linux-kernel - Re: [PATCH v3 21/22] netoops: Add user-programmable boot

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Date:	Tue, 14 Dec 2010 15:19:50 -0800
From:	Mike Waychison <mikew@...gle.com>
To:	Matt Mackall <mpm@...enic.com>
Cc:	simon.kagstrom@...insight.net, davem@...emloft.net,
	nhorman@...driver.com, adurbin@...gle.com,
	linux-kernel@...r.kernel.org, chavey@...gle.com,
	Greg KH <greg@...ah.com>, netdev@...r.kernel.org,
	Américo Wang <xiyou.wangcong@...il.com>,
	akpm@...ux-foundation.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v3 21/22] netoops: Add user-programmable boot_id

On Tue, Dec 14, 2010 at 2:47 PM, Matt Mackall <mpm@...enic.com> wrote:
> On Tue, 2010-12-14 at 14:33 -0800, Mike Waychison wrote:
>> On Tue, Dec 14, 2010 at 2:06 PM, Matt Mackall <mpm@...enic.com> wrote:
>> > What happens if you oops before userspace is available?
>> >
>>
>> Either one of two general cases:
>>   - The crash is a one-off and the machine comes back.  The boot
>> number sequence will see a hole in it, which is a clue that something
>> bad happened.
>>   - The machine is in a crash loop.  This has the same failure mode
>> for us as if the machine never made it onto the network due to
>> whatever reason: bad cables, bad firmware, bad ram, ...
>>
>> In both cases, we can detect that something is wrong and handle it.
>> Note that our firmware is responsible for incrementing the boot
>> sequence at bootup, which is why the above works.   In general though,
>> our machines do make it up to userland -- staying alive once booted is
>> the hard part ;)
>
> Interesting. Is this Google-specific firmware magic?

Ya, this is a Google-ism.  I'd be surprised if there weren't other
platforms that had the same thing though (though I don't know of
anything standard on x86).

> I'd probably accept
> a hook in random.c to fold a number into the UUID, which would unify
> things.

I'm not sure there is a _good_ way to support this, is there?  I just
read through RFC 4122 and UUIDs seem to be pretty well structured;
it's probably not such a great idea to allow folks to override
portions of it.  Like I mentioned in my last email though, I'm okay
pushing this boot sequence ID down into the user blob which acts like
a place for "vendor extensions" if there isn't a good place for it in
the kernel.
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