fallocate


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

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

DESCRIPTION
       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 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-
       tion.

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

       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.

       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
              filesystem.

       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().

       EOPNOTSUPP
              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 and the file referred to
              by fd is marked append-only (see chattr(1)).

       ESPIPE fd refers to a pipe or FIFO.

VERSIONS
       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.

CONFORMING TO
       fallocate() is Linux-specific.

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

COLOPHON
       This page is part of release 3.54 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                             2013-06-10                      FALLOCATE(2)
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