From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boaz Harrosh <bharrosh@panasas.com>
Subject: Re: [PATCH 03/14] block: implement blk_rq_map_kern_prealloc()
Date: Thu, 26 Mar 2009 10:05:57 +0200
Message-ID: <49CB3765.4070406@panasas.com>
References: <1237910776-10983-1-git-send-email-tj@kernel.org> <1237910776-10983-4-git-send-email-tj@kernel.org> <49CA4B4B.50408@panasas.com> <49CAE425.5050009@kernel.org> <49CB31DB.2040608@gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Return-path: <linux-kernel-owner+glk-linux-kernel-3=40m.gmane.org-S1756529AbZCZIJU@vger.kernel.org>
In-Reply-To: <49CB31DB.2040608@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
To: Tejun Heo <htejun@gmail.com>
Cc: bzolnier@gmail.com, linux-kernel@vger.kernel.org, axboe@kernel.dk, linux-ide@vger.kernel.org
List-Id: linux-ide@vger.kernel.org

On 03/26/2009 09:42 AM, Tejun Heo wrote:
> Hello,
> 
> A few issues.
> 
> Tejun Heo wrote:
>>> Perhaps you could reorder the code below a bit?
>>>
>>> My proposal is:
>>> * blk_rq_map_kern_prealloc => is simplified to be
>>>     int blk_rq_map_bio(struct request_queue *q, struct request *rq,
>>> 		       struct bio *bio);
> 
> The thing is that the prealloc variant should be allowed to be called
> from IRQ context and blk_queue_bounce() shouldn't be called.
> Hmmm... well, the caller is supposed to know what it's doing and maybe
> we can just add a comment that it shouldn't be called with buffers
> which might get bounced from IRQ context.
> 

Hmm that is a problem. I would suggest a flag or a check. My bios come
from VFS they need bouncing.

Can you think of a solution?

We could just call blk_queue_bounce(). IRQ callers need to make sure their
buffers don't need bouncing anyway, so there is no such bug right? If a programmer
gets it wrong he will get a BUG check that tells him that.

>>> * The extra checks currently inside blk_rq_map_kern_prealloc are moved
>>>   to bio_map_kern_prealloc()
>>>
>>> * Users call bio_map_kern_prealloc() directly and then use blk_rq_map_bio()
>>>   in a two stage process.
> 
> This breaks consistency with blk_rq_map_*() family of functions.  Do
> you have a plan to make them all consistent?  I think we really need
> to maintain API consistency.
> 

I agree, that is why I called it blk_make_request originally. But this is not good
for you since your request is pre-allocated as well as the bio.

It needs a different name, blk_rq_set_bio(), I don't know do you have any ideas?

> Thanks.
> 

Thanks

Boaz