Re: [PATCH RFC v2] m68k: remove get_fs()/set_fs()

On Fri, Jul 9, 2021 at 1:03 PM Linus Torvalds
[off-list ref] wrote:

Except maybe there's some 32-bit architecture that doesn't support
8-byte get/put_user(), which may be why it's a copy_to_user().

I _think_ we made the rule be that everybody had to support 1/2/4/8
byte accesses, but maybe I remember incorrectly.

We're _almost_ correct.

nios2 doesn't seem to support 8-byte user accesses.

Everybody else does seem to have a 'case 8:' at least according to my
simplistic grep (but that grep might have been _too_ simplistic).

Added nios2 and the arch list.

I think we could easily just say "you have to support a 8-byte
get/put_user()". At worst, an architecture can just implement it using
copy_from_user() like some already do, ie something like

        case 8: {                                                       \
                u64 __x;                                                \
                if (unlikely(copy_from_user(&__x, ptr, 8))) {         \
                        retval = -EFAULT;                               \
                        (x) = (__typeof__(*(ptr)))0;                    \
                } else {                                                \
                        (x) = *(__force __typeof__(*(ptr)) *)&__x;      \
                }                                                       \
                break;                                                  \
        }                                                               \

so if somebody wants to make 'sys_llseek()' use put_user(), I'm ok with that.

              Linus