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

From: James Bottomley (
Date: Mon Jun 10 2002 - 21:46:44 EST

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

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.

This is part of a set of three patches which provide a sample implementation
of a SCSI driver using the generic TCQ code.

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.

James Bottomley

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