Re: [PATCH v2] module: Rename EXPORT_SYMBOL_GPL_FOR_MODULES to EXPORT_SYMBOL_FOR_MODULES

[Daniel Gomez <da.gomez@kernel.org>]

On 11/07/2025 16.05, Vlastimil Babka wrote:
> Christoph suggested that the explicit _GPL_ can be dropped from the
> module namespace export macro, as it's intended for in-tree modules
> only. It would be possible to resrict it technically, but it was pointed
> out [2] that some cases of using an out-of-tree build of an in-tree
> module with the same name are legitimate. But in that case those also
> have to be GPL anyway so it's unnecessary to spell it out.
> 
> Link: https://lore.kernel.org/all/aFleJN_fE-RbSoFD@infradead.org/ [1]
> Link: https://lore.kernel.org/all/CAK7LNATRkZHwJGpojCnvdiaoDnP%2BaeUXgdey5sb_8muzdWTMkA@mail.gmail.com/ [2]
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Reviewed-by: Shivank Garg <shivankg@amd.com>
> Acked-by: Christian Brauner <brauner@kernel.org>
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> Christian asked [1] for EXPORT_SYMBOL_FOR_MODULES() without the _GPL_
> part to avoid controversy converting selected existing EXPORT_SYMBOL().
> Christoph argued [2] that the _FOR_MODULES() export is intended for
> in-tree modules and thus GPL is implied anyway and can be simply dropped
> from the export macro name. Peter agreed [3] about the intention for
> in-tree modules only, although nothing currently enforces it.
> 
> It seemed straightforward to add this enforcement, so v1 did that. But
> there were concerns of breaking the (apparently legitimate) usecases of
> loading an updated/development out of tree built version of an in-tree
> module.
> 
> So leave out the enforcement part and just drop the _GPL_ from the
> export macro name and so we're left with EXPORT_SYMBOL_FOR_MODULES()
> only. Any in-tree module used in an out-of-tree way will have to be GPL
> anyway by definition.
> 
> Current -next has some new instances of EXPORT_SYMBOL_GPL_FOR_MODULES()
> in drivers/tty/serial/8250/8250_rsa.c by commit b20d6576cdb3 ("serial:
> 8250: export RSA functions"). Hopefully it's resolvable by a merge
> commit fixup and we don't need to provide a temporary alias.
> 
> [1] https://lore.kernel.org/all/20250623-warmwasser-giftig-ff656fce89ad@brauner/
> [2] https://lore.kernel.org/all/aFleJN_fE-RbSoFD@infradead.org/
> [3] https://lore.kernel.org/all/20250623142836.GT1613200@noisy.programming.kicks-ass.net/
> ---
> Changes in v2:
> - drop the patch to restrict module namespace export for in-tree modules
> - fix a pre-existing documentation typo (Nicolas Schier)
> - Link to v1: https://patch.msgid.link/20250708-export_modules-v1-0-fbf7a282d23f@suse.cz
> ---
>  Documentation/core-api/symbol-namespaces.rst | 8 ++++----
>  fs/anon_inodes.c                             | 2 +-
>  include/linux/export.h                       | 2 +-
>  3 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/core-api/symbol-namespaces.rst b/Documentation/core-api/symbol-namespaces.rst
> index 32fc73dc5529e8844c2ce2580987155bcd13cd09..6f7f4f47d43cdeb3b5008c795d254ca2661d39a6 100644
> --- a/Documentation/core-api/symbol-namespaces.rst
> +++ b/Documentation/core-api/symbol-namespaces.rst
> @@ -76,8 +76,8 @@ A second option to define the default namespace is directly in the compilation
>  within the corresponding compilation unit before the #include for
>  <linux/export.h>. Typically it's placed before the first #include statement.
>  
> -Using the EXPORT_SYMBOL_GPL_FOR_MODULES() macro
> ------------------------------------------------
> +Using the EXPORT_SYMBOL_FOR_MODULES() macro
> +-------------------------------------------
>  
>  Symbols exported using this macro are put into a module namespace. This
>  namespace cannot be imported.

The new naming makes sense, but it breaks the pattern with _GPL suffix:

* EXPORT_SYMBOL(sym)
* EXPORT_SYMBOL_GPL(sym)
* EXPORT_SYMBOL_NS(sym, ns)
* EXPORT_SYMBOL_NS_GPL(sym, ns)
* EXPORT_SYMBOL_FOR_MODULES(sym, mods)

So I think when reading this one may forget about the _obvious_ reason. That's
why I think clarifying that in the documentation would be great. Something like:

Symbols exported using this macro are put into a module namespace. This
namespace cannot be imported. And it's implicitly GPL-only as it's only intended
for in-tree modules.

Other than that, it looks good.

Reviewed-by: Daniel Gomez <da.gomez@samsung.com>