On Mon, 2 May 2011, Christoph Hellwig wrote: > On Mon, May 02, 2011 at 09:13:08AM +0100, Alasdair G Kergon wrote: > > On Mon, May 02, 2011 at 09:16:21AM +0200, Lukas Czerner wrote: > > > However when we have dm device where part of the device supports > > > discard due to underlying hardware capability we just can not return > > > EOPNOTSUPP from blkdev_issue_discard, because it is just not true! > > > > EOPNOTSUPP from dm means the operation was not supported on that *one* bio. > > It does *not* tell you anything in general about the device, or whether > > you'd get the same error from different bios in future. > > Exactly. We already have the information in the queue limits to tell > the filesystem if discard is supported at all or not. > So I gave it a try. First of all the device composed of SSD and spinning disk does export discard_support information properly, however it also advertise discard_zeroes_data which is wrong and possibly dangerous and should be fixed! And second of all, strictly speaking if EOPNOTSUPP from dm means that operation was not supported on that *one* bio, blkdev_issue_discard() should handle that and do not return EOPNOTSUPP further if queue limits tells that device has discard support. Is this acceptable solution for you guys ? I can make that change since I am changing blkdev_issue_discard() anyway. Or, we can make that change in filesystem where we disable discard on mount time, when we notice that discard mount option was specified, but the device does not support it (we should probably do this regardless on blkdev_issue_discard() change). Thanks! -Lukas -- 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
