SYNC_FILE_RANGE(2) Linux Programmer's Manual SYNC_FILE_RANGE(2)NAMEsync_file_range - sync a file segment with disk
void sync_file_range(int fd, off64_t offset, off64_t nbytes,
unsigned int flags);
DESCRIPTIONsync_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:
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.
Wait upon write-out of all pages in the range after performing
Specifying flags as 0 is permitted, as a no-op.
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 call‐
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
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 |
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.
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.
This system call is Linux specific, and should be avoided in portable
SEE ALSOfdatasync(2), fsync(2), msync(2), sync(2)Linux 2.6.17 2006-07-05 SYNC_FILE_RANGE(2)