On 1/16/19 8:41 AM, Arnd Bergmann wrote:
> 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.
I kind of like that, that gets rid of having to wrap it in a struct. If
I later wanted to abuse it, arg could point to a struct...
I'll make this change.
--
Jens Axboe
