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

NAME
       fallocate - manipulate file space

SYNOPSIS
       #define _GNU_SOURCE
       #include <fcntl.h>

       int fallocate(int fd, int mode, off_t offset, off_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 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‐
	      set+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  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.

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.  Support is pro‐
       vided by glibc since version 2.10.

CONFORMING TO
       fallocate() is Linux-specific.

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

COLOPHON
       This  page  is  part of release 3.23 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				  2009-03-13			  FALLOCATE(2)
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