Re: [PATCH v1 2/2] signal: add procfd_signal() syscall

Christian Brauner
2018-11-20T00:33:00Z

On Mon, Nov 19, 2018 at 04:27:49PM -0800, Andy Lutomirski wrote:
> On Mon, Nov 19, 2018 at 3:07 PM Tycho Andersen <tycho@tycho.ws> wrote:
> > > These tools also care about ioctls. Adding a system call is a pain,
> > > but the solution is to make adding system calls less of a pain, not to
> > > permanently make the Linux ABI worse.
> >
> > For user-defined values of "worse" :)
> >
>
> I tend to agree with Tycho here. But I'm wondering if it might be
> worth considering a better ioctl.
>
> /me dons flame-proof hat
>
> We could do:
>
> long better_ioctl(int fd, u32 nr, const void *inbuf, size_t inlen,
> const void *outbuf, size_t outlen);

I'm the writer of this patch so take this with a grain of salt.
I think it is a bad idea to stop this patch and force us to introduce a
new type of ioctl().
An ioctl() is also not easy to use for this task because we want to add
a siginfo_t argument which I actually think provides value and makes
this interface more useful.

>
> and have a central table in the kernel listing all possible nr values
> along with which driver they belong to. We could have a sane
> signature and get rid of the nr collision problem.
>
> The major problem I see is that u32 isn't really enough to have a sane
> way to allow out-of-tree drivers to use this, and that we can't
> readily use anything bigger than u32 without indirection because we're
> out of syscall argument space.