linux-kernel - Re: [PATCH] pstore: gracefully handle NULL pstore

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Message-ID: <CA+8MBb+SEF_0ORtbHq+ZpxQyE=WTVrGCPoY7ZH1zCDD8zoJ=Zg@mail.gmail.com>
Date:	Thu, 17 Nov 2011 11:13:22 -0800
From:	Tony Luck <tony.luck@...il.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org, Matthew Garrett <mjg@...hat.com>,
	Chen Gong <gong.chen@...ux.intel.com>,
	Don Zickus <dzickus@...hat.com>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] pstore: gracefully handle NULL pstore_info functions

On Thu, Nov 17, 2011 at 10:42 AM, Kees Cook <keescook@...omium.org> wrote:
> -       kmsg_dump_register(&pstore_dumper);
> +       if (psi->write && psi->buf && psi->bufsize)
> +               kmsg_dump_register(&pstore_dumper);

I can see that you might not need the other parts of the pstore
interface if your back-end is very simple (e.g. only has space for a
single record). But stub functions are cheap - so it isn't clear who
should pay the overhead.

BUT - without psi->write!? What use is it!?  I think in an early version
I refused the registration with -EINVAL - but akpm convinced me it
was a waste of electrons:

On Wed, 1 Dec 2010 16:51:39 Andrew Morton <akpm@...ux-foundation.org> wrote:
>> +     if (!psi->reader || !psi->writer || !psi->eraser) {
>> +             spin_unlock(&pstore_lock);
>> +             return -EINVAL;
>
> It doesn't seem appropriate to check this here.  It's a programming
> error!  Just install the thing and let the kernel oops - the programmer
> will notice.

Hiding the lack of a ->write function by quietly accepting the registration, but
not hooking into kmsg_dump doesn't sound useful in any scenario.

-Tony

Dang - pstore is coming up on a year old - time flies when you're having fun.
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