bpftool: fix percpu maps updating

When updating a percpu map, bpftool currently copies the provided
value only into the first per CPU copy of the specified value,
all others instances are left zeroed.

This change explicitly copies the user-provided bytes to all the
per CPU instances, keeping the sub-command syntax unchanged.

v2 -> v3:
 - drop unused argument, as per Quentin's suggestion
v1 -> v2:
 - rename the helper as per Quentin's suggestion

Fixes: 71bb428f ("tools: bpf: add bpftool")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/map.c

@@ -347,6 +347,20 @@ static char **parse_bytes(char **argv, const char *name, unsigned char *val,
 	return argv + i;
 }
 
+/* on per cpu maps we must copy the provided value on all value instances */
+static void fill_per_cpu_value(struct bpf_map_info *info, void *value)
+{
+	unsigned int i, n, step;
+
+	if (!map_is_per_cpu(info->type))
+		return;
+
+	n = get_possible_cpus();
+	step = round_up(info->value_size, 8);
+	for (i = 1; i < n; i++)
+		memcpy(value + i * step, value, info->value_size);
+}
+
 static int parse_elem(char **argv, struct bpf_map_info *info,
 		      void *key, void *value, __u32 key_size, __u32 value_size,
 		      __u32 *flags, __u32 **value_fd)
@@ -426,6 +440,8 @@ static int parse_elem(char **argv, struct bpf_map_info *info,
 			argv = parse_bytes(argv, "value", value, value_size);
 			if (!argv)
 				return -1;
+
+			fill_per_cpu_value(info, value);
 		}
 
 		return parse_elem(argv, info, key, NULL, key_size, value_size,