ftrace 跟踪位域

举个栗子
sk_buff 的成员

   [0x80] __u8 ignore_df : 1;
   [0x80] __u8 nf_trace : 1;
   [0x80] __u8 ip_summed : 2;
   [0x80] __u8 ooo_okay : 1;

   [0x81] __u8 l4_hash : 1;
   [0x81] __u8 sw_hash : 1;
   [0x81] __u8 wifi_acked_valid : 1;
   [0x81] __u8 wifi_acked : 1;
   [0x81] __u8 no_fcs : 1;
   [0x81] __u8 encapsulation : 1;
   [0x81] __u8 encap_hdr_csum : 1;
   [0x81] __u8 csum_valid : 1;

   [0x82] __u8 __pkt_vlan_present_offset[0];
   [0x82] __u8 vlan_present : 1;
   [0x82] __u8 csum_complete_sw : 1;



判断csum_valid  checksum是否有效

echo 'p:xx icmp_rcv csum_valid =+0x81(%di):b1@7/8' > kprobe_events

位宽 1 8bit  ，便宜7位为csum_valid

    | |         |   ||||      |         |
      <idle>-0       [003] ..s. 30288.516996: xx: (icmp_rcv+0x0/0x390) csum_valid =1
      <idle>-0       [003] .Ns. 30289.519752: xx: (icmp_rcv+0x0/0x390) csum_valid =1
      <idle>-0       [003] ..s. 30290.524699: xx: (icmp_rcv+0x0/0x390) csum_valid =1
      <idle>-0       [003] ..s. 30291.529767: xx: (icmp_rcv+0x0/0x390) csum_valid =1

参考
https://www.kernel.org/doc/html/latest/trace/kprobetrace.html