Btrfs: Change the super to point to a tree of trees to enable persistent snapshots

Signed-off-by: Chris Mason <chris.mason@oracle.com>

10 files changed, 445 insertions, 65 deletions

diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
index f8532200e9ad..13ed6313ac85 100644
--- a/fs/btrfs/Makefile
+++ b/fs/btrfs/Makefile
@@ -2,7 +2,8 @@
 CC=gcc
 CFLAGS = -g -Wall
 headers = radix-tree.h ctree.h disk-io.h kerncompat.h print-tree.h list.h
-objects = ctree.o disk-io.o radix-tree.o mkfs.o extent-tree.o print-tree.o
+objects = ctree.o disk-io.o radix-tree.o mkfs.o extent-tree.o print-tree.o \
+          root-tree.o
 
 # if you don't have sparse installed, use ls instead
 CHECKFLAGS=-D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ -Wbitwise \
diff --git a/fs/btrfs/TODO b/fs/btrfs/TODO
index ad29267b8738..ff90e5eaf431 100644
--- a/fs/btrfs/TODO
+++ b/fs/btrfs/TODO
@@ -5,6 +5,7 @@
 * make a real mkfs and superblock
 * Do checksumming
 * Define FS objects in terms of different item types
+* add inode tree
 * Add block mapping tree (simple dm layer)
 * Add simple tree locking (semaphore per tree)
 * Make allocator smarter
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 5dfcc90812c1..0968899fb7f9 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -4,8 +4,13 @@
 #include "list.h"
 #include "kerncompat.h"
 
+#define BTRFS_MAGIC "_BtRfS_M"
 #define BTRFS_BLOCKSIZE 1024
 
+#define BTRFS_ROOT_TREE_OBJECTID 1
+#define BTRFS_EXTENT_TREE_OBJECTID 2
+#define BTRFS_FS_TREE_OBJECTID 3
+
 /*
  * the key defines the order in the tree, and so it also defines (optimal)
  * block layout.  objectid corresonds to the inode number.  The flags
@@ -36,7 +41,7 @@ struct btrfs_key {
  * every tree block (leaf or node) starts with this header.
  */
 struct btrfs_header {
-        __le64 fsid[2]; /* FS specific uuid */
+        u8 fsid[16]; /* FS specific uuid */
         __le64 blocknr; /* which block this node is supposed to live in */
         __le64 parentid; /* objectid of the tree root */
         __le32 csum;
@@ -52,6 +57,14 @@ struct btrfs_header {
 
 struct btrfs_buffer;
 
+struct btrfs_root_item {
+        __le64 blocknr;
+        __le32 flags;
+        __le64 block_limit;
+        __le64 blocks_used;
+        __le32 refs;
+};
+
 /*
  * in ram representation of the tree.  extent_root is used for all allocations
  * and for the extent tree extent_root root.  current_insert is used
@@ -61,6 +74,7 @@ struct btrfs_root {
         struct btrfs_buffer *node;
         struct btrfs_buffer *commit_root;
         struct btrfs_root *extent_root;
+        struct btrfs_root *tree_root;
         struct btrfs_key current_insert;
         struct btrfs_key last_insert;
         int fp;
@@ -69,28 +83,25 @@ struct btrfs_root {
         struct list_head trans;
         struct list_head cache;
         int cache_size;
+        int ref_cows;
+        struct btrfs_root_item root_item;
+        struct btrfs_key root_key;
 };
 
 /*
- * describes a tree on disk
- */
-struct btrfs_root_info {
-        u64 fsid[2]; /* FS specific uuid */
-        u64 blocknr; /* blocknr of this block */
-        u64 objectid; /* inode number of this root */
-        u64 tree_root; /* the tree root block */
-        u32 csum;
-        u32 ham;
-        u64 snapuuid[2]; /* root specific uuid */
-} __attribute__ ((__packed__));
-
-/*
  * the super block basically lists the main trees of the FS
  * it currently lacks any block count etc etc
  */
 struct btrfs_super_block {
-        struct btrfs_root_info root_info;
-        struct btrfs_root_info extent_info;
+        u8 fsid[16];    /* FS specific uuid */
+        __le64 blocknr; /* this block number */
+        __le32 csum;
+        __le64 magic;
+        __le16 blocksize;
+        __le64 generation;
+        __le64 root;
+        __le64 total_blocks;
+        __le64 blocks_used;
 } __attribute__ ((__packed__));
 
