linux-kernel - Re: [PATCH 1/2] random: Add support for architectural random hooks

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Date:	Sat, 30 Jul 2011 12:45:59 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	Theodore Ts'o <tytso@....edu>, Jeff Garzik <jgarzik@...ox.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] random: Add support for architectural random hooks

On Fri, 2011-07-29 at 23:20 -0700, Linus Torvalds wrote:
> On Fri, Jul 29, 2011 at 2:16 PM, Matt Mackall <mpm@...enic.com> wrote:
> >
> > I have already NAKed this approach in no uncertain terms.
> 
> Doesn't matter.

Good to know, feel free to drop me from MAINTAINERS.

> Talking about "standard hardware random number drivers" is just crazy
> talk, when the instruction is a single instruction that takes tens of
> nanoseconds to run. Any driver overhead would be just crazy, and no
> user would ever want that anyway.

Did you even look at these patches?

Here's Peter's interface:

+       ssize_t (*get_entropy_krnl)(void *buf, size_t nbytes);

Here's the hwrng interface:

	int (*read)(struct hwrng *rng, void *data, size_t max, bool wait);

The overhead on the kernel side for an "architectural random hook" and a
bog-standard HWRNG is basically the same. Here's a buffer, put N bytes
in it.

But then, the bulk of this patch is actually putting in a fast path to
pass this off to user space through /dev/urandom.

So here you are yammering on about "any driver overhead would be just
crazy" when the whole point of these patches is in fact CHARACTER
DRIVERS. We could already have a HWRNG interface that's just as fast in
the time we've spent debating this.

If you want to add a function get_fast_random_bytes() that turns into
inline assembly on Intel (and Via Padlock and whatever else shows up)
and falls back to get_random_bytes, great. That has nothing to do with
these patches.

-- 
Mathematics is the supreme nostalgia of our time.

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