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Date: Fri, 15 May 2009 17:16:45 -0600
From: Pete Zaitcev <zaitcev@redhat.com>
To: Tejun Heo <htejun@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>,
       James Bottomley <James.Bottomley@HansenPartnership.com>,
       Boaz Harrosh <bharrosh@panasas.com>,
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       Eric Moore <Eric.Moore@lsi.com>, "Darrick J. Wong" <djwong@us.ibm.com>,
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Subject: Re: [PATCH block#for-2.6.31 2/3] block: set rq->resid_len to
 blk_rq_bytes() on issue
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On Sat, 16 May 2009 07:14:44 +0900, Tejun Heo <htejun@gmail.com> wrote:

> So, I could have written
> 
>  if (cmd->act_len >= rq->resid_len)
> 	rq->resid_len = 0;
>  else
> 	rq->resid_len -= cmd->act_len
> 
> Instead I wrote
> 
>  rq->resid_len -= min(cmd->act_len, rq->resid_len);
> 
> It's just capping the amount to be subtracted so that resid_len
> doesn't underflow.  What is so wrong or bad style about that?

Curse of the gifted, I guess. To use a subtraction instead of zero
this way looks like a pointless, even mischievous obfuscation to me.

Also, we probably want a stack_dump or a printk when actual length
exceeds the requested length, don't we? If it ever happens, we
might be overwriting some I/O buffer somewhere.

-- Pete