On Wed, Jun 4, 2025 at 3:24 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
>
> On 2025/06/04 10:27, Jason Wang wrote:
> > On Fri, May 30, 2025 at 12:50 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
> >>
> >> This clarifies a steering eBPF program takes precedence over the other
> >> steering algorithms.
> >
> > Let's give an example on the use case for this.
> >
> >>
> >> Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
> >> ---
> >> Documentation/networking/tuntap.rst | 7 +++++++
> >> drivers/net/tun.c | 28 +++++++++++++++++-----------
> >> include/uapi/linux/if_tun.h | 9 +++++++++
> >> 3 files changed, 33 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/Documentation/networking/tuntap.rst b/Documentation/networking/tuntap.rst
> >> index 4d7087f727be..86b4ae8caa8a 100644
> >> --- a/Documentation/networking/tuntap.rst
> >> +++ b/Documentation/networking/tuntap.rst
> >> @@ -206,6 +206,13 @@ enable is true we enable it, otherwise we disable it::
> >> return ioctl(fd, TUNSETQUEUE, (void *)&ifr);
> >> }
> >>
> >> +3.4 Reference
> >> +-------------
> >> +
> >> +``linux/if_tun.h`` defines the interface described below:
> >> +
> >> +.. kernel-doc:: include/uapi/linux/if_tun.h
> >> +
> >> Universal TUN/TAP device driver Frequently Asked Question
> >> =========================================================
> >>
> >> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> >> index d8f4d3e996a7..9133ab9ed3f5 100644
> >> --- a/drivers/net/tun.c
> >> +++ b/drivers/net/tun.c
> >> @@ -476,21 +476,29 @@ static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
> >> return txq;
> >> }
> >>
> >> -static u16 tun_ebpf_select_queue(struct tun_struct *tun, struct sk_buff *skb)
> >> +static bool tun_ebpf_select_queue(struct tun_struct *tun, struct sk_buff *skb,
> >> + u16 *ret)
> >> {
> >> struct tun_prog *prog;
> >> u32 numqueues;
> >> - u16 ret = 0;
> >> + u32 prog_ret;
> >> +
> >> + prog = rcu_dereference(tun->steering_prog);
> >> + if (!prog)
> >> + return false;
> >>
> >> numqueues = READ_ONCE(tun->numqueues);
> >> - if (!numqueues)
> >> - return 0;
> >> + if (!numqueues) {
> >> + *ret = 0;
> >> + return true;
> >> + }
> >>
> >> - prog = rcu_dereference(tun->steering_prog);
> >> - if (prog)
> >> - ret = bpf_prog_run_clear_cb(prog->prog, skb);
> >> + prog_ret = bpf_prog_run_clear_cb(prog->prog, skb);
> >> + if (prog_ret == TUN_STEERINGEBPF_FALLBACK)
> >> + return false;
> >
> > This seems to break the uAPI. So I think we need a new ioctl to enable
> > the behaviour
>
> I assumed it is fine to repurpose one of the 32-bit integer values since
> 32-bit integer is too big to specify the queue number, but it may not be
> fine. I don't have a concrete use case either.
>
> Perhaps it is safer to note that TUNSETSTEERINGEBPF takes precedence
> over TUNSETVNETRSS to allow such an extension in the future (but without
> implementing one now).
Yes, that's my original point. Let's start from something that is
simpler and safer.
Thanks
