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

[Jeff Garzik]

Jens Axboe wrote:
> On Tue, Apr 07 2009, Jeff Garzik wrote:
> > 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?
>
> Completely agree, if you want to support passing in a chain, you better
> make the first bio just part of the chain (not some header bio).
>
> And Jeff, you still have that bio_clone() bug in your v2 posting.

Yep, that was noted in the patch description as "The major remaining 
pre-merge FIXME" :)

	Jeff


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