tools: bpftool: add probes for a network device

bpftool gained support for probing the current system in order to see
what program and map types, and what helpers are available on that
system. This patch adds the possibility to pass an interface index to
libbpf (and hence to the kernel) when trying to load the programs or to
create the maps, in order to see what items a given network device can
support.

A new keyword "dev <ifname>" can be used as an alternative to "kernel"
to indicate that the given device should be tested. If no target ("dev"
or "kernel") is specified bpftool defaults to probing the kernel.

Sample output:

    # bpftool -p feature probe dev lo
    {
        "syscall_config": {
            "have_bpf_syscall": true
        },
        "program_types": {
            "have_sched_cls_prog_type": false,
            "have_xdp_prog_type": false
        },
        ...
    }

As the target is a network device, /proc/ parameters and kernel
configuration are NOT dumped. Availability of the bpf() syscall is
still probed, so we can return early if that syscall is not usable
(since there is no point in attempting the remaining probes in this
case).

Among the program types, only the ones that can be offloaded are probed.
All map types are probed, as there is no specific rule telling which one
could or could not be supported by a device in the future. All helpers
are probed (but only for offload-able program types).

Caveat: as bpftool does not attempt to attach programs to the device at
the moment, probes do not entirely reflect what the device accepts:
typically, for Netronome's nfp, results will announce that TC cls
offload is available even if support has been deactivated (with e.g.
ethtool -K eth1 hw-tc-offload off).

v2:
- All helpers are probed, whereas previous version would only probe the
  ones compatible with an offload-able program type. This is because we
  do not keep a default compatible program type for each helper anymore.
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/Documentation/bpftool-feature.rst

@@ -19,14 +19,18 @@ SYNOPSIS
 MAP COMMANDS
 =============
 
-|	**bpftool** **feature probe** [**kernel**] [**macros** [**prefix** *PREFIX*]]
+|	**bpftool** **feature probe** [*COMPONENT*] [**macros** [**prefix** *PREFIX*]]
 |	**bpftool** **feature help**
+|
+|	*COMPONENT* := { **kernel** | **dev** *NAME* }
 
 DESCRIPTION
 ===========
 	**bpftool feature probe** [**kernel**] [**macros** [**prefix** *PREFIX*]]
 		  Probe the running kernel and dump a number of eBPF-related
-		  parameters, such as availability of the **bpf()** system call.
+		  parameters, such as availability of the **bpf()** system call,
+		  JIT status, eBPF program types availability, eBPF helper
+		  functions availability, and more.
 
 		  If the **macros** keyword (but not the **-j** option) is
 		  passed, a subset of the output is dumped as a list of
@@ -37,12 +41,20 @@ DESCRIPTION
 		  avoid conflicts on macro names when including the output of
 		  this command as a header file.
 
-		  Keyword **kernel** can be omitted.
+		  Keyword **kernel** can be omitted. If no probe target is
+		  specified, probing the kernel is the default behaviour.
 
 		  Note that when probed, some eBPF helpers (e.g.
 		  **bpf_trace_printk**\ () or **bpf_probe_write_user**\ ()) may
 		  print warnings to kernel logs.
 
+	**bpftool feature probe dev** *NAME* [**macros** [**prefix** *PREFIX*]]
+		  Probe network device for supported eBPF features and dump
+		  results to the console.
+
+		  The two keywords **macros** and **prefix** have the same
+		  role as when probing the kernel.
+
 	**bpftool feature help**
 		  Print short help message.
 

tools/bpf/bpftool/feature.c

@@ -5,6 +5,7 @@
 #include <errno.h>
 #include <string.h>
 #include <unistd.h>
+#include <net/if.h>
 #include <sys/utsname.h>
 #include <sys/vfs.h>
 
@@ -23,6 +24,7 @@
 enum probe_component {
 	COMPONENT_UNSPEC,
 	COMPONENT_KERNEL,
+	COMPONENT_DEVICE,
 };
 
 #define BPF_HELPER_MAKE_ENTRY(name)	[BPF_FUNC_ ## name] = "bpf_" # name
@@ -456,14 +458,24 @@ static bool probe_bpf_syscall(const char *define_prefix)
 
 static void
 probe_prog_type(enum bpf_prog_type prog_type, bool *supported_types,
-		const char *define_prefix)
+		const char *define_prefix, __u32 ifindex)
 {
 	char feat_name[128], plain_desc[128], define_name[128];
 	const char *plain_comment = "eBPF program_type ";
 	size_t maxlen;
 	bool res;
 
-	res = bpf_probe_prog_type(prog_type, 0);
+	if (ifindex)
+		/* Only test offload-able program types */
+		switch (prog_type) {
+		case BPF_PROG_TYPE_SCHED_CLS:
+		case BPF_PROG_TYPE_XDP:
+			break;
+		default:
+			return;
+		}
+
+	res = bpf_probe_prog_type(prog_type, ifindex);
 
 	supported_types[prog_type] |= res;
 
@@ -482,14 +494,15 @@ probe_prog_type(enum bpf_prog_type prog_type, bool *supported_types,
 }
 
 static void
-probe_map_type(enum bpf_map_type map_type, const char *define_prefix)
+probe_map_type(enum bpf_map_type map_type, const char *define_prefix,
+	       __u32 ifindex)
 {
 	char feat_name[128], plain_desc[128], define_name[128];
 	const char *plain_comment = "eBPF map_type ";
 	size_t maxlen;
 	bool res;
 
