linux-kernel - Re: [PATCH block#for-2.6.31] block: add request clone interface (v2)

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Message-ID: <x49vdn3lynd.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 11 Jun 2009 08:53:42 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Kiyoshi Ueda <k-ueda@...jp.nec.com>, linux-kernel@...r.kernel.org,
	device-mapper development <dm-devel@...hat.com>,
	Boaz Harrosh <bharrosh@...asas.com>,
	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
Subject: Re: [PATCH block#for-2.6.31] block: add request clone interface (v2)

Jens Axboe <jens.axboe@...cle.com> writes:

> On Thu, Jun 11 2009, Kiyoshi Ueda wrote:
>> Hi Jens,
>> 
>> This patch adds the following 2 interfaces for request-stacking drivers:
>> 
>>   - blk_rq_prep_clone(struct request *clone, struct request *orig,
>> 		      struct bio_set *bs, gfp_t gfp_mask,
>> 		      int (*bio_ctr)(struct bio *, struct bio*, void *),
>> 		      void *data)
>>       * Clones bios in the original request to the clone request
>>         (bio_ctr is called for each cloned bios.)
>>       * Copies attributes of the original request to the clone request.
>>         The actual data parts (e.g. ->cmd, ->buffer, ->sense) are not
>>         copied.
>> 
>>   - blk_rq_unprep_clone(struct request *clone)
>>       * Frees cloned bios from the clone request.
>> 
>> Request stacking drivers (e.g. request-based dm) need to make a clone
>> request for a submitted request and dispatch it to other devices.
>> 
>> To allocate request for the clone, request stacking drivers may not
>> be able to use blk_get_request() because the allocation may be done
>> in an irq-disabled context.
>> So blk_rq_prep_clone() takes a request allocated by the caller
>> as an argument.
>> 
>> For each clone bio in the clone request, request stacking drivers
>> should be able to set up their own completion handler.
>> So blk_rq_prep_clone() takes a callback function which is called
>> for each clone bio, and a pointer for private data which is passed
>> to the callback.
>> 
>> NOTE:
>> blk_rq_prep_clone() doesn't copy any actual data of the original
>> request.  Pages are shared between original bios and cloned bios.
>> So caller must not complete the original request before the clone
>> request.
>
> This looks good to me now, I've applied it.

Is blk_rq_unprep_clone really the best name?
          ^^^^^^

Cheers,
Jeff
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