linux-kernel - Re: New Mitsumi legacy CD-ROM driver

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Message-ID: <46407D75.7050603@gmail.com>
Date:	Tue, 08 May 2007 15:39:01 +0200
From:	Rene Herman <rene.herman@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	Andrew Morton <akpm@...l.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: New Mitsumi legacy CD-ROM driver

On 05/08/2007 12:35 PM, Jens Axboe wrote:

Thanks very much for the prompt answer!

> bio[n - 1].bi_sector + bio_sectors(bio[n - 1]) == bio[n].bi_sector
> 
> IOW, the bio's in the chain on the request are contig in the lba space.

Okay great, thanks, everything fine then.

> Yeah, I think it's pointless to support highmem. And as long as you
> don't call blk_queue_bounce_limit() to actively enable highmem, you are
> not going to receive a bio/request with highmem pages.

Yep, the driver is setting BLK_BOUNCE_ANY.

> The block layer wil bounce any highmem pages before it reaches you. So
> for a driver like this, I would recommend just forgetting the mapping
> aspect.

Okay, I agree highmem doesn't make any practical sense for this driver but 
I'm not really sure what it would gain. if !CONFIG_HIGHMEM the bvec_kmap_irq 
turns info "(page_address((bvec)->bv_page) + (bvec)->bv_offset)" directly 
anyway. I am a bit unsure about it all but it's not the case that we can 
then leave out the entire bio_for_each_segnment() loop is it?

(generic kernels with HIGHMEM enabled are I guess an argument...)

> I don't have time to review your driver right now, but I will applaud
> your effort to write a maintenable mitsumi driver! Basically all the old
> cdrom drivers are utter crap, so they are destined for removal.

I noticed by the way there was a bit too much emphasis on the "I" in this 
message; it's in fact Pekka Enberg who  started this and did the core stuff!

Yes ,the current legacy CD-ROM drivers really are complete crap by now. Once 
this mitsumi driver is in final shape it should serve as a nice template for 
the few other types that I'd like to keep supported and the rest can just go.

Thanks again for the prompt comments.

Rene.

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