On 11/23/22 15:52, Matthew Wilcox wrote:

On Wed, Nov 23, 2022 at 02:59:00PM +0100, Maximilian Luz wrote:

quoted

On 11/23/22 14:34, Andy Shevchenko wrote:

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On Wed, Nov 23, 2022 at 02:14:31PM +0100, Maximilian Luz wrote:

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On 11/23/22 13:25, Greg Kroah-Hartman wrote:

quoted

The uevent() callback in struct device_type should not be modifying the
device that is passed into it, so mark it as a const * and propagate the
function signature changes out into all relevant subsystems that use
this callback.

[...]

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-static inline struct ssam_device *to_ssam_device(struct device *d)
+static inline struct ssam_device *to_ssam_device(const struct device *d)
    {
    	return container_of(d, struct ssam_device, dev);
    }

I am slightly conflicted about this change as that now more or less
implicitly drops the const. So I'm wondering if it wouldn't be better to
either create a function specifically for const pointers or to just
open-code it in the instance above.

I guess we could also convert this to a macro. Then at least there
wouldn't be an explicit and potentially misleading const-conversion
indicated in the function signature.

This is an intermediate step as far as I know since moving container_of to
recognize const is a bit noisy right now. I guess you can find a discussion
on the topic between Greg and Sakari.

Thanks! I assume you are referring to the following?

	https://lore.kernel.org/lkml/4218173bd72b4f1899d4c41a8e251f0d@AcuMS.aculab.com/T/ (local)

As far as I can tell this is only a warning in documentation, not
compile time (which would probably be impossible?).

As I've said I'd be fine with converting the function to a macro (and
preferably adding a similar warning like the one proposed in that
thread). The point that irks me up is just that, as proposed, the
function signature would now advertise a conversion that should never be
happening.

Having two separate functions would create a compile-time guarantee, so
I'd prefer that, but I can understand if that might be considered too
noisy in code. Or if there is a push to make container_of() emit a
compile-time warning I'd also be perfectly happy with converting it to a
macro now as that'd alleviate the need for functions in the future.

Can't we do:

static inline const struct ssam_device *to_ssam_device(const struct device *d)
{
	return container_of(d, const struct ssam_device, dev);
}

There are at least a couple of places (device/driver-management and
device-removal related, I think) using this function and requiring
non-const access.

A bunch of other instances could be converted to const-access only, but
that would require a couple more function signature changes (I should
probably set up a patch for that regardless of this here as being a bit
more strict about this makes sense).

Regards,
Max