Messages in this thread | | | Date | Thu, 6 Dec 2007 10:09:50 -0600 | From | Matt Mackall <> | Subject | Re: Why does reading from /dev/urandom deplete entropy so much? |
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On Thu, Dec 06, 2007 at 08:02:33AM +0100, Eric Dumazet wrote: > Matt Mackall a ?crit : > >On Tue, Dec 04, 2007 at 07:17:58PM +0100, Eric Dumazet wrote: > >>Alan Cox a ?crit : > >>>>No matter what you consider as being better, changing a 12 years old > >>>>and widely used userspace interface like /dev/urandom is simply not an > >>>>option. > >>>> > >>>Fixing it to be more efficient in its use of entropy and also fixing the > >>>fact its not actually a good random number source would be worth looking > >>>at however. > >>> > >>Yes, since current behavior on network irq is very pessimistic. > > > >No, it's very optimistic. The network should not be trusted. > > You keep saying that. I am refering to your previous attempts last year to > remove net drivers from sources of entropy. No real changes were done.
Dave and I are both a bit stubborn on this point. I've been meaning to respin those patches..
> If the network should not be trusted, then a patch should make sure network > interrupts feed /dev/urandom but not /dev/random at all. (ie not calling > credit_entropy_store() at all)
Yes. My plan is to change the interface from SA_SAMPLE_RANDOM to add_network_entropy. The SA_SAMPLE_RANDOM interface sucks because it doesn't tell the core what kind of source it's dealing with.
> There is a big difference on get_cycles() and jiffies. You should try to > measure it on a typical x86_64 platform.
I'm well aware of that. We'd use get_cycles() exclusively, but it returns zero on lots of platforms. We used to use sched_clock(), I can't remember why that got changed.
> >Also, for future reference, patches for /dev/random go through me, not > >through Dave. > > Why ? David is the network maintainer, and he was the one who rejected your > previous patches.
Because I'm the /dev/random maintainer and it's considered the polite thing to do, damnit.
-- Mathematics is the supreme nostalgia of our time.
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