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FALLOCATE(2)		   Linux Programmer's Manual		  FALLOCATE(2)

       fallocate - manipulate file space

       #define _GNU_SOURCE	       /* See feature_test_macros(7) */
       #include <fcntl.h>

       int fallocate(int fd, int mode, off_t offset, off_t len);

       This  is	 a nonportable, Linux-specific system call.  For the portable,
       POSIX.1-specified method of ensuring that  space	 is  allocated	for  a
       file, see posix_fallocate(3).

       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.  Details of the supported operations are given  in  the  subsec‐
       tions below.

   Allocating disk space
       The default operation (i.e., mode is zero) of fallocate() allocates the
       disk space within the range specified by offset and len.	 The file size
       (as  reported by stat(2)) will be changed if offset+len is greater than
       the file size.  Any subregion within the range specified by offset  and
       len  that  did  not contain data before the call will be initialized to
       zero.  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.

       After a successful call, subsequent writes into the range specified  by
       offset  and  len	 are  guaranteed  not  to fail because of lack of disk

       If the FALLOC_FL_KEEP_SIZE flag is specified in mode, the  behavior  of
       the call is similar, but the file size will not be changed even if off‐
       set+len is greater than the file	 size.	 Preallocating	zeroed	blocks
       beyond  the  end	 of  the  file in this manner is useful for optimizing
       append workloads.

       Because allocation is done in block size chunks, fallocate() may	 allo‐
       cate a larger range of disk space than was specified.

   Deallocating file space
       Specifying the FALLOC_FL_PUNCH_HOLE flag (available since Linux 2.6.38)
       in mode deallocates space (i.e., creates a  hole)  in  the  byte	 range
       starting	 at offset and continuing for len bytes.  Within the specified
       range, partial filesystem  blocks  are  zeroed,	and  whole  filesystem
       blocks  are removed from the file.  After a successful call, subsequent
       reads from this range will return zeroes.

       The FALLOC_FL_PUNCH_HOLE flag must be ORed with FALLOC_FL_KEEP_SIZE  in
       mode;  in  other words, even when punching off the end of the file, the
       file size (as reported by stat(2)) does not change.

       Not all	filesystems  support  FALLOC_FL_PUNCH_HOLE;  if	 a  filesystem
       doesn't	support the operation, an error is returned.  The operation is
       supported on at least the following filesystems

       *  XFS (since Linux 2.6.38)

       *  ext4 (since Linux 3.0)

       *  Btrfs (since Linux 3.7)

       *  tmpfs (since Linux 3.5)

   Collapsing file space
       Specifying the FALLOC_FL_COLLAPSE_RANGE	flag  (available  since	 Linux
       3.15) in mode removes a byte range from a file, without leaving a hole.
       The byte range to be collapsed starts at offset and continues  for  len
       bytes.	At  the	 completion of the operation, the contents of the file
       starting at the location offset+len will be appended  at	 the  location
       offset, and the file will be len bytes smaller.

       A filesystem may place limitations on the granularity of the operation,
       in order to ensure efficient implementation.  Typically, offset and len
       must  be	 a multiple of the filesystem logical block size, which varies
       according to the filesystem type and configuration.   If	 a  filesystem
       has  such a requirement, fallocate() will fail with the error EINVAL if
       this requirement is violated.

       If the region specified by offset plus len reaches or passes the end of
       file,  an  error	 is  returned; instead, use ftruncate(2) to truncate a

       No other flags may be  specified	 in  mode  in  conjunction  with  FAL‐

       As  at  Linux 3.15, FALLOC_FL_COLLAPSE_RANGE is supported by ext4 (only
       for extent-based files) and XFS.

       On success, fallocate() returns zero.  On error,	 -1  is	 returned  and
       errno is set to indicate the error.

       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.

       EINVAL mode is FALLOC_FL_COLLAPSE_RANGE and the range specified by off‐
	      set plus len reaches or passes the end of the file.

       EINVAL mode is FALLOC_FL_COLLAPSE_RANGE, but either offset  or  len  is
	      not a multiple of the filesystem block size.

       EINVAL mode  contains both FALLOC_FL_COLLAPSE_RANGE and other flags; no
	      other flags are permitted with FALLOC_FL_COLLAPSE_RANGE.

       mode   is FALLOC_FL_COLLAPSE_RANGE, but the file referred to by	fd  is
	      not a regular file.

       EIO    An  I/O  error  occurred	while  reading	from  or  writing to a

       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 This kernel does not implement fallocate().

	      The filesystem containing the file referred to by	 fd  does  not
	      support  this  operation;	 or  the  mode is not supported by the
	      filesystem containing the file referred to by fd.

       EPERM  The file referred to by fd is marked immutable (see  chattr(1)).
	      Or:   mode   specifies  FALLOC_FL_PUNCH_HOLE  or	FALLOC_FL_COL‐
	      LAPSE_RANGE and the file referred to by fd is marked append-only
	      (see chattr(1)).

       ESPIPE fd refers to a pipe or FIFO.

	      mode  specifies  FALLOC_FL_COLLAPSE_RANGE, but the file referred
	      to by fd is currently being executed.

       fallocate() is available on Linux since kernel 2.6.23.  Support is pro‐
       vided  by  glibc since version 2.10.  The FALLOC_FL_* flags are defined
       in glibc headers only since version 2.18.

       fallocate() is Linux-specific.

       fallocate(1), ftruncate(2), posix_fadvise(3), posix_fallocate(3)

       This page is part of release 3.65 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/.

Linux				  2014-04-17			  FALLOCATE(2)

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