-	res = bpf_probe_map_type(map_type, 0);
+	res = bpf_probe_map_type(map_type, ifindex);
 
 	maxlen = sizeof(plain_desc) - strlen(plain_comment) - 1;
 	if (strlen(map_type_name[map_type]) > maxlen) {
@@ -507,13 +520,23 @@ probe_map_type(enum bpf_map_type map_type, const char *define_prefix)
 
 static void
 probe_helpers_for_progtype(enum bpf_prog_type prog_type, bool supported_type,
-			   const char *define_prefix)
+			   const char *define_prefix, __u32 ifindex)
 {
 	const char *ptype_name = prog_type_name[prog_type];
 	char feat_name[128];
 	unsigned int id;
 	bool res;
 
+	if (ifindex)
+		/* Only test helpers for offload-able program types */
+		switch (prog_type) {
+		case BPF_PROG_TYPE_SCHED_CLS:
+		case BPF_PROG_TYPE_XDP:
+			break;
+		default:
+			return;
+		}
+
 	if (json_output) {
 		sprintf(feat_name, "%s_available_helpers", ptype_name);
 		jsonw_name(json_wtr, feat_name);
@@ -527,7 +550,7 @@ probe_helpers_for_progtype(enum bpf_prog_type prog_type, bool supported_type,
 		if (!supported_type)
 			res = false;
 		else
-			res = bpf_probe_helper(id, prog_type, 0);
+			res = bpf_probe_helper(id, prog_type, ifindex);
 
 		if (json_output) {
 			if (res)
@@ -553,7 +576,9 @@ static int do_probe(int argc, char **argv)
 	enum probe_component target = COMPONENT_UNSPEC;
 	const char *define_prefix = NULL;
 	bool supported_types[128] = {};
+	__u32 ifindex = 0;
 	unsigned int i;
+	char *ifname;
 
 	/* Detection assumes user has sufficient privileges (CAP_SYS_ADMIN).
 	 * Let's approximate, and restrict usage to root user only.
@@ -573,6 +598,24 @@ static int do_probe(int argc, char **argv)
 			}
 			target = COMPONENT_KERNEL;
 			NEXT_ARG();
+		} else if (is_prefix(*argv, "dev")) {
+			NEXT_ARG();
+
+			if (target != COMPONENT_UNSPEC || ifindex) {
+				p_err("component to probe already specified");
+				return -1;
+			}
+			if (!REQ_ARGS(1))
+				return -1;
+
+			target = COMPONENT_DEVICE;
+			ifname = GET_ARG();
+			ifindex = if_nametoindex(ifname);
+			if (!ifindex) {
+				p_err("unrecognized netdevice '%s': %s", ifname,
+				      strerror(errno));
+				return -1;
+			}
 		} else if (is_prefix(*argv, "macros") && !define_prefix) {
 			define_prefix = "";
 			NEXT_ARG();
@@ -591,7 +634,7 @@ static int do_probe(int argc, char **argv)
 				return -1;
 			define_prefix = GET_ARG();
 		} else {
-			p_err("expected no more arguments, 'kernel', 'macros' or 'prefix', got: '%s'?",
+			p_err("expected no more arguments, 'kernel', 'dev', 'macros' or 'prefix', got: '%s'?",
 			      *argv);
 			return -1;
 		}
@@ -627,6 +670,8 @@ static int do_probe(int argc, char **argv)
 		else
 			printf("\n");
 		break;
+	default:
+		break;
 	}
 
 	print_start_section("syscall_config",
@@ -644,7 +689,7 @@ static int do_probe(int argc, char **argv)
 				     define_prefix);
 
 	for (i = BPF_PROG_TYPE_UNSPEC + 1; i < ARRAY_SIZE(prog_type_name); i++)
-		probe_prog_type(i, supported_types, define_prefix);
+		probe_prog_type(i, supported_types, define_prefix, ifindex);
 
 	print_end_then_start_section("map_types",
 				     "Scanning eBPF map types...",
@@ -652,7 +697,7 @@ static int do_probe(int argc, char **argv)
 				     define_prefix);
 
 	for (i = BPF_MAP_TYPE_UNSPEC + 1; i < map_type_name_size; i++)
-		probe_map_type(i, define_prefix);
+		probe_map_type(i, define_prefix, ifindex);
 
 	print_end_then_start_section("helpers",
 				     "Scanning eBPF helper functions...",
@@ -676,7 +721,7 @@ static int do_probe(int argc, char **argv)
 		       define_prefix);
 	for (i = BPF_PROG_TYPE_UNSPEC + 1; i < ARRAY_SIZE(prog_type_name); i++)
 		probe_helpers_for_progtype(i, supported_types[i],
-					   define_prefix);
+					   define_prefix, ifindex);
 
 exit_close_json:
 	if (json_output) {
@@ -697,8 +742,10 @@ static int do_help(int argc, char **argv)
 	}
 
 	fprintf(stderr,
-		"Usage: %s %s probe [kernel] [macros [prefix PREFIX]]\n"
+		"Usage: %s %s probe [COMPONENT] [macros [prefix PREFIX]]\n"
 		"       %s %s help\n"
+		"\n"
+		"       COMPONENT := { kernel | dev NAME }\n"
 		"",
 		bin_name, argv[-2], bin_name, argv[-2]);