linux-kernel - Re: b43 wireless driver inhibits access to /dev/hwrng

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Message-ID: <20100723153101.GA12795@darkside.kls.lan>
Date:	Fri, 23 Jul 2010 17:31:02 +0200
From:	"Mario 'BitKoenig' Holbe" <Mario.Holbe@...Ilmenau.DE>
To:	"John W. Linville" <linville@...driver.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: b43 wireless driver inhibits access to /dev/hwrng

On Fri, Jul 23, 2010 at 10:32:19AM -0400, John W. Linville wrote:
> The hwrng driver is provided by the b43 hardware, which is shutdown
> when the network interface is down.  I'm not sure how one could expect
> this to work.

Nope. It's provided by the VIA PadLock hardware (through the via-rng
driver). I'm not sure how one could expect this not to work when the
network interface provided by the b43 driver is down.

Well, maybe let's try to become a bit less offensive... :)
Probably there are two Hardware RNGs on that machine: one provided by
VIA PadLock through via-rng, one provided by BCM4312 through b43:
	hw_random/via-rng.c:    err = hwrng_register(&via_rng);
	b43/main.c: err = hwrng_register(&wl->rng);

But at least now it's a bit more likely that the problem is located in
the rng core which should not render /dev/hwrng inaccessible when only
one of the RNGs unregisters.

However, what I don't fully understand is: I find only one way where b43
unregisters its RNG, which is via
	b43_remove() -> b43_rng_exit() -> hwrng_unregister()
And, I'm really not sure if I got this right, but... I guess,
b43_remove() is only called when the module is removed from the kernel
and not when the network interface is shut down.

So, maybe it's not really rng core's fault?
I guess, b43 just stops delivering data through b43_rng_read() when the
hardware is shut down and instead returns ENODEV (which is btw. what I
get when I'm trying to read /dev/hwrng while b43 is down), and the rng
core just delivers this error up when it's trying to deliver the read
request to the b43 RNG.

Mario
-- 
User sind wie ideale Gase - sie verteilen sich gleichmaessig ueber alle Platten

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