[PATCH] Dump map id instead of value for map_of_maps types

[Xueming Feng]

When using `bpftool map dump` in plain format, it is usually
more convenient to show the inner map id instead of raw value.
Changing this behavior would help with quick debugging with
`bpftool`, without disruption scripted behavior. Since user
could dump the inner map with id, but need to convert value.

Signed-off-by: Xueming Feng <kuro@xxxxxxxx>
---
 tools/bpf/bpftool/main.c | 16 ++++++++++++++++
 tools/bpf/bpftool/main.h |  1 +
 tools/bpf/bpftool/map.c  |  9 +++++++--
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 08d0ac543c67..d297200c91f7 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -251,6 +251,22 @@ int detect_common_prefix(const char *arg, ...)
 	return 0;
 }
 
+void fprint_uint(FILE *f, void *arg, unsigned int n)
+{
+	unsigned char *data = arg;
+	unsigned int data_uint = 0;
+
+	for (unsigned int i = 0; i < n && i < 4; i++) {
+	#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+		data_uint |= data[i] << (i * 8);
+	#else
+		data_uint |= data[i] << ((n - i - 1) * 8);
+	#endif
+	}
+
+	fprintf(f, "%d", data_uint);
+}
+
 void fprint_hex(FILE *f, void *arg, unsigned int n, const char *sep)
 {
 	unsigned char *data = arg;
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index 0ef373cef4c7..7488ef38e7a9 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -90,6 +90,7 @@ void __printf(1, 2) p_info(const char *fmt, ...);
 
 bool is_prefix(const char *pfx, const char *str);
 int detect_common_prefix(const char *arg, ...);
+void fprint_uint(FILE *f, void *arg, unsigned int n);
 void fprint_hex(FILE *f, void *arg, unsigned int n, const char *sep);
 void usage(void) __noreturn;
 
diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index aaeb8939e137..638bd8de8135 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -259,8 +259,13 @@ static void print_entry_plain(struct bpf_map_info *info, unsigned char *key,
 		}
 
 		if (info->value_size) {
-			printf("value:%c", break_names ? '\n' : ' ');
-			fprint_hex(stdout, value, info->value_size, " ");
+			if (map_is_map_of_maps(info->type)) {
+				printf("id:%c", break_names ? '\n' : ' ');
+				fprint_uint(stdout, value, info->value_size);
+			} else {
+				printf("value:%c", break_names ? '\n' : ' ');
+				fprint_hex(stdout, value, info->value_size, " ");
+			}
 		}
 
 		printf("\n");
-- 
2.37.1 (Apple Git-137.1)