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

       fallocate - manipulate file space

       #define _GNU_SOURCE
       #include <fcntl.h>

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

       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.  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 and
       initializes to zero 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.   This  default  behavior
       closely	resembles the behavior of the posix_fallocate(3) library func‐
       tion, and is intended as a method of optimally implementing that	 func‐

       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.

       fallocate() returns zero on success, and -1 on failure.

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

       fallocate() is Linux-specific.

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

       This page is part of release 3.22 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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