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

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Message-Id: <20060927203417.f07674de.akpm@osdl.org>
Date:	Wed, 27 Sep 2006 20:34:17 -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 Wed, 27 Sep 2006 21:48:42 -0400
Jeff Garzik <jeff@...zik.org> wrote:

> The usage model should not be _forced_ upon the caller, since it might 
> not be needed.

IMO: tough titty.

This isn't some random crappy perl script.  Nor is it even some random
crappy sound card driver.  This is our scsi stack.  The heart of our
MissionCriticalEnterpriseReadyCoreOfAThirtyBillionDollarIndustry operating
system.  Picture yourself telling a Fortune 100 CTO why his kernel is
cheerily discarding errors (and hence his reliability and possibly data)
all over the place.  Take a peek at spi_dv_device() and its callees...	

I was astonished at the number of ignored errors all over the
sysfs/driver-model code.  And that's only there to detect programming
errors.  That's nothing compared to these bugs.

Discarding already-detected hardware or software errors in the storage
stack is toe-curlingly lame, and completely trumps the inconvenience of
developers seeing a few warnings, or having to put artificial warning
shutter-uppers in a few places.

Now I'm sure I'm about to be flooded with long-winded explanations about
why all of this can never happen.  But y'know what?  I don't care. 
Hardware errors can sometimes happen.  As can programming errors, as can
memory-corruption and dropped-bit errors and all the other things we
regularly see.  The kernel should be robust in the presence of unexpected
events.  *Particularly* those parts which are handling storage.  Any
void-returning function in a driver or a mid-layer is a huge red flag.

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.

There, I feel better now.  If you want to see the other warnings, set
CONFIG_ENABLE_MUST_CHECK=n.

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