Btrfs: Support reading/writing on disk free ino cache

This is similar to block group caching.

We dedicate a special inode in fs tree to save free ino cache.

At the very first time we create/delete a file after mount, the free ino
cache will be loaded from disk into memory. When the fs tree is commited,
the cache will be written back to disk.

To keep compatibility, we check the root generation against the generation
of the special inode when loading the cache, so the loading will fail
if the btrfs filesystem was mounted in an older kernel before.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 28 insertions, 17 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index adec22884a3e..b78d3ab789ca 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -745,6 +745,15 @@ static u64 get_extent_allocation_hint(struct inode *inode, u64 start,
         return alloc_hint;
 }
 
+static inline bool is_free_space_inode(struct btrfs_root *root,
+                                       struct inode *inode)
+{
+        if (root == root->fs_info->tree_root ||
+            BTRFS_I(inode)->location.objectid == BTRFS_FREE_INO_OBJECTID)
+                return true;
+        return false;
+}
+
 /*
  * when extent_io.c finds a delayed allocation range in the file,
  * the call backs end up in this code.  The basic idea is to
@@ -777,7 +786,7 @@ static noinline int cow_file_range(struct inode *inode,
         struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
         int ret = 0;
 
-        BUG_ON(root == root->fs_info->tree_root);
+        BUG_ON(is_free_space_inode(root, inode));
         trans = btrfs_join_transaction(root, 1);
         BUG_ON(IS_ERR(trans));
         btrfs_set_trans_block_group(trans, inode);
@@ -1048,17 +1057,18 @@ static noinline int run_delalloc_nocow(struct inode *inode,
         int type;
         int nocow;
         int check_prev = 1;
-        bool nolock = false;
+        bool nolock;
         u64 ino = btrfs_ino(inode);
 
         path = btrfs_alloc_path();
         BUG_ON(!path);
-        if (root == root->fs_info->tree_root) {
-                nolock = true;
+
+        nolock = is_free_space_inode(root, inode);
+
+        if (nolock)
                 trans = btrfs_join_transaction_nolock(root, 1);
-        } else {
+        else
                 trans = btrfs_join_transaction(root, 1);
-        }
         BUG_ON(IS_ERR(trans));
 
         cow_start = (u64)-1;
@@ -1316,8 +1326,7 @@ static int btrfs_set_bit_hook(struct inode *inode,
         if (!(state->state & EXTENT_DELALLOC) && (*bits & EXTENT_DELALLOC)) {
                 struct btrfs_root *root = BTRFS_I(inode)->root;
                 u64 len = state->end + 1 - state->start;
-                int do_list = (root->root_key.objectid !=
-                               BTRFS_ROOT_TREE_OBJECTID);
+                bool do_list = !is_free_space_inode(root, inode);
 
                 if (*bits & EXTENT_FIRST_DELALLOC)
                         *bits &= ~EXTENT_FIRST_DELALLOC;
@@ -1350,8 +1359,7 @@ static int btrfs_clear_bit_hook(struct inode *inode,
         if ((state->state & EXTENT_DELALLOC) && (*bits & EXTENT_DELALLOC)) {
                 struct btrfs_root *root = BTRFS_I(inode)->root;
                 u64 len = state->end + 1 - state->start;
-                int do_list = (root->root_key.objectid !=
-                               BTRFS_ROOT_TREE_OBJECTID);
+                bool do_list = !is_free_space_inode(root, inode);
 
                 if (*bits & EXTENT_FIRST_DELALLOC)
                         *bits &= ~EXTENT_FIRST_DELALLOC;
@@ -1458,7 +1466,7 @@ static int btrfs_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
 
         skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;
 
-        if (root == root->fs_info->tree_root)
+        if (is_free_space_inode(root, inode))
                 ret = btrfs_bio_wq_end_io(root->fs_info, bio, 2);
         else
                 ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
@@ -1701,7 +1709,7 @@ static int btrfs_finish_ordered_io(struct inode *inode, u64 start, u64 end)
         struct extent_state *cached_state = NULL;
         int compress_type = 0;
         int ret;
-        bool nolock = false;
+        bool nolock;
 
         ret = btrfs_dec_test_ordered_pending(inode, &ordered_extent, start,
                                              end - start + 1);
@@ -1709,7 +1717,7 @@ static int btrfs_finish_ordered_io(struct inode *inode, u64 start, u64 end)
                 return 0;
         BUG_ON(!ordered_extent);
 
-        nolock = (root == root->fs_info->tree_root);
+        nolock = is_free_space_inode(root, inode);
 
         if (test_bit(BTRFS_ORDERED_NOCOW, &ordered_extent->flags)) {
                 BUG_ON(!list_empty(&ordered_extent->list));
@@ -3473,7 +3481,9 @@ delete:
 
                 if (path->slots[0] == 0 ||
                     path->slots[0] != pending_del_slot) {
-                        if (root->ref_cows) {
+                        if (root->ref_cows &&
+                            BTRFS_I(inode)->location.objectid !=
+                                                BTRFS_FREE_INO_OBJECTID) {
                                 err = -EAGAIN;
                                 goto out;
                         }
@@ -3765,7 +3775,7 @@ void btrfs_evict_inode(struct inode *inode)
 
         truncate_inode_pages(&inode->i_data, 0);
         if (inode->i_nlink && (btrfs_root_refs(&root->root_item) != 0 ||
-                               root == root->fs_info->tree_root))
+                               is_free_space_inode(root, inode)))
                 goto no_delete;
 
         if (is_bad_inode(inode)) {
@@ -4382,7 +4392,8 @@ int btrfs_write_inode(struct inode *inode, struct writeback_control *wbc)
                 return 0;
 
         smp_mb();
-        nolock = (root->fs_info->closing && root == root->fs_info->tree_root);
+        if (root->fs_info->closing && is_free_space_inode(root, inode))
+                nolock = true;
 
         if (wbc->sync_mode == WB_SYNC_ALL) {
                 if (nolock)
@@ -6900,7 +6911,7 @@ int btrfs_drop_inode(struct inode *inode)
         struct btrfs_root *root = BTRFS_I(inode)->root;
 
         if (btrfs_root_refs(&root->root_item) == 0 &&
-            root != root->fs_info->tree_root)
+            !is_free_space_inode(root, inode))
                 return 1;
         else
                 return generic_drop_inode(inode);