On Wed, Jan 29, 2025 at 10:33:56AM +0300, Dan Carpenter wrote:
> On Wed, Jan 29, 2025 at 10:29:24AM +0300, Dan Carpenter wrote:
> > drivers/iommu/iommufd/iommufd_private.h
> > 243 static inline struct iommufd_ioas *iommufd_get_ioas(struct
> > iommufd_ctx *ictx,
> > 244 u32 id)
> > 245 {
> > 246 return container_of(iommufd_get_object(ictx, id,
> > 247 IOMMUFD_OBJ_IOAS),
> > 248 struct iommufd_ioas, obj);
> > 249 }
> >
> > It's just a cast like you say, but it looks like pointer math. It would
> > be more readable as container_of_first().
>
> I left out the important bit... iommufd_get_object() returns error pointers.
> It doesn't make sense to pass error pointers to container_of() unless the
> offset is zero.
Ick, agreed. you should never be checking the return value of
container_of(). Shouldn't we somehow check for that? Is there the
inverse of __must_check where we "just" want to use the value but never
compare it to anything?
> Smatch could check that the offset is zero, but Coccinelle can't. There are
> a bunch of advantages to Coccinelle at times so this will improve the
> readability and make it easier for static checkers as well.
But I don't see how container_first() will do anything to help the above
type of code. Gustavo, have any examples of what you need this for?
thanks,
greg k-h
