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FALLOCATE(2)		   Linux Programmers Manual		 FALLOCATE(2)

       fallocate - manipulate file space


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

       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:

	      This flag allocates and  initializes  to	zero  the  disk  space
	      within  the range specified by offset and len.  After a success
	      ful 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  off

       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  dif
       ference	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  allo
       cate a larger range than that which was specified.

       fallocate()  returns  zero  on  success, or an error number on failure.
       Note that errno is not set.

       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

       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.

	      The mode is not supported by the file system containing the file
	      referred to by fd.

       fallocate() is available on Linux since kernel 2.6.23.

       fallocate() is Linux-specific.

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

       This page is part of release 3.05 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				  2007-07-20			  FALLOCATE(2)

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