Btrfs: create special free space cache inode

In order to save free space cache, we need an inode to hold the data, and we
need a special item to point at the right inode for the right block group.  So
first, create a special item that will point to the right inode, and the number
of extent entries we will have and the number of bitmaps we will have.  We
truncate and pre-allocate space everytime to make sure it's uptodate.

This feature will be turned on as soon as you mount with -o space_cache, however
it is safe to boot into old kernels, they will just generate the cache the old
fashion way.  When you boot back into a newer kernel we will notice that we
modified and not the cache and automatically discard the cache.

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 87 insertions, 4 deletions

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index b37d723b9d4a..af339eee55b8 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -29,6 +29,7 @@
 #include "locking.h"
 #include "btrfs_inode.h"
 #include "async-thread.h"
+#include "free-space-cache.h"
 
 /*
  * backref_node, mapping_node and tree_block start with this
@@ -3191,6 +3192,54 @@ static int block_use_full_backref(struct reloc_control *rc,
         return ret;
 }
 
+static int delete_block_group_cache(struct btrfs_fs_info *fs_info,
+                                    struct inode *inode, u64 ino)
+{
+        struct btrfs_key key;
+        struct btrfs_path *path;
+        struct btrfs_root *root = fs_info->tree_root;
+        struct btrfs_trans_handle *trans;
+        unsigned long nr;
+        int ret = 0;
+
+        if (inode)
+                goto truncate;
+
+        key.objectid = ino;
+        key.type = BTRFS_INODE_ITEM_KEY;
+        key.offset = 0;
+
+        inode = btrfs_iget(fs_info->sb, &key, root, NULL);
+        if (!inode || IS_ERR(inode) || is_bad_inode(inode)) {
+                if (inode && !IS_ERR(inode))
+                        iput(inode);
+                return -ENOENT;
+        }
+
+truncate:
+        path = btrfs_alloc_path();
+        if (!path) {
+                ret = -ENOMEM;
+                goto out;
+        }
+
+        trans = btrfs_join_transaction(root, 0);
+        if (IS_ERR(trans)) {
+                btrfs_free_path(path);
+                goto out;
+        }
+
+        ret = btrfs_truncate_free_space_cache(root, trans, path, inode);
+
+        btrfs_free_path(path);
+        nr = trans->blocks_used;
+        btrfs_end_transaction(trans, root);
+        btrfs_btree_balance_dirty(root, nr);
+out:
+        iput(inode);
+        return ret;
+}
+
 /*
  * helper to add tree blocks for backref of type BTRFS_EXTENT_DATA_REF_KEY
  * this function scans fs tree to find blocks reference the data extent
@@ -3217,15 +3266,27 @@ static int find_data_references(struct reloc_control *rc,
         int counted;
         int ret;
 
-        path = btrfs_alloc_path();
-        if (!path)
-                return -ENOMEM;
-
         ref_root = btrfs_extent_data_ref_root(leaf, ref);
         ref_objectid = btrfs_extent_data_ref_objectid(leaf, ref);
         ref_offset = btrfs_extent_data_ref_offset(leaf, ref);
         ref_count = btrfs_extent_data_ref_count(leaf, ref);
 
+        /*
+         * This is an extent belonging to the free space cache, lets just delete
+         * it and redo the search.
+         */
+        if (ref_root == BTRFS_ROOT_TREE_OBJECTID) {
+                ret = delete_block_group_cache(rc->extent_root->fs_info,
+                                               NULL, ref_objectid);
+                if (ret != -ENOENT)
+                        return ret;
+                ret = 0;
+        }
+
+        path = btrfs_alloc_path();
+        if (!path)
+                return -ENOMEM;
+
         root = read_fs_root(rc->extent_root->fs_info, ref_root);
         if (IS_ERR(root)) {
                 err = PTR_ERR(root);
@@ -3860,6 +3921,8 @@ int btrfs_relocate_block_group(struct btrfs_root *extent_root, u64 group_start)
 {
         struct btrfs_fs_info *fs_info = extent_root->fs_info;
         struct reloc_control *rc;
+        struct inode *inode;
+        struct btrfs_path *path;
         int ret;
         int rw = 0;
         int err = 0;
@@ -3882,6 +3945,26 @@ int btrfs_relocate_block_group(struct btrfs_root *extent_root, u64 group_start)
                 rw = 1;
         }
 
+        path = btrfs_alloc_path();
+        if (!path) {
+                err = -ENOMEM;
+                goto out;
+        }
+
+        inode = lookup_free_space_inode(fs_info->tree_root, rc->block_group,
+                                        path);
+        btrfs_free_path(path);
+
+        if (!IS_ERR(inode))
+                ret = delete_block_group_cache(fs_info, inode, 0);
+        else
+                ret = PTR_ERR(inode);
+
+        if (ret && ret != -ENOENT) {
+                err = ret;
+                goto out;
+        }
+
         rc->data_inode = create_reloc_inode(fs_info, rc->block_group);
         if (IS_ERR(rc->data_inode)) {
                 err = PTR_ERR(rc->data_inode);