2007-10-02 15:26:05

by Yakov Lerner

Subject: get amount of "entropy" in /dev/random ?

>From the userlevel, can I get an estimate of "amount of entropy"
in /dev/random, that is, the estimate of number of bytes
readable until it blocks ? Of course multiple processes
can read bytes and this would not be exact ... but still .. as an upper
boundary estimate ?

Thanks
Yakov

2007-10-02 15:37:49

by Michal Schmidt

Subject: Re: get amount of "entropy" in /dev/random ?

Yakov Lerner wrote:
> >From the userlevel, can I get an estimate of "amount of entropy"
> in /dev/random, that is, the estimate of number of bytes
> readable until it blocks ? Of course multiple processes
> can read bytes and this would not be exact ... but still .. as an upper
> boundary estimate ?
>
> Thanks
> Yakov

Try ioctl(fd, RNDGETENTCNT, &entropy_count)

Michal

2007-10-02 15:49:57

by David Schwartz

Subject: RE: get amount of "entropy" in /dev/random ?

> From the userlevel, can I get an estimate of "amount of entropy"
> in /dev/random, that is, the estimate of number of bytes
> readable until it blocks ? Of course multiple processes
> can read bytes and this would not be exact ... but still .. as an upper
> boundary estimate ?
>
> Thanks
> Yakov

Yes. Look in drivers/char/random.c at the random_ioctl handler. You will see
RNDGETENTCNT.

DS