On Fri, 2008-08-08 at 13:44 +0200, Jens Axboe wrote: > > Sigh indeed, ->issue_flush_fn() was the actual issuer, not the preparer. > Let me send a new diff. This adds the ->prepare_discard_fn() to do the > transformation, and also extends blkdev_issue_flush() to return error if > the IO was never queued because of some device in the stack not > supporting it. I think we still want the DISCARD flag in rq->cmd_flags. We can't rely on rq->cmd_type == REQ_TYPE_DISCARD because that may well be changed to something else (like REQ_TYPE_BLOCK_PC). I was thinking of REQ_TYPE_DISCARD as a special case for some block devices, just as REQ_TYPE_FLUSH is a special case for the ps3disk.c driver (nobody else uses it). In fact, perhaps both of them should be switched to REQ_TYPE_LINUX_BLOCK or REQ_TYPE_SPECIAL? I was actually tempted to leave REQ_TYPE_DISCARD out of the original patch 1/5 completely, and add it only as part of the FTL patch. I don't think it's something for the core code to be caring about -- let the flag in rq->cmd_flags do that. > Until we have overlap detection, I think we should make the discard > request a explicit barrier. Otherwise we could have problems with a > discard being passed by a write request and such. I think that making it an explicit barrier is a reasonable thing to do for now. We can work on merges as a next step. -- David Woodhouse Open Source Technology Centre David.Woodhouse@xxxxxxxxx Intel Corporation -- 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
