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

       fallocate - manipulate file space

       #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.  Details of
       the supported operations are given in the subsections 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 function.

       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 offset+len is greater than  the  file  size.
       Preallocating  zeroed blocks beyond the end of the file in this manner is useful for opti-
       mizing append workloads.

       Because allocation is done in block size chunks, fallocate() may allocate 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 deallo-
       cates space (i.e., creates a hole) in the byte range starting at offset and continuing for
       len  bytes.   Within the specified range, partial file system blocks are zeroed, and whole
       file system 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  file  systems support FALLOC_FL_PUNCH_HOLE; if a file system doesn't support the
       operation, an error is returned.

       On success, fallocate() returns zero.  On error, -1 is returned and errno is set to  indi-
       cate the error.

       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 This kernel does not implement fallocate().

	      The file system containing the file referred to by fd does not support this  opera-
	      tion;  or the mode is not supported by the file system 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

       ESPIPE fd refers to a pipe or FIFO.

       fallocate() is available on Linux since kernel 2.6.23.  Support is provided by glibc since
       version 2.10.  The FALLOC_FL_* flags are defined in glibc headers only since version 2.18.

       fallocate() is Linux-specific.

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

       This  page  is  part of release 3.53 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at

Linux					    2013-06-10				     FALLOCATE(2)
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