[v3,2/2] ss: pretty-print BPF socket-local storage

Commit Message

Quentin Deslandes Dec. 20, 2023, 1:23 p.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.

COL_SKSTOR's header is replaced with an empty string, as it doesn't need to
be printed anymore; it's used as a "virtual" column to refer to the
socket-local storage dump, which will be printed under the socket information.
The column's width is fixed to 1, so it doesn't mess up ss' output.

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]>
Reviewed-by: Alan Maguire <[e-mail]>
---
 misc/ss.c | 164 +++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 150 insertions(+), 14 deletions(-)

Comments

Martin KaFai Lau Jan. 3, 2024, 7:51 p.m. UTC | #1

On 12/20/23 5:23 AM, Quentin Deslandes wrote:
> diff --git a/misc/ss.c b/misc/ss.c
> index 689972d7..6e1ddfa5 100644
> --- a/misc/ss.c
> +++ b/misc/ss.c
> @@ -51,8 +51,13 @@
>   #include <linux/tls.h>
>   #include <linux/mptcp.h>
>   
> +#ifdef HAVE_LIBBPF
> +#include <linux/btf.h>

nit. Instead of adding another "#ifdef HAVE_LIBBPF", move this line to the same 
"#ifdef HAVE_LIBBPF" below?

> +#endif
> +
>   #ifdef HAVE_LIBBPF
>   #include <bpf/bpf.h>
> +#include <bpf/btf.h>
>   #include <bpf/libbpf.h>
>   #endif
>   

[ ... ]

> +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 int bpf_map_opts_add_all(void)
>   {
>   	unsigned int i;
> @@ -3418,6 +3452,7 @@ static int bpf_map_opts_add_all(void)
>   	while (1) {
>   		struct bpf_map_info info = {};
>   		uint32_t len = sizeof(info);
> +		struct btf *btf;
>   
>   		r = bpf_map_get_next_id(id, &id);
>   		if (r) {
> @@ -3462,8 +3497,18 @@ static int bpf_map_opts_add_all(void)
>   			continue;
>   		}
>   
> +		r = bpf_maps_opts_load_btf(&info, &btf);
> +		if (r) {
> +			fprintf(stderr, "ss: failed to get BTF data for BPF map ID: %u\n",
> +				id);

This will be a duplicated fprintf(stderr) with the bpf_maps_opts_load_btf() 
above. Remove either one of them.

The same goes for the bpf_map_opts_add_id().

[ ... ]

> +static void out_bpf_sk_storage(int map_id, const void *data, size_t len)
> +{
> +	uint32_t type_id;
> +	const struct bpf_sk_storage_map_info *map_info;
> +	struct btf_dump *dump;
> +	struct btf_dump_type_data_opts opts = {
> +		.sz = sizeof(struct btf_dump_type_data_opts),
> +		.indent_str = SK_STORAGE_INDENT_STR,
> +		.indent_level = 2,
> +		.emit_zeroes = 1
> +	};
> +	struct btf_dump_opts dopts = {
> +		.sz = sizeof(struct btf_dump_opts)
> +	};
> +	int r;
> +
> +	map_info = bpf_map_opts_get_info(map_id);
> +	if (!map_info) {
> +		fprintf(stderr, "map_id: %d: missing map info", map_id);

With the 'total_size = RTA_LENGTH(0)' change during show_all == true case in 
patch 1, this fprintf(stderr) should be removed. A new bpf_sk_storage_map has 
just been created after the ss has started which is fine to skip. The next ss 
run will be able to show it.

In the future, it could be improved to give it another try here to get the btf 
info of this new map on-demand.

> +		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;
> +	}
> +
> +	type_id = map_info->info.btf_value_type_id;
> +
> +	dump = btf_dump__new(map_info->btf, out_bpf_sk_storage_print_fn, NULL, &dopts);

nit. just noticed this one also. Instead of recreating the "dump" obj for each 
printed sk, can it be created once and stored in "struct bpf_sk_storage_map_info 
{ ... } maps[MAX_NR_BPF_MAP_ID_OPTS];"?

