[PATCH v8 9/9] manual: Add documentation for arc4random functions

[Adhemerval Zanella]

> On 29 Jun 2022, at 18:45, Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> 
> On Wed, Jun 29, 2022 at 2:36 PM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
>> 
>> ---
>> manual/math.texi | 45 +++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 45 insertions(+)
>> 
>> diff --git a/manual/math.texi b/manual/math.texi
>> index 477a18b6d1..ab96726e57 100644
>> --- a/manual/math.texi
>> +++ b/manual/math.texi
>> @@ -1447,6 +1447,7 @@ systems.
>> * ISO Random:: @code{rand} and friends.
>> * BSD Random:: @code{random} and friends.
>> * SVID Random:: @code{drand48} and friends.
>> +* High Quality Random:: @code{arc4random} and friends.
>> @end menu
>> 
>> @node ISO Random
>> @@ -1985,6 +1986,50 @@ This function is a GNU extension and should not be used in portable
>> programs.
>> @end deftypefun
>> 
>> +@node High Quality Random
>> +@subsection High Quality Random Number Functions
>> +
>> +This section describes the random number functions provided as a GNU
>> +extension, based on OpenBSD interfaces.
>> +
>> +@Theglibc{} uses kernel entropy obtained either through @code{getrandom}
>> +or by reading @file{/dev/urandom} to seed and periodically re-seed the
>> +internal state. A per-thread data pool is used, which allows fast output
>> +generation.
>> +
> 
> Are we committing to per-thread data pools? I thought there were ideas to
> use rseq.

For this version yes, since it works on all supported kernels (even for the
ones without getentropy support) and on all architectures.  I do not know how 
feasible it would be to implement per-cpu caches along with rseq and it would
require a fallback for older kernel (most likely a per-thread cache as this
version), although it might be future improvement.