btrfs-progs: check: lowmem: Add ability to repair dir item with mismatched hash

For DIR_ITEM with mismatch hash, we could just remove the offending dir
item from the tree.

Lowmem mode will handle the rest, either re-create the correct dir_item
or move the orphan inode to lost+found.

This is especially important for old filesystems, since later kernel
introduces stricter tree-checker, which could detect such hash mismatch
and refuse to read the corrupted leaf.

With this repair ability, user could repair with 'btrfs check
--mode=lowmem --repair'.

Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1111991
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

check/mode-common.c

@@ -744,3 +744,54 @@ void cleanup_excluded_extents(struct btrfs_fs_info *fs_info)
 	}
 	fs_info->excluded_extents = NULL;
 }
+
+/*
+ * Delete one corrupted dir item whose hash doesn't match its name.
+ *
+ * Since its hash is incorrect, we can't use btrfs_name_hash() to calculate
+ * the search key, but rely on @di_key parameter to do the search.
+ */
+int delete_corrupted_dir_item(struct btrfs_trans_handle *trans,
+			      struct btrfs_root *root,
+			      struct btrfs_key *di_key, char *namebuf,
+			      u32 namelen)
+{
+	struct btrfs_dir_item *di_item;
+	struct btrfs_path path;
+	int ret;
+
+	btrfs_init_path(&path);
+	ret = btrfs_search_slot(trans, root, di_key, &path, 0, 1);
+	if (ret > 0) {
+		error("key (%llu %u %llu) doesn't exist in root %llu",
+			di_key->objectid, di_key->type, di_key->offset,
+			root->root_key.objectid);
+		ret = -ENOENT;
+		goto out;
+	}
+	if (ret < 0) {
+		error("failed to search root %llu: %d",
+			root->root_key.objectid, ret);
+		goto out;
+	}
+
+	di_item = btrfs_match_dir_item_name(root, &path, namebuf, namelen);
+	if (!di_item) {
+		/*
+		 * This is possible if the dir_item has incorrect namelen.
+		 * But in that case, we shouldn't reach repair path here.
+		 */
+		error("no dir item named '%s' found with key (%llu %u %llu)",
+			namebuf, di_key->objectid, di_key->type,
+			di_key->offset);
+		ret = -ENOENT;
+		goto out;
+	}
+	ret = btrfs_delete_one_dir_name(trans, root, &path, di_item);
+	if (ret < 0)
+		error("failed to delete one dir name: %d", ret);
+
+out:
+	btrfs_release_path(&path);
+	return ret;
+}

check/mode-common.h

@@ -121,5 +121,9 @@ void reset_cached_block_groups(struct btrfs_fs_info *fs_info);
 int pin_metadata_blocks(struct btrfs_fs_info *fs_info);
 int exclude_metadata_blocks(struct btrfs_fs_info *fs_info);
 void cleanup_excluded_extents(struct btrfs_fs_info *fs_info);
+int delete_corrupted_dir_item(struct btrfs_trans_handle *trans,
+			      struct btrfs_root *root,
+			      struct btrfs_key *di_key, char *namebuf,
+			      u32 namelen);
 
 #endif

check/mode-lowmem.c

@@ -1473,17 +1473,53 @@ out:
 	return ret;
 }
 
+/*
+ * A wrapper for delete_corrupted_dir_item(), with support part like
+ * start/commit transaction.
+ */
+static int lowmem_delete_corrupted_dir_item(struct btrfs_root *root,
+					    struct btrfs_key *di_key,
+					    char *namebuf, u32 name_len)
+{
+	struct btrfs_trans_handle *trans;
+	int ret;
+
+	trans = btrfs_start_transaction(root, 1);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		error("failed to start transaction: %d", ret);
+		return ret;
+	}
+
+	ret = delete_corrupted_dir_item(trans, root, di_key, namebuf, name_len);
+	if (ret < 0) {
+		btrfs_abort_transaction(trans, ret);
+	} else {
+		ret = btrfs_commit_transaction(trans, root);
+		if (ret < 0)
+			error("failed to commit transaction: %d", ret);
+	}
+	return ret;
+}
+
 /*
  * Call repair_inode_item_missing and repair_ternary_lowmem to repair
  *
  * Returns error after repair
  */
-static int repair_dir_item(struct btrfs_root *root, u64 dirid, u64 ino,
+static int repair_dir_item(struct btrfs_root *root, struct btrfs_key *di_key,
-			   u64 index, u8 filetype, char *namebuf, u32 name_len,
+			   u64 ino, u64 index, u8 filetype, char *namebuf,
-			   int err)
+			   u32 name_len, int err)
 {
+	u64 dirid = di_key->objectid;
 	int ret;
 
