Messages in this thread | | | Date | Tue, 11 Jun 2002 07:50:14 +0200 | From | Jens Axboe <> | Subject | Re: Proposed changes to generic blk tag for use in SCSI (1/3) |
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On Mon, Jun 10 2002, James Bottomley wrote: > The attached is what I needed in the generic block layer to get the SCSI > subsystem using it for Tag Command Queueing. > > The changes are basically > > 1) I need a function to find the tagged request given the queue and the tag, > which I've added as a function in the block layer
Ehm it's already there, one could argue that it's pretty core functionality for this type of stuff :-). It's called blk_queue_get_tag(q, tag), and it's in blkdev.h. However, I agree that we should just move it into ll_rw_blk.c. That gets better documented as well. Could you redo that part?
> 2) The SCSI queue will stall if it gets an untagged request in the stream, so > once tagged queueing is enabled, all commands (including SPECIALS) must be > tagged. I altered the check in blk_queue_start_tag to permit this.
I completely agree with this, blk_queue_start_tag() should not need to know about these things so just checking if the request is already marked tagged is fine with me. But please make that a warning, like
if (rq->flags & REQ_QUEUED) { printk("blk_queue_start_tag: rq already tagged\n"); return 1; }
Also, you need to fix drivers/ide/tcq.c to make sure it doesn't call blk_queue_start_tag() for non REQ_CMD requests. Ah wait, I'll just change that. And also _please_ fix the comment about REQ_CMD and not just the code, it's doesn't stand anymore.
> This is part of a set of three patches which provide a sample implementation > of a SCSI driver using the generic TCQ code.
Cool! Looking forward to reviewing it later today.
-- Jens Axboe
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