[uml-devel] Entropy on boot

[uml-devel] Entropy on boot

[Paul Warren]

We've recently prepared a filesystem image for the latest Debian
distribution, and hit a problem with it hanging on starting Apache2.  We
traced this to a lack of entropy to feed /dev/random, causing the
Apache's startssl to block.

Chris Lightfoot has developed this patch to feed the guest's entropy
pool with data read from the host's /dev/random on boot:

	http://mythic-beasts.com/uml/random-seed.patch

Paul


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Re: [uml-devel] Entropy on boot

[Jeff Dike]

On Mon, Jun 20, 2005 at 08:25:49PM +0100, Paul Warren wrote:
> We've recently prepared a filesystem image for the latest Debian
> distribution, and hit a problem with it hanging on starting Apache2.  We
> traced this to a lack of entropy to feed /dev/random, causing the
> Apache's startssl to block.
> 
> Chris Lightfoot has developed this patch to feed the guest's entropy
> pool with data read from the host's /dev/random on boot:
> 
> 	http://mythic-beasts.com/uml/random-seed.patch
> 
> Paul

Are you using UML's hwrng driver?  Did it not help?

				Jeff


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Re: [uml-devel] Entropy on boot

[Paul Warren]

On Mon, Jun 20, 2005 at 05:16:38PM -0400, Jeff Dike wrote:
> Are you using UML's hwrng driver?  Did it not help?

Unless I've missed something, that doesn't solve the problem for an
out-of-the-box Linux distro, which expects to read from /dev/random.

Paul


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Re: [uml-devel] Entropy on boot

[Jeff Dike]

On Tue, Jun 21, 2005 at 07:50:47PM +0100, Paul Warren wrote:
> Unless I've missed something, that doesn't solve the problem for an
> out-of-the-box Linux distro, which expects to read from /dev/random.

I guess out-of-the-box Linux distros aren't intended for entroy-starved
environments.

So, I guess you can fix your distro to use the driver that UML provides
or you can put up with the starvation.  The hwrng driver is the right 
solution, and is far preferable to whacking a bunch into random.c.

That would never make it anywhere near mainline, so you would have a
choice of dumping that into every UML pool you build or fixing your
filesystems to use the rngtools.

				Jef


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Re: [uml-devel] Entropy on boot

[Chris Lightfoot]

On Tue, Jun 21, 2005 at 05:02:36PM -0400, Jeff Dike wrote:
> That would never make it anywhere near mainline, so you would have a
> choice of dumping that into every UML pool you build or fixing your
> filesystems to use the rngtools.

Yeah -- it comes down to how often you build new
distributions vs how often you build new kernels. Oh, and
whether you anticipate tech support load from people who
disable the hwrng userland tools and then discover that
their virtual machine hangs on boot.

-- 
``If you can tell good advice from bad advice, you don't need any advice.''


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Re: [uml-devel] Entropy on boot

[Paul Warren]

On Tue, Jun 21, 2005 at 10:19:08PM +0100, Chris Lightfoot wrote:
> On Tue, Jun 21, 2005 at 05:02:36PM -0400, Jeff Dike wrote:
> > That would never make it anywhere near mainline, so you would have a
> > choice of dumping that into every UML pool you build or fixing your
> > filesystems to use the rngtools.
> 
> Yeah -- it comes down to how often you build new
> distributions vs how often you build new kernels. Oh, and
> whether you anticipate tech support load from people who
> disable the hwrng userland tools and then discover that
> their virtual machine hangs on boot.

Quite - supporting kernel patches is much easier than O/S changes.  This
is why we now enforce cad = halt by disabling reboot functionality in
the kernel, rather than maintaining a change to /etc/inittab.

I admit that a proper pass-through drive for /dev/random might be a
nicer solution, but for us, hwrng is not.

Paul



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