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

[Guenter Roeck]

On 9/4/19 1:45 AM, Masahiro Yamada wrote:
> On Wed, Sep 4, 2019 at 1:10 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On Tue, Sep 03, 2019 at 04:06:38PM +0100, Matthias Maennich wrote:
> > > Modules using symbols from the WATCHDOG_CORE namespace are required to
> > > explicitly import the namespace. This patch was generated with the
> > > following steps and serves as a reference to use the symbol namespace
> > > feature:
> > >
> > >   1) Use EXPORT_SYMBOL_NS* macros instead of EXPORT_SYMBOL* for symbols
> > >      in watchdog_core.c
> > >   2) make  (see warnings during modpost about missing imports)
> > >   3) make nsdeps
> > >
> > > I used 'allmodconfig' for the above steps to ensure all occurrences are
> > > patched.
> > >
> > > Defining DEFAULT_SYMBOL_NAMESPACE in the Makefile is not trivial in this
> > > case as not only watchdog_core is defined in drivers/watchdog/Makefile.
> > > Hence this patch uses the variant of using the EXPORT_SYMBOL_NS* macros
> > > to export into a different namespace.
> > >
> > > An alternative to this patch would be a single definition line before
> > > any use of EXPORT_SYMBOL*:
> > >   #define DEFAULT_SYMBOL_NAMESPACE WATCHDOG_CORE
> > >
> > > This patch serves as a reference on how to use the symbol namespaces.
> > >
> > > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Matthias Maennich <maennich@xxxxxxxxxx>
> >
> > As mentioned before, I am opposed to this set of changes. I don't see
> > the point of restricting the use of exported symbols in WATCHDOG_CORE.
> >
> > Guenter
>
>
> I agree.
>
> I do not like this patch set either.

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 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.

Guenter