 /*
@@ -317,6 +328,79 @@ static inline int btrfs_is_leaf(struct btrfs_node *n)
         return (btrfs_header_level(&n->header) == 0);
 }
 
+static inline u64 btrfs_root_blocknr(struct btrfs_root_item *item)
+{
+        return le64_to_cpu(item->blocknr);
+}
+
+static inline void btrfs_set_root_blocknr(struct btrfs_root_item *item, u64 val)
+{
+        item->blocknr = cpu_to_le64(val);
+}
+
+static inline u32 btrfs_root_refs(struct btrfs_root_item *item)
+{
+        return le32_to_cpu(item->refs);
+}
+
+static inline void btrfs_set_root_refs(struct btrfs_root_item *item, u32 val)
+{
+        item->refs = cpu_to_le32(val);
+}
+
+static inline u64 btrfs_super_blocknr(struct btrfs_super_block *s)
+{
+        return le64_to_cpu(s->blocknr);
+}
+
+static inline void btrfs_set_super_blocknr(struct btrfs_super_block *s, u64 val)
+{
+        s->blocknr = cpu_to_le64(val);
+}
+
+static inline u64 btrfs_super_root(struct btrfs_super_block *s)
+{
+        return le64_to_cpu(s->root);
+}
+
+static inline void btrfs_set_super_root(struct btrfs_super_block *s, u64 val)
+{
+        s->root = cpu_to_le64(val);
+}
+
+static inline u64 btrfs_super_total_blocks(struct btrfs_super_block *s)
+{
+        return le64_to_cpu(s->total_blocks);
+}
+
+static inline void btrfs_set_super_total_blocks(struct btrfs_super_block *s,
+                                                u64 val)
+{
+        s->total_blocks = cpu_to_le64(val);
+}
+
+static inline u64 btrfs_super_blocks_used(struct btrfs_super_block *s)
+{
+        return le64_to_cpu(s->blocks_used);
+}
+
+static inline void btrfs_set_super_blocks_used(struct btrfs_super_block *s,
+                                                u64 val)
+{
+        s->blocks_used = cpu_to_le64(val);
+}
+
+static inline u16 btrfs_super_blocksize(struct btrfs_super_block *s)
+{
+        return le16_to_cpu(s->blocksize);
+}
+
+static inline void btrfs_set_super_blocksize(struct btrfs_super_block *s,
+                                                u16 val)
+{
+        s->blocksize = cpu_to_le16(val);
+}
+
 struct btrfs_buffer *btrfs_alloc_free_block(struct btrfs_root *root);
 int btrfs_inc_ref(struct btrfs_root *root, struct btrfs_buffer *buf);
 int btrfs_free_extent(struct btrfs_root *root, u64 blocknr, u64 num_blocks);
@@ -331,4 +415,11 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path);
 int btrfs_leaf_free_space(struct btrfs_leaf *leaf);
 int btrfs_drop_snapshot(struct btrfs_root *root, struct btrfs_buffer *snap);
 int btrfs_finish_extent_commit(struct btrfs_root *root);
+int btrfs_del_root(struct btrfs_root *root, struct btrfs_key *key);
+int btrfs_insert_root(struct btrfs_root *root, struct btrfs_key *key,
+                      struct btrfs_root_item *item);
+int btrfs_update_root(struct btrfs_root *root, struct btrfs_key *key,
+                      struct btrfs_root_item *item);
+int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
+                        struct btrfs_root_item *item, struct btrfs_key *key);
 #endif
diff --git a/fs/btrfs/debug-tree.c b/fs/btrfs/debug-tree.c
index 6da0a7aa0f47..de45fb4dfddd 100644
--- a/fs/btrfs/debug-tree.c
+++ b/fs/btrfs/debug-tree.c
@@ -11,9 +11,11 @@ int main(int ac, char **av) {
         struct btrfs_root *root;
         radix_tree_init();
         root = open_ctree("dbfile", &super);
-        printf("root tree\n");
+        printf("fs tree\n");
         btrfs_print_tree(root, root->node);
         printf("map tree\n");
         btrfs_print_tree(root->extent_root, root->extent_root->node);
+        printf("root tree\n");
+        btrfs_print_tree(root->tree_root, root->tree_root->node);
         return 0;
 }
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index c34c0c60935f..3d4bf6833f2a 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -154,41 +154,96 @@ static int __commit_transaction(struct btrfs_root *root)
         return ret;
 }
 
