libbpf: add error reporting in XDP

Parse netlink ext attribute to get the error message returned by
the card. Code is partially take from libnl.

We add netlink.h to the uapi include of tools. And we need to
avoid include of userspace netlink header to have a successful
build of sample so nlattr.h has a define to avoid
the inclusion. Using a direct define could have been an issue
as NLMSGERR_ATTR_MAX can change in the future.

We also define SOL_NETLINK if not defined to avoid to have to
copy socket.h for a fixed value.

Signed-off-by: Eric Leblond <eric@regit.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index bf2772566240..9c88f6e4156d 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -32,6 +32,10 @@
 #include <sys/socket.h>
 #include <errno.h>
 
+#ifndef SOL_NETLINK
+#define SOL_NETLINK 270
+#endif
+
 /*
  * When building perf, unistd.h is overridden. __NR_bpf is
  * required to be defined explicitly.
@@ -436,6 +440,7 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
         struct nlmsghdr *nh;
         struct nlmsgerr *err;
         socklen_t addrlen;
+        int one = 1;
 
         memset(&sa, 0, sizeof(sa));
         sa.nl_family = AF_NETLINK;
@@ -445,6 +450,11 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
                 return -errno;
         }
 
+        if (setsockopt(sock, SOL_NETLINK, NETLINK_EXT_ACK,
+                       &one, sizeof(one)) < 0) {
+                fprintf(stderr, "Netlink error reporting not supported\n");
+        }
+
         if (bind(sock, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
                 ret = -errno;
                 goto cleanup;
@@ -521,6 +531,7 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
                         if (!err->error)
                                 continue;
                         ret = err->error;
+                        nla_dump_errormsg(nh);
                         goto cleanup;
                 case NLMSG_DONE:
                         break;