linux-kernel - Re: [block #for-next] block: clear req->errors on bio completion only for fs requests

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Message-ID: <20090416061949.GQ5178@kernel.dk>
Date:	Thu, 16 Apr 2009 08:19:49 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	petkovbb@...glemail.com
Subject: Re: [block #for-next] block: clear req->errors on bio completion
	only  for fs requests

On Thu, Apr 16 2009, Tejun Heo wrote:
> Impact: subtle behavior change
> 
> For fs requests, rq is only carrier of bios and rq error status as a
> whole doesn't mean much.  This is the reason why rq->errors is being
> cleared on each partial completion of a request as on each partial
> completion the error status is transferred to the respective bios.
> 
> For pc requests, rq->errors is used to carry error status to the
> issuer and thus __end_that_request_first() doesn't clear it on such
> cases.
> 
> The condition was fine till now as only fs and pc requests have used
> bio and thus the bio completion path.  However, future changes will
> unify data accesses to bio and all non fs users care about rq error
> status.  Clear rq->errors on bio completion only for fs requests.
> 
> In general, the implicit clearing is a bit too subtle especially as
> the meaning of rq->errors is completely dependent on low level
> drivers.  Unifying / cleaning up rq->errors usage and letting llds
> manage it would be better.  TODO comment added.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Jens Axboe <axboe@...nel.dk>
> ---
> Jens, can you please ack this patch?  With FUJITA's scsi_lib cleanup
> and Borislav's patch to make ide not use preallocated data structures,
> this is the only block bit which is necessary for ide cleanup
> patchets.  If you're okay with it, I'd like to push this through
> Bartlomiej's tree.

Sure, you can add my acked-by.

-- 
Jens Axboe

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