btrfs-progs: Allow open_ctree to return fs_info even chunk tree is corrupted

Current open_ctree_fs_info() won't return anything if chunk tree root is
corrupted.
This makes some function, like btrfs-find-root, unable to find any older
chunk tree root, even it is possible to use system_chunk_array in super
block.

And at least two users in mail list has reported such heavily chunk
corruption.
Although we have 'btrfs rescue chunk-recovery' but it's too time
consuming and sometimes not able to cope with a specific filesystem
corruption.

This patch adds a new open ctree flag,
OPEN_CTREE_IGNORE_CHUNK_TREE_ERROR, allowing fs_info to be returned from
open_ctree_fs_info() even there is no valid tree root in it.

Also adds a new close_ctree() variant, close_ctree_fs_info() to handle
possible fs_info without any root.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
[ adjusted error messages ]
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/disk-io.h b/disk-io.h
index d3e3aaac..c2eb1d6e 100644
--- a/disk-io.h
+++ b/disk-io.h
@@ -53,7 +53,15 @@ enum btrfs_open_ctree_flags {
 	 * Like split PARTIAL into SKIP_CSUM/SKIP_EXTENT
 	 */
 
-	OPEN_CTREE_IGNORE_FSID_MISMATCH	= (1 << 10)
+	OPEN_CTREE_IGNORE_FSID_MISMATCH	= (1 << 10),
+
+	/*
+	 * Allow open_ctree_fs_info() to return a incomplete fs_info with
+	 * system chunks from super block only.
+	 * It's useful for chunk corruption case.
+	 * Makes no sense for open_ctree variants returning btrfs_root.
+	 */
+	OPEN_CTREE_IGNORE_CHUNK_TREE_ERROR = (1 << 11)
 };
 
 static inline u64 btrfs_sb_offset(int mirror)
@@ -101,7 +109,13 @@ struct btrfs_root *open_ctree_fd(int fp, const char *path, u64 sb_bytenr,
 struct btrfs_fs_info *open_ctree_fs_info(const char *filename,
 					 u64 sb_bytenr, u64 root_tree_bytenr,
 					 enum btrfs_open_ctree_flags flags);
-int close_ctree(struct btrfs_root *root);
+int close_ctree_fs_info(struct btrfs_fs_info *fs_info);
+static inline int close_ctree(struct btrfs_root *root)
+{
+	BUG_ON(!root);
+	return close_ctree_fs_info(root->fs_info);
+}
+
 int write_all_supers(struct btrfs_root *root);
 int write_ctree_super(struct btrfs_trans_handle *trans,
 		      struct btrfs_root *root);