On Tue, Apr 19 2005, Jens Axboe wrote: > On Tue, Apr 19 2005, James Bottomley wrote: > > On Tue, 2005-04-19 at 14:34 +0200, Jens Axboe wrote: > > > On Mon, Apr 18 2005, Tejun Heo wrote: > > > > And, James, regarding REQ_SOFTBARRIER, if the REQ_SOFTBARRIER thing can > > > > be removed from SCSI midlayer, do you agree to change REQ_SPECIAL to > > > > mean special requests? If so, I have three proposals. > > > > > > > > * move REQ_SOFTBARRIER setting to right after the allocation of > > > > scsi_cmnd in scsi_prep_fn(). This will be the only place where > > > > REQ_SOFTBARRIER is used in SCSI midlayer, making it less pervasive. > > > > * Or, make another API which sets REQ_SOFTBARRIER on requeue. maybe > > > > blk_requeue_ordered_request()? > > > > * Or, make blk_insert_request() not set REQ_SPECIAL on requeue. IMHO, > > > > this is a bit too subtle. > > > > > > > > I like #1 or #2. Jens, what do you think? Do you agree to remove > > > > requeue feature from blk_insert_request()? > > > > > > #2 is the best, imho. We really want to maintain ordering on requeue > > > always, marking it softbarrier automatically in the block layer means > > > the io schedulers don't have to do anything specific to handle it. > > > > This is my preference too. In general, block is the only one that > > should care what the REQ_SOFTBARRIER flag actually means. SCSI only > > cares that it submits a non mergeable request. > > > > I'm happy to separate the meaning of REQ_SPECIAL from req->special. > > Isn't it just duplicate information anyways? I mean, just clear > ->special if it isn't valid anymore. Having a seperate flag to indicate > this seems a little suboptimal. It made more sense when ->cmd was a > integer being READ, WRITE, etc. But as a seperate state now it doesn't. Oh, and this is only true of SCSI, btw. REQ_SPECIAL should not be seen outside of driver code, its meaning is defined solely by the driver. SCSI ties it to ->special, but that is not necessarily true for any other driver. -- Jens Axboe - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