+static int commit_extent_and_tree_roots(struct btrfs_root *tree_root,
+                                        struct btrfs_root *extent_root)
+{
+        int ret;
+        u64 old_extent_block;
+
+        while(1) {
+                old_extent_block = btrfs_root_blocknr(&extent_root->root_item);
+                if (old_extent_block == extent_root->node->blocknr)
+                        break;
+                btrfs_set_root_blocknr(&extent_root->root_item,
+                                       extent_root->node->blocknr);
+                ret = btrfs_update_root(tree_root,
+                                        &extent_root->root_key,
+                                        &extent_root->root_item);
+                BUG_ON(ret);
+        }
+        __commit_transaction(extent_root);
+        __commit_transaction(tree_root);
+        return 0;
+}
+
 int btrfs_commit_transaction(struct btrfs_root *root,
                              struct btrfs_super_block *s)
 {
         int ret = 0;
+        struct btrfs_buffer *snap = root->commit_root;
+        struct btrfs_key snap_key;
 
         ret = __commit_transaction(root);
-        if (!ret && root != root->extent_root)
-                ret = __commit_transaction(root->extent_root);
         BUG_ON(ret);
-        if (root->commit_root != root->node) {
-                struct btrfs_buffer *snap = root->commit_root;
-                root->commit_root = root->node;
-                root->node->count++;
-                ret = btrfs_drop_snapshot(root, snap);
-                BUG_ON(ret);
-                // btrfs_block_release(root, snap);
-        }
+
+        if (root->commit_root == root->node)
+                return 0;
+
+        memcpy(&snap_key, &root->root_key, sizeof(snap_key));
+        root->root_key.offset++;
+
+        btrfs_set_root_blocknr(&root->root_item, root->node->blocknr);
+        ret = btrfs_insert_root(root->tree_root, &root->root_key,
+                                &root->root_item);
+        BUG_ON(ret);
+
+        ret = commit_extent_and_tree_roots(root->tree_root, root->extent_root);
+        BUG_ON(ret);
+
         write_ctree_super(root, s);
-        btrfs_finish_extent_commit(root);
+        btrfs_finish_extent_commit(root->extent_root);
+        btrfs_finish_extent_commit(root->tree_root);
+
+        root->commit_root = root->node;
+        root->node->count++;
+        ret = btrfs_drop_snapshot(root, snap);
+        BUG_ON(ret);
+
+        ret = btrfs_del_root(root->tree_root, &snap_key);
+        BUG_ON(ret);
+
         return ret;
 }
 