> +	if (!dump) {
> +		fprintf(stderr, "Failed to create btf_dump object\n");
> +		return;
> +	}
> +
> +	out(SK_STORAGE_INDENT_STR "map_id: %d [\n", map_id);
> +	r = btf_dump__dump_type_data(dump, type_id, data, len, &opts);
> +	if (r < 0)
> +		out(SK_STORAGE_INDENT_STR SK_STORAGE_INDENT_STR "failed to dump data: %d", r);
> +	out("\n" SK_STORAGE_INDENT_STR "]");
> +
> +	btf_dump__free(dump);
> +}
> +
>   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)) {
> @@ -3605,8 +3731,13 @@ 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]));
> +			out("\n");
> +
> +			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));
>   		}
>   	}
>   }
> @@ -6004,6 +6135,11 @@ int main(int argc, char *argv[])
>   		}
>   	}
>   
> +	if (oneline && (bpf_map_opts.nr_maps || bpf_map_opts.show_all)) {

This will not compile if HAVE_LIBBPF is not set. Please test with the 
HAVE_LIBBPF is false condition.

May be revisit my earlier suggestion to create a few helper functions here when 
HAVE_LIBBPF is not set instead of adding "#ifdef HAVE_LIBBPF" here. Something like:

#ifdef HAVE_LIBBPF
static bool bpf_map_opts_is_enabled(void)
{
         return bpf_map_opts.nr_maps;
}
#else
static bool bpf_map_opts_is_enabled(void)
{
         return false;
}
#endif


> +		fprintf(stderr, "ss: --oneline, --bpf-maps, and --bpf-map-id are incompatible\n");
> +		exit(-1);
> +	}
> +
>   	if (show_processes || show_threads || show_proc_ctx || show_sock_ctx)
>   		user_ent_hash_build();
>

Patch

diff --git a/misc/ss.c b/misc/ss.c
index 689972d7..6e1ddfa5 100644
--- a/misc/ss.c
+++ b/misc/ss.c
@@ -51,8 +51,13 @@ 
 #include <linux/tls.h>
 #include <linux/mptcp.h>
 
+#ifdef HAVE_LIBBPF
+#include <linux/btf.h>
+#endif
+
 #ifdef HAVE_LIBBPF
 #include <bpf/bpf.h>
+#include <bpf/btf.h>
 #include <bpf/libbpf.h>
 #endif
 
@@ -136,7 +141,7 @@  static struct column columns[] = {
 	{ ALIGN_RIGHT,	"Peer Address:",	" ",	0, 0, 0 },
 	{ ALIGN_LEFT,	"Port",			"",	0, 0, 0 },
 	{ ALIGN_LEFT,	"Process",		"",	0, 0, 0 },
-	{ ALIGN_LEFT,	"Socket storage",	"",	1, 0, 0 },
+	{ ALIGN_LEFT,	"",			"",	1, 0, 0 },
 	{ ALIGN_LEFT,	"",			"",	0, 0, 0 },
 };
 
@@ -1039,11 +1044,10 @@  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 +1058,27 @@  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;
@@ -1213,6 +1226,9 @@  static void render_calc_width(void)
 		 */
 		c->width = min(c->width, screen_width);
 
+		if (c == &columns[COL_SKSTOR])
+			c->width = 1;
+
 		if (c->width)
 			first = 0;
 	}
@@ -3392,6 +3408,8 @@  static struct bpf_map_opts {
 	struct bpf_sk_storage_map_info {
 		unsigned int id;
 		int fd;
+		struct bpf_map_info info;
+		struct btf *btf;
 	} maps[MAX_NR_BPF_MAP_ID_OPTS];
 	bool show_all;
 	struct btf *kernel_btf;
@@ -3403,6 +3421,22 @@  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 int bpf_map_opts_add_all(void)
 {
 	unsigned int i;
@@ -3418,6 +3452,7 @@  static int bpf_map_opts_add_all(void)
 	while (1) {
 		struct bpf_map_info info = {};
 		uint32_t len = sizeof(info);
+		struct btf *btf;
 
 		r = bpf_map_get_next_id(id, &id);
 		if (r) {
@@ -3462,8 +3497,18 @@  static int bpf_map_opts_add_all(void)
 			continue;
 		}
 
