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

[Jeff Garzik]

Boaz Harrosh wrote:
> 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?

As passed to us from the block layer, there is nothing special about the 
size of the first bio, AFAIK.

This seems like a libosd bug?  If you want to support chained bio's, I 
would presume you would either walk the list and sum all sizes, or in 
some other way input the total request size?

	Jeff



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