Messages in this thread | | | Date | Mon, 9 Mar 2015 16:28:22 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/2] move offsetofend() from vfio.h to stddef.h |
| |
* Denys Vlasenko <vda.linux@googlemail.com> wrote:
> On Mon, Mar 9, 2015 at 3:58 PM, Ingo Molnar <mingo@kernel.org> wrote: > >> -/** > >> - * offsetofend(TYPE, MEMBER) > >> - * > >> - * @TYPE: The type of the structure > >> - * @MEMBER: The member within the structure to get the end offset of > >> - * > >> - * Simple helper macro for dealing with variable sized structures passed > >> - * from user space. This allows us to easily determine if the provided > >> - * structure is sized to include various fields. > >> - */ > >> -#define offsetofend(TYPE, MEMBER) \ > >> - (offsetof(TYPE, MEMBER) + sizeof(((TYPE *)0)->MEMBER)) > > > > So I like it, and because it is not particularly trivial when to use > > this primitive it was explained nicely in a description in the vfio.h > > version. > > > > But you lost that nice description during the code move!! > > That description was clearly specific to how that macro is used in > drivers/vfio/*.c, along the lines of > > minsz = offsetofend(struct vfio_eeh_pe_op, op);
Hm, but here 'minsz' == sizeof(struct vfio_eeh_pe_op), so the vfio usage does not seem to be justified.
> if (copy_from_user(&op, (void __user *)arg, minsz)) > return -EFAULT; > if (op.argsz < minsz || op.flags) > return -EINVAL; > > But the macro is generic, it has many other uses besides this one.
So I might be missing something, but what generic uses does it have, beyond structures that have some rare size related weirdness, such as alignment attributes? In 99% of the cases:
sizeof(struct) == offsetofend(struct, last_member)
right?
> Nevertheless, I can resend a version where comment survives if you > want...
So maybe extend it to a description that you think describes its uses correctly? People will keep wondering about when to use this.
Thanks,
Ingo
| |