Avoid tree of tree root cow when committing a clean FS

The root node generation number code made commit_tree_root look like the
kernel code.  It forces a cow of the tree of tree roots even when
the FS hasn't changed.

This causes errors during fsck and other readonly operations.  This adds
a check to see if commit_tree_root is going to trigger writes to the
tree of tree roots, and bails if none are pending.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/disk-io.c b/disk-io.c
index 06815728..3caf3a03 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -293,6 +293,9 @@ static int commit_tree_roots(struct btrfs_trans_handle *trans,
 	struct list_head *next;
 	struct extent_buffer *eb;
 
+	if (fs_info->readonly)
+		return 0;
+
 	eb = fs_info->tree_root->node;
 	extent_buffer_get(eb);
 	btrfs_cow_block(trans, fs_info->tree_root, eb, NULL, 0, &eb);