Re: Proposed changes to generic blk tag for use in SCSI (1/3)

From: Doug Ledford (
Date: Thu Jun 13 2002 - 16:01:41 EST

On Mon, Jun 10, 2002 at 10:46:44PM -0400, James Bottomley wrote:
> 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.

Hmmm...this seems broken to me. Switching from tagged to untagged
momentarily and then back is perfectly valid. Can the bio layer
handle this and not the scsi layer, or are both layers unable to handle
this sort of tag manipulation?

> There are several shortcomings of the prototype, most notably it doesn't have
> tag starvation detection and processing. However, I think I can re-introduce
> this as part of the error handler functions.

If you are using the bio layer tag processing, then it should be
doing this part I would think. If it isn't, then it sounds like either
it's design is missing some key elements required to be fully functional
or the integration between the scsi layer and the bio layer needs some
additional work.

  Doug Ledford <>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606

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