5 files changed, 107 insertions, 2 deletions
diff --git a/tools/include/uapi/linux/if_link.h b/tools/include/uapi/linux/if_link.h
index 024af2d1d0af..b1ec7c949e6a 100644
--- a/tools/include/uapi/linux/if_link.h
+++ b/tools/include/uapi/linux/if_link.h
@@ -960,11 +960,12 @@ enum {
 #define XDP_FLAGS_SKB_MODE		(1U << 1)
 #define XDP_FLAGS_DRV_MODE		(1U << 2)
 #define XDP_FLAGS_HW_MODE		(1U << 3)
+#define XDP_FLAGS_REPLACE		(1U << 4)
 #define XDP_FLAGS_MODES			(XDP_FLAGS_SKB_MODE | \
 					 XDP_FLAGS_DRV_MODE | \
 					 XDP_FLAGS_HW_MODE)
 #define XDP_FLAGS_MASK			(XDP_FLAGS_UPDATE_IF_NOEXIST | \
-					 XDP_FLAGS_MODES)
+					 XDP_FLAGS_MODES | XDP_FLAGS_REPLACE)
 
 /* These are stored into IFLA_XDP_ATTACHED on dump. */
 enum {
@@ -984,6 +985,7 @@ enum {
 	IFLA_XDP_DRV_PROG_ID,
 	IFLA_XDP_SKB_PROG_ID,
 	IFLA_XDP_HW_PROG_ID,
+	IFLA_XDP_EXPECTED_FD,
 	__IFLA_XDP_MAX,
 };
 
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d38d7a629417..bf7a35a9556d 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -444,7 +444,15 @@ struct xdp_link_info {
 	__u8 attach_mode;
 };
 
+struct bpf_xdp_set_link_opts {
+	size_t sz;
+	__u32 old_fd;
+};
+#define bpf_xdp_set_link_opts__last_field old_fd
+
 LIBBPF_API int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags);
+LIBBPF_API int bpf_set_link_xdp_fd_opts(int ifindex, int fd, __u32 flags,
+					const struct bpf_xdp_set_link_opts *opts);
 LIBBPF_API int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags);
 LIBBPF_API int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
 				     size_t info_size, __u32 flags);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 5129283c0284..dcc87db3ca8a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -244,4 +244,5 @@ LIBBPF_0.0.8 {
 		bpf_link__pin_path;
 		bpf_link__unpin;
 		bpf_program__set_attach_target;
+		bpf_set_link_xdp_fd_opts;
 } LIBBPF_0.0.7;
diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 431bd25c6cdb..18b5319025e1 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -132,7 +132,8 @@ done:
 	return ret;
 }
 
-int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
+static int __bpf_set_link_xdp_fd_replace(int ifindex, int fd, int old_fd,
+					 __u32 flags)
 {
 	int sock, seq = 0, ret;
 	struct nlattr *nla, *nla_xdp;
@@ -178,6 +179,14 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
 		nla->nla_len += nla_xdp->nla_len;
 	}
 
+	if (flags & XDP_FLAGS_REPLACE) {
+		nla_xdp = (struct nlattr *)((char *)nla + nla->nla_len);
+		nla_xdp->nla_type = IFLA_XDP_EXPECTED_FD;
+		nla_xdp->nla_len = NLA_HDRLEN + sizeof(old_fd);
+		memcpy((char *)nla_xdp + NLA_HDRLEN, &old_fd, sizeof(old_fd));
+		nla->nla_len += nla_xdp->nla_len;
+	}
+
 	req.nh.nlmsg_len += NLA_ALIGN(nla->nla_len);
 
 	if (send(sock, &req, req.nh.nlmsg_len, 0) < 0) {
@@ -191,6 +200,29 @@ cleanup:
 	return ret;
 }
 
+int bpf_set_link_xdp_fd_opts(int ifindex, int fd, __u32 flags,
+			     const struct bpf_xdp_set_link_opts *opts)
+{
+	int old_fd = -1;
+
+	if (!OPTS_VALID(opts, bpf_xdp_set_link_opts))
+		return -EINVAL;
+
+	if (OPTS_HAS(opts, old_fd)) {
+		old_fd = OPTS_GET(opts, old_fd, -1);
+		flags |= XDP_FLAGS_REPLACE;
+	}
+
+	return __bpf_set_link_xdp_fd_replace(ifindex, fd,
+					     old_fd,
+					     flags);
+}
+
+int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
+{
+	return __bpf_set_link_xdp_fd_replace(ifindex, fd, 0, flags);
+}
+
 static int __dump_link_nlmsg(struct nlmsghdr *nlh,
 			     libbpf_dump_nlmsg_t dump_link_nlmsg, void *cookie)
 {
diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_attach.c b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
new file mode 100644
index 000000000000..05b294d6b923
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_attach.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+
+#define IFINDEX_LO 1
+#define XDP_FLAGS_REPLACE		(1U << 4)
+
+void test_xdp_attach(void)
+{
+	struct bpf_object *obj1, *obj2, *obj3;
+	const char *file = "./test_xdp.o";
+	int err, fd1, fd2, fd3;
+	__u32 duration = 0;
+	DECLARE_LIBBPF_OPTS(bpf_xdp_set_link_opts, opts,
+			    .old_fd = -1);
+
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj1, &fd1);
+	if (CHECK_FAIL(err))
+		return;
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj2, &fd2);
+	if (CHECK_FAIL(err))
+		goto out_1;
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj3, &fd3);
+	if (CHECK_FAIL(err))
+		goto out_2;
+
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, fd1, XDP_FLAGS_REPLACE,
+				       &opts);
+	if (CHECK(err, "load_ok", "initial load failed"))
+		goto out_close;
+
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, fd2, XDP_FLAGS_REPLACE,
+				       &opts);
+	if (CHECK(!err, "load_fail", "load with expected id didn't fail"))
+		goto out;
+
+	opts.old_fd = fd1;
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, fd2, 0, &opts);
+	if (CHECK(err, "replace_ok", "replace valid old_fd failed"))
+		goto out;
+
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, fd3, 0, &opts);
+	if (CHECK(!err, "replace_fail", "replace invalid old_fd didn't fail"))
+		goto out;
+
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, -1, 0, &opts);
+	if (CHECK(!err, "remove_fail", "remove invalid old_fd didn't fail"))
+		goto out;
+
+	opts.old_fd = fd2;
+	err = bpf_set_link_xdp_fd_opts(IFINDEX_LO, -1, 0, &opts);
+	if (CHECK(err, "remove_ok", "remove valid old_fd failed"))
+		goto out;
+
+out:
+	bpf_set_link_xdp_fd(IFINDEX_LO, -1, 0);
+out_close:
+	bpf_object__close(obj3);
+out_2:
+	bpf_object__close(obj2);
+out_1:
+	bpf_object__close(obj1);
+}