samples/bpf: export map_data[] for more info on maps

Giving *_user.c side tools access to map_data[] provides easier
access to information on the maps being loaded.  Still provide
the guarantee that the order maps are being defined in inside the
_kern.c file corresponds with the order in the array.  Now user
tools are not blind, but can inspect and verify the maps that got
loaded from the ELF binary.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

samples/bpf/bpf_load.h

@@ -24,12 +24,18 @@ struct bpf_map_data {
 
 typedef void (*fixup_map_cb)(struct bpf_map_data *map, int idx);
 
-extern int map_fd[MAX_MAPS];
 extern int prog_fd[MAX_PROGS];
 extern int event_fd[MAX_PROGS];
 extern char bpf_log_buf[BPF_LOG_BUF_SIZE];
 extern int prog_cnt;
 
+/* There is a one-to-one mapping between map_fd[] and map_data[].
+ * The map_data[] just contains more rich info on the given map.
+ */
+extern int map_fd[MAX_MAPS];
+extern struct bpf_map_data map_data[MAX_MAPS];
+extern int map_data_count;
+
 /* parses elf file compiled by llvm .c->.o
  * . parses 'maps' section and creates maps via BPF syscall
  * . parses 'license' section and passes it to syscall