linux-kernel - Re: regression: CD burning (k3b) went broke

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Message-Id: <1204092010.9934.31.camel@homer.simson.net>
Date:	Wed, 27 Feb 2008 07:00:10 +0100
From:	Mike Galbraith <efault@....de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Tejun Heo <htejun@...il.com>, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: regression: CD burning (k3b) went broke


On Wed, 2008-02-27 at 03:24 +0100, Mike Galbraith wrote:
> On Tue, 2008-02-26 at 15:08 -0800, Andrew Morton wrote:
 
> > So this change fixes a bug?  Can we have a recap of how it does this?
> 
> Yeah, it fixes the problem.  (wrt recap, if I could write it, it would
> be a changelog;)

Hm.  After rummaging around some more in both kernel and userland, I
think this patchlet is not only functional, but  (random accident)
technically correct.  What the heck, let's see if it flies...

snippet from userland:
/*
 * Return the residual DMA count for last command.
 * If this count is < 0, then a DMA overrun occured.
 */
EXPORT int
scg_getresid(scgp)
	SCSI	*scgp;
{
	return (scgp->scmd->resid);
}

This function is used all over the place in cdrecord to determine
transfer size.

(patchlet takes wing, and... goes splat?)
 
Fix CD burning regression introduced by
6b00769fe1502b4ad97bb327ef7ac971b208bfb5.  raw_data_len must be updated
to reflect residual data upon IO completion because it is used by
blk_complete_sghdr_rq() to set hdr->resid which eventually becomes
visible to userland.

Signed-off-by: Mike Galbraith <efault@....de>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index ba21d97..7a6f784 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -871,7 +871,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd,
unsigned int good_bytes)
 			scsi_end_bidi_request(cmd);
 			return;
 		}
-		req->data_len = scsi_get_resid(cmd);
+		req->data_len = req->raw_data_len = scsi_get_resid(cmd);
 	}
 
 	BUG_ON(blk_bidi_rq(req)); /* bidi not support for !blk_pc_request yet
*/


	-Mike

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