linux-kernel - Re: [PATCH] Illustration of warning explosion silliness

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Message-Id: <20060927213628.ef12b1ed.akpm@osdl.org>
Date:	Wed, 27 Sep 2006 21:36:28 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	linux-scsi@...r.kernel.org, Greg KH <greg@...ah.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [PATCH] Illustration of warning explosion silliness

On Thu, 28 Sep 2006 00:19:36 -0400
Jeff Garzik <jeff@...zik.org> wrote:

> Andrew Morton wrote:
> > And it's not sufficient to say "gee, I can't think of any reason why this
> > handler would return an error, so I'll design its callers to assume that". 
> > It is _much_ better to design the callers to assume that callees _can_
> > fail, and to stick the `return 0;' into the terminal callee.  Because
> > things can change.
> 
> huh?  You're going off on a tangent.  I agree with the above, just like 
> I already agreed that SCSI needs better error checking.

No I'm not.  I'm saying that the bugs which this exposed are a far, far
more serious matter than a few false-positive warnings which need
workarounds.

> You're ignoring the API issue at hand.  Let me say it again for the 
> cheap seats:  "search"  You search a list, and stick a pointer somewhere 
> when found.  No hardware touched.  No allocations.  Real world.  There 
> is an example of usage in the kernel today.

If it's called in that fashion then the caller should still check the
device_for_each_child() return value to find out if it actually got a
match.

Now it could be that the mysterious caller to which you refer uses the
non-NULLness of some pointer to work out if a match occurred.  Well shrug -
add a BUG_ON(!device_for_each_child_return_value) or something.

Or write a new version of device_for_each_child() which returns void and
don't tell anyone about it.

But let's not encourage error-ignoring.

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