[iproute2,v8,2/3] ss: pretty-print BPF socket-local storage

Commit Message

Quentin Deslandes Feb. 14, 2024, 8:42 a.m. UTC

ss is able to print the map ID(s) for which a given socket has BPF
socket-local storage defined (using --bpf-maps or --bpf-map-id=). However,
the actual content of the map remains hidden.

This change aims to pretty-print the socket-local storage content following
the socket details, similar to what `bpftool map dump` would do. The exact
output format is inspired by drgn, while the BTF data processing is similar
to bpftool's.

ss will use libbpf's btf_dump__dump_type_data() to ease pretty-printing
of binary data. This requires out_bpf_sk_storage_print_fn() as a print
callback function used by btf_dump__dump_type_data(). vout() is also
introduced, which is similar to out() but accepts a va_list as
parameter.

ss' output remains unchanged unless --bpf-maps or --bpf-map-id= is used,
in which case each socket containing BPF local storage will be followed by
the content of the storage before the next socket's info is displayed.

Signed-off-by: Quentin Deslandes <[e-mail]>
Acked-by: Martin KaFai Lau <[e-mail]>
---
 misc/ss.c | 148 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 137 insertions(+), 11 deletions(-)

Patch

diff --git a/misc/ss.c b/misc/ss.c
index 7f47b489..73be95a5 100644
--- a/misc/ss.c
+++ b/misc/ss.c
@@ -53,7 +53,9 @@ 
 
 #ifdef HAVE_LIBBPF
 #include <bpf/bpf.h>
+#include <bpf/btf.h>
 #include <bpf/libbpf.h>
+#include <linux/btf.h>
 #endif
 
 #if HAVE_RPC
@@ -1039,11 +1041,10 @@  static int buf_update(int len)
 }
 
 /* Append content to buffer as part of the current field */
-__attribute__((format(printf, 1, 2)))
-static void out(const char *fmt, ...)
+static void vout(const char *fmt, va_list args)
 {
 	struct column *f = current_field;
-	va_list args;
+	va_list _args;
 	char *pos;
 	int len;
 
@@ -1054,18 +1055,27 @@  static void out(const char *fmt, ...)
 		buffer.head = buf_chunk_new();
 
 again:	/* Append to buffer: if we have a new chunk, print again */
+	va_copy(_args, args);
 
 	pos = buffer.cur->data + buffer.cur->len;
-	va_start(args, fmt);
 
 	/* Limit to tail room. If we hit the limit, buf_update() will tell us */
-	len = vsnprintf(pos, buf_chunk_avail(buffer.tail), fmt, args);
-	va_end(args);
+	len = vsnprintf(pos, buf_chunk_avail(buffer.tail), fmt, _args);
 
 	if (buf_update(len))
 		goto again;
 }
 
+__attribute__((format(printf, 1, 2)))
+static void out(const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	vout(fmt, args);
+	va_end(args);
+}
+
 static int print_left_spacing(struct column *f, int stored, int printed)
 {
 	int s;
@@ -3396,6 +3406,9 @@  static struct bpf_map_opts {
 	struct bpf_sk_storage_map_info {
 		unsigned int id;
 		int fd;
+		struct bpf_map_info info;
+		struct btf *btf;
+		struct btf_dump *dump;
 	} maps[MAX_NR_BPF_MAP_ID_OPTS];
 	bool show_all;
 } bpf_map_opts;
@@ -3406,10 +3419,36 @@  static void bpf_map_opts_mixed_error(void)
 		"ss: --bpf-maps and --bpf-map-id cannot be used together\n");
 }
 
+static int bpf_maps_opts_load_btf(struct bpf_map_info *info, struct btf **btf)
+{
+	if (info->btf_value_type_id) {
+		*btf = btf__load_from_kernel_by_id(info->btf_id);
+		if (!*btf) {
+			fprintf(stderr, "ss: failed to load BTF for map ID %u\n",
+				info->id);
+			return -1;
+		}
+	} else {
+		*btf = NULL;
+	}
+
+	return 0;
+}
+
+static void out_bpf_sk_storage_print_fn(void *ctx, const char *fmt, va_list args)
+{
+	vout(fmt, args);
+}
+
 static int bpf_map_opts_load_info(unsigned int map_id)
 {
+	struct btf_dump_opts dopts = {
+		.sz = sizeof(struct btf_dump_opts)
+	};
 	struct bpf_map_info info = {};
 	uint32_t len = sizeof(info);
+	struct btf_dump *dump;
+	struct btf *btf;
 	int fd;
 	int r;
 
@@ -3446,8 +3485,25 @@  static int bpf_map_opts_load_info(unsigned int map_id)
 		return -1;
 	}
 