-static int __setup_root(struct btrfs_root *root, struct btrfs_root *extent_root,
-                        struct btrfs_root_info *info, int fp)
+static int __setup_root(struct btrfs_root *root, u64 objectid, int fp)
 {
         INIT_LIST_HEAD(&root->trans);
         INIT_LIST_HEAD(&root->cache);
         root->cache_size = 0;
         root->fp = fp;
         root->node = NULL;
-        root->extent_root = extent_root;
         root->commit_root = NULL;
-        root->node = read_tree_block(root, info->tree_root);
         memset(&root->current_insert, 0, sizeof(root->current_insert));
         memset(&root->last_insert, 0, sizeof(root->last_insert));
+        memset(&root->root_key, 0, sizeof(root->root_key));
+        memset(&root->root_item, 0, sizeof(root->root_item));
+        return 0;
+}
+
+static int find_and_setup_root(struct btrfs_root *tree_root, u64 objectid,
+                        struct btrfs_root *root, int fp)
+{
+        int ret;
+
+        __setup_root(root, objectid, fp);
+        ret = btrfs_find_last_root(tree_root, objectid,
+                                   &root->root_item, &root->root_key);
+        BUG_ON(ret);
+
+        root->node = read_tree_block(root,
+                                     btrfs_root_blocknr(&root->root_item));
+        root->ref_cows = 0;
+        BUG_ON(!root->node);
         return 0;
 }
 
@@ -196,9 +251,19 @@ struct btrfs_root *open_ctree(char *filename, struct btrfs_super_block *super)
 {
         struct btrfs_root *root = malloc(sizeof(struct btrfs_root));
         struct btrfs_root *extent_root = malloc(sizeof(struct btrfs_root));
+        struct btrfs_root *tree_root = malloc(sizeof(struct btrfs_root));
         int fp;
         int ret;
 
+        root->extent_root = extent_root;
+        root->tree_root = tree_root;
+
+        extent_root->extent_root = extent_root;
+        extent_root->tree_root = tree_root;
+
+        tree_root->extent_root = extent_root;
+        tree_root->tree_root = tree_root;
+
         fp = open(filename, O_CREAT | O_RDWR, 0600);
         if (fp < 0) {
                 free(root);
@@ -208,11 +273,14 @@ struct btrfs_root *open_ctree(char *filename, struct btrfs_super_block *super)
         INIT_RADIX_TREE(&root->pinned_radix, GFP_KERNEL);
         INIT_RADIX_TREE(&extent_root->pinned_radix, GFP_KERNEL);
         INIT_RADIX_TREE(&extent_root->cache_radix, GFP_KERNEL);
+        INIT_RADIX_TREE(&tree_root->pinned_radix, GFP_KERNEL);
+        INIT_RADIX_TREE(&tree_root->cache_radix, GFP_KERNEL);
+
         ret = pread(fp, super, sizeof(struct btrfs_super_block),
                      BTRFS_SUPER_INFO_OFFSET(BTRFS_BLOCKSIZE));
-        if (ret == 0 || super->root_info.tree_root == 0) {
+        if (ret == 0 || btrfs_super_root(super) == 0) {
                 printf("making new FS!\n");
-                ret = mkfs(fp);
+                ret = mkfs(fp, 0, BTRFS_BLOCKSIZE);
                 if (ret)
                         return NULL;
                 ret = pread(fp, super, sizeof(struct btrfs_super_block),
@@ -221,24 +289,29 @@ struct btrfs_root *open_ctree(char *filename, struct btrfs_super_block *super)
                         return NULL;
         }
         BUG_ON(ret < 0);
-        __setup_root(root, extent_root, &super->root_info, fp);
-        __setup_root(extent_root, extent_root, &super->extent_info, fp);
+
+        __setup_root(tree_root, BTRFS_ROOT_TREE_OBJECTID, fp);
+        tree_root->node = read_tree_block(tree_root, btrfs_super_root(super));
+        BUG_ON(!tree_root->node);
+
+        ret = find_and_setup_root(tree_root, BTRFS_EXTENT_TREE_OBJECTID,
+                                  extent_root, fp);
+        BUG_ON(ret);
+
+        ret = find_and_setup_root(tree_root, BTRFS_FS_TREE_OBJECTID,
+                                  root, fp);
+        BUG_ON(ret);
+
         root->commit_root = root->node;
         root->node->count++;
+        root->ref_cows = 1;
         return root;
 }
 
