| Message ID | Zu1vekikKNR5oUoM@elsanto (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] container_of: add container_first() macro | expand |
On Fri, Sep 20, 2024 at 02:50:02PM +0200, Gustavo A. R. Silva wrote: > This is like container_of() but it has an assert to ensure that it's > using the first struct member. > I just remembered that Greg wanted this based on container_of_const(). Really container_of_const() should be renamed to container_of() and container_of() should be renamed to container_of_helper() and we would add a #define container_of_const container_of for the transition. > Co-developed-by: Dan Carpenter <dan.carpenter@linaro.org> > Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> > --- > include/linux/container_of.h | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/include/linux/container_of.h b/include/linux/container_of.h > index 713890c867be..928c5865c1b4 100644 > --- a/include/linux/container_of.h > +++ b/include/linux/container_of.h > @@ -22,6 +22,24 @@ > "pointer type mismatch in container_of()"); \ > ((type *)(__mptr - offsetof(type, member))); }) > > +/** > + * container_first - cast first member of a structure out to the containing > + * structure > + * @ptr: the pointer to the member. > + * @type: the type of the container struct this is embedded in. > + * @member: the name of the member within the struct. > + * > + * WARNING: any const qualifier of @ptr is lost. > + */ > +#define container_first(ptr, type, member) ({ \ > + void *__mptr = (void *)(ptr); \ > + static_assert(__same_type(*(ptr), ((type *)0)->member) || \ > + __same_type(*(ptr), void), \ > + "pointer type mismatch in container_of()"); \ > + static_assert(offsetof(type, member) == 0, "not first member"); \ > + ((type *)(__mptr - offsetof(type, member))); }) > + > + I added too many blank lines. regards, dan carpenter
On Sat, Sep 21, 2024 at 08:45:28AM +0300, Dan Carpenter wrote: > On Fri, Sep 20, 2024 at 02:50:02PM +0200, Gustavo A. R. Silva wrote: > > This is like container_of() but it has an assert to ensure that it's > > using the first struct member. > > > > I just remembered that Greg wanted this based on container_of_const(). Yes, that would be best. > Really container_of_const() should be renamed to container_of() and > container_of() should be renamed to container_of_helper() and we > would add a #define container_of_const container_of for the transition. I agree, but I wonder if it's safe to just do that already and how many build warnings would happen. Last I checked it was a lot. thanks, greg k-h
On 21/09/24 07:52, Greg KH wrote: > On Sat, Sep 21, 2024 at 08:45:28AM +0300, Dan Carpenter wrote: >> On Fri, Sep 20, 2024 at 02:50:02PM +0200, Gustavo A. R. Silva wrote: >>> This is like container_of() but it has an assert to ensure that it's >>> using the first struct member. >>> >> >> I just remembered that Greg wanted this based on container_of_const(). > > Yes, that would be best. Okay, I'll change that. -- Gustavo > >> Really container_of_const() should be renamed to container_of() and >> container_of() should be renamed to container_of_helper() and we >> would add a #define container_of_const container_of for the transition. > > I agree, but I wonder if it's safe to just do that already and how many > build warnings would happen. Last I checked it was a lot. > > thanks, > > greg k-h >
diff --git a/include/linux/container_of.h b/include/linux/container_of.h index 713890c867be..928c5865c1b4 100644 --- a/include/linux/container_of.h +++ b/include/linux/container_of.h @@ -22,6 +22,24 @@ "pointer type mismatch in container_of()"); \ ((type *)(__mptr - offsetof(type, member))); }) +/** + * container_first - cast first member of a structure out to the containing + * structure + * @ptr: the pointer to the member. + * @type: the type of the container struct this is embedded in. + * @member: the name of the member within the struct. + * + * WARNING: any const qualifier of @ptr is lost. + */ +#define container_first(ptr, type, member) ({ \ + void *__mptr = (void *)(ptr); \ + static_assert(__same_type(*(ptr), ((type *)0)->member) || \ + __same_type(*(ptr), void), \ + "pointer type mismatch in container_of()"); \ + static_assert(offsetof(type, member) == 0, "not first member"); \ + ((type *)(__mptr - offsetof(type, member))); }) + + /** * container_of_const - cast a member of a structure out to the containing * structure and preserve the const-ness of the pointer