Re: [usb-storage] Re: [PATCH v4 12/12] RFC: watchdog: export core symbols in WATCHDOG_CORE namespace

[Jessica Yu]

+++ Matthew Dharm [04/09/19 09:16 -0700]:
> On Wed, Sep 4, 2019 at 5:12 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > Note that I don't object to the patch set in general. There may be symbols
> > which only need be exported in the context of a single subsystem or even
> > driver (if a driver consists of more than one module). For example, a mfd
> > driver may export symbols which should only be called by its client drivers.
> > In such a situation, it may well be beneficial to limit the use of exported
> > symbols.
>
> I can appreciate this benefit.
>
> > I am not sure what good that does in practice (if I understand correctly,
> > a driver only has to declare that it wants to use a restricted use symbol
> > if it wants to use it), but that is a different question.
>
> I think this question implies that you are coming from the perspective
> of "security" or wanting to restrict access to the underlying
> functions, rather than wanting to clean-up the way symbols are handled
> for manageability / maintainability purposes (which is the goal, as I
> understand it).
>
> HOWEVER, I have one question:  If these patches are included, and
> someone wants to introduce a bit of code which needs to use two
> symbols from different namespaces but with the same name, can that be
> done?  That is, if driver A has symbol 'foo' and driver B has symbol
> 'foo' (both in their respective namespaces), and driver C wants to use
> A.foo and B.foo, can that be supported?

As of now, we currently don't support this - modpost will warn if a
symbol is exported more than once (across modules + vmlinux), and the
module loader currently assumes exported symbol names are unique.  Do
you have a concrete use case? If there is a strong need for this, I
don't think it'd be too hard to implement.

Thanks,

Jessica