On Tue, Feb 11, 2025 at 07:45:30PM +0100, Uwe Kleine-König wrote: > Hello Andy, > > On Tue, Feb 11, 2025 at 04:35:34PM +0200, Andy Shevchenko wrote: > > On Tue, Feb 11, 2025 at 04:31:45PM +0200, Andy Shevchenko wrote: > > > On Tue, Feb 11, 2025 at 04:29:33PM +0200, Andy Shevchenko wrote: > > > > On Tue, Feb 11, 2025 at 04:20:50PM +0200, Andy Shevchenko wrote: > > > > > On Tue, Feb 11, 2025 at 01:00:08PM +0000, Mark Brown wrote: > > > > > > On Mon, Feb 10, 2025 at 10:33:31PM +0200, Andy Shevchenko wrote: > > > > > > > On Mon, Feb 10, 2025 at 05:48:00PM +0000, Mark Brown wrote: > > > > > > > > On Mon, Feb 10, 2025 at 11:11:23AM -0600, David Lechner wrote: > > > > > > > > > > > > > > > In this case, we specifically split up the headers so that the only time you > > > > > > > > > would ever include this header is if you need to call functions in this > > > > > > > > > namespace (i.e. struct definitions are in linux/spi/offload/types.h which > > > > > > > > > doesn't import the namespace). So this doesn't actually seem like a problem > > > > > > > > > to me. > > > > > > > > > > > > > > Indeed - I can't see any case where a user would need the header without > > > > > > > > needing the namespace. > > > > > > > > > > > > > You are looking from the other end. What I'm telling is that anyone who adds > > > > > > > a header, automatically gets a namespace. What's the point to have namespace > > > > > > > if it won't easily prevent from (ab)using it in the code. I consider putting > > > > > > > MODULE_IMPORT_NS() in the headers a bit weird. > > There was a similar discussion some time ago about the lpss pwm driver > (https://lore.kernel.org/linux-pwm/Z09YJGifvpENYNPy@xxxxxxxxxxxxxxxxxx/). > The arguments that you didn't accept back then already are similar to > the ones that were brought forward here. > The TL;DR; is: Adding MODULE_IMPORT_NS() to a header makes it easier for > code to use the exported symbols. Yes, that includes abusers of the > code. > > But if you mostly care about the regular users of an API/ABI, making > things easy for those is the thing that matters. Agreed, if you think > that module namespaces are primarily a line of defence against abusers, > adding the import to the header weakens that defence (a bit). However a > typical header includes function prototypes and macros. Those also make > it easier for abusers. With your argumentation we better don't create > headers at all? > > There are other benefits of module namespaces like reducing the set of > globally available symbols which speeds up module loading or the > ability to see in the module meta data that a namespace is used. Thank you for summarizing the previous discussion. > > > > > > Sure, but there's no case where anyone should ever be adding the header > > > > > > without adding the namespace which does rather sound like the sort of > > > > > > thing where you should just move the namespace addition to the header. > > > > > > > > > > $ git grep -lw MODULE_IMPORT_NS | wc -l > > > > > 651 > > > > > > > > > > $ git grep -lw MODULE_IMPORT_NS | grep '\.h$' > > > > > > > > > > drivers/base/firmware_loader/sysfs.h > > > > > drivers/iio/adc/ltc2497.h > > > > > drivers/pwm/pwm-dwc.h > > > > > ^^^ These ones are probably fine as they are not in include/ > > > > > > > > > > include/kunit/visibility.h > > > > > include/linux/module.h > > > > > include/linux/pwm.h > > > > > > > > > > I believe these three are misuses of MODULE_IMPORT_NS(). Because one may add > > > > > > > > _Two_, of course, module.h provides the macro :-) > > > > > > And after looking into include/kunit/visibility.h it becomes only a single one. > > > So, PWM is abuser of MODULE_IMPORT_NS() and this series added one more. > > > > > > > a header just as a "proxy" one (copy'n'paste, for example) and we know that is > > > > > real as we saw a lot of code that has semi-random header inclusion blocks. > > > > And thinking of more realistic example when we want header and do *not* want a > > namespace is the simple use of the macro / or data type from it without > > actually relying on the APIs. > > The problem of your more realistic example is that it doesn't apply > here. A user of include/linux/pwm.h (or the header under discussion > here) won't only use a macro or two and so not benefit from the imported > module namespace. It may not apply _today_, but it may be applicable tomorrow as headers are tend to grow and use another headers and so on. > Nobody intends to import all possible namespaces in <linux/kernel.h>. > > > So, in case of the header structure like > > > > foo_constants.h > > foo_types.h > > foo_api.h > > foo_uplevel_something.h > > > > The MODULE_IMPORT_NS() would make sense only to foo_api.h. And I still would > > question that. As I explained that header may simply become a stale one or > > being used by a mistake. > > I have no problem here. If the header becomes stale we will most > probably notice that eventually and remove it. Lol. Look at the header hell we have now. 98% code in the drivers/ just show that the developers either don't care or do not understand C (in terms of what headers are for and why it's important to follow IWYU principle). > Maybe the unused namespace even makes it easier to spot that issue. Do we have an existing tools for that? > See > https://lore.kernel.org/r/20250123103939.357160-2-u.kleine-koenig@xxxxxxxxxxxx > for an example which I found exactly like that. -- With Best Regards, Andy Shevchenko
