Section (2) sync_file_range
sync_file_range — sync a file segment with disk
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h>
|unsigned int flags
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
through to the end of file are synchronized. Synchronization
is in units of the system page size:
offset is rounded down to a
(offset+nbytes-1) is rounded
up to a page boundary.
argument can include any of the following values:
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.
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.
Wait upon write-out of all pages in the range after performing any write.
as 0 is permitted, as a no-op.
This system call is extremely dangerous and should not
be used in portable programs. None of these operations
writes out the file_zsingle_quotesz_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. There is no
user interface to know if a write is purely an overwrite.
On filesystems using copy-on-write semantics (e.g.,
overwrite of existing allocated blocks is impossible. When
writing into preallocated space, many filesystems also
require calls into the block allocator, which this system
call does not sync out to disk. This system call does not
flush disk write caches and thus does not provide any data
integrity on systems with volatile disk write caches.
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.
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.
- 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.
sync_file_range() returns 0; on failure
−1 is returned and
is set to indicate the error.
fdis not a valid file descriptor.
flagsspecifies an invalid bit; or
Out of memory.
Out of disk space.
fdrefers to something other than a regular file, a block device, or a directory.
Some architectures (e.g., PowerPC, ARM) need 64-bit
arguments to be aligned in a suitable pair of registers. On
such architectures, the call signature of
sync_file_range() shown in the SYNOPSIS
would force a register to be wasted as padding between the
offset arguments. (See
syscall(2) for details.)
Therefore, these architectures define a different system
call that orders the arguments suitably:
unsigned int flags,
The behavior of this system call is otherwise exactly
the same as
A system call with this signature first appeared on the
ARM architecture in Linux 2.6.20, with the name
arm_sync_file_range(). It was
renamed in Linux 2.6.22, when the analogous system call was
added for PowerPC. On architectures where glibc support is
provided, glibc transparently wraps
sync_file_range2() under the name
This page is part of release 4.16 of the Linux
man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright (c) 2006 Andrew Morton <akpmosdl.org>
and Copyright 2006 Michael Kerrisk <mtk.manpagesgmail.com>
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
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein. The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
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_zsingle_quotesz_s comments in fs/sync.c
2010-10-09, mtk, Document sync_file_range2()