Messages in this thread | | | Date | Tue, 1 Feb 2000 18:43:33 -0800 | From | David Schleef <> | Subject | Re: /dev/random oddness |
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On Tue, Feb 01, 2000 at 11:18:01PM +0000, Russell King wrote: > Hi, > > I've just had a report that I've confirmed that /dev/random on ARM doesn't > behave the same as /dev/random on x86. > > I've confirmed this by comparing a NetWinder with an IBM thinkpad. Both these > have PS/2 mice. The NetWinder is running 2.3.41, which uses the standard > random.c and pc_keyb.c sources. The thinkpad is running untouched 2.2.12 at > the moment. > > On the thinkpad, doing an 'od -t x1 -Ax /dev/random' and moving the mouse in > a console results in a lot of bytes being generated from the device. However, > on a NetWinder, it results in very few, less than 1/10th of what the x86 > machine produces. > > I have also compared it with other ARM architectures (on 2.2.14) use the > busmice code (which got added to 2.3 iirc) to add randomness, and that behaves > in the same manner as the NetWinder. > > Does anyone have any clues what might be causing this odd behaviour? I haven't > scanned over random.c in any great depth yet.
Yes. The random driver on i386 uses the current cycle counter on Pentium+ machines for a few extra bits of randomness. Unfortunately, this is not implemented for other architectures. There was a discussion about this a few days ago concerning the alpha.
dave...
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