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, 78 insertions, 17 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index c03864406af3..1af1ea88e8a8 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1700,6 +1700,7 @@ static int btrfs_finish_ordered_io(struct inode *inode, u64 start, u64 end)
                                                 ordered_extent->len);
                 BUG_ON(ret);
         } else {
+                BUG_ON(root == root->fs_info->tree_root);
                 ret = insert_reserved_file_extent(trans, inode,
                                                 ordered_extent->file_offset,
                                                 ordered_extent->start,
@@ -3196,7 +3197,7 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 
         BUG_ON(new_size > 0 && min_type != BTRFS_EXTENT_DATA_KEY);
 
-        if (root->ref_cows)
+        if (root->ref_cows || root == root->fs_info->tree_root)
                 btrfs_drop_extent_cache(inode, new_size & (~mask), (u64)-1, 0);
 
         path = btrfs_alloc_path();
@@ -3344,7 +3345,8 @@ delete:
                 } else {
                         break;
                 }
-                if (found_extent && root->ref_cows) {
+                if (found_extent && (root->ref_cows ||
+                                     root == root->fs_info->tree_root)) {
                         btrfs_set_path_blocking(path);
                         ret = btrfs_free_extent(trans, root, extent_start,
                                                 extent_num_bytes, 0,
@@ -3675,7 +3677,8 @@ void btrfs_evict_inode(struct inode *inode)
         int ret;
 
         truncate_inode_pages(&inode->i_data, 0);
-        if (inode->i_nlink && btrfs_root_refs(&root->root_item) != 0)
+        if (inode->i_nlink && (btrfs_root_refs(&root->root_item) != 0 ||
+                               root == root->fs_info->tree_root))
                 goto no_delete;
 
         if (is_bad_inode(inode)) {
@@ -3888,7 +3891,14 @@ static void inode_tree_del(struct inode *inode)
         }
         spin_unlock(&root->inode_lock);
 
-        if (empty && btrfs_root_refs(&root->root_item) == 0) {
+        /*
+         * Free space cache has inodes in the tree root, but the tree root has a
+         * root_refs of 0, so this could end up dropping the tree root as a
+         * snapshot, so we need the extra !root->fs_info->tree_root check to
+         * make sure we don't drop it.
+         */
+        if (empty && btrfs_root_refs(&root->root_item) == 0 &&
+            root != root->fs_info->tree_root) {
                 synchronize_srcu(&root->fs_info->subvol_srcu);
                 spin_lock(&root->inode_lock);
                 empty = RB_EMPTY_ROOT(&root->inode_tree);
@@ -4282,14 +4292,24 @@ int btrfs_write_inode(struct inode *inode, struct writeback_control *wbc)
         struct btrfs_root *root = BTRFS_I(inode)->root;
         struct btrfs_trans_handle *trans;
         int ret = 0;
+        bool nolock = false;
 
         if (BTRFS_I(inode)->dummy_inode)
                 return 0;
 
+        smp_mb();
+        nolock = (root->fs_info->closing && root == root->fs_info->tree_root);
+
         if (wbc->sync_mode == WB_SYNC_ALL) {
-                trans = btrfs_join_transaction(root, 1);
+                if (nolock)
+                        trans = btrfs_join_transaction_nolock(root, 1);
+                else
+                        trans = btrfs_join_transaction(root, 1);
                 btrfs_set_trans_block_group(trans, inode);
-                ret = btrfs_commit_transaction(trans, root);
+                if (nolock)
+                        ret = btrfs_end_transaction_nolock(trans, root);
+                else
+                        ret = btrfs_commit_transaction(trans, root);
         }
         return ret;
 }
@@ -6308,6 +6328,21 @@ void btrfs_destroy_inode(struct inode *inode)
                 spin_unlock(&root->fs_info->ordered_extent_lock);
         }
 
