Btrfs: add sequence numbers to delayed refs

Sequence numbers are needed to reconstruct the backrefs of a given extent to
a certain point in time. The total set of backrefs consist of the set of
backrefs recorded on disk plus the enqueued delayed refs for it that existed
at that moment.

This patch also adds a list that records all delayed refs which are
currently in the process of being added.

When walking all refs of an extent in btrfs_find_all_roots(), we freeze the
current state of delayed refs, honor anythinh up to this point and prevent
processing newer delayed refs to assert consistency.

Signed-off-by: Arne Jansen <sensille@gmx.net>
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

1 files changed, 34 insertions, 0 deletions

diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index babd37badb43..a405db0320e8 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -101,6 +101,11 @@ static int comp_entry(struct btrfs_delayed_ref_node *ref2,
                 return -1;
         if (ref1->type > ref2->type)
                 return 1;
+        /* merging of sequenced refs is not allowed */
+        if (ref1->seq < ref2->seq)
+                return -1;
+        if (ref1->seq > ref2->seq)
+                return 1;
         if (ref1->type == BTRFS_TREE_BLOCK_REF_KEY ||
             ref1->type == BTRFS_SHARED_BLOCK_REF_KEY) {
                 return comp_tree_refs(btrfs_delayed_node_to_tree_ref(ref2),
@@ -209,6 +214,24 @@ int btrfs_delayed_ref_lock(struct btrfs_trans_handle *trans,
         return 0;
 }
 
+int btrfs_check_delayed_seq(struct btrfs_delayed_ref_root *delayed_refs,
+                            u64 seq)
+{
+        struct seq_list *elem;
+
+        assert_spin_locked(&delayed_refs->lock);
+        if (list_empty(&delayed_refs->seq_head))
+                return 0;
+
+        elem = list_first_entry(&delayed_refs->seq_head, struct seq_list, list);
+        if (seq >= elem->seq) {
+                pr_debug("holding back delayed_ref %llu, lowest is %llu (%p)\n",
+                         seq, elem->seq, delayed_refs);
+                return 1;
+        }
+        return 0;
+}
+
 int btrfs_find_ref_cluster(struct btrfs_trans_handle *trans,
                            struct list_head *cluster, u64 start)
 {
@@ -438,6 +461,7 @@ static noinline int add_delayed_ref_head(struct btrfs_fs_info *fs_info,
         ref->action  = 0;
         ref->is_head = 1;
         ref->in_tree = 1;
+        ref->seq = 0;
 
         head_ref = btrfs_delayed_node_to_head(ref);
         head_ref->must_insert_reserved = must_insert_reserved;
@@ -479,6 +503,7 @@ static noinline int add_delayed_tree_ref(struct btrfs_fs_info *fs_info,
         struct btrfs_delayed_ref_node *existing;
         struct btrfs_delayed_tree_ref *full_ref;
         struct btrfs_delayed_ref_root *delayed_refs;
+        u64 seq = 0;
 
         if (action == BTRFS_ADD_DELAYED_EXTENT)
                 action = BTRFS_ADD_DELAYED_REF;
@@ -494,6 +519,10 @@ static noinline int add_delayed_tree_ref(struct btrfs_fs_info *fs_info,
         ref->is_head = 0;
         ref->in_tree = 1;
 
+        if (need_ref_seq(for_cow, ref_root))
+                seq = inc_delayed_seq(delayed_refs);
+        ref->seq = seq;
+
         full_ref = btrfs_delayed_node_to_tree_ref(ref);
         full_ref->parent = parent;
         full_ref->root = ref_root;
@@ -534,6 +563,7 @@ static noinline int add_delayed_data_ref(struct btrfs_fs_info *fs_info,
         struct btrfs_delayed_ref_node *existing;
         struct btrfs_delayed_data_ref *full_ref;
         struct btrfs_delayed_ref_root *delayed_refs;
+        u64 seq = 0;
 
         if (action == BTRFS_ADD_DELAYED_EXTENT)
                 action = BTRFS_ADD_DELAYED_REF;
@@ -549,6 +579,10 @@ static noinline int add_delayed_data_ref(struct btrfs_fs_info *fs_info,
         ref->is_head = 0;
         ref->in_tree = 1;
 
+        if (need_ref_seq(for_cow, ref_root))
+                seq = inc_delayed_seq(delayed_refs);
+        ref->seq = seq;
+
         full_ref = btrfs_delayed_node_to_data_ref(ref);
         full_ref->parent = parent;
         full_ref->root = ref_root;