.

[ESPIPE]
    The fd argument is associated with a pipe or FIFO.

SEE ALSO
ftruncate(2), open(2), unlink(2), creat(3)

STANDARDS
The posix_fallocate() system call conforms to p1003.1-2004.

HISTORY
The posix_fallocate() function appeared in FreeBSD 9.0 and was ported to DragonFly 6.1.

AUTHORS
posix_fallocate() and this manual page were initially written by Matthew Fleming <mdf@FreeBSD.org>.