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



NAME
       sync_file_range - sync a file segment with disk

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 syn-
       chronized.  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 perform-
       ing 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 caller.

       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_WRITE
              Start write-out of all dirty pages in the specified range which are not presently under write-out.  This
              is an asynchronous flush-to-disk operation.  This is not suitable for data integrity operations.

       SYNC_FILE_RANGE_WAIT_BEFORE (or SYNC_FILE_RANGE_WAIT_AFTER)
              Wait for completion of write-out of all pages in the specified range.  This can be used after an earlier
              SYNC_FILE_RANGE_WAIT_BEFORE  | SYNC_FILE_RANGE_WRITE operation to wait for completion of that operation,
              and obtain its result.

       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 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-05-27                SYNC_FILE_RANGE(2)