+	if (err & (DIR_ITEM_HASH_MISMATCH)) {
+		ret = lowmem_delete_corrupted_dir_item(root, di_key, namebuf,
+						       name_len);
+		if (!ret)
+			err &= ~(DIR_ITEM_HASH_MISMATCH);
+	}
 	if (err & INODE_ITEM_MISSING) {
 		ret = repair_inode_item_missing(root, ino, filetype);
 		if (!ret)
@@ -1631,11 +1667,12 @@ begin:
 
 		if (di_key->type == BTRFS_DIR_ITEM_KEY &&
 		    di_key->offset != btrfs_name_hash(namebuf, len)) {
-			err |= -EIO;
 			error("root %llu DIR_ITEM[%llu %llu] name %s namelen %u filetype %u mismatch with its hash, wanted %llu have %llu",
 			root->objectid, di_key->objectid, di_key->offset,
 			namebuf, len, filetype, di_key->offset,
 			btrfs_name_hash(namebuf, len));
+			tmp_err |= DIR_ITEM_HASH_MISMATCH;
+			goto next;
 		}
 
 		btrfs_dir_item_key_to_cpu(node, di, &location);
@@ -1683,7 +1720,7 @@ begin:
 next:
 
 		if (tmp_err && repair) {
-			ret = repair_dir_item(root, di_key->objectid,
+			ret = repair_dir_item(root, di_key,
 					      location.objectid, index,
 					      imode_to_type(mode), namebuf,
 					      name_len, tmp_err);

check/mode-lowmem.h

@@ -45,6 +45,7 @@
 #define BG_ACCOUNTING_ERROR     (1<<21) /* Block group accounting error */
 #define FATAL_ERROR             (1<<22) /* Fatal bit for errno */
 #define INODE_FLAGS_ERROR	(1<<23) /* Invalid inode flags */
+#define DIR_ITEM_HASH_MISMATCH	(1<<24) /* Dir item hash mismatch */
 
 /*
  * Error bit for low memory mode check.

ctree.h

@@ -2722,6 +2722,10 @@ int btrfs_insert_xattr_item(struct btrfs_trans_handle *trans,
 			    struct btrfs_root *root, const char *name,
 			    u16 name_len, const void *data, u16 data_len,
 			    u64 dir);
+struct btrfs_dir_item *btrfs_match_dir_item_name(struct btrfs_root *root,
+			      struct btrfs_path *path,
+			      const char *name, int name_len);
+
 /* inode-map.c */
 int btrfs_find_free_objectid(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *fs_root,

dir-item.c

@@ -22,10 +22,6 @@
 #include "hash.h"
 #include "transaction.h"
 
-static struct btrfs_dir_item *btrfs_match_dir_item_name(struct btrfs_root *root,
-			      struct btrfs_path *path,
-			      const char *name, int name_len);
-
 static struct btrfs_dir_item *insert_with_overflow(struct btrfs_trans_handle
 						   *trans,
 						   struct btrfs_root *root,
@@ -323,7 +319,7 @@ static int verify_dir_item(struct btrfs_root *root,
 	return 0;
 }
 
-static struct btrfs_dir_item *btrfs_match_dir_item_name(struct btrfs_root *root,
+struct btrfs_dir_item *btrfs_match_dir_item_name(struct btrfs_root *root,
 			      struct btrfs_path *path,
 			      const char *name, int name_len)
 {