Add perf_submit_skb

For BPF_PROG_TYPE_SCHED_CLS/ACT, the upstream kernel has recently added a
feature to efficiently output skb + meta data:
commit 555c8a8623a3 ("bpf: avoid stack copy and use skb ctx for event output")

This patch adds perf_submit_skb to BPF_PERF_OUTPUT macro.  It takes
an extra u32 argument.  perf_submit_skb will then be expanded to
bpf_perf_event_output properly to consider the newly added
u32 argument as the skb's len.

Other than the above described changes, perf_submit_skb is almost
a carbon copy of the perf_submit except the removal of the 'string name'
variable since I cannot find a specific use of it.

Note that the 3rd param type of bpf_perf_event_output has also been
changed from u32 to u64.

Added a sample program tc_perf_event.py.  Here is how the output
looks like:
[root@arch-fb-vm1 networking]# ./tc_perf_event.py
Try: "ping -6 ff02::1%me"

CPU SRC IP                           DST IP       Magic
0   fe80::982f:5dff:fec1:e52b        ff02::1      0xfaceb00c
0   fe80::982f:5dff:fec1:e52b        ff02::1      0xfaceb00c
0   fe80::982f:5dff:fec1:e52b        ff02::1      0xfaceb00c
1   fe80::982f:5dff:fec1:e52b        ff02::1      0xfaceb00c
1   fe80::982f:5dff:fec1:e52b        ff02::1      0xfaceb00c
1   fe80::982f:5dff:fec1:e52b        ff02::1      0xfaceb00c

examples/networking/CMakeLists.txt

 set(EXAMPLE_FILES simulation.py)
 set(EXAMPLE_PROGRAMS simple_tc.py)
+set(EXAMPLE_PROGRAMS tc_perf_event.py)
 install(FILES ${EXAMPLE_FILES} DESTINATION share/bcc/examples/networking)
 install(PROGRAMS ${EXAMPLE_PROGRAMS} DESTINATION share/bcc/examples/networking)
 

examples/networking/tc_perf_event.py

+#!/usr/bin/env python
+#
+# tc_perf_event.py  Output skb and meta data through perf event
+#
+# Copyright (c) 2016-present, Facebook, Inc.
+# Licensed under the Apache License, Version 2.0 (the "License")
+
+from bcc import BPF
+import ctypes as ct
+import pyroute2
+import socket
+
+bpf_txt = """
+#include <uapi/linux/if_ether.h>
+#include <uapi/linux/in6.h>
+#include <uapi/linux/ipv6.h>
+#include <uapi/linux/pkt_cls.h>
+#include <uapi/linux/bpf.h>
+
+BPF_PERF_OUTPUT(skb_events);
+
+struct eth_hdr {
+	unsigned char   h_dest[ETH_ALEN];
+	unsigned char   h_source[ETH_ALEN];
+	unsigned short  h_proto;
+};
+
+int handle_egress(struct __sk_buff *skb)
+{
+	void *data = (void *)(long)skb->data;
+	void *data_end = (void *)(long)skb->data_end;
+	struct eth_hdr *eth = data;
+	struct ipv6hdr *ip6h = data + sizeof(*eth);
+	u32 magic = 0xfaceb00c;
+
+	/* single length check */
+	if (data + sizeof(*eth) + sizeof(*ip6h) > data_end)
+		return TC_ACT_OK;
+
+	if (eth->h_proto == htons(ETH_P_IPV6) &&
+	    ip6h->nexthdr == IPPROTO_ICMPV6)
+	        skb_events.perf_submit_skb(skb, skb->len, &magic, sizeof(magic));
+
+	return TC_ACT_OK;
+}"""
+
+def print_skb_event(cpu, data, size):
+    class SkbEvent(ct.Structure):
+        _fields_ =  [ ("magic", ct.c_uint32),
+                      ("raw", ct.c_ubyte * (size - ct.sizeof(ct.c_uint32))) ]
+
+    skb_event = ct.cast(data, ct.POINTER(SkbEvent)).contents
+    icmp_type = int(skb_event.raw[54])
+
+    # Only print for echo request
+    if icmp_type == 128:
+        src_ip = bytes(skb_event.raw[22:38])
+        dst_ip = bytes(skb_event.raw[38:54])
+        print("%-3s %-32s %-12s 0x%08x" %
+              (cpu, socket.inet_ntop(socket.AF_INET6, src_ip),
+               socket.inet_ntop(socket.AF_INET6, dst_ip),
+               skb_event.magic))
+
+try:
+    b = BPF(text=bpf_txt)
+    fn = b.load_func("handle_egress", BPF.SCHED_CLS)
+
+    ipr = pyroute2.IPRoute()
+    ipr.link("add", ifname="me", kind="veth", peer="you")
+    me = ipr.link_lookup(ifname="me")[0]
+    you = ipr.link_lookup(ifname="you")[0]
+    for idx in (me, you):
+        ipr.link('set', index=idx, state='up')
+
+    ipr.tc("add", "clsact", me)
+    ipr.tc("add-filter", "bpf", me, ":1", fd=fn.fd, name=fn.name,
+           parent="ffff:fff3", classid=1, direct_action=True)
+
+    b["skb_events"].open_perf_buffer(print_skb_event)
+    print('Try: "ping -6 ff02::1%me"\n')
+    print("%-3s %-32s %-12s %-10s" % ("CPU", "SRC IP", "DST IP", "Magic"))
+    while True:
+        b.kprobe_poll()
+finally:
+    if "me" in locals(): ipr.link("del", index=me)

