Name
sync_file_range — sync a file segment with disk
Synopsis
int
sync_file_range( |
int |
fd, |
| |
off64_t |
offset, |
| |
off64_t |
nbytes, |
| |
unsigned int |
flags); |
DESCRIPTION
sync_file_range() permits
fine control when synchronising the open file referred to by
the file descriptor fd with disk.
offset is the
starting byte of the file range to be synchronised.
nbytes specifies the
length of the range to be synchronised, in bytes; if
nbytes is zero, then
all bytes from offset
through to the end of file are synchronised. Synchronisation
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.
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.
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 traditional fdatasync(2)
operation. It 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.
- EIO
-
I/O error.
- EINVAL
-
flags
specifies an invalid bit; or offset or nbytes is invalid.
- 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)
Copyright (c) 2006 Andrew Morton <akpm@osdl.org>
and Copyright 2006 Michael Kerrisk <mtk-manpages@gmx.net>
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
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Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date. The author(s) assume no
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the use of the information contained herein. The author(s) may not
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Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
2006-07-05 Initial creation, Michael Kerrisk based on
Andrew Morton's comments in fs/sync.c
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