Add support for generic XDP mode

Reused some of the code and command-line format from kernel XDP samples.

$ sudo ./xdp_drop_count.py -S enp1s0
Printing drops per IP protocol-number, hit CTRL+C to stop
17: 36616 pkt/s
17: 19720757 pkt/s
17: 19685768 pkt/s
17: 19643601 pkt/s
17: 19694537 pkt/s
[...]
$ sudo ./xdp_drop_count.py enp1s0
Printing drops per IP protocol-number, hit CTRL+C to stop
17: 7029 pkt/s
17: 29996706 pkt/s
17: 30048705 pkt/s
17: 30261417 pkt/s
17: 30291967 pkt/s
[...]

Throughput difference is expected since generic XDP takes more
instructions per packet than optimized XDP.

v2: switch __u32 to uint32_t in bpf_attach_xdp
Signed-off-by: Andy Gospodarek <gospo@broadcom.com>

examples/networking/xdp/xdp_drop_count.py

@@ -12,11 +12,28 @@ import pyroute2
 import time
 import sys
 
-if len(sys.argv) != 2:
-    print("Usage: {0} <ifdev>\n\ne.g.: {0} eth0".format(sys.argv[0]))
+flags = 0
+def usage():
+    print("Usage: {0} [-S] <ifdev>".format(sys.argv[0]))
+    print("       -S: use skb mode\n")
+    print("e.g.: {0} eth0\n".format(sys.argv[0]))
     exit(1)
 
-device = sys.argv[1]
+if len(sys.argv) < 2 or len(sys.argv) > 3:
+    usage()
+
+if len(sys.argv) == 2:
+    device = sys.argv[1]
+
+if len(sys.argv) == 3:
+    if "-S" in sys.argv:
+        # XDP_FLAGS_SKB_MODE
+        flags |= 2 << 0
+
+    if "-S" == sys.argv[1]:
+        device = sys.argv[2]
+    else:
+        device = sys.argv[1]
 
 mode = BPF.XDP
 #mode = BPF.SCHED_CLS
@@ -116,7 +133,7 @@ int xdp_prog1(struct CTXTYPE *ctx) {
 fn = b.load_func("xdp_prog1", mode)
 
 if mode == BPF.XDP:
-    b.attach_xdp(device, fn)
+    b.attach_xdp(device, fn, flags)
 else:
     ip = pyroute2.IPRoute()
     ipdb = pyroute2.IPDB(nl=ip)

src/cc/libbpf.c

@@ -649,7 +649,7 @@ int bpf_open_perf_event(uint32_t type, uint64_t config, int pid, int cpu) {
   return fd;
 }
 
-int bpf_attach_xdp(const char *dev_name, int progfd) {
+int bpf_attach_xdp(const char *dev_name, int progfd, uint32_t flags) {
     struct sockaddr_nl sa;
     int sock, seq = 0, len, ret = -1;
     char buf[4096];
@@ -694,12 +694,22 @@ int bpf_attach_xdp(const char *dev_name, int progfd) {
     nla->nla_type = NLA_F_NESTED | 43/*IFLA_XDP*/;
 
     nla_xdp = (struct nlattr *)((char *)nla + NLA_HDRLEN);
+    nla->nla_len = NLA_HDRLEN;
 
     // we specify the FD passed over by the user
     nla_xdp->nla_type = 1/*IFLA_XDP_FD*/;
     nla_xdp->nla_len = NLA_HDRLEN + sizeof(progfd);
     memcpy((char *)nla_xdp + NLA_HDRLEN, &progfd, sizeof(progfd));
-    nla->nla_len = NLA_HDRLEN + nla_xdp->nla_len;
+    nla->nla_len += nla_xdp->nla_len;
+
+    // parse flags as passed by the user
+    if (flags) {
+        nla_xdp = (struct nlattr *)((char *)nla + nla->nla_len);
+        nla_xdp->nla_type = 3/*IFLA_XDP_SKB*/;
+        nla_xdp->nla_len = NLA_HDRLEN + sizeof(flags);
+        memcpy((char *)nla_xdp + NLA_HDRLEN, &flags, sizeof(flags));
+        nla->nla_len += nla_xdp->nla_len;
+    }
 
     req.nh.nlmsg_len += NLA_ALIGN(nla->nla_len);
 

src/cc/libbpf.h

@@ -75,7 +75,7 @@ void * bpf_open_perf_buffer(perf_reader_raw_cb raw_cb,
                             int pid, int cpu, int page_cnt);
 
 /* attached a prog expressed by progfd to the device specified in dev_name */
-int bpf_attach_xdp(const char *dev_name, int progfd);
+int bpf_attach_xdp(const char *dev_name, int progfd, uint32_t flags);
 
 // attach a prog expressed by progfd to run on a specific perf event, with
 // certain sample period or sample frequency

src/python/bcc/__init__.py

@@ -571,14 +571,14 @@ class BPF(object):
         self._del_kprobe(ev_name)
 
     @staticmethod
-    def attach_xdp(dev, fn):
+    def attach_xdp(dev, fn, flags):
         '''
             This function attaches a BPF function to a device on the device
             driver level (XDP)
         '''
         if not isinstance(fn, BPF.Function):
             raise Exception("arg 1 must be of type BPF.Function")
-        res = lib.bpf_attach_xdp(dev.encode("ascii"), fn.fd)
+        res = lib.bpf_attach_xdp(dev.encode("ascii"), fn.fd, flags)
         if res < 0:
             err_no = ct.get_errno()
             if err_no == errno.EBADMSG:
@@ -595,7 +595,7 @@ class BPF(object):
             This function removes any BPF function from a device on the
             device driver level (XDP)
         '''
-        res = lib.bpf_attach_xdp(dev.encode("ascii"), -1)
+        res = lib.bpf_attach_xdp(dev.encode("ascii"), -1, 0)
         if res < 0:
             errstr = os.strerror(ct.get_errno())
             raise Exception("Failed to detach BPF from device %s: %s"

src/python/bcc/libbcc.py

@@ -116,7 +116,7 @@ lib.perf_reader_fd.restype = int
 lib.perf_reader_fd.argtypes = [ct.c_void_p]
 
 lib.bpf_attach_xdp.restype = ct.c_int;
-lib.bpf_attach_xdp.argtypes = [ct.c_char_p, ct.c_int]
+lib.bpf_attach_xdp.argtypes = [ct.c_char_p, ct.c_int, ct.c_uint]
 
 lib.bpf_attach_perf_event.restype = ct.c_int;
 lib.bpf_attach_perf_event.argtype = [ct.c_int, ct.c_uint, ct.c_uint, ct.c_ulonglong, ct.c_ulonglong,