On Tue, Aug 25, 2015 at 09:46:11AM +1000, Dave Chinner wrote: > On Mon, Aug 24, 2015 at 01:19:24PM -0400, Jeff Moyer wrote: > > Brian Norris <computersforpeace@xxxxxxxxx> writes: > > > > > On Mon, Aug 24, 2015 at 10:13:25AM +0300, Artem Bityutskiy wrote: > > >> Now, some user-space fails when direct I/O is not supported. > > > > > > I think the whole argument rested on what it means when "some user space > > > fails"; apparently that "user space" is just a test suite (which > > > can/should be fixed). > > > > Even if it wasn't a test suite it should still fail. Either the fs > > supports O_DIRECT or it doesn't. Right now, the only way an application > > can figure this out is to try an open and see if it fails. Don't break > > that. > > Who cares how a filesystem implements O_DIRECT as long as it does > not corrupt data? ext3 fell back to buffered IO in many situations, > yet the only complaints about that were performance. IOWs, it's long been > true that if the user cares about O_DIRECT *performance* then they > have to be careful about their choice of filesystem. > > But if it's only 5 lines of code per filesystem to support O_DIRECT > *correctly* via buffered IO, then exactly why should userspace have > to jump through hoops to explicitly handle open(O_DIRECT) failure? > Especially when you consider that all they can do is fall back to > buffered IO themselves.... This is what btrfs already does for O_DIRECT plus compressed, or other cases where people don't want their applications to break on top of new features that aren't quite compatible with it. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