+	r = bpf_maps_opts_load_btf(&info, &btf);
+	if (r) {
+		close(fd);
+		return -1;
+	}
+
+	dump = btf_dump__new(btf, out_bpf_sk_storage_print_fn, NULL, &dopts);
+	if (!dump) {
+		btf__free(btf);
+		close(fd);
+		fprintf(stderr, "Failed to create btf_dump object\n");
+		return -1;
+	}
+
 	bpf_map_opts.maps[bpf_map_opts.nr_maps].id = map_id;
-	bpf_map_opts.maps[bpf_map_opts.nr_maps++].fd = fd;
+	bpf_map_opts.maps[bpf_map_opts.nr_maps].fd = fd;
+	bpf_map_opts.maps[bpf_map_opts.nr_maps].info = info;
+	bpf_map_opts.maps[bpf_map_opts.nr_maps].btf = btf;
+	bpf_map_opts.maps[bpf_map_opts.nr_maps++].dump = dump;
 
 	return 0;
 }
@@ -3499,8 +3555,11 @@  static void bpf_map_opts_destroy(void)
 {
 	int i;
 
-	for (i = 0; i < bpf_map_opts.nr_maps; ++i)
+	for (i = 0; i < bpf_map_opts.nr_maps; ++i) {
+		btf_dump__free(bpf_map_opts.maps[i].dump);
+		btf__free(bpf_map_opts.maps[i].btf);
 		close(bpf_map_opts.maps[i].fd);
+	}
 }
 
 static struct rtattr *bpf_map_opts_alloc_rta(void)
@@ -3553,10 +3612,74 @@  static struct rtattr *bpf_map_opts_alloc_rta(void)
 	return stgs_rta;
 }
 
+static void out_bpf_sk_storage_oneline(struct bpf_sk_storage_map_info *info,
+	const void *data, size_t len)
+{
+	struct btf_dump_type_data_opts opts = {
+		.sz = sizeof(struct btf_dump_type_data_opts),
+		.emit_zeroes = 1,
+		.compact = 1
+	};
+	int r;
+
+	out(" map_id:%d", info->id);
+	r = btf_dump__dump_type_data(info->dump, info->info.btf_value_type_id,
+				     data, len, &opts);
+	if (r < 0)
+		out("failed to dump data: %d", r);
+}
+
+static void out_bpf_sk_storage_multiline(struct bpf_sk_storage_map_info *info,
+	const void *data, size_t len)
+{
+	struct btf_dump_type_data_opts opts = {
+		.sz = sizeof(struct btf_dump_type_data_opts),
+		.indent_level = 2,
+		.emit_zeroes = 1
+	};
+	int r;
+
+	out("\n\tmap_id:%d [\n", info->id);
+
+	r = btf_dump__dump_type_data(info->dump, info->info.btf_value_type_id,
+				     data, len, &opts);
+	if (r < 0)
+		out("\t\tfailed to dump data: %d", r);
+
+	out("\n\t]");
+}
+
+static void out_bpf_sk_storage(int map_id, const void *data, size_t len)
+{
+	struct bpf_sk_storage_map_info *map_info;
+
+	map_info = bpf_map_opts_get_info(map_id);
+	if (!map_info) {
+		/* The kernel might return a map we can't get info for, skip
+		 * it but print the other ones.
+		 */
+		out("\n\tmap_id: %d failed to fetch info, skipping\n", map_id);
+		return;
+	}
+
+	if (map_info->info.value_size != len) {
+		fprintf(stderr,
+			"map_id: %d: invalid value size, expecting %u, got %lu\n",
+			map_id, map_info->info.value_size, len);
+		return;
+	}
+
+	if (oneline)
+		out_bpf_sk_storage_oneline(map_info, data, len);
+	else
+		out_bpf_sk_storage_multiline(map_info, data, len);
+}
+
 static void show_sk_bpf_storages(struct rtattr *bpf_stgs)
 {
 	struct rtattr *tb[SK_DIAG_BPF_STORAGE_MAX + 1], *bpf_stg;
-	unsigned int rem;
+	unsigned int rem, map_id;
+	struct rtattr *value;
 
 	for (bpf_stg = RTA_DATA(bpf_stgs), rem = RTA_PAYLOAD(bpf_stgs);
 		RTA_OK(bpf_stg, rem); bpf_stg = RTA_NEXT(bpf_stg, rem)) {
@@ -3568,8 +3691,11 @@  static void show_sk_bpf_storages(struct rtattr *bpf_stgs)
 				    (struct rtattr *)bpf_stg);
 
 		if (tb[SK_DIAG_BPF_STORAGE_MAP_ID]) {
-			out(" map_id:%u",
-			    rta_getattr_u32(tb[SK_DIAG_BPF_STORAGE_MAP_ID]));
+			map_id = rta_getattr_u32(tb[SK_DIAG_BPF_STORAGE_MAP_ID]);
+			value = tb[SK_DIAG_BPF_STORAGE_MAP_VALUE];
+
+			out_bpf_sk_storage(map_id, RTA_DATA(value),
+					   RTA_PAYLOAD(value));
 		}
 	}
 }