目前想做个功能， 一些简单转发就在内核中直接转发走，所以想到了XDP，但是呢，部分网卡驱动不支持XDP程序，能不能在netif_recv收包接口或者驱动的hook钩子挂载一个通用接口来处理XDP，
目前看linux-5-18内核是已经加了此功能！
if (static_branch_unlikely(&generic_xdp_needed_key)) {
int ret2;
preempt_disable();// 需要禁止抢占？软中断上下问需要？ 难道是ksoftirq 线程中处理 需要关闭抢占
ret2 = do_xdp_generic(rcu_dereference(skb->dev->xdp_prog), skb);
preempt_enable();
if (ret2 != XDP_PASS) {
ret = NET_RX_DROP;
goto out;
}
skb_reset_mac_len(skb);
}int do_xdp_generic(struct bpf_prog *xdp_prog, struct sk_buff *skb)
{
if (xdp_prog) {
act = netif_receive_generic_xdp(skb, &xdp, xdp_prog);
------------------return XDP_PASS;
---------------------
}static u32 netif_receive_generic_xdp(struct sk_buff *skb,
struct xdp_buff *xdp,
struct bpf_prog *xdp_prog)
{
struct netdev_rx_queue *rxqueue;
void *orig_data, *orig_data_end;
u32 metalen, act = XDP_DROP;
__be16 orig_eth_type;
struct ethhdr *eth;
bool orig_bcast;
int hlen, off;
u32 mac_len;
/* Reinjected packets coming from act_mirred or similar should
* not get XDP generic processing.
*/
if (skb_is_redirected(skb))
return XDP_PASS;
/* XDP packets must be linear and must have sufficient headroom
* of XDP_PACKET_HEADROOM bytes. This is the guarantee that also
* native XDP provides, thus we need to do it here as well.
*/
if (skb_cloned(skb) || skb_is_nonlinear(skb) ||
skb_headroom(skb) < XDP_PACKET_HEADROOM) {
int hroom = XDP_PACKET_HEADROOM - skb_headroom(skb);
int troom = skb->tail + skb->data_len - skb->end;
/* In case we have to go down the path and also linearize,
* then lets do the pskb_expand_head() work just once here.
*/
if (pskb_expand_head(skb,
hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0,
troom > 0 ? troom + 128 : 0, GFP_ATOMIC))
goto do_drop;
if (skb_linearize(skb))
goto do_drop;
}
/* The XDP program wants to see the packet starting at the MAC
* header. 准备 XDP 元数据，即准备 XDP 程序的第一个参数
*/
mac_len = skb->data - skb_mac_header(skb);
hlen = skb_headlen(skb) + mac_len;
xdp->data = skb->data - mac_len;//xdp->data 网络包起始地址指向二层头部
xdp->data_meta = xdp->data;
xdp->data_end = xdp->data + hlen;
xdp->data_hard_start = skb->data - skb_headroom(skb);
/* SKB "head" area always have tailroom for skb_shared_info */
xdp->frame_sz = (void *)skb_end_pointer(skb) - xdp->data_hard_start;
xdp->frame_sz += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
orig_data_end = xdp->data_end;
orig_data = xdp->data;
eth = (struct ethhdr *)xdp->data;
orig_bcast = is_multicast_ether_addr_64bits(eth->h_dest);
orig_eth_type = eth->h_proto;
rxqueue = netif_get_rxqueue(skb);
xdp->rxq = &rxqueue->xdp_rxq;
act = bpf_prog_run_xdp(xdp_prog, xdp);//运行 XDP 程序
/* check if bpf_xdp_adjust_head was used */
off = xdp->data - orig_data;
if (off) {
if (off > 0)
__skb_pull(skb, off);
else if (off < 0)
__skb_push(skb, -off);
skb->mac_header += off;
skb_reset_network_header(skb);
}
/* check if bpf_xdp_adjust_tail was used */
off = xdp->data_end - orig_data_end;
if (off != 0) {
skb_set_tail_pointer(skb, xdp->data_end - xdp->data);
skb->len += off; /* positive on grow, negative on shrink */
}
/* check if XDP changed eth hdr such SKB needs update */
eth = (struct ethhdr *)xdp->data;
if ((orig_eth_type != eth->h_proto) ||
(orig_bcast != is_multicast_ether_addr_64bits(eth->h_dest))) {
__skb_push(skb, ETH_HLEN);
skb->protocol = eth_type_trans(skb, skb->dev);
}
switch (act) {
case XDP_REDIRECT:
case XDP_TX:
__skb_push(skb, mac_len);
break;
case XDP_PASS:
metalen = xdp->data - xdp->data_meta;
if (metalen)
skb_metadata_set(skb, metalen);
break;
default:
bpf_warn_invalid_xdp_action(act);
/* fall through */
case XDP_ABORTED://对 XDP 程序运行结果进行简单处理，其中 XDP_ABORTED 和 XDP_DROP 直接释放 skb
trace_xdp_exception(skb->dev, xdp_prog, act);
/* fall through */
case XDP_DROP:
do_drop:
kfree_skb(skb);
break;
}
return act;
}View Code
一个问题？ 目前内核是怎样将bpf程序和map 挂载到内核中以及如何绑定？
Loading via iproute2 ip
It does seem overkill to write a C program to simply load and attach a specific BPF-program. However, we still include this in the tutorial since it will help you integrate BPF into other Open Source projects.
As an alternative to writing a new loader, the standard iproute2 tool also contains a BPF ELF loader. However, this loader is not based on libbpf, which unfortunately makes it incompatible when starting to use BPF maps.
The iproute2 loader can be used with the standard ip tool; so in this case you can actually load our ELF-file xdp_pass_kern.o (where we named our ELF section “xdp”) like this:
ip link set dev lo xdpgeneric obj xdp_pass_kern.o sec xdp
http代理服务器（3-4-7层代理）-网络事件库公共组件、内核kernel驱动 摄像头驱动 tcpip网络协议栈、netfilter、bridge 好像看过！！！！ 但行好事 莫问前程 --身高体重180的胖子
