On Fri, Sep 20, 2019 at 11:58:43AM -0700, Matthew Cover wrote:
> Treat a negative return from a TUNSETSTEERINGEBPF bpf prog as a signal
> to fallback to tun_automq_select_queue() for tx queue selection.
>
> Compilation of this exact patch was tested.
>
> For functional testing 3 additional printk()s were added.
>
> Functional testing results (on 2 txq tap device):
>
> [Fri Sep 20 18:33:27 2019] ========== tun no prog ==========
> [Fri Sep 20 18:33:27 2019] tuntap: tun_ebpf_select_queue() returned '-1'
> [Fri Sep 20 18:33:27 2019] tuntap: tun_automq_select_queue() ran
> [Fri Sep 20 18:33:27 2019] ========== tun prog -1 ==========
> [Fri Sep 20 18:33:27 2019] tuntap: bpf_prog_run_clear_cb() returned '-1'
> [Fri Sep 20 18:33:27 2019] tuntap: tun_ebpf_select_queue() returned '-1'
> [Fri Sep 20 18:33:27 2019] tuntap: tun_automq_select_queue() ran
> [Fri Sep 20 18:33:27 2019] ========== tun prog 0 ==========
> [Fri Sep 20 18:33:27 2019] tuntap: bpf_prog_run_clear_cb() returned '0'
> [Fri Sep 20 18:33:27 2019] tuntap: tun_ebpf_select_queue() returned '0'
> [Fri Sep 20 18:33:27 2019] ========== tun prog 1 ==========
> [Fri Sep 20 18:33:27 2019] tuntap: bpf_prog_run_clear_cb() returned '1'
> [Fri Sep 20 18:33:27 2019] tuntap: tun_ebpf_select_queue() returned '1'
> [Fri Sep 20 18:33:27 2019] ========== tun prog 2 ==========
> [Fri Sep 20 18:33:27 2019] tuntap: bpf_prog_run_clear_cb() returned '2'
> [Fri Sep 20 18:33:27 2019] tuntap: tun_ebpf_select_queue() returned '0'
>
> Signed-off-by: Matthew Cover <matthew.cover@xxxxxxxxxxxxx>
Could you add a bit more motivation data here?
1. why is this a good idea
2. how do we know existing userspace does not rely on existing behaviour
3. why doesn't userspace need a way to figure out whether it runs on a kernel with and
without this patch
thanks,
MST
> ---
> drivers/net/tun.c | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index aab0be4..173d159 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -583,35 +583,37 @@ 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 int tun_ebpf_select_queue(struct tun_struct *tun, struct sk_buff *skb)
> {
> struct tun_prog *prog;
> u32 numqueues;
> - u16 ret = 0;
> + int ret = -1;
>
> numqueues = READ_ONCE(tun->numqueues);
> if (!numqueues)
> return 0;
>
> + rcu_read_lock();
> prog = rcu_dereference(tun->steering_prog);
> if (prog)
> ret = bpf_prog_run_clear_cb(prog->prog, skb);
> + rcu_read_unlock();
>
> - return ret % numqueues;
> + if (ret >= 0)
> + ret %= numqueues;
> +
> + return ret;
> }
>
> static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
> struct net_device *sb_dev)
> {
> struct tun_struct *tun = netdev_priv(dev);
> - u16 ret;
> + int ret;
>
> - rcu_read_lock();
> - if (rcu_dereference(tun->steering_prog))
> - ret = tun_ebpf_select_queue(tun, skb);
> - else
> + ret = tun_ebpf_select_queue(tun, skb);
> + if (ret < 0)
> ret = tun_automq_select_queue(tun, skb);
> - rcu_read_unlock();
>
> return ret;
> }
> --
> 1.8.3.1
