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       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.  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 successful 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 offset+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 difference 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 allocate 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 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

              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)).

       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.


       fallocate() is Linux-specific.


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


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