Re: [PATCH] btrfs-progs: utils: use better wrappered random generator

[David Sterba <dsterba@suse.cz>]

On Wed, May 25, 2016 at 08:33:45AM +0800, Qu Wenruo wrote:
> 
> 
> David Sterba wrote on 2016/05/24 11:51 +0200:
> > On Tue, May 24, 2016 at 08:31:01AM +0800, Qu Wenruo wrote:
> >>> This could be made static (with thread local storage) so the state does
> >>> not get regenerated all the time. Possibly it could be initialize from
> >>> some true random source, not time or pid.
> >>
> >> I also considered true random source like /dev/random, but since it's
> >> possible to wait for entropy pool, it would be quite slow and confusing
> >> for users.
> >
> > How would it be confusing? We'll once seed the random generator from
> > /dev/random, reading 3 * 16bit for the nrand generator context.
> 
> Reading from /dev/random may sleep, until the entropy pool is filled.

I know, but does this apply in our case? We're going to get just a few
bytes to seed.  I want to avoid inventing own random number generation
schemes, so we'll use a standard random number source or API.

/dev/random gives about 1-2MB/s of random data on several machines I've
tried.