src/cc/export/helpers.h

@@ -67,6 +67,7 @@ struct _name##_table_t { \
   u32 leaf; \
   /* map.perf_submit(ctx, data, data_size) */ \
   int (*perf_submit) (void *, void *, u32); \
+  int (*perf_submit_skb) (void *, u32, void *, u32); \
   u32 data[0]; \
 }; \
 __attribute__((section("maps/perf_output"))) \
@@ -171,7 +172,7 @@ static int (*bpf_redirect)(int ifindex, u32 flags) =
   (void *) BPF_FUNC_redirect;
 static u32 (*bpf_get_route_realm)(void *ctx) =
   (void *) BPF_FUNC_get_route_realm;
-static int (*bpf_perf_event_output)(void *ctx, void *map, u32 index, void *data, u32 size) =
+static int (*bpf_perf_event_output)(void *ctx, void *map, u64 index, void *data, u32 size) =
   (void *) BPF_FUNC_perf_event_output;
 static int (*bpf_skb_load_bytes)(void *ctx, int offset, void *to, u32 len) =
   (void *) BPF_FUNC_skb_load_bytes;

src/cc/frontends/clang/b_frontend_action.cc

@@ -396,6 +396,21 @@ bool BTypeVisitor::VisitCallExpr(CallExpr *Call) {
                                                                      Call->getArg(2)->getLocEnd()));
           txt = "bpf_perf_event_output(" + arg0 + ", bpf_pseudo_fd(1, " + fd + ")";
           txt += ", bpf_get_smp_processor_id(), " + args_other + ")";
+        } else if (memb_name == "perf_submit_skb") {
+          string skb = rewriter_.getRewrittenText(SourceRange(Call->getArg(0)->getLocStart(),
+                                                               Call->getArg(0)->getLocEnd()));
+          string skb_len = rewriter_.getRewrittenText(SourceRange(Call->getArg(1)->getLocStart(),
+                                                                  Call->getArg(1)->getLocEnd()));
+          string meta = rewriter_.getRewrittenText(SourceRange(Call->getArg(2)->getLocStart(),
+                                                               Call->getArg(2)->getLocEnd()));
+          string meta_len = rewriter_.getRewrittenText(SourceRange(Call->getArg(3)->getLocStart(),
+                                                                   Call->getArg(3)->getLocEnd()));
+          txt = "bpf_perf_event_output(" +
+            skb + ", " +
+            "bpf_pseudo_fd(1, " + fd + "), " +
+            "((__u64)" + skb_len + " << 32) | BPF_F_CURRENT_CPU, " +
+            meta + ", " +
+            meta_len + ");";
         } else if (memb_name == "get_stackid") {
             if (table_it->type == BPF_MAP_TYPE_STACK_TRACE) {
               string arg0 = rewriter_.getRewrittenText(SourceRange(Call->getArg(0)->getLocStart(),