Messages in this thread | | | Date | Wed, 23 Nov 2022 16:14:21 +0100 | Subject | Re: [PATCH 3/5] driver core: make struct device_type.uevent() take a const * | From | Maximilian Luz <> |
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On 11/23/22 15:52, Matthew Wilcox wrote: > On Wed, Nov 23, 2022 at 02:59:00PM +0100, Maximilian Luz wrote: >> On 11/23/22 14:34, Andy Shevchenko wrote: >>> On Wed, Nov 23, 2022 at 02:14:31PM +0100, Maximilian Luz wrote: >>>> On 11/23/22 13:25, Greg Kroah-Hartman wrote: >>>>> 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. >>> >>> [...] >>> >>>>> -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/ >> >> 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
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