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

[Jeff Garzik <jeff@garzik.org>]

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