Re: [PATCH 0/5] add initial io_uring_cmd support for sockets

Willem de Bruijn
2023-04-12T14:28:55Z

Breno Leitao wrote:
> On Tue, Apr 11, 2023 at 09:28:29AM -0600, Jens Axboe wrote:
> > On 4/11/23 9:24?AM, Willem de Bruijn wrote:
> > > Jens Axboe wrote:
> > >> On 4/11/23 9:00?AM, Willem de Bruijn wrote:
> > >> But that doesn't work, because sock->ops->ioctl() assumes the arg is
> > >> memory in userspace. Or do you mean change all of the sock->ops->ioctl()
> > >> to pass in on-stack memory (or similar) and have it work with a kernel
> > >> address?
> > >
> > > That was what I suggested indeed.
> > >
> > > It's about as much code change as this patch series. But it avoids
> > > the code duplication.
> >
> > Breno, want to tackle that as a prep patch first? Should make the
> > functional changes afterwards much more straightforward, and will allow
> > support for anything really.
>
> Absolutely. I just want to make sure that I got the proper approach that
> we agreed here.
>
> Let me explain what I understood taking TCP as an example:
>
> 1) Rename tcp_ioctl() to something as _tcp_ioctl() where the 'arg'
> argument is now just a kernel memory (located in the stack frame from the
> callee).
>
> 2) Recreate "tcp_ioctl()" that will basically allocate a 'arg' in the
> stack and call _tcp_ioctl() passing that 'arg' argument. At the bottom of
> this (tcp_ioctl() function) function, call `put_user(in_kernel_arg, userspace_arg)
>
> 3) Repeat it for the 20 protocols that implement ioctl:
>
> ag "struct proto .* = {" -A 20 net/ | grep \.ioctl
> net/dccp/ipv6.c .ioctl = dccp_ioctl,
> net/dccp/ipv4.c .ioctl = dccp_ioctl,
> net/ieee802154/socket.c .ioctl = dgram_ioctl,
> net/ipv4/udplite.c .ioctl = udp_ioctl,
> net/ipv4/raw.c .ioctl = raw_ioctl,
> net/ipv4/udp.c .ioctl = udp_ioctl,
> net/ipv4/tcp_ipv4.c .ioctl = tcp_ioctl,
> net/ipv6/raw.c .ioctl = rawv6_ioctl,
> net/ipv6/tcp_ipv6.c .ioctl = tcp_ioctl,
> net/ipv6/udp.c .ioctl = udp_ioctl,
> net/ipv6/udplite.c .ioctl = udp_ioctl,
> net/l2tp/l2tp_ip6.c .ioctl = l2tp_ioctl,
> net/l2tp/l2tp_ip.c .ioctl = l2tp_ioctl,
> net/phonet/datagram.: .ioctl = pn_ioctl,
> net/phonet/pep.c .ioctl = pep_ioctl,
> net/rds/af_rds.c .ioctl = rds_ioctl,
> net/sctp/socket.c .ioctl = sctp_ioctl,
> net/sctp/socket.c .ioctl = sctp_ioctl,
> net/xdp/xsk.c .ioctl = sock_no_ioctl,
> net/mptcp/protocol.c .ioctl = mptcp_ioctl,
>
> Am I missing something?

The suggestion is to convert all to take kernel memory and do the
put_cmsg in the caller of .ioctl. Rather than create a wrapper for
each individual instance and add a separate .iouring_cmd for each.

"change all of the sock->ops->ioctl() to pass in on-stack memory
(or similar) and have it work with a kernel address"