Provided by:
manpages-dev_2.62-1_all 
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 synchronising 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.
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.
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.
This system call is Linux specific, and should be avoided in portable
programs.
fdatasync(2), fsync(2), msync(2), sync(2), feature_test_macros(7)