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

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Message-ID: <4A2F66ED.80206@panasas.com>
Date:	Wed, 10 Jun 2009 10:55:25 +0300
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Kiyoshi Ueda <k-ueda@...jp.nec.com>, Tejun Heo <tj@...nel.org>
CC:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	device-mapper development <dm-devel@...hat.com>,
	Jun'ichi Nomura <j-nomura@...jp.nec.com>
Subject: Re: [PATCH block#for-2.6.31] block: add request clone interface

On 06/10/2009 05:15 AM, Kiyoshi Ueda wrote:
> Hi Jens,
> 
> On 06/10/2009 03:03 AM +0900, Jens Axboe wrote:
>> On Tue, Jun 09 2009, Kiyoshi Ueda wrote:
>>> Hi Jens,
>>>
>>> +/*
>>> + * Copy request information of the original request to the clone request.
>>> + */
>>> +static void __blk_rq_prep_clone(struct request *dst, struct request *src)
>>> +{
>>> +	dst->cpu = src->cpu;
>>> +	dst->cmd_flags = (rq_data_dir(src) | REQ_NOMERGE);
>>> +	dst->cmd_type = src->cmd_type;
>>> +	dst->__sector = blk_rq_pos(src);
>>> +	dst->__data_len = blk_rq_bytes(src);
>>> +	dst->nr_phys_segments = src->nr_phys_segments;
>>> +	dst->ioprio = src->ioprio;
>>> +	dst->buffer = src->buffer;
>>> +	dst->cmd_len = src->cmd_len;
>>> +	dst->cmd = src->cmd;
>> Are you making sure that 'src' always exists while 'dst' is alive?
> 
> Yes.
> Request-based dm is the owner of 'src' (original) and
> it never frees 'src' until the 'dst' (clone) are completed.
> 
> I avoided deep-copying __cmd/buffer/sense as it's costly
> (additional allocation and memcpy).

For my needs for example dst->cmd will be different then
src->cmd. Could be untouched. The caller will set what he
needs.

dst->sense should be untouched, caller can set to src->sense
if he wants to. Or like me he already have another buffer.

dst->buffer is always NULL in my path so I don't know
what that is. Tejun?

It should only be about bios and lengths.

And a big fat comment about what it does and what it
does not.

> And I don't think there are any needs for that.
> But if anyone really wants that even with the copying cost,
> please speak up.
> 
> Thanks,
> Kiyoshi Ueda

Thanks
Boaz
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