+		r = bpf_maps_opts_load_btf(&info, &btf);
+		if (r) {
+			fprintf(stderr, "ss: failed to get BTF data for BPF map ID: %u\n",
+				id);
+			close(fd);
+			goto err;
+		}
+
 		bpf_map_opts.maps[bpf_map_opts.nr_maps].id = 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.show_all = true;
@@ -3471,8 +3516,10 @@  static int bpf_map_opts_add_all(void)
 	return 0;
 
 err:
-	for (i = 0; i < bpf_map_opts.nr_maps; ++i)
+	for (i = 0; i < bpf_map_opts.nr_maps; ++i) {
 		close(bpf_map_opts.maps[i].fd);
+		btf__free(bpf_map_opts.maps[i].btf);
+	}
 
 	return -1;
 }
@@ -3482,6 +3529,7 @@  static int bpf_map_opts_add_id(const char *optarg)
 	struct bpf_map_info info = {};
 	uint32_t len = sizeof(info);
 	size_t optarg_len;
+	struct btf *btf;
 	unsigned long id;
 	unsigned int i;
 	char *end;
@@ -3539,8 +3587,18 @@  static int bpf_map_opts_add_id(const char *optarg)
 		return -1;
 	}
 
+	r = bpf_maps_opts_load_btf(&info, &btf);
+	if (r) {
+		fprintf(stderr, "ss: failed to get BTF data for BPF map ID: %lu\n",
+			id);
+		close(fd);
+		return -1;
+	}
+
 	bpf_map_opts.maps[bpf_map_opts.nr_maps].id = 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;
 
 	return 0;
 }
@@ -3549,8 +3607,23 @@  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__free(bpf_map_opts.maps[i].btf);
 		close(bpf_map_opts.maps[i].fd);
+	}
+}
+
+static const struct bpf_sk_storage_map_info *bpf_map_opts_get_info(
+	unsigned int map_id)
+{
+	unsigned int i;
+
+	for (i = 0; i < bpf_map_opts.nr_maps; ++i) {
+		if (bpf_map_opts.maps[i].id == map_id)
+			return &bpf_map_opts.maps[i];
+	}
+
+	return NULL;
 }
 
 static bool bpf_map_opts_is_enabled(void)
@@ -3590,10 +3663,63 @@  static struct rtattr *bpf_map_opts_alloc_rta(void)
 	return stgs_rta;
 }
 
+static void out_bpf_sk_storage_print_fn(void *ctx, const char *fmt, va_list args)
+{
+	vout(fmt, args);
+}
+
+#define SK_STORAGE_INDENT_STR "    "
+
+static void out_bpf_sk_storage(int map_id, const void *data, size_t len)
+{
+	uint32_t type_id;
+	const struct bpf_sk_storage_map_info *map_info;
+	struct btf_dump *dump;
+	struct btf_dump_type_data_opts opts = {
+		.sz = sizeof(struct btf_dump_type_data_opts),
+		.indent_str = SK_STORAGE_INDENT_STR,
+		.indent_level = 2,
+		.emit_zeroes = 1
+	};
+	struct btf_dump_opts dopts = {
+		.sz = sizeof(struct btf_dump_opts)
+	};
+	int r;
+
+	map_info = bpf_map_opts_get_info(map_id);
+	if (!map_info) {
+		fprintf(stderr, "map_id: %d: missing map info", 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;
+	}
+
+	type_id = map_info->info.btf_value_type_id;
+
+	dump = btf_dump__new(map_info->btf, out_bpf_sk_storage_print_fn, NULL, &dopts);
+	if (!dump) {
+		fprintf(stderr, "Failed to create btf_dump object\n");
+		return;
+	}
+
+	out(SK_STORAGE_INDENT_STR "map_id: %d [\n", map_id);
+	r = btf_dump__dump_type_data(dump, type_id, data, len, &opts);
+	if (r < 0)
+		out(SK_STORAGE_INDENT_STR SK_STORAGE_INDENT_STR "failed to dump data: %d", r);
+	out("\n" SK_STORAGE_INDENT_STR "]");
+
+	btf_dump__free(dump);
+}
+
 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)) {
@@ -3605,8 +3731,13 @@  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]));
+			out("\n");
+
+			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));
 		}
 	}
 }
@@ -6004,6 +6135,11 @@  int main(int argc, char *argv[])
 		}
 	}
 
+	if (oneline && (bpf_map_opts.nr_maps || bpf_map_opts.show_all)) {
+		fprintf(stderr, "ss: --oneline, --bpf-maps, and --bpf-map-id are incompatible\n");
+		exit(-1);
+	}
+
 	if (show_processes || show_threads || show_proc_ctx || show_sock_ctx)
 		user_ent_hash_build();