random(4) plugin infrastructure for mulitple RNG in a modular fashion

[Steve Kargl]

On Thu, Aug 08, 2013 at 10:23:52AM -0400, John Baldwin wrote:
> On Wednesday, August 07, 2013 4:20:29 pm Peter Wemm wrote:
> > On Wed, Aug 7, 2013 at 12:27 PM, Steve Kargl
> > <sgk at troutmask.apl.washington.edu> wrote:
> > > On Wed, Aug 07, 2013 at 11:28:58AM -0700, David O'Brien wrote:
> > >>
> > >> * Make Yarrow an optional kernel component -- enabled by "YARROW_RNG"
> > >>   option.  The files sha2.c, hash.c, randomdev_soft.c and yarrow.c
> > >>   comprise yarrow.  random(4) device doesn't really depend on
> > >>   rijndael-*.  Yarrow, however, does.
> > >>
> > >> * If the kernel doesn't have any random_adaptor adapters present then
> > >>   the creation of /dev/random is postponed until next random_adaptor
> > >>    is kldload'ed.
> > >
> > > My kernel config files have included the following 2 lines for
> > > ages:
> > >
> > > makeoptions  NO_MODULES
> > > device       random
> > >
> > > If I try to build a new kernel under your scheme, will the
> > > build die with an error about a missing option?  If the answer
> > > is 'no', then the yarrow adaptor should be opt-out.
> > 
> > That's the main point here.
> > 
> > If I'm running on a working system, I have a reasonable expectation
> > that the kernel config I was using yesterday will work sufficiently
> > tomorrow that I won't get hosed by doing a 'svn update && make
> > buildkernel && make installkernel'.
> > 
> > If that's not the case and there is a required change in order to not
> > hose your system then POLA dictates that not making the required
> > changes causes a build failure.
> > 
> > There's more leeway on head than a stable branch, but remember that
> > when people upgrade from 9.x to 10.x they tend to take their 9.x
> > kernel configs and make whatever changes are needed to get it to
> > build.  The 9-stable -> 10-release config path needs to catch fatal
> > errors like this at build time.
> > 
> > Patching GENERIC isn't a complete solution.  It doesn't solve the
> > 'yesterday it worked, today it's a brick' problem.
> 
> The counter to this is that in the recent past, any suggestion to add anything
> to DEFAULTS was met with "that's the wrong way".  In actual fact, changes
> to GENERIC happen quite often, and we often break older kernel configs from
> older branches (ATA_CAM is no longer in 10 for example).  I'm not sure I buy 
> the argument that we can never break kernel configs from older branches.

When ATA_CAM went away, if one had not updated his kernel config file,
then 'make buildkernel' failed.  With David's change, one would build
a seemingly fine kernel, and when it boots "Bad Things" (tm) can/may/will
occur.  

Also note, yarrow is already the default (P)RNG.  David is decoupling
it from /dev/random.  By adding it to DEFAULTS, one is only making the
current relationship between /dev/random and yarrow explicit.

-- 
Steve