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, 155 insertions, 0 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index f488fac04d99..05efcc7061a7 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -23,10 +23,165 @@
 #include "ctree.h"
 #include "free-space-cache.h"
 #include "transaction.h"
+#include "disk-io.h"
 
 #define BITS_PER_BITMAP         (PAGE_CACHE_SIZE * 8)
 #define MAX_CACHE_BYTES_PER_GIG (32 * 1024)
 
+struct inode *lookup_free_space_inode(struct btrfs_root *root,
+                                      struct btrfs_block_group_cache
+                                      *block_group, struct btrfs_path *path)
+{
+        struct btrfs_key key;
+        struct btrfs_key location;
+        struct btrfs_disk_key disk_key;
+        struct btrfs_free_space_header *header;
+        struct extent_buffer *leaf;
+        struct inode *inode = NULL;
+        int ret;
+
+        spin_lock(&block_group->lock);
+        if (block_group->inode)
+                inode = igrab(block_group->inode);
+        spin_unlock(&block_group->lock);
+        if (inode)
+                return inode;
+
+        key.objectid = BTRFS_FREE_SPACE_OBJECTID;
+        key.offset = block_group->key.objectid;
+        key.type = 0;
+
+        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+        if (ret < 0)
+                return ERR_PTR(ret);
+        if (ret > 0) {
+                btrfs_release_path(root, path);
+                return ERR_PTR(-ENOENT);
+        }
+
+        leaf = path->nodes[0];
+        header = btrfs_item_ptr(leaf, path->slots[0],
+                                struct btrfs_free_space_header);
+        btrfs_free_space_key(leaf, header, &disk_key);
+        btrfs_disk_key_to_cpu(&location, &disk_key);
+        btrfs_release_path(root, path);
+
+        inode = btrfs_iget(root->fs_info->sb, &location, root, NULL);
+        if (!inode)
+                return ERR_PTR(-ENOENT);
+        if (IS_ERR(inode))
+                return inode;
+        if (is_bad_inode(inode)) {
+                iput(inode);
+                return ERR_PTR(-ENOENT);
+        }
+
+        spin_lock(&block_group->lock);
+        if (!root->fs_info->closing) {
+                block_group->inode = igrab(inode);
+                block_group->iref = 1;
+        }
+        spin_unlock(&block_group->lock);
+
+        return inode;
+}
+
+int create_free_space_inode(struct btrfs_root *root,
+                            struct btrfs_trans_handle *trans,
+                            struct btrfs_block_group_cache *block_group,
+                            struct btrfs_path *path)
+{
+        struct btrfs_key key;
+        struct btrfs_disk_key disk_key;
+        struct btrfs_free_space_header *header;
+        struct btrfs_inode_item *inode_item;
+        struct extent_buffer *leaf;
+        u64 objectid;
+        int ret;
+
+        ret = btrfs_find_free_objectid(trans, root, 0, &objectid);
+        if (ret < 0)
+                return ret;
+
+        ret = btrfs_insert_empty_inode(trans, root, path, objectid);
+        if (ret)
+                return ret;
+
+        leaf = path->nodes[0];
+        inode_item = btrfs_item_ptr(leaf, path->slots[0],
+                                    struct btrfs_inode_item);
+        btrfs_item_key(leaf, &disk_key, path->slots[0]);
+        memset_extent_buffer(leaf, 0, (unsigned long)inode_item,
+                             sizeof(*inode_item));
+        btrfs_set_inode_generation(leaf, inode_item, trans->transid);
+        btrfs_set_inode_size(leaf, inode_item, 0);
+        btrfs_set_inode_nbytes(leaf, inode_item, 0);
+        btrfs_set_inode_uid(leaf, inode_item, 0);
+        btrfs_set_inode_gid(leaf, inode_item, 0);
+        btrfs_set_inode_mode(leaf, inode_item, S_IFREG | 0600);
+        btrfs_set_inode_flags(leaf, inode_item, BTRFS_INODE_NOCOMPRESS |
+                              BTRFS_INODE_PREALLOC | BTRFS_INODE_NODATASUM);
+        btrfs_set_inode_nlink(leaf, inode_item, 1);
+        btrfs_set_inode_transid(leaf, inode_item, trans->transid);
+        btrfs_set_inode_block_group(leaf, inode_item,
+                                    block_group->key.objectid);
+        btrfs_mark_buffer_dirty(leaf);
+        btrfs_release_path(root, path);
+
+        key.objectid = BTRFS_FREE_SPACE_OBJECTID;
+        key.offset = block_group->key.objectid;
+        key.type = 0;
+
+        ret = btrfs_insert_empty_item(trans, root, path, &key,
+                                      sizeof(struct btrfs_free_space_header));
+        if (ret < 0) {
+                btrfs_release_path(root, path);
+                return ret;
+        }
+        leaf = path->nodes[0];
+        header = btrfs_item_ptr(leaf, path->slots[0],
+                                struct btrfs_free_space_header);
+        memset_extent_buffer(leaf, 0, (unsigned long)header, sizeof(*header));
+        btrfs_set_free_space_key(leaf, header, &disk_key);
+        btrfs_mark_buffer_dirty(leaf);
+        btrfs_release_path(root, path);
+
+        return 0;
+}
+
+int btrfs_truncate_free_space_cache(struct btrfs_root *root,
+                                    struct btrfs_trans_handle *trans,
+                                    struct btrfs_path *path,
+                                    struct inode *inode)
+{
+        loff_t oldsize;
+        int ret = 0;
+
+        trans->block_rsv = root->orphan_block_rsv;
+        ret = btrfs_block_rsv_check(trans, root,
+                                    root->orphan_block_rsv,
+                                    0, 5);
+        if (ret)
+                return ret;
+
+        oldsize = i_size_read(inode);
+        btrfs_i_size_write(inode, 0);
+        truncate_pagecache(inode, oldsize, 0);
+
+        /*
+         * We don't need an orphan item because truncating the free space cache
+         * will never be split across transactions.
+         */
+        ret = btrfs_truncate_inode_items(trans, root, inode,
+                                         0, BTRFS_EXTENT_DATA_KEY);
+        if (ret) {
+                WARN_ON(1);
+                return ret;
+        }
+
+        return btrfs_update_inode(trans, root, inode);
+}
+
 static inline unsigned long offset_to_bit(u64 bitmap_start, u64 sectorsize,
                                           u64 offset)
 {