Btrfs: Add a clear_cache mount option

If something goes wrong with the free space cache we need a way to make sure
it's not loaded on mount and that it's cleared for everybody.  When you pass the
clear_cache option it will make it so all block groups are setup to be cleared,
which keeps them from being loaded and then they will be truncated when the
transaction is committed.  Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>

fs/btrfs/ctree.h

@@ -1229,6 +1229,7 @@ struct btrfs_root {
 #define BTRFS_MOUNT_DISCARD		(1 << 10)
 #define BTRFS_MOUNT_FORCE_COMPRESS      (1 << 11)
 #define BTRFS_MOUNT_SPACE_CACHE		(1 << 12)
+#define BTRFS_MOUNT_CLEAR_CACHE		(1 << 13)
 
 #define btrfs_clear_opt(o, opt)		((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)		((o) |= BTRFS_MOUNT_##opt)

fs/btrfs/extent-tree.c

@@ -8198,6 +8198,8 @@ int btrfs_read_block_groups(struct btrfs_root *root)
 	if (cache_gen != 0 &&
 	    btrfs_super_generation(&root->fs_info->super_copy) != cache_gen)
 		need_clear = 1;
+	if (btrfs_test_opt(root, CLEAR_CACHE))
+		need_clear = 1;
 
 	while (1) {
 		ret = find_first_block_group(root, path, &key);

fs/btrfs/free-space-cache.c

@@ -242,8 +242,6 @@ int load_free_space_cache(struct btrfs_fs_info *fs_info,
 	 */
 	spin_lock(&block_group->lock);
 	if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
-		printk(KERN_ERR "not reading block group %llu, dcs is %d\n", block_group->key.objectid,
-		       block_group->disk_cache_state);
 		spin_unlock(&block_group->lock);
 		return 0;
 	}

fs/btrfs/super.c

@@ -68,7 +68,7 @@ enum {
 	Opt_nodatacow, Opt_max_inline, Opt_alloc_start, Opt_nobarrier, Opt_ssd,
 	Opt_nossd, Opt_ssd_spread, Opt_thread_pool, Opt_noacl, Opt_compress,
 	Opt_compress_force, Opt_notreelog, Opt_ratio, Opt_flushoncommit,
-	Opt_discard, Opt_space_cache, Opt_err,
+	Opt_discard, Opt_space_cache, Opt_clear_cache, Opt_err,
 };
 
 static match_table_t tokens = {
@@ -93,6 +93,7 @@ static match_table_t tokens = {
 	{Opt_ratio, "metadata_ratio=%d"},
 	{Opt_discard, "discard"},
 	{Opt_space_cache, "space_cache"},
+	{Opt_clear_cache, "clear_cache"},
 	{Opt_err, NULL},
 };
 
@@ -239,6 +240,9 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 		case Opt_space_cache:
 			printk(KERN_INFO "btrfs: enabling disk space caching\n");
 			btrfs_set_opt(info->mount_opt, SPACE_CACHE);
+		case Opt_clear_cache:
+			printk(KERN_INFO "btrfs: force clearing of disk cache\n");
+			btrfs_set_opt(info->mount_opt, CLEAR_CACHE);
 			break;
 		case Opt_err:
 			printk(KERN_INFO "btrfs: unrecognized mount option "