linux-kernel - Re: [PATCH]: Rename REQ_COPY_USER to more descriptive REQ_HAS_TAIL_SPACE_FOR

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Date:	Tue, 14 Jul 2009 20:34:43 +0400
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	scst-devel@...ts.sourceforge.net, Tejun Heo <tj@...nel.org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: Re: [PATCH]: Rename REQ_COPY_USER to more descriptive REQ_HAS_TAIL_SPACE_FOR_PADDING

Vladislav Bolkhovitin, on 07/09/2009 10:30 PM wrote:
> Jens Axboe, on 07/09/2009 10:17 PM wrote:
>> On Thu, Jul 09 2009, Vladislav Bolkhovitin wrote:
>>> Currently names of REQ_COPY_USER and __REQ_COPY_USER constants are confusing,
>>> because they actually mean that the buffer for the corresponding requests
>>> has space in the tail for padding in case of DMA padding restrictions.
>> No, that's not what it means, the fact that there's padding room is a
>> side effect of the map type. So I'd suggest adding a comment above that
>> if {} in blk_rq_map_sg(), something that should have been there from the
>> beginning.
> 
> Can you elaborate a bit more about what REQ_COPY_USER should mean, please?
> 
> As far as I can see from the sources, currently it's used to only to 
> determine if there is the padding space. Maybe, the original meaning 
> doesn't make sense anymore?

Jens,

Sorry for bothering you, but with use of the kernel-generated buffers, 
like in the patch I sent in 
http://groups.google.com/group/linux.kernel/browse_thread/thread/b5127eeadbef934e/5da7ec7b424d2f36?lnk=raot 
name REQ_COPY_USER becomes quite misleading.

For instance, for blk_rq_map_kern_sg() usage of REQ_COPY_USER the 
buffers neither copied, nor from user. Plus, as I wrote above, in 2.6.30 
REQ_COPY_USER used only to determine if there is the padding space in 
the end. Hence, I suggested the rename.

Thanks,
Vlad
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