[PATCH v2 5/6] btrfs-progs: implement btrfs check --clear-space-cache v2

[Omar Sandoval <osandov@osandov.com>]

From: Omar Sandoval <osandov@fb.com>

Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 Documentation/btrfs-check.asciidoc | 14 +++++++++-----
 cmds-check.c                       | 34 +++++++++++++++++++++++++---------
 2 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/Documentation/btrfs-check.asciidoc b/Documentation/btrfs-check.asciidoc
index 5ef414e..633cbbf 100644
--- a/Documentation/btrfs-check.asciidoc
+++ b/Documentation/btrfs-check.asciidoc
@@ -80,12 +80,16 @@ superblock is damaged.
 
 --clear-space-cache v1|v2::
 completely wipe all free space cache of given type
-
-NOTE: Only v1 free space cache supported is implemented.
 +
-Kernel mount option 'clear_cache' is only designed to rebuild free space cache
-which is modified during the lifetime of that mount option.  It doesn't rebuild
-all free space cache, nor clear them out.
+For free space cache 'v1', the 'clear_cache' kernel mount option only rebuilds
+the free space cache for block groups that are modified while the filesystem is
+mounted with that option. Thus, using this option with 'v1' makes it possible
+to actually clear the entire free space cache.
++
+For free space cache 'v2', the 'clear_cache' kernel mount option does destroy
+the entire free space cache. This option with 'v2' provides an alternative
+method of clearing the free space cache that doesn't require mounting the
+filesystem.
 
 
 DANGEROUS OPTIONS
diff --git a/cmds-check.c b/cmds-check.c
index 57c4300..0eca102 100644
--- a/cmds-check.c
+++ b/cmds-check.c
@@ -11170,7 +11170,6 @@ const char * const cmd_check_usage[] = {
 	"--chunk-root <bytenr>       use the given bytenr for the chunk tree root",
 	"-p|--progress               indicate progress",
 	"--clear-space-cache v1|v2   clear space cache for v1 or v2",
-	"                            NOTE: v1 support implemented",
 	NULL
 };
 
@@ -11292,13 +11291,16 @@ int cmd_check(int argc, char **argv)
 				}
 				break;
 			case GETOPT_VAL_CLEAR_SPACE_CACHE:
-				if (strcmp(optarg, "v1") != 0) {
-					error(
-			"only v1 support implmented, unrecognized value %s",
-			optarg);
+				if (strcmp(optarg, "v1") == 0) {
+					clear_space_cache = 1;
+				} else if (strcmp(optarg, "v2") == 0) {
+					clear_space_cache = 2;
+					ctree_flags |= OPEN_CTREE_INVALIDATE_FST;
+				} else {
+					error("invalid argument to --clear-space-cache; "
+					      "must be v1 or v2");
 					exit(1);
 				}
-				clear_space_cache = 1;
 				ctree_flags |= OPEN_CTREE_WRITES;
 				break;
 		}
@@ -11352,11 +11354,10 @@ int cmd_check(int argc, char **argv)
 
 	global_info = info;
 	root = info->fs_root;
-	if (clear_space_cache) {
+	if (clear_space_cache == 1) {
 		if (btrfs_fs_compat_ro(info,
 				BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE)) {
-			error(
-			"free space cache v2 detected, clearing not implemented");
+			error("free space cache v2 detected; use --clear-space-cache v2");
 			ret = 1;
 			goto close_out;
 		}
@@ -11369,6 +11370,21 @@ int cmd_check(int argc, char **argv)
 			printf("Free space cache cleared\n");
 		}
 		goto close_out;
+	} else if (clear_space_cache == 2) {
+		if (!btrfs_fs_compat_ro(info, BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE)) {
+			printf("No free space cache v2 to clear\n");
+			ret = 0;
+			goto close_out;
+		}
+		printf("Clear free space cache v2\n");
+		ret = btrfs_clear_free_space_tree(info);
+		if (ret) {
+			error("Failed to clear free space cache v2");
+			ret = 1;
+		} else {
+			printf("Free space cache v2 cleared\n");
+		}
+		goto close_out;
 	}
 
 	/*
-- 
2.10.2