Btrfs: update nodatacow code v2

This patch simplifies the nodatacow checker. If all references
were created after the latest snapshot, then we can avoid COW
safely. This patch also updates run_delalloc_nocow to do more
fine-grained checking.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

1 files changed, 18 insertions, 113 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 535cee47fcfb..1eb69a91b727 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -848,9 +848,8 @@ out:
         return 0;
 }
 
-static int get_reference_status(struct btrfs_root *root, u64 bytenr,
-                                u64 parent_gen, u64 ref_objectid,
-                                u64 *min_generation, u32 *ref_count)
+int btrfs_cross_ref_exist(struct btrfs_trans_handle *trans,
+                          struct btrfs_root *root, u64 bytenr)
 {
         struct btrfs_root *extent_root = root->fs_info->extent_root;
         struct btrfs_path *path;
@@ -858,8 +857,8 @@ static int get_reference_status(struct btrfs_root *root, u64 bytenr,
         struct btrfs_extent_ref *ref_item;
         struct btrfs_key key;
         struct btrfs_key found_key;
-        u64 root_objectid = root->root_key.objectid;
-        u64 ref_generation;
+        u64 ref_root;
+        u64 last_snapshot;
         u32 nritems;
         int ret;
 
@@ -872,7 +871,9 @@ static int get_reference_status(struct btrfs_root *root, u64 bytenr,
         if (ret < 0)
                 goto out;
         BUG_ON(ret == 0);
-        if (ret < 0 || path->slots[0] == 0)
+
+        ret = -ENOENT;
+        if (path->slots[0] == 0)
                 goto out;
 
         path->slots[0]--;
@@ -880,14 +881,10 @@ static int get_reference_status(struct btrfs_root *root, u64 bytenr,
         btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
 
         if (found_key.objectid != bytenr ||
-            found_key.type != BTRFS_EXTENT_ITEM_KEY) {
-                ret = 1;
+            found_key.type != BTRFS_EXTENT_ITEM_KEY)
                 goto out;
-        }
-
-        *ref_count = 0;
-        *min_generation = (u64)-1;
 
+        last_snapshot = btrfs_root_last_snapshot(&root->root_item);
         while (1) {
                 leaf = path->nodes[0];
                 nritems = btrfs_header_nritems(leaf);
@@ -910,114 +907,22 @@ static int get_reference_status(struct btrfs_root *root, u64 bytenr,
 
                 ref_item = btrfs_item_ptr(leaf, path->slots[0],
                                           struct btrfs_extent_ref);
-                ref_generation = btrfs_ref_generation(leaf, ref_item);
-                /*
-                 * For (parent_gen > 0 && parent_gen > ref_generation):
-                 *
-                 * we reach here through the oldest root, therefore
-                 * all other reference from same snapshot should have
-                 * a larger generation.
-                 */
-                if ((root_objectid != btrfs_ref_root(leaf, ref_item)) ||
-                    (parent_gen > 0 && parent_gen > ref_generation) ||
-                    (ref_objectid >= BTRFS_FIRST_FREE_OBJECTID &&
-                     ref_objectid != btrfs_ref_objectid(leaf, ref_item))) {
-                        *ref_count = 2;
-                        break;
-                }
-
-                *ref_count = 1;
-                if (*min_generation > ref_generation)
-                        *min_generation = ref_generation;
-
-                path->slots[0]++;
-        }
-        ret = 0;
-out:
-        btrfs_free_path(path);
-        return ret;
-}
-
-int btrfs_cross_ref_exists(struct btrfs_trans_handle *trans,
-                           struct btrfs_root *root,
-                           struct btrfs_key *key, u64 bytenr)
-{
-        struct btrfs_root *old_root;
-        struct btrfs_path *path = NULL;
-        struct extent_buffer *eb;
-        struct btrfs_file_extent_item *item;
-        u64 ref_generation;
-        u64 min_generation;
-        u64 extent_start;
-        u32 ref_count;
-        int level;
-        int ret;
-
-        BUG_ON(trans == NULL);
-        BUG_ON(key->type != BTRFS_EXTENT_DATA_KEY);
-        ret = get_reference_status(root, bytenr, 0, key->objectid,
-                                   &min_generation, &ref_count);
-        if (ret)
-                return ret;
-
-        if (ref_count != 1)
-                return 1;
-
-        old_root = root->dirty_root->root;
-        ref_generation = old_root->root_key.offset;
-
-        /* all references are created in running transaction */
-        if (min_generation > ref_generation) {
-                ret = 0;
-                goto out;
-        }
-
-        path = btrfs_alloc_path();
-        if (!path) {
-                ret = -ENOMEM;
-                goto out;
-        }
-
-        path->skip_locking = 1;
-        /* if no item found, the extent is referenced by other snapshot */
-        ret = btrfs_search_slot(NULL, old_root, key, path, 0, 0);
-        if (ret)
-                goto out;
-
-        eb = path->nodes[0];
-        item = btrfs_item_ptr(eb, path->slots[0],
-                              struct btrfs_file_extent_item);
-        if (btrfs_file_extent_type(eb, item) != BTRFS_FILE_EXTENT_REG ||
-            btrfs_file_extent_disk_bytenr(eb, item) != bytenr) {
-                ret = 1;
-                goto out;
-        }
-
-        for (level = BTRFS_MAX_LEVEL - 1; level >= -1; level--) {
-                if (level >= 0) {
-                        eb = path->nodes[level];
-                        if (!eb)
-                                continue;
-                        extent_start = eb->start;
-                } else
-                        extent_start = bytenr;
-
-                ret = get_reference_status(root, extent_start, ref_generation,
-                                           0, &min_generation, &ref_count);
-                if (ret)
+                ref_root = btrfs_ref_root(leaf, ref_item);
+                if (ref_root != root->root_key.objectid &&
+                    ref_root != BTRFS_TREE_LOG_OBJECTID) {
+                        ret = 1;
                         goto out;
-
-                if (ref_count != 1) {
+                }
+                if (btrfs_ref_generation(leaf, ref_item) <= last_snapshot) {
                         ret = 1;
                         goto out;
                 }
-                if (level >= 0)
-                        ref_generation = btrfs_header_generation(eb);
+
+                path->slots[0]++;
         }
         ret = 0;
 out:
-        if (path)
-                btrfs_free_path(path);
+        btrfs_free_path(path);
         return ret;
 }