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 caller.
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.
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.
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.
This page is part of release 3.14 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/.
