On 10/05/2017 12:19 PM, Shaohua Li wrote: > On Wed, Oct 04, 2017 at 08:55:02AM -0500, Goldwyn Rodrigues wrote: >> This is a continuation of the nowait support which was incorporated >> a while back. We introduced REQ_NOWAIT which would return immediately >> if the call would block at the block layer. Request based-devices >> do not wait. However, bio based devices (the ones which exclusively >> call make_request_fn) need to be trained to handle REQ_NOWAIT. >> >> This effort covers the devices under MD and DM which would block >> for any reason. If there should be more devices or situations >> which need to be covered, please let me know. >> >> The problem with partial writes discussed during v1 turned out >> to be a bug in partial writes during direct I/O and is fixed >> by the submitted patch[1]. >> >> Changes since v1: >> - mddev to return early in case the device is suspended, within the md code >> as opposed to ->make_request() >> - Check for nowait support with all the lower devices. Same with if adding >> a device which does not support nowait. >> - Nowait under each raid is checked before the final I/O submission for the >> entire I/O. >> >> [1] https://patchwork.kernel.org/patch/9979887/ > > Does this fix the partial IO issue we discussed before? It looks not to me. > The > partial IO bailed out could be any part of an IO, so simply returning the > successed size doesn't help. Am I missing anything? I didn't follow the > discussion, maybe Jens knew. >
If the partial IO bailed out is any part of IO, isn't it supposed to return the size of the IO succeeded _so far_? If a latter part of the IO succeeds (with a failure in between) what are you supposed to return to user in case of direct write()s? Would that even be correct in case it is a file overwrite? -- Goldwyn
