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

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

       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.  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, 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

       EPERM  The file referred to by fd is marked immutable (see chattr(1)).

       ESPIPE fd refers to a pipe or FIFO.

       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 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.

Linux                             2011-09-19                      FALLOCATE(2)
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