Re: [PATCH 1/8] kbuild, PCI: generic,versatile: comment out MODULE_LICENSE in non-modules

On 10 Feb 2023, Rob Herring uttered the following:

On Fri, Feb 10, 2023 at 11:05 AM Nick Alcock [off-list ref] wrote:

quoted

Since commit 8b41fc4454e ("kbuild: create modules.builtin without
Makefile.modbuiltin or tristate.conf"), MODULE_LICENSE declarations
are used to identify modules. As a consequence, uses of the macro
in non-modules will cause modprobe to misidentify their containing
object file as a module when it is not (false positives), and modprobe
might succeed rather than failing with a suitable error message.

How is there an issue when any given module could be built-in instead?

"modprobe module-that-might-be-built-in" is always meant to succeed if
the module is built-in; but "modprobe thing-that-can't-be-a-module-at-all"
is meant to fail. e.g. on a system in which ext4 is built in, I see

loom:~# modprobe ext4
loom:~# lsmod | grep ext4

(with either reporting any answer, and the modprobe returning exitcode 0).

But trying to modprobe something that cannot be a module says, e.g.
(sorry for old kernel, just happens to be what I can lay my hands on
easily right now):

loom:~# modprobe slab
modprobe: FATAL: Module slab not found in directory /lib/modules/5.16.19-00037-ge8dfda4e77fb-dirty
[exitcode nonzero]

This is what is expected, even though slab is built in. It's not a
module, it cannot be a module, so trying to modprobe it should fail.

But right now we have things like this:

silk:~# modprobe zswap
[nothing, exitcode 0]

zswap cannot be built as a module, so this output is wrong (and
inconsistent with the slab attempt above). (Sure, this isn't exactly a
disastrous consequence, but I have other things I'm going to contribute
after this series that depend on this being got right consistently.)

The general trend is to make all PCI host drivers modules, the primary
reason this one, IIRC, is not a module is because it is missing
remove() hook to de-init the PCI bus. Not too hard to add, but I
wanted to do a common devm hook to do that instead of an explicit
.remove() hook in each driver. I suppose we could just ignore that and
allow building as a module. Unloading is optional anyways.

That's perfectly acceptable for me -- I'm not saying that these things
should not be modular, only that *as long as* they are not modular, they
should not have a MODULE_LICENSE. Making it possible to build them as
modules again is fine!

-- 
NULL && (void)