FSYNC(2) System Calls Manual FSYNC(2)
fsync, fsync_range -- synchronize a file's in-core state with that on
Standard C Library (libc, -lc)
fsync_range(int fd, int how, off_t start, off_t length);
fsync() causes all modified data and attributes of fd to be moved to a
permanent storage device. This normally results in all in-core modified
copies of buffers for the associated file to be written to a disk.
fsync() should be used by programs that require a file to be in a known
state, for example, in building a simple transaction facility.
fsync_range() causes all modified data starting at start for length
length of fd to be written to permanent storage. Note that fsync_range()
requires that the file fd must be open for writing.
fsync_range() may flush the file data in one of two manners:
FDATASYNC Synchronize the file data and sufficient meta-data to
retrieve the data for the specified range.
FFILESYNC Synchronize all modified file data and meta-data for the
By default, fsync_range() does not flush disk caches, assuming that
storage media are able to ensure completed writes are transfered to
media. The FDISKSYNC flag may be included in the how parameter to
trigger flushing of all disk caches for the file.
If the length parameter is zero, fsync_range() will synchronize all of
the file data.
A 0 value is returned on success. A -1 value indicates an error.
fsync() or fsync_range() fail if:
[EBADF] fd is not a valid descriptor.
[EINVAL] fd refers to a socket, not to a file.
[EIO] An I/O error occurred while reading from or writing to
the file system.
Additionally, fsync_range() fails if:
[EBADF] fd is not open for writing.
[EINVAL] start + length is less than start.
For optimal efficiency, the fsync_range() call requires that the file
system containing the file referenced by fd support partial
synchronization of file data. For file systems which do not support
partial synchronization, the entire file will be synchronized and the
call will be the equivalent of calling fsync().
The fsync() function call appeared in 4.2BSD.
The fsync_range() function call first appeared in NetBSD 2.0 and is
modeled after the function available in AIX.
NetBSD 6.1.5 May 17, 2010 NetBSD 6.1.5