Re: [PATCH 2/6] module: add support for symbol namespaces.

[Jessica Yu <jeyu@kernel.org>]

+++ Martijn Coenen [20/07/18 17:42 +0200]:
>On Fri, Jul 20, 2018 at 4:49 PM, Jessica Yu <jeyu@kernel.org> wrote:
>> Thanks. Also, it looks like we're currently just warning (in both
>> modpost and on module load) if a module uses symbols from a namespace
>> it doesn't import. Are you also planning to eventually introduce
>> namespace enforcement?
>
>This is something I've definitely been thinking about, and was curious
>what others would think. My main concern with enforcement is that it
>will start failing to load out-of-tree modules that use newly
>namespaced symbols. On the other hand, I think those modules will need
>to be rebuilt anyway to be able to load, because the changes to struct
>kernel_symbol make them incompatible with the current kernel. That
>could be another reason for having these symbols in a special section
>(with its own struct namespaced_kernel_symbol); but on the other hand,
>it would make the module loader more complex just to facilitate
>out-of-tree drivers, and I'm not sure where the trade-off between
>those two falls.

IMO I don't think we should bend over backwards to accommodate
out-of-tree modules - modifying the module loader to recognize even
more special sections to accommodate these OOT modules would be where
we'd draw the line I think.

>> It'd be trivial to fail the module build in
>> modpost as well as reject the module on load if it uses an exported
>> symbol belonging to a namespace it doesn't import. Although, I'd go
>> with the warnings for a development cycle or two, to gently introduce
>> the change in API and let other subsystems as well as out-of-tree
>> module developers catch up.
>
>An approach like that makes sense to me. Another alternative would be
>to make it a CONFIG_ option, and let distros/etc. decide what they are
>comfortable with.

I think going forward I would prefer to have export namespaces to be a
normal and regular part of kernel API (as in, we shouldn't require a
new option for it), and that the warnings for 1-2 cycles are courteous
enough - but anyone with stronger opinions about this should speak up.

Thanks,

Jessica