linux-kernel - Re: [patch 1/1] Switch ioctl functions of drivers/scsi/sg.c to unlocked

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Date:	Thu, 10 Jan 2008 12:03:24 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Andre Noll <maan@...temlinux.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Richard Knutsson <ricknu-0@...dent.ltu.se>
Subject: Re: [patch 1/1] Switch ioctl functions of drivers/scsi/sg.c to unlocked_ioctl

On Thu, Jan 10, 2008 at 07:59:44PM +0100, Andi Kleen wrote:
> > Really, all this is doing is open coding what the ioctl handler is doing
> > anyway, isn't it? in which case, why bother to change it at all?
> 
> Because once it's open coded it is visible and can then be eliminated.
> Does SCSI need the BKL at all?
> 
> But perhaps for such a long ioctl handler it would be better to move
> the lock/unlock_kernel()s into the individual case ...: statements;
> then it could be eliminated step by step.

This style of conversion is going to cause a lot of churn --
re-architecting this function to be single-exit, then presumably when
the lock_kernel calls are pushed further down or eliminated, turning it
back into a multiple-exit function.

I suggest that for complex ioctl handlers, it be left to the maintainers
to handle, and handle it properly all at once, rather than a gradual
pushdown.

You could argue that unlocked_ioctl has been around for a long time and
people haven't made that move yet.  But there's been no pressure before
now to do so, and I think people would rather convert their own code
than have somebody else do it.

-- 
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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