btrfs-progs: dump-tree: add option to print children nodes of a given block

When debuging with "btrfs inspect dump-tree", it's not that handy if we
want to iterate all child tree blocks starting from a specified block.

-b can only print a single block, while without -b "btrfs inspect dump-tree"
will need extra tree roots fulfilled to continue, which is not possible
for a damaged filesystem.

Add a new option --follow to iterate a sub-tree starting from block
specified by --block.

Signed-off-by: Qu Wenruo <wqu@suse.com>
[ remove the short option for now ]
Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/btrfs-inspect-internal.asciidoc

@@ -87,6 +87,8 @@ the respective tree root block offset
 print only the uuid tree information, empty output if the tree does not exist
 -b <block_num>::::
 print info of the specified block only
+--follow::::
+use with '-b', print all children tree blocks of '<block_num>'
 -t <tree_id>::::
 print only the tree with the specified ID, where the ID can be numerical or
 common name in a flexible human readable form

cmds-inspect-dump-tree.c

@@ -198,6 +198,7 @@ const char * const cmd_inspect_dump_tree_usage[] = {
 	"-u|--uuid              print only the uuid tree",
 	"-b|--block <block_num> print info from the specified block only",
 	"-t|--tree <tree_id>    print only tree with the given id (string or number)",
+	"--follow               use with -b, to show all children tree blocks of <block_num>",
 	NULL
 };
 
@@ -223,9 +224,11 @@ int cmd_inspect_dump_tree(int argc, char **argv)
 	u64 block_only = 0;
 	struct btrfs_root *tree_root_scan;
 	u64 tree_id = 0;
+	bool follow = false;
 
 	while (1) {
 		int c;
+		enum { GETOPT_VAL_FOLLOW = 256 };
 		static const struct option long_options[] = {
 			{ "extents", no_argument, NULL, 'e'},
 			{ "device", no_argument, NULL, 'd'},
@@ -234,6 +237,7 @@ int cmd_inspect_dump_tree(int argc, char **argv)
 			{ "uuid", no_argument, NULL, 'u'},
 			{ "block", required_argument, NULL, 'b'},
 			{ "tree", required_argument, NULL, 't'},
+			{ "follow", no_argument, NULL, GETOPT_VAL_FOLLOW },
 			{ NULL, 0, NULL, 0 }
 		};
 
@@ -286,6 +290,9 @@ int cmd_inspect_dump_tree(int argc, char **argv)
 			}
 			break;
 			}
+		case GETOPT_VAL_FOLLOW:
+			follow = true;
+			break;
 		default:
 			usage(cmd_inspect_dump_tree_usage);
 		}
@@ -324,7 +331,7 @@ int cmd_inspect_dump_tree(int argc, char **argv)
 				(unsigned long long)block_only);
 			goto close_root;
 		}
-		btrfs_print_tree(root, leaf, 0);
+		btrfs_print_tree(root, leaf, follow);
 		free_extent_buffer(leaf);
 		goto close_root;
 	}