btrfs-progs: add -P option to only list parent subvolumes

btrfs-list.c

@@ -1175,6 +1175,11 @@ static int filter_deleted(struct root_info *ri, u64 data)
 	return ri->deleted;
 }
 
+static int filter_parent_subvol_only(struct root_info *ri, u64 data)
+{
+	return uuid_is_null(ri->puuid);
+}
+
 static btrfs_list_filter_func all_filter_funcs[] = {
 	[BTRFS_LIST_FILTER_ROOTID]		= filter_by_rootid,
 	[BTRFS_LIST_FILTER_SNAPSHOT_ONLY]	= filter_snapshot,
@@ -1189,6 +1194,7 @@ static btrfs_list_filter_func all_filter_funcs[] = {
 	[BTRFS_LIST_FILTER_FULL_PATH]		= filter_full_path,
 	[BTRFS_LIST_FILTER_BY_PARENT]		= filter_by_parent,
 	[BTRFS_LIST_FILTER_DELETED]		= filter_deleted,
+	[BTRFS_LIST_FILTER_PARENT_SUBVOL_ONLY]	= filter_parent_subvol_only,
 };
 
 struct btrfs_list_filter_set *btrfs_list_alloc_filter_set(void)

btrfs-list.h

@@ -142,6 +142,7 @@ enum btrfs_list_filter_enum {
 	BTRFS_LIST_FILTER_FULL_PATH,
 	BTRFS_LIST_FILTER_BY_PARENT,
 	BTRFS_LIST_FILTER_DELETED,
+	BTRFS_LIST_FILTER_PARENT_SUBVOL_ONLY,
 	BTRFS_LIST_FILTER_MAX,
 };
 

cmds-subvolume.c

@@ -404,6 +404,7 @@ static const char * const cmd_subvol_list_usage[] = {
 	"-q           print the parent uuid of the snapshots",
 	"-R           print the uuid of the received snapshots",
 	"-t           print the result as a table",
+	"-P           list parent subvolumes only",
 	"-s           list snapshots only in the filesystem",
 	"-r           list readonly subvolumes (including snapshots)",
 	"-d           list deleted subvolumes that are not yet cleaned",
@@ -445,7 +446,7 @@ static int cmd_subvol_list(int argc, char **argv)
 		};
 
 		c = getopt_long(argc, argv,
-				    "acdgopqsurRG:C:t", long_options, NULL);
+				    "acdgopPqsurRG:C:t", long_options, NULL);
 		if (c < 0)
 			break;
 
@@ -473,6 +474,11 @@ static int cmd_subvol_list(int argc, char **argv)
 		case 't':
 			is_tab_result = 1;
 			break;
+		case 'P':
+			btrfs_list_setup_filter(&filter_set,
+						BTRFS_LIST_FILTER_PARENT_SUBVOL_ONLY,
+						0);
+			break;
 		case 's':
 			btrfs_list_setup_filter(&filter_set,
 						BTRFS_LIST_FILTER_SNAPSHOT_ONLY,