Re: POSIX.1 semaphores vs message queues

[Paul Goyette <paul%vps1.whooppee.com@localhost>]

On Mon, 9 Nov 2015, Masao Uebayashi wrote:

> I think that anything that is initialized after uvm_init() from
> sys/kern/init_main.c:main() is worth being modularized, even if it
> cannot be dynamically loaded.  Here, being modularized means that it
> has a module name, it describes dependency on other modules, and has a
> decent xxx_modcmd() entry (or better, kctors/kdtors).

I agree.

I also strongly believe that if such a module can be dynamically loaded,
then dynamic loading should be permitted - or at least _not_prevented_.
Building the module separately, and loading it under a kernel with as
few other built-in modules as possible, makes it much easier to find
inter-module dependencies (such as the recent discovery that the 
compat_netbsd32 module requires mqueue, and compat_linux similarly needs
compat_sysv).  It also provides an additional environment under which
latent bugs might be exposed, allowing us to fix them.

Whether or not dynamic loading is "normal" or "expected" is a separate
question from whether such loading should be permitted/possible.



> On Mon, Nov 9, 2015 at 11:15 AM, Masao Uebayashi <uebayasi%gmail.com@localhost> wrote:
> > On Mon, Nov 9, 2015 at 9:21 AM, Joerg Sonnenberger
> > <joerg%britannica.bec.de@localhost> wrote:
> > > On Mon, Nov 09, 2015 at 08:05:43AM +0800, Paul Goyette wrote:
> > > > Well, both EXEC_SCRIPT and COREDUMP are modularized, and they _are_
> > > > optional.
> > >
> > > See part about modularity masturbation. Making things optional for the
> > > sake of making them optional is just as wrong.
> > >
> > > > Both EXEC_SCRIPT and COREDUMP are also much smaller than the ksem code;
> > > > these two optional/removeable modules together add up to just about
> > > > the size of a SEMAPHORE module.  (On amd64 we have exec_script weighing
> > > > in at 1285 bytes and coredump at 3895 bytes, while ksem tips the scales
> > > > at 5186 bytes).  There are numerous other modules which are similar in
> > > > size to the SEMAPHORE module.
> > >
> > > Add in the page alignment and the cost becomes even larger. There is
> > > nothing to be gained.
> >
> > Please don't (intentionally) confuse module in general and dynamic loading.
> >
> > For buiit-in modules, the extra size is code added by #ifdef _MODULE.
> > In the long run, xxx_modcmd() functions are merged into kctors.  If
> > other metada consume more than expected, it will be addressed and
> > reconsidered.  But that goes away in !MODULAR kernels.  So virtually
> > you lose nothing.

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