Btrfs: Add mount option to turn off data cow

A number of workloads do not require copy on write data or checksumming.
mount -o nodatasum to disable checksums and -o nodatacow to disable
both copy on write and checksumming.

In nodatacow mode, copy on write is still performed when a given extent
is under snapshot.

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

1 files changed, 52 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index fd8233e05cf4..585f279d1112 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -70,7 +70,58 @@ void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p)
         memset(p, 0, sizeof(*p));
 }
 
-static int __btrfs_cow_block(struct btrfs_trans_handle *trans,
+int btrfs_copy_root(struct btrfs_trans_handle *trans,
+                      struct btrfs_root *root,
+                      struct extent_buffer *buf,
+                      struct extent_buffer **cow_ret, u64 new_root_objectid)
+{
+        struct extent_buffer *cow;
+        u32 nritems;
+        int ret = 0;
+        int level;
+        struct btrfs_key first_key;
+        struct btrfs_root new_root;
+
+        memcpy(&new_root, root, sizeof(new_root));
+        new_root.root_key.objectid = new_root_objectid;
+
+        WARN_ON(root->ref_cows && trans->transid !=
+                root->fs_info->running_transaction->transid);
+        WARN_ON(root->ref_cows && trans->transid != root->last_trans);
+
+        level = btrfs_header_level(buf);
+        nritems = btrfs_header_nritems(buf);
+        if (nritems) {
+                if (level == 0)
+                        btrfs_item_key_to_cpu(buf, &first_key, 0);
+                else
+                        btrfs_node_key_to_cpu(buf, &first_key, 0);
+        } else {
+                first_key.objectid = 0;
+        }
+        cow = __btrfs_alloc_free_block(trans, &new_root, buf->len,
+                                       new_root_objectid,
+                                       trans->transid, first_key.objectid,
+                                       level, buf->start, 0);
+        if (IS_ERR(cow))
+                return PTR_ERR(cow);
+
+        copy_extent_buffer(cow, buf, 0, 0, cow->len);
+        btrfs_set_header_bytenr(cow, cow->start);
+        btrfs_set_header_generation(cow, trans->transid);
+        btrfs_set_header_owner(cow, new_root_objectid);
+
+        WARN_ON(btrfs_header_generation(buf) > trans->transid);
+        ret = btrfs_inc_ref(trans, &new_root, buf);
+        if (ret)
+                return ret;
+
+        btrfs_mark_buffer_dirty(cow);
+        *cow_ret = cow;
+        return 0;
+}
+
+int __btrfs_cow_block(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root,
                              struct extent_buffer *buf,
                              struct extent_buffer *parent, int parent_slot,