Re: [PATCH] Illustration of warning explosion silliness

Andrew Morton
2006-09-28T03:34:26Z

On Wed, 27 Sep 2006 21:48:42 -0400
Jeff Garzik <jeff@garzik.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.