Btrfs: Update and fix mount -o nodatacow

To check whether a given file extent is referenced by multiple snapshots, the
checker walks down the fs tree through dead root and checks all tree blocks in
the path.

We can easily detect whether a given tree block is directly referenced by other
snapshot. We can also detect any indirect reference from other snapshot by
checking reference's generation. The checker can always detect multiple
references, but can't reliably detect cases of single reference. So btrfs may
do file data cow even there is only one reference.

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

1 files changed, 5 insertions, 11 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index b8be670..216f315 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -32,12 +32,6 @@ extern struct kmem_cache *btrfs_transaction_cachep;
 
 #define BTRFS_ROOT_TRANS_TAG 0
 
-struct dirty_root {
-	struct list_head list;
-	struct btrfs_root *root;
-	struct btrfs_root *latest_root;
-};
-
 static noinline void put_transaction(struct btrfs_transaction *transaction)
 {
 	WARN_ON(transaction->use_count == 0);
@@ -91,7 +85,7 @@ static noinline int join_transaction(struct btrfs_root *root)
 
 static noinline int record_root_in_trans(struct btrfs_root *root)
 {
-	struct dirty_root *dirty;
+	struct btrfs_dirty_root *dirty;
 	u64 running_trans_id = root->fs_info->running_transaction->transid;
 	if (root->ref_cows && root->last_trans < running_trans_id) {
 		WARN_ON(root == root->fs_info->extent_root);
@@ -372,7 +366,7 @@ int btrfs_add_dead_root(struct btrfs_root *root,
 			struct btrfs_root *latest,
 			struct list_head *dead_list)
 {
-	struct dirty_root *dirty;
+	struct btrfs_dirty_root *dirty;
 
 	dirty = kmalloc(sizeof(*dirty), GFP_NOFS);
 	if (!dirty)
@@ -387,7 +381,7 @@ static noinline int add_dirty_roots(struct btrfs_trans_handle *trans,
 				    struct radix_tree_root *radix,
 				    struct list_head *list)
 {
-	struct dirty_root *dirty;
+	struct btrfs_dirty_root *dirty;
 	struct btrfs_root *gang[8];
 	struct btrfs_root *root;
 	int i;
@@ -498,7 +492,7 @@ int btrfs_defrag_root(struct btrfs_root *root, int cacheonly)
 static noinline int drop_dirty_roots(struct btrfs_root *tree_root,
 				     struct list_head *list)
 {
-	struct dirty_root *dirty;
+	struct btrfs_dirty_root *dirty;
 	struct btrfs_trans_handle *trans;
 	unsigned long nr;
 	u64 num_bytes;
@@ -509,7 +503,7 @@ static noinline int drop_dirty_roots(struct btrfs_root *tree_root,
 	while(!list_empty(list)) {
 		struct btrfs_root *root;
 
-		dirty = list_entry(list->prev, struct dirty_root, list);
+		dirty = list_entry(list->prev, struct btrfs_dirty_root, list);
 		list_del_init(&dirty->list);
 
 		num_bytes = btrfs_root_used(&dirty->root->root_item);