[PATCH bpf-next 8/9] libbpf: Add support for setting and getting XDP chain maps

[Toke Høiland-Jørgensen <toke@xxxxxxxxxx>]

From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>

This adds two new API functions for setting and getting XDP programs with
associated chain map IDs. Programs are expected to pair them, so that if a
program uses the chain map-aware setter, it should also use the associated
getter.

Programs using the old non-chain aware variants of the functions will not
set the XDP chain map attribute on the netlink message, resulting in the
kernel rejecting the command if a chain map has already been loaded.

Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
---
 tools/lib/bpf/libbpf.h   |    4 ++++
 tools/lib/bpf/libbpf.map |    2 ++
 tools/lib/bpf/netlink.c  |   49 ++++++++++++++++++++++++++++++++++++++++++----
 3 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index e8f70977d137..0a459840e32c 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -357,7 +357,11 @@ LIBBPF_API int bpf_prog_load(const char *file, enum bpf_prog_type type,
 			     struct bpf_object **pobj, int *prog_fd);
 
 LIBBPF_API int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags);
+LIBBPF_API int bpf_set_link_xdp_chain(int ifindex, int prog_fd, int chain_map_fd,
+				      __u32 flags);
 LIBBPF_API int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags);
+LIBBPF_API int bpf_get_link_xdp_chain(int ifindex, __u32 *prog_id, __u32 *chain_map_id,
+				      __u32 flags);
 
 struct perf_buffer;
 
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 8d10ca03d78d..59f412680292 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -192,4 +192,6 @@ LIBBPF_0.0.5 {
 } LIBBPF_0.0.4;
 
 LIBBPF_0.0.6 {
+		bpf_set_link_xdp_chain;
+		bpf_get_link_xdp_chain;
 } LIBBPF_0.0.5;
diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index ce3ec81b71c0..c6f63bdab2e6 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -25,6 +25,7 @@ struct xdp_id_md {
 	int ifindex;
 	__u32 flags;
 	__u32 id;
+	__u32 chain_map_id;
 };
 
 int libbpf_netlink_open(__u32 *nl_pid)
@@ -128,7 +129,8 @@ static int bpf_netlink_recv(int sock, __u32 nl_pid, int seq,
 	return ret;
 }
 
-int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
+static int __bpf_set_link_xdp_fd(int ifindex, int *prog_fd, int *chain_map_fd,
+				 __u32 flags)
 {
 	int sock, seq = 0, ret;
 	struct nlattr *nla, *nla_xdp;
@@ -162,9 +164,19 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
 	nla_xdp = (struct nlattr *)((char *)nla + nla->nla_len);
 	nla_xdp->nla_type = IFLA_XDP_FD;
 	nla_xdp->nla_len = NLA_HDRLEN + sizeof(int);
-	memcpy((char *)nla_xdp + NLA_HDRLEN, &fd, sizeof(fd));
+	memcpy((char *)nla_xdp + NLA_HDRLEN, prog_fd, sizeof(*prog_fd));
 	nla->nla_len += nla_xdp->nla_len;
 
+	if (chain_map_fd) {
+		/* add XDP chain map */
+		nla_xdp = (struct nlattr *)((char *)nla + nla->nla_len);
+		nla_xdp->nla_type = IFLA_XDP_CHAIN_MAP_FD;
+		nla_xdp->nla_len = NLA_HDRLEN + sizeof(int);
+		memcpy((char *)nla_xdp + NLA_HDRLEN, chain_map_fd,
+		       sizeof(*chain_map_fd));
+		nla->nla_len += nla_xdp->nla_len;
+	}
+
 	/* if user passed in any flags, add those too */
 	if (flags) {
 		nla_xdp = (struct nlattr *)((char *)nla + nla->nla_len);
@@ -187,6 +199,17 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
 	return ret;
 }
 
+int bpf_set_link_xdp_chain(int ifindex, int prog_fd, int chain_map_fd,
+			   __u32 flags)
+{
+	return __bpf_set_link_xdp_fd(ifindex, &prog_fd, &chain_map_fd, flags);
+}
+
+int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
+{
+	return __bpf_set_link_xdp_fd(ifindex, &fd, NULL, flags);
+}
+
 static int __dump_link_nlmsg(struct nlmsghdr *nlh,
 			     libbpf_dump_nlmsg_t dump_link_nlmsg, void *cookie)
 {
@@ -247,10 +270,13 @@ static int get_xdp_id(void *cookie, void *msg, struct nlattr **tb)
 
 	xdp_id->id = libbpf_nla_getattr_u32(xdp_tb[xdp_attr]);
 
+	if (xdp_tb[IFLA_XDP_CHAIN_MAP_ID])
+		xdp_id->chain_map_id = libbpf_nla_getattr_u32(xdp_tb[IFLA_XDP_CHAIN_MAP_ID]);
+
 	return 0;
 }
 
-int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
+static int __bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 *chain_map_id, __u32 flags)
 {
 	struct xdp_id_md xdp_id = {};
 	int sock, ret;
@@ -274,13 +300,28 @@ int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
 	xdp_id.flags = flags;
 
 	ret = libbpf_nl_get_link(sock, nl_pid, get_xdp_id, &xdp_id);
-	if (!ret)
+	if (!ret) {
 		*prog_id = xdp_id.id;
 
+		if (chain_map_id)
+			*chain_map_id = xdp_id.chain_map_id;
+	}
+
 	close(sock);
 	return ret;
 }
 
+int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
+{
+	return __bpf_get_link_xdp_id(ifindex, prog_id, NULL, flags);
+}
+
+int bpf_get_link_xdp_chain(int ifindex, __u32 *prog_id, __u32 *chain_map_id,
+			   __u32 flags)
+{
+	return __bpf_get_link_xdp_id(ifindex, prog_id, chain_map_id, flags);
+}
+
 int libbpf_nl_get_link(int sock, unsigned int nl_pid,
 		       libbpf_dump_nlmsg_t dump_link_nlmsg, void *cookie)
 {