Re: Modules loading modules?

[Andrew Doran <ad%NetBSD.org@localhost>]

On Mon, Jul 26, 2010 at 02:49:56PM +0300, Antti Kantee wrote:
> On Sun Jul 25 2010 at 15:17:29 -0700, Paul Goyette wrote:
> > On Mon, 26 Jul 2010, matthew green wrote:
> > 
> > >
> > >it seems to me the root problem is that module_mutex is held while
> > >calling into the module startup routines.
> > >
> > >thus, the right solution is to remove this requirement.
> > 
> > Yes, that's what is needed.
> 
> I'm far from convinced that's a good idea.  First, it will probably
> make the module code a nightmare -- what happens when you have multiple
> interleaved loads, some of which fail at some point in their dependency
> stack, and let's just throw in a manual modunload to mix up things
> further.  Second, and pretty much related to number one, it goes against
> one of the most fundamental principles of robust code: atomic actions.

This: atomicity.  The atomic behaviour is relied upon to give "all or
nothing" semantics upon load and unload, like transactions in a database.

Admittely some modules (not of my making) are sloppy about this and so
break that bit of the interface contract.

> If modload-from-modcmd is found necessary, sounds more like a case for
> the infamous recursive lock.

Recursive lock is the way to go.  I think the same lock should also cover
all device configuration activites (i.e. autoconf) and any other 
heavy lifting where we have chunks of the system coming and going.