print parent ID in btrfs suvolume list

There was some discussion on "where" subvolumes live in. Why do we not
simply print the parent ID for each subvolume in btrfs subvolume list?
This patch adds this functionality when called with parameter "-p".

Signed-off-by: Andreas Philipp <philipp.andreas@gmail.com>
Signed-off-by: Hugo Mills <hugo@carfax.org.uk>

btrfs-list.c

@@ -200,9 +200,10 @@ static int add_root(struct root_lookup *root_lookup,
  * This can't be called until all the root_info->path fields are filled
  * in by lookup_ino_path
  */
-static int resolve_root(struct root_lookup *rl, struct root_info *ri)
+static int resolve_root(struct root_lookup *rl, struct root_info *ri, int print_parent)
 {
 	u64 top_id;
+	u64 parent_id = 0;
 	char *full_path = NULL;
 	int len = 0;
 	struct root_info *found;
@@ -233,6 +234,11 @@ static int resolve_root(struct root_lookup *rl, struct root_info *ri)
 		}
 
 		next = found->ref_tree;
+		/* record the first parent */
+		if ( parent_id == 0 ) {
+			parent_id = next;
+		}
+
 		/* if the ref_tree refers to ourselves, we're at the top */
 		if (next == found->root_id) {
 			top_id = next;
@@ -249,9 +255,15 @@ static int resolve_root(struct root_lookup *rl, struct root_info *ri)
 			break;
 		}
 	}
-	printf("ID %llu top level %llu path %s\n",
-	       (unsigned long long)ri->root_id, (unsigned long long)top_id,
-	       full_path);
+	if (print_parent) {
+		printf("ID %llu parent %llu top level %llu path %s\n",
+		       (unsigned long long)ri->root_id, (unsigned long long)parent_id, (unsigned long long)top_id,
+			full_path);
+	} else {
+		printf("ID %llu top level %llu path %s\n",
+		       (unsigned long long)ri->root_id, (unsigned long long)top_id,
+			full_path);
+	}
 	free(full_path);
 	return 0;
 }
@@ -549,7 +561,7 @@ build:
 	return full;
 }
 
-int list_subvols(int fd)
+int list_subvols(int fd, int print_parent)
 {
 	struct root_lookup root_lookup;
 	struct rb_node *n;
@@ -666,7 +678,7 @@ int list_subvols(int fd)
 	while (n) {
 		struct root_info *entry;
 		entry = rb_entry(n, struct root_info, rb_node);
-		resolve_root(&root_lookup, entry);
+		resolve_root(&root_lookup, entry, print_parent);
 		n = rb_prev(n);
 	}
 

btrfs.c

@@ -66,9 +66,11 @@ static struct Command commands[] = {
 		"not passed).",
 	  NULL
 	},
-	{ do_subvol_list, 1, "subvolume list", "<path>\n"
+	{ do_subvol_list, -1, "subvolume list", "[-p] <path>\n"
 		"List the snapshot/subvolume of a filesystem.",
-	  NULL
+		"[-p] <path>\n"
+		"List the snapshot/subvolume of a filesystem.\n"
+		"-p	   print parent ID"
 	},
 	{ do_set_default_subvol, 2,
 	  "subvolume set-default", "<id> <path>\n"

btrfs_cmds.c

@@ -302,9 +302,27 @@ int do_subvol_list(int argc, char **argv)
 {
 	int fd;
 	int ret;
+	int print_parent = 0;
 	char *subvol;
+        int optind = 1;
 
-	subvol = argv[1];
+	while(1) {
+		int c = getopt(argc, argv, "p");
+		if (c < 0) break;
+		switch(c) {
+		case 'p':
+			print_parent = 1;
+			optind++;
+			break;
+		}
+	}
+	
+	if (argc - optind != 1) {
+		fprintf(stderr, "ERROR: invalid arguments for subvolume list\n");
+		return 1;
+	}
+
+	subvol = argv[optind];
 
 	ret = test_issubvolume(subvol);
 	if (ret < 0) {
@@ -321,7 +339,7 @@ int do_subvol_list(int argc, char **argv)
 		fprintf(stderr, "ERROR: can't access '%s'\n", subvol);
 		return 12;
 	}
-	ret = list_subvols(fd);
+	ret = list_subvols(fd, print_parent);
 	if (ret)
 		return 19;
 	return 0;

btrfs_cmds.h

@@ -28,7 +28,7 @@ int do_scan(int nargs, char **argv);
 int do_resize(int nargs, char **argv);
 int do_subvol_list(int nargs, char **argv);
 int do_set_default_subvol(int nargs, char **argv);
-int list_subvols(int fd);
+int list_subvols(int fd, int print_parent);
 int do_df_filesystem(int nargs, char **argv);
 int find_updated_files(int fd, u64 root_id, u64 oldest_gen);
 int do_find_newer(int argc, char **argv);