+        if (root == root->fs_info->tree_root) {
+                struct btrfs_block_group_cache *block_group;
+
+                block_group = btrfs_lookup_block_group(root->fs_info,
+                                                BTRFS_I(inode)->block_group);
+                if (block_group && block_group->inode == inode) {
+                        spin_lock(&block_group->lock);
+                        block_group->inode = NULL;
+                        spin_unlock(&block_group->lock);
+                        btrfs_put_block_group(block_group);
+                } else if (block_group) {
+                        btrfs_put_block_group(block_group);
+                }
+        }
+
         spin_lock(&root->orphan_lock);
         if (!list_empty(&BTRFS_I(inode)->i_orphan)) {
                 printk(KERN_INFO "BTRFS: inode %lu still on the orphan list\n",
@@ -6340,7 +6375,8 @@ int btrfs_drop_inode(struct inode *inode)
 {
         struct btrfs_root *root = BTRFS_I(inode)->root;
 
-        if (btrfs_root_refs(&root->root_item) == 0)
+        if (btrfs_root_refs(&root->root_item) == 0 &&
+            root != root->fs_info->tree_root)
                 return 1;
         else
                 return generic_drop_inode(inode);
@@ -6757,27 +6793,33 @@ out_unlock:
         return err;
 }
 
-int btrfs_prealloc_file_range(struct inode *inode, int mode,
-                              u64 start, u64 num_bytes, u64 min_size,
-                              loff_t actual_len, u64 *alloc_hint)
+static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
+                                       u64 start, u64 num_bytes, u64 min_size,
+                                       loff_t actual_len, u64 *alloc_hint,
+                                       struct btrfs_trans_handle *trans)
 {
-        struct btrfs_trans_handle *trans;
         struct btrfs_root *root = BTRFS_I(inode)->root;
         struct btrfs_key ins;
         u64 cur_offset = start;
         int ret = 0;
+        bool own_trans = true;
 
+        if (trans)
+                own_trans = false;
         while (num_bytes > 0) {
-                trans = btrfs_start_transaction(root, 3);
-                if (IS_ERR(trans)) {
-                        ret = PTR_ERR(trans);
-                        break;
+                if (own_trans) {
+                        trans = btrfs_start_transaction(root, 3);
+                        if (IS_ERR(trans)) {
+                                ret = PTR_ERR(trans);
+                                break;
+                        }
                 }
 
                 ret = btrfs_reserve_extent(trans, root, num_bytes, min_size,
                                            0, *alloc_hint, (u64)-1, &ins, 1);
                 if (ret) {
-                        btrfs_end_transaction(trans, root);
+                        if (own_trans)
+                                btrfs_end_transaction(trans, root);
                         break;
                 }
 
@@ -6810,11 +6852,30 @@ int btrfs_prealloc_file_range(struct inode *inode, int mode,
                 ret = btrfs_update_inode(trans, root, inode);
                 BUG_ON(ret);
 
-                btrfs_end_transaction(trans, root);
+                if (own_trans)
+                        btrfs_end_transaction(trans, root);
         }
         return ret;
 }
 
+int btrfs_prealloc_file_range(struct inode *inode, int mode,
+                              u64 start, u64 num_bytes, u64 min_size,
+                              loff_t actual_len, u64 *alloc_hint)
+{
+        return __btrfs_prealloc_file_range(inode, mode, start, num_bytes,
+                                           min_size, actual_len, alloc_hint,
+                                           NULL);
+}
+
+int btrfs_prealloc_file_range_trans(struct inode *inode,
+                                    struct btrfs_trans_handle *trans, int mode,
+                                    u64 start, u64 num_bytes, u64 min_size,
+                                    loff_t actual_len, u64 *alloc_hint)
+{
+        return __btrfs_prealloc_file_range(inode, mode, start, num_bytes,
+                                           min_size, actual_len, alloc_hint, trans);
+}
+
 static long btrfs_fallocate(struct inode *inode, int mode,
                             loff_t offset, loff_t len)
 {