linux-kernel - Re: [PATCH] osdblk: a Linux block device for OSD objects

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Message-ID: <49D8856E.3090903@panasas.com>
Date:	Sun, 05 Apr 2009 13:18:22 +0300
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Jens Axboe <jens.axboe@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-scsi@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] osdblk: a Linux block device for OSD objects

On 04/03/2009 12:58 PM, Jeff Garzik wrote:
> Jens Axboe wrote:
>> This wont work, GFP_NOIO inside the queue lock. You are also only
>> cloning the front bio, what happens if you have > 1 bio on the request?
>> You seem to dequeue the request and complete all of it, regardless of
>> whether bio->bi_size == blk_rq_bytes(rq). I'm assuming you have to clone
>> because of how the osd_req_{read,write} works, so I'd suggest storing
>> the byte size in your osdblk_request and only completing that in
>> osdblk_end_request(). Then do a rq_for_each_bio() look in there, and
>> only dequeue if you manage to start an osd request for each of them,
>> THEN moving on to the next request.
> 

There is nothing preventing from issuing a linked bio list. The only thing
is that osd_read/write looks at the first bio for total size.
If the first bio->bi_size does not specify the full length of the chain
then we should add another parameter to osd_read/write for that.

The original idea was to specifically allow chained bios.

Please advise?

> Thanks for the review.  Will fix...
> 
> 	Jeff
> 

Thanks
Boaz
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