On Mon, Jul 27, 2015 at 05:53:33AM -0400, Ming Lei wrote: > On Mon, Jul 27, 2015 at 5:45 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Mon, Jul 27, 2015 at 05:41:57AM -0400, Ming Lei wrote: > >> > Why the hardcoded value? I suspect this should be more like: > >> > > >> > if (dio && inode->i_sb->s_bdev && > >> > (lo->lo_offset & (bdev_io_min(inode->i_sb->s_bdev) - 1)) != 0) > >> > dio = false; > >> > >> The above can't work if the backing device has a bigger sector size > >> (such as 4K), that is why loop's direct-io requires 512 min_io_size of > >> backing device. > > > > Why doesn't it work? If the backing device sector size is 4k > > and lo_offset is 0 or a multiple of 4k it should allow direct I/O, > > and my code sniplet will allow that. > > Because size has to be 4k aligned too. So check that, too. Any >= 4k block size filesystem should be doing mostly 4k aligned and sized IO... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
