Support dumping skb hash

[borkmann]

Extend pwru to support duming:

• skb hash
• whether the skb hash is L4 hash (vs L3 or lower)
• whether the skb hash is SW hash (vs HW)

It would be useful to see this meta data at each traced function.

For example, packet comes in from HW/NIC, gets into Cilium, is rewritten (K8s services) and pushed via tunnel device to a backend. It would be useful to analyze the skb hash at each of these stages.

[Asphaltt]

Hi Daniel,

I don't think we should add more output options to pwru in order to output skb meta data.

With the PR #499, we're able to filter skb/xdp meta data by --filter-skb-expr/--filter-xdp-expr.

Then, like this PR, it's better to output skb meta data by --output-skb-meta skb->hash, --output-skb-meta skb->l4_hash and --output-skb-meta skb->sw_hash.

The expected result would be skb->hash=0xXX skb->l4_hash=0xXX skb->sw_hash=0xXX.

After the PR #499 getting merged, I'll try to implement --output-skb-meta and --output-xdp-meta options.

[jschwinger233]

I just checked, --output-skb already gives the .hash fields:

0xffff88fb4a98c8e8 3   ~in/curl:1517270 4026534376 0            eth0:70      0x0800 65536 146   172.18.0.5:57858->172.18.0.2:8472(udp)     __iptunnel_pull_header       vxlan_rcv[vxlan]
(struct sk_buff){
 (union){
  (struct){
   (union){
    .dev = (struct net_device *)0x0000000054c482f3,
    .dev_scratch = (long unsigned int)18446613216915714048,
   },
  },
  .rbnode = (struct rb_node){
   .rb_left = (struct rb_node *)0x0000000054c482f3,
  },
 },
 .cb = (char[])[
  'F',
 ],
 (union){
  (struct){
   ._skb_refdst = (long unsigned int)18446613228463974465,
  },
  .tcp_tsorted_anchor = (struct list_head){
   .next = (struct list_head *)0x0000000066cd7982,
  },
  ._sk_redir = (long unsigned int)18446613228463974465,
 },
 .len = (unsigned int)146,
 .data_len = (unsigned int)20,
 .mac_len = (__u16)14,
 .fclone = (__u8)0x2,
 (union){
  (struct){
   .ooo_okay = (__u8)0x1,
   .tc_at_ingress = (__u8)0x1,
   .l4_hash = (__u8)0x1,
   .csum_valid = (__u8)0x1,
   .slow_gro = (__u8)0x1,
   .alloc_cpu = (u16)3,
   (union){
    .csum = (__wsum)1048856,
    (struct){
     .csum_start = (__u16)280,
     .csum_offset = (__u16)16,
    },
   },
   .skb_iif = (int)70,
   .hash = (__u32)2372300512,
   (union){
    .napi_id = (unsigned int)4,
    .sender_cpu = (unsigned int)4,
   },
   (union){
    .inner_protocol = (__be16)22629,
    .inner_ipproto = (__u8)101,
   },
   .inner_transport_header = (__u16)244,
   .inner_network_header = (__u16)224,
   .inner_mac_header = (__u16)210,
   .protocol = (__be16)8,
   .transport_header = (__u16)194,
   .network_header = (__u16)174,
   .mac_header = (__u16)160,
  },
  .headers = (struct){
   .ooo_okay = (__u8)0x1,
   .tc_at_ingress = (__u8)0x1,
   .l4_hash = (__u8)0x1,
   .csum_valid = (__u8)0x1,
   .slow_gro = (__u8)0x1,
   .alloc_cpu = (u16)3,
   (union){
    .csum = (__wsum)1048856,
    (struct){
     .csum_start = (__u16)280,
     .csum_offset = (__u16)16,
    },
   },
   .skb_iif = (int)70,
   .hash = (__u32)2372300512,
   (union){
    .napi_id = (unsigned int)4,
    .sender_cpu = (unsigned int)4,
   },
   (union){
    .inner_protocol = (__be16)22629,
    .inner_ipproto = (__u8)101,
   },
   .inner_transport_header = (__u16)244,
   .inner_network_header = (__u16)224,
   .in

There are two issues:

1. Incorrect global variables usage for outputting skb and shinfo #491
2. buff size is still too small, we can see from above the output has been truncated.