-static int __update_root(struct btrfs_root *root, struct btrfs_root_info *info)
-{
-        info->tree_root = root->node->blocknr;
-        return 0;
-}
-
 int write_ctree_super(struct btrfs_root *root, struct btrfs_super_block *s)
 {
         int ret;
-        __update_root(root, &s->root_info);
-        __update_root(root->extent_root, &s->extent_info);
+        btrfs_set_super_root(s, root->tree_root->node->blocknr);
         ret = pwrite(root->fp, s, sizeof(*s),
                      BTRFS_SUPER_INFO_OFFSET(BTRFS_BLOCKSIZE));
         if (ret != sizeof(*s)) {
@@ -260,19 +333,25 @@ static int drop_cache(struct btrfs_root *root)
 }
 int close_ctree(struct btrfs_root *root, struct btrfs_super_block *s)
 {
+        int ret;
         btrfs_commit_transaction(root, s);
-        __commit_transaction(root->extent_root);
+        ret = commit_extent_and_tree_roots(root->tree_root, root->extent_root);
+        BUG_ON(ret);
         write_ctree_super(root, s);
         drop_cache(root->extent_root);
+        drop_cache(root->tree_root);
         drop_cache(root);
         BUG_ON(!list_empty(&root->trans));
         BUG_ON(!list_empty(&root->extent_root->trans));
+        BUG_ON(!list_empty(&root->tree_root->trans));
 
         close(root->fp);
         if (root->node)
                 btrfs_block_release(root, root->node);
         if (root->extent_root->node)
                 btrfs_block_release(root->extent_root, root->extent_root->node);
+        if (root->tree_root->node)
+                btrfs_block_release(root->tree_root, root->tree_root->node);
         btrfs_block_release(root, root->commit_root);
         free(root);
         printf("on close %d blocks are allocated\n", allocated_blocks);
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index b391335864b1..c22a61f9233f 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -24,7 +24,8 @@ struct btrfs_root *open_ctree(char *filename, struct btrfs_super_block *s);
 int close_ctree(struct btrfs_root *root, struct btrfs_super_block *s);
 void btrfs_block_release(struct btrfs_root *root, struct btrfs_buffer *buf);
 int write_ctree_super(struct btrfs_root *root, struct btrfs_super_block *s);
-int mkfs(int fd);
+int mkfs(int fd, u64 num_blocks, u16 blocksize);
+
 
 #define BTRFS_SUPER_INFO_OFFSET(bs) (16 * (bs))
 
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a6969538bca2..21f39b404697 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -82,7 +82,7 @@ int btrfs_inc_ref(struct btrfs_root *root, struct btrfs_buffer *buf)
         u64 blocknr;
         int i;
 
-        if (root == root->extent_root)
+        if (!root->ref_cows)
                 return 0;
         if (btrfs_is_leaf(&buf->node))
                 return 0;
@@ -96,23 +96,22 @@ int btrfs_inc_ref(struct btrfs_root *root, struct btrfs_buffer *buf)
 
 int btrfs_finish_extent_commit(struct btrfs_root *root)
 {
-        struct btrfs_root *extent_root = root->extent_root;
         unsigned long gang[8];
         int ret;
         int i;
 
         while(1) {
-                ret = radix_tree_gang_lookup(&extent_root->pinned_radix,
+                ret = radix_tree_gang_lookup(&root->pinned_radix,
                                                  (void **)gang, 0,
                                                  ARRAY_SIZE(gang));
                 if (!ret)
                         break;
                 for (i = 0; i < ret; i++) {
-                        radix_tree_delete(&extent_root->pinned_radix, gang[i]);
+                        radix_tree_delete(&root->pinned_radix, gang[i]);
                 }
         }
-        extent_root->last_insert.objectid = 0;
-        extent_root->last_insert.offset = 0;
+        root->last_insert.objectid = 0;
+        root->last_insert.offset = 0;
         return 0;
 }
 
