On Tue, Apr 26, 2016 at 11:25:26PM -0400, Theodore Ts'o wrote: > On Wed, Apr 27, 2016 at 12:27:46PM +1000, Dave Chinner wrote: > > > At this point I wonder if we should simply treat O_DIRECT as a hint > > > and always allow it, and just let the file system optimize for it > > > (skip buffering, require alignment, relaxed Posix atomicy requirements) > > > if it is set. > > > > I thought that's how most filesystems treated it, anyway. i.e. > > anything they can't do via direct IO, they fell back to buffered IO > > to complete (e.g. for allocation or append writes, etc). Hence why I > > suggested the fallback rather than erroring out.... > > No, some file systems return EINVAL on the open. In fact that's what > the _require_odirect test in xfstests relies upon.... Sure, but that doesn't change the fact that many of the filesystems that "support O_DIRECT" don't always do O_DIRECT - they transparently do buffered IO instead and hence are treating O_DIRECT as a hint once the file has been opened. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
