Messages in this thread | | | Date | Mon, 17 Oct 2022 09:39:27 +0000 | From | Sakari Ailus <> | Subject | Re: [PATCH v2] driver core: allow kobj_to_dev() to take a const pointer |
| |
Hi Greg,
On Mon, Oct 17, 2022 at 10:04:14AM +0200, Greg Kroah-Hartman wrote: > On Mon, Oct 17, 2022 at 07:54:52AM +0000, Sakari Ailus wrote: > > Hi Greg, > > > > On Sun, Oct 16, 2022 at 12:41:26PM +0200, Greg Kroah-Hartman wrote: > > > If a const * to a kobject is passed to kobj_to_dev(), we want to return > > > back a const * to a device as the driver core shouldn't be modifying a > > > constant structure. But when dealing with container_of() the pointer > > > const attribute is cast away, so we need to manually handle this by > > > determining the type of the pointer passed in to know the type of the > > > pointer to pass out. > > > > Alternatively container_of() could be fixed, but that will likely produce > > lots of warnings currently. > > Yeah, we can not do that because, as you found out, there's just too > many warnings that it would cause. Let's work on the individual > subsystems to clean them all up first before worrying about the core > container_of() macro as that should fix the majority of the build > warnings.
Sounds reasonable.
> > > > Luckily _Generic can do this type of magic, and as the kernel now > > > supports C11 it is availble to us to handle this type of build-time type > > > detection. > > > > > > Cc: Sakari Ailus <sakari.ailus@linux.intel.com> > > > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > > > Cc: "Rafael J. Wysocki" <rafael@kernel.org> > > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > > --- > > > v2 - use _Generic() to make this type safe as pointed out by Sakari > > > > > > include/linux/device.h | 18 +++++++++++++++++- > > > 1 file changed, 17 insertions(+), 1 deletion(-) > > > > > > diff --git a/include/linux/device.h b/include/linux/device.h > > > index 424b55df0272..023ea50b1916 100644 > > > --- a/include/linux/device.h > > > +++ b/include/linux/device.h > > > @@ -680,11 +680,27 @@ struct device_link { > > > bool supplier_preactivated; /* Owned by consumer probe. */ > > > }; > > > > > > -static inline struct device *kobj_to_dev(struct kobject *kobj) > > > +static inline struct device *__kobj_to_dev(struct kobject *kobj) > > > { > > > return container_of(kobj, struct device, kobj); > > > } > > > > > > +static inline const struct device *__kobj_to_dev_const(const struct kobject *kobj) > > > +{ > > > + return container_of(kobj, const struct device, kobj); > > > +} > > > + > > > +/* > > > + * container_of() will happily take a const * and spit back a non-const * as it > > > + * is just doing pointer math. But we want to be a bit more careful in the > > > + * driver code, so manually force any const * of a kobject to also be a const * > > > + * to a device. > > > + */ > > > > container_of() documentation has (probably?) never warned about this. > > We never thought of it before :( > > > Wouldn't such a comment be more appropriate there? Albeit it wouldn't be > > needed if container_of() were fixed. > > Some comment added to container_of() would be great, but that does not > remove the need to keep this one.
I can send a patch for that.
For this one:
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
-- Kind regards,
Sakari Ailus
| |