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SubjectRe: [RFC] frandom - fast random generator module
Eli Billauer wrote:
> I suppose you're asking why having a /dev/frandom device at all. Why not
> let everyone write their own little random generator (based upon
> well-known C functions) whenever random data is needed.
>
> There are plenty of handy things in the kernel, that could be done in
> userspace. /dev/zero is my favourite example, but I'm sure there are
> other cases where things were put in the kernel simply because people
> found them handy. Which is a good reason, if you ask me.
>
> Besides, it's quite easy to do something wrong with random numbers. By
> having a good source of random data, I suppose we can spare a lot of
> people the headache of getting their own user-space application right
> for the one-off thing they want to do.

This is completely bogus logic. I can use this (incorrect) argument to
similar push for applications doing bsearch(3) or qsort(3) via a system
call.

When the _implementation_ requires that a piece of code be in-kernel
(for performance or security, usually), it is.

In this case, there is no such requirement. More below.


> But it's really a matter of taste. That's why I bring up the subject here.


Processors are trending towards putting RNG on the CPU. VIA won't be
the last, I predict. When generating random bits is a single
instruction, "xstore", userspace applications _should_ be directly using
this. It should not be in-kernel. And similarly, if there is no
requirement that the kernel's entropy pool is used, the userspace
application _should_ be where the implementation lives.

So, given that trend and also given the existing /dev/[u]random, I
disagree completely: /dev/frandom is the perfect example of something
that should _not_ be in the kernel. If you want /dev/urandom faster,
then solve _that_ problem. Don't try to solve a /dev/urandom problem by
creating something totally new.

Jeff


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