SYNOPSIS
       #define _GNU_SOURCE
       #include <fcntl.h>

       int sync_file_range(int fd, off64_t offset, off64_t nbytes,
                           unsigned int flags);

DESCRIPTION
       sync_file_range() permits fine control when synchronizing the open file
       referred to by the file descriptor fd with disk.

       offset is the starting byte of  the  file  range  to  be  synchronized.
       nbytes  specifies the length of the range to be synchronized, in bytes;
       if nbytes is zero, then all bytes from offset through  to  the  end  of
       file  are synchronized.  Synchronization is in units of the system page
       size: offset is rounded down to a page boundary;  (offset+nbytes-1)  is
       rounded up to a page boundary.

       The flags bit-mask argument can include any of the following values:

       SYNC_FILE_RANGE_WAIT_BEFORE
              Wait  upon  write-out  of  all pages in the specified range that
              have already been submitted to the device driver  for  write-out
              before performing any write.

       SYNC_FILE_RANGE_WRITE
              Initiate  write-out  of  all  dirty pages in the specified range
              which are not presently submitted  write-out.   Note  that  even
              this  may  block if you attempt to write more than request queue
              size.

       SYNC_FILE_RANGE_WAIT_AFTER
              Wait upon write-out of all pages in the range  after  performing
              any write.

       Specifying flags as 0 is permitted, as a no-op.

   Some details
       None  of  these  operations  write out the file's metadata.  Therefore,
       unless the application is strictly performing  overwrites  of  already-
       instantiated disk blocks, there are no guarantees that the data will be
       available after a crash.

       SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will  detect
       any  I/O errors or ENOSPC conditions and will return these to the call-
       er.

       Useful combinations of the flags bits are:

       SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE
              Ensures that all pages in the specified range which  were  dirty
              when  sync_file_range()  was  called are placed under write-out.
              This is a start-write-for-data-integrity operation.

       SYNC_FILE_RANGE_WAIT_BEFORE       |       SYNC_FILE_RANGE_WRITE       |
       SYNC_FILE_RANGE_WAIT_AFTER
              This  is  a  write-for-data-integrity operation that will ensure
              that all pages in the specified  range  which  were  dirty  when
              sync_file_range() was called are committed to disk.

RETURN VALUE
       On  success, sync_file_range() returns 0; on failure -1 is returned and
       errno is set to indicate the error.

ERRORS
       EBADF  fd is not a valid file descriptor.

       EINVAL flags specifies an invalid bit; or offset or nbytes is invalid.

       EIO    I/O error.

       ENOMEM Out of memory.

       ENOSPC Out of disk space.

       ESPIPE fd refers to something  other  than  a  regular  file,  a  block
              device, a directory, or a symbolic link.

VERSIONS
       sync_file_range() appeared on Linux in kernel 2.6.17.

CONFORMING TO
       This  system  call is Linux-specific, and should be avoided in portable
       programs.

SEE ALSO
       fdatasync(2), fsync(2), msync(2), sync(2), feature_test_macros(7)

COLOPHON
       This page is part of release 3.23 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/.