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



NAME
       fallocate - manipulate file space

SYNOPSIS
       #include <&lt;linux/falloc.h>&gt;

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

DESCRIPTION
       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, or an error number on failure.
       Note that errno is not set.

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.

CONFORMING TO
       fallocate() is Linux-specific.

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

COLOPHON
       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)