@@ -173,7 +172,7 @@ static int __free_extent(struct btrfs_root *root, u64 blocknr, u64 num_blocks)
         refs = btrfs_extent_refs(ei) - 1;
         btrfs_set_extent_refs(ei, refs);
         if (refs == 0) {
-                if (root == extent_root) {
+                if (!root->ref_cows) {
                         int err;
                         radix_tree_preload(GFP_KERNEL);
                         err = radix_tree_insert(&extent_root->pinned_radix,
@@ -513,7 +512,7 @@ static int walk_up_tree(struct btrfs_root *root, struct btrfs_path *path,
  */
 int btrfs_drop_snapshot(struct btrfs_root *root, struct btrfs_buffer *snap)
 {
-        int ret = 0;;
+        int ret = 0;
         int wret;
         int level;
         struct btrfs_path path;
diff --git a/fs/btrfs/mkfs.c b/fs/btrfs/mkfs.c
index fc1923320de3..dd14ed4fea6c 100644
--- a/fs/btrfs/mkfs.c
+++ b/fs/btrfs/mkfs.c
@@ -10,6 +10,120 @@
 #include "ctree.h"
 #include "disk-io.h"
 
+int mkfs(int fd, u64 num_blocks, u16 blocksize)
+{
+        struct btrfs_super_block super;
+        struct btrfs_leaf empty_leaf;
+        struct btrfs_root_item root_item;
+        struct btrfs_item item;
+        struct btrfs_extent_item extent_item;
+        char *block;
+        int ret;
+        u16 itemoff;
+
+        btrfs_set_super_blocknr(&super, 16);
+        btrfs_set_super_root(&super, 17);
+        strcpy((char *)(&super.magic), BTRFS_MAGIC);
+        btrfs_set_super_blocksize(&super, blocksize);
+        btrfs_set_super_total_blocks(&super, num_blocks);
+        btrfs_set_super_blocks_used(&super, 0);
+
+        block = malloc(blocksize);
+        memset(block, 0, blocksize);
+        BUG_ON(sizeof(super) > blocksize);
+        memcpy(block, &super, sizeof(super));
+        ret = pwrite(fd, block, blocksize, BTRFS_SUPER_INFO_OFFSET(blocksize));
+        BUG_ON(ret != blocksize);
+
+        /* create the tree of root objects */
+        memset(&empty_leaf, 0, sizeof(empty_leaf));
+        btrfs_set_header_parentid(&empty_leaf.header, BTRFS_ROOT_TREE_OBJECTID);
+        btrfs_set_header_blocknr(&empty_leaf.header, 17);
+        btrfs_set_header_nritems(&empty_leaf.header, 2);
+
+        /* create the items for the root tree */
+        btrfs_set_root_blocknr(&root_item, 18);
+        btrfs_set_root_refs(&root_item, 1);
+        itemoff = LEAF_DATA_SIZE - sizeof(root_item);
+        btrfs_set_item_offset(&item, itemoff);
+        btrfs_set_item_size(&item, sizeof(root_item));
+        btrfs_set_key_objectid(&item.key, BTRFS_EXTENT_TREE_OBJECTID);
+        btrfs_set_key_offset(&item.key, 0);
+        btrfs_set_key_flags(&item.key, 0);
+        memcpy(empty_leaf.items, &item, sizeof(item));
+        memcpy(empty_leaf.data + itemoff, &root_item, sizeof(root_item));
+
+        btrfs_set_root_blocknr(&root_item, 19);
+        itemoff = itemoff - sizeof(root_item);
+        btrfs_set_item_offset(&item, itemoff);
+        btrfs_set_key_objectid(&item.key, BTRFS_FS_TREE_OBJECTID);
+        memcpy(empty_leaf.items + 1, &item, sizeof(item));
+        memcpy(empty_leaf.data + itemoff, &root_item, sizeof(root_item));
+        ret = pwrite(fd, &empty_leaf, blocksize, 17 * blocksize);
+
+        /* create the items for the extent tree */
+        btrfs_set_header_parentid(&empty_leaf.header,
+                                  BTRFS_EXTENT_TREE_OBJECTID);
+        btrfs_set_header_blocknr(&empty_leaf.header, 18);
+        btrfs_set_header_nritems(&empty_leaf.header, 4);
+
+        /* item1, reserve blocks 0-16 */
+        btrfs_set_key_objectid(&item.key, 0);
+        btrfs_set_key_offset(&item.key, 17);
+        btrfs_set_key_flags(&item.key, 0);
+        itemoff = LEAF_DATA_SIZE - sizeof(struct btrfs_extent_item);
+        btrfs_set_item_offset(&item, itemoff);
+        btrfs_set_item_size(&item, sizeof(struct btrfs_extent_item));
+        btrfs_set_extent_refs(&extent_item, 1);
+        btrfs_set_extent_owner(&extent_item, 0);
+        memcpy(empty_leaf.items, &item, sizeof(item));
+        memcpy(empty_leaf.data + btrfs_item_offset(&item), &extent_item,
+                btrfs_item_size(&item));
+
+        /* item2, give block 17 to the root */
+        btrfs_set_key_objectid(&item.key, 17);
+        btrfs_set_key_offset(&item.key, 1);
+        itemoff = itemoff - sizeof(struct btrfs_extent_item);
+        btrfs_set_item_offset(&item, itemoff);
+        btrfs_set_extent_owner(&extent_item, BTRFS_ROOT_TREE_OBJECTID);
+        memcpy(empty_leaf.items + 1, &item, sizeof(item));
+        memcpy(empty_leaf.data + btrfs_item_offset(&item), &extent_item,
+                btrfs_item_size(&item));
+
+        /* item3, give block 18 to the extent root */
+        btrfs_set_key_objectid(&item.key, 18);
+        btrfs_set_key_offset(&item.key, 1);
+        itemoff = itemoff - sizeof(struct btrfs_extent_item);
+        btrfs_set_item_offset(&item, itemoff);
+        btrfs_set_extent_owner(&extent_item, BTRFS_EXTENT_TREE_OBJECTID);
+        memcpy(empty_leaf.items + 2, &item, sizeof(item));
+        memcpy(empty_leaf.data + btrfs_item_offset(&item), &extent_item,
+                btrfs_item_size(&item));
+
+        /* item4, give block 19 to the FS root */
+        btrfs_set_key_objectid(&item.key, 19);
+        btrfs_set_key_offset(&item.key, 1);
+        itemoff = itemoff - sizeof(struct btrfs_extent_item);
+        btrfs_set_item_offset(&item, itemoff);
+        btrfs_set_extent_owner(&extent_item, BTRFS_FS_TREE_OBJECTID);
+        memcpy(empty_leaf.items + 3, &item, sizeof(item));
+        memcpy(empty_leaf.data + btrfs_item_offset(&item), &extent_item,
+                btrfs_item_size(&item));
+        ret = pwrite(fd, &empty_leaf, blocksize, 18 * blocksize);
+        if (ret != sizeof(empty_leaf))
+                return -1;
+
+        /* finally create the FS root */
+        btrfs_set_header_parentid(&empty_leaf.header, BTRFS_FS_TREE_OBJECTID);
+        btrfs_set_header_blocknr(&empty_leaf.header, 19);
+        btrfs_set_header_nritems(&empty_leaf.header, 0);
+        ret = pwrite(fd, &empty_leaf, blocksize, 19 * blocksize);
+        if (ret != sizeof(empty_leaf))
+                return -1;
+        return 0;
+}
+
+#if 0
 int mkfs(int fd)
 {
         struct btrfs_root_info info[2];
@@ -20,13 +134,14 @@ int mkfs(int fd)
 
         /* setup the super block area */
         memset(info, 0, sizeof(info));
-        info[0].blocknr = 16;
-        info[0].objectid = 1;
-        info[0].tree_root = 17;
+        btrfs_set_root_blocknr(info, 16);
+        btrfs_set_root_objectid(info, 1);
+        btrfs_set_root_tree_root(info, 17);
+
+        btrfs_set_root_blocknr(info + 1, 16);
+        btrfs