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>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 0041483..1412d55 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -679,6 +679,104 @@
return 0;
}
+u32 btrfs_count_snapshots_in_path(struct btrfs_root *root,
+ struct btrfs_path *count_path,
+ u64 first_extent)
+{
+ struct btrfs_root *extent_root = root->fs_info->extent_root;
+ struct btrfs_path *path;
+ u64 bytenr;
+ u64 found_objectid;
+ u64 root_objectid = 0;
+ u32 total_count = 0;
+ u32 cur_count;
+ u32 refs;
+ u32 nritems;
+ int ret;
+ struct btrfs_key key;
+ struct btrfs_key found_key;
+ struct extent_buffer *l;
+ struct btrfs_extent_item *item;
+ struct btrfs_extent_ref *ref_item;
+ int level = -1;
+
+ path = btrfs_alloc_path();
+again:
+ if (level == -1)
+ bytenr = first_extent;
+ else
+ bytenr = count_path->nodes[level]->start;
+
+ cur_count = 0;
+ key.objectid = bytenr;
+ key.offset = 0;
+
+ btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
+ ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
+ if (ret < 0)
+ goto out;
+ BUG_ON(ret == 0);
+
+ l = path->nodes[0];
+ btrfs_item_key_to_cpu(l, &found_key, path->slots[0]);
+
+ if (found_key.objectid != bytenr ||
+ found_key.type != BTRFS_EXTENT_ITEM_KEY) {
+ goto out;
+ }
+
+ item = btrfs_item_ptr(l, path->slots[0], struct btrfs_extent_item);
+ refs = btrfs_extent_refs(l, item);
+ while (1) {
+ nritems = btrfs_header_nritems(l);
+ if (path->slots[0] >= nritems) {
+ ret = btrfs_next_leaf(extent_root, path);
+ if (ret == 0)
+ continue;
+ break;
+ }
+ btrfs_item_key_to_cpu(l, &found_key, path->slots[0]);
+ if (found_key.objectid != bytenr)
+ break;
+ if (found_key.type != BTRFS_EXTENT_REF_KEY) {
+ path->slots[0]++;
+ continue;
+ }
+
+ cur_count++;
+ ref_item = btrfs_item_ptr(l, path->slots[0],
+ struct btrfs_extent_ref);
+ found_objectid = btrfs_ref_root(l, ref_item);
+
+ if (found_objectid != root_objectid)
+ total_count++;
+
+ if (total_count > 1)
+ goto out;
+
+ if (root_objectid == 0)
+ root_objectid = found_objectid;
+
+ path->slots[0]++;
+ }
+ if (cur_count == 0) {
+ total_count = 0;
+ goto out;
+ }
+ if (total_count > 1)
+ goto out;
+ if (level >= 0 && root->node == count_path->nodes[level])
+ goto out;
+ level++;
+ btrfs_release_path(root, path);
+ goto again;
+
+out:
+ btrfs_free_path(path);
+ return total_count;
+
+}
+
int btrfs_inc_root_ref(struct btrfs_trans_handle *trans,
struct btrfs_root *root, u64 owner_objectid)
{
@@ -1127,9 +1225,6 @@
if (!path)
return -ENOMEM;
- if (ref_generation && owner_objectid == 0 && root_objectid == 3) {
-//printk("drop backref root %Lu gen %Lu byte %Lu\n", root_objectid, ref_generation, bytenr );
- }
ret = lookup_extent_backref(trans, extent_root, path,
bytenr, root_objectid,
ref_generation,