Merge branch 'bpf-xdp-sample-libbpf'

Maciej Fijalkowski says:

====================
This patchset tries to address the situation where:
* user loads a particular xdp sample application that does stats polling
* user loads another sample application on the same interface
* then, user sends SIGINT/SIGTERM to the app that was attached as a first one
* second application ends up with an unloaded xdp program

1st patch contains a helper libbpf function for getting the map fd by a
given map name.
In patch 2 Jesper removes the read_trace_pipe usage from xdp_redirect_cpu which
was a blocker for converting this sample to libbpf usage.
3rd patch updates a bunch of xdp samples to make the use of libbpf.
Patch 4 adjusts RLIMIT_MEMLOCK for two samples touched in this patchset.
In patch 5 extack messages are added for cases where dev_change_xdp_fd returns
with an error so user has an idea what was the reason for not attaching the
xdp program onto interface.
Patch 6 makes the samples behavior similar to what iproute2 does when loading
xdp prog - the "force" flag is introduced.
Patch 7 introduces the libbpf function that will query the driver from
userspace about the currently attached xdp prog id.

Use it in samples that do polling by checking the prog id in signal handler
and comparing it with previously stored one which is the scope of patch 8.

Thanks!

v1->v2:
* add a libbpf helper for getting a prog via relative index
* include xdp_redirect_cpu into conversion

v2->v3: mostly addressing Daniel's/Jesper's comments
* get rid of the helper from v1->v2
* feed the xdp_redirect_cpu with program name instead of number

v3->v4:
* fix help message in xdp_sample_pkts

v4->v5:
* in get_link_xdp_fd, assign prog_id only when libbpf_nl_get_link returned
  with 0
* add extack messages in dev_change_xdp_fd
* check the return value of bpf_get_link_xdp_id when exiting from sample progs

v5->v6:
* rebase
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

4 files changed, 97 insertions, 0 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2ccde17957e6..03bc01ca2577 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2884,6 +2884,12 @@ bpf_object__find_map_by_name(struct bpf_object *obj, const char *name)
 	return NULL;
 }
 
+int
+bpf_object__find_map_fd_by_name(struct bpf_object *obj, const char *name)
+{
+	return bpf_map__fd(bpf_object__find_map_by_name(obj, name));
+}
+
 struct bpf_map *
 bpf_object__find_map_by_offset(struct bpf_object *obj, size_t offset)
 {
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 62ae6cb93da1..43c77e98df6f 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -264,6 +264,9 @@ struct bpf_map;
 LIBBPF_API struct bpf_map *
 bpf_object__find_map_by_name(struct bpf_object *obj, const char *name);
 
+LIBBPF_API int
+bpf_object__find_map_fd_by_name(struct bpf_object *obj, const char *name);
+
 /*
  * Get bpf_map through the offset of corresponding struct bpf_map_def
  * in the BPF object file.
@@ -314,6 +317,7 @@ 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_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags);
 
 enum bpf_perf_event_ret {
 	LIBBPF_PERF_EVENT_DONE	= 0,
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index f6f96fc38c50..62c680fb13d1 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -131,4 +131,6 @@ LIBBPF_0.0.2 {
 		bpf_probe_map_type;
 		bpf_probe_prog_type;
 		bpf_map_lookup_elem_flags;
+		bpf_object__find_map_fd_by_name;
+		bpf_get_link_xdp_id;
 } LIBBPF_0.0.1;
diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 0ce67aea8f3b..ce3ec81b71c0 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -21,6 +21,12 @@
 typedef int (*__dump_nlmsg_t)(struct nlmsghdr *nlmsg, libbpf_dump_nlmsg_t,
 			      void *cookie);
 
+struct xdp_id_md {
+	int ifindex;
+	__u32 flags;
+	__u32 id;
+};
+
 int libbpf_netlink_open(__u32 *nl_pid)
 {
 	struct sockaddr_nl sa;
@@ -196,6 +202,85 @@ static int __dump_link_nlmsg(struct nlmsghdr *nlh,
 	return dump_link_nlmsg(cookie, ifi, tb);
 }
 
+static unsigned char get_xdp_id_attr(unsigned char mode, __u32 flags)
+{
+	if (mode != XDP_ATTACHED_MULTI)
+		return IFLA_XDP_PROG_ID;
+	if (flags & XDP_FLAGS_DRV_MODE)
+		return IFLA_XDP_DRV_PROG_ID;
+	if (flags & XDP_FLAGS_HW_MODE)
+		return IFLA_XDP_HW_PROG_ID;
+	if (flags & XDP_FLAGS_SKB_MODE)
+		return IFLA_XDP_SKB_PROG_ID;
+
+	return IFLA_XDP_UNSPEC;
+}
+
+static int get_xdp_id(void *cookie, void *msg, struct nlattr **tb)
+{
+	struct nlattr *xdp_tb[IFLA_XDP_MAX + 1];
+	struct xdp_id_md *xdp_id = cookie;
+	struct ifinfomsg *ifinfo = msg;
+	unsigned char mode, xdp_attr;
+	int ret;
+
+	if (xdp_id->ifindex && xdp_id->ifindex != ifinfo->ifi_index)
+		return 0;
+
+	if (!tb[IFLA_XDP])
+		return 0;
+
+	ret = libbpf_nla_parse_nested(xdp_tb, IFLA_XDP_MAX, tb[IFLA_XDP], NULL);
+	if (ret)
+		return ret;
+
+	if (!xdp_tb[IFLA_XDP_ATTACHED])
+		return 0;
+
+	mode = libbpf_nla_getattr_u8(xdp_tb[IFLA_XDP_ATTACHED]);
+	if (mode == XDP_ATTACHED_NONE)
+		return 0;
+
+	xdp_attr = get_xdp_id_attr(mode, xdp_id->flags);
+	if (!xdp_attr || !xdp_tb[xdp_attr])
+		return 0;
+
+	xdp_id->id = libbpf_nla_getattr_u32(xdp_tb[xdp_attr]);
+
+	return 0;
+}
+
+int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
+{
+	struct xdp_id_md xdp_id = {};
+	int sock, ret;
+	__u32 nl_pid;
+	__u32 mask;
+
+	if (flags & ~XDP_FLAGS_MASK)
+		return -EINVAL;
+
+	/* Check whether the single {HW,DRV,SKB} mode is set */
+	flags &= (XDP_FLAGS_SKB_MODE | XDP_FLAGS_DRV_MODE | XDP_FLAGS_HW_MODE);
+	mask = flags - 1;
+	if (flags && flags & mask)
+		return -EINVAL;
+
+	sock = libbpf_netlink_open(&nl_pid);
+	if (sock < 0)
+		return sock;
+
+	xdp_id.ifindex = ifindex;
+	xdp_id.flags = flags;
+
+	ret = libbpf_nl_get_link(sock, nl_pid, get_xdp_id, &xdp_id);
+	if (!ret)
+		*prog_id = xdp_id.id;
+
+	close(sock);
+	return ret;
+}
+
 int libbpf_nl_get_link(int sock, unsigned int nl_pid,
 		       libbpf_dump_nlmsg_t dump_link_nlmsg, void *cookie)
 {