On Wed, Jan 16, 2019 at 4:32 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
>
> On 1/16/19 8:14 AM, Jens Axboe wrote:
> > On 1/16/19 3:53 AM, Arnd Bergmann wrote:
> >> On Tue, Jan 15, 2019 at 3:56 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
> >>
> >>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> >>> index 542757a4c898..e36c264d74e8 100644
> >>> --- a/include/linux/syscalls.h
> >>> +++ b/include/linux/syscalls.h
> >>> @@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
> >>> struct io_uring_params __user *p);
> >>> asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
> >>> u32 min_complete, u32 flags);
> >>> +asmlinkage long sys_io_uring_register(unsigned int fd, unsigned op,
> >>> + void __user *arg);
> >>>
> >>
> >> Would it be possible to make this a typed pointer instead? If this needs to
> >> be extended later to pass a different structure, a new system call may
> >> be better for consistency than overloading the argument in various
> >> ways.
> >
> > As you can see from the later patch for registering files, it'll be used
> > for other structs too. Feels a little silly to add an extra system call
> > for that. I agree the void * isn't the prettiest thing in the world, but
> > at least it allows us to extend the API without having to add even more
> > system calls down the line.
>
> With the __u64 changes, we end up with this:
>
> struct io_uring_register_buffers {
> __u64 iovecs; /* pointer to iovecs array */
> __u32 nr_iovecs; /* number of iovecs in array */
> __u32 pad;
> };
>
> struct io_uring_register_files {
> __u64 fds;
> __u32 nr_fds;
> __u32 pad;
> };
>
> which are identical. So the question then becomes if I should just make
> these opaque enough to be the same thing, ala:
>
> struct io_uring_register_data {
> __u64 data;
> __u32 nr_elems;
> __u32 pad;
> };
Right, that looks good in either form.
> and then probably add a bit more reserved space so we have something
> that can be extended...
Or maybe go the opposite way and pass the two members you have
directly to the system call:
int io_uring_register(unsigned int fd, unsigned int opcode, void
__user *, arg, unsigned count)
{
...
}
Where 'arg' now points to the array of iovecs or the the array of file
descriptors, or whatever else you need.
Arnd
