Jesper Dangaard Brouer wrote: > On Fri, 30 Oct 2020 13:36:05 -0700 > John Fastabend <john.fastabend@xxxxxxxxx> wrote: > > > Jesper Dangaard Brouer wrote: > > > The use-case for dropping the MTU check when TC-BPF does redirect to > > > ingress, is described by Eyal Birger in email[0]. The summary is the > > > ability to increase packet size (e.g. with IPv6 headers for NAT64) and > > > ingress redirect packet and let normal netstack fragment packet as needed. > > > > > > [0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@xxxxxxxxxxxxxx/ > > > > > > V4: > > > - Keep net_device "up" (IFF_UP) check. > > > - Adjustment to handle bpf_redirect_peer() helper > > > > > > Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> > > > --- > > > include/linux/netdevice.h | 31 +++++++++++++++++++++++++++++-- > > > net/core/dev.c | 19 ++----------------- > > > net/core/filter.c | 14 +++++++++++--- > > > 3 files changed, 42 insertions(+), 22 deletions(-) > > > > > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > > > index 964b494b0e8d..bd02ddab8dfe 100644 > > > --- a/include/linux/netdevice.h > > > +++ b/include/linux/netdevice.h > > > @@ -3891,11 +3891,38 @@ int dev_forward_skb(struct net_device *dev, struct sk_buff *skb); > > > bool is_skb_forwardable(const struct net_device *dev, > > > const struct sk_buff *skb); > > > > > > +static __always_inline bool __is_skb_forwardable(const struct net_device *dev, > > > + const struct sk_buff *skb, > > > + const bool check_mtu) > > > > It looks like if check_mtu=false then this is just an interface up check. > > Can we leave is_skb_forwardable logic alone and just change the spots where > > this is called with false to something with a name that describes the check, > > such as is_dev_up(dev). I think it will make this change smaller and the > > code easier to read. Did I miss something? > > People should realized that this is constructed such, the compiler will > compile-time remove the actual argument (the const bool check_mtu). > And this propagates also to ____dev_forward_skb() where the call places > are also inlined. The comment was about human reading the code not what gets generated by the compiler. > > Yes, this (check_mtu=false) is basically an interface up check, but the > only place it is used directly is in the ndo_get_peer_dev() case, and > reading the code I find it more readable that is says > __is_skb_forwardable because this is used as part of a forwarding step, > and is_dev_up() doesn't convey the intent in this use-case. OK. [...] > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index bd4a416bd9ad..71b78b8d443c 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -2083,13 +2083,21 @@ static const struct bpf_func_proto bpf_csum_level_proto = { > > > > static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb) > > { > > - return dev_forward_skb(dev, skb); > > + int ret = ____dev_forward_skb(dev, skb, false); > > + > > + if (likely(!ret)) { > > + skb->protocol = eth_type_trans(skb, dev); > > + skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN); > > + ret = netif_rx(skb); > > + } > > + > > + return ret; > > } > > I'm replicating two lines from dev_forward_skb(), but I couldn't find a > way to avoid this, without causing larger code changes (and slower code). > OK looks good to me then. > > > > Other than style aspects it looks correct to me. > > > > > if (skb_orphan_frags(skb, GFP_ATOMIC) || > > > - unlikely(!is_skb_forwardable(dev, skb))) { > > > + unlikely(!__is_skb_forwardable(dev, skb, check_mtu))) { > > > atomic_long_inc(&dev->rx_dropped); > > > kfree_skb(skb); > > > return NET_RX_DROP; > > > diff --git a/net/core/dev.c b/net/core/dev.c > > > index 9499a414d67e..445ccf92c149 100644 > > > --- a/net/core/dev.c > > > +++ b/net/core/dev.c > > > @@ -2188,28 +2188,13 @@ static inline void net_timestamp_set(struct sk_buff *skb) > > > > > > > > > -- > Best regards, > Jesper Dangaard Brouer > MSc.CS, Principal Kernel Engineer at Red Hat > LinkedIn: http://www.linkedin.com/in/brouer >
