FALLOCATE(2)

NAME
fallocate - manipulate file space

SYNOPSIS
#include <linux/falloc.h>

long fallocate(int fd, int mode, loff_t offset, loff_t len);

DESCRIPTION
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, 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.

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
fallocate() is Linux specific.

SEE ALSO
ftruncate(2), posix_fallocate(3), posix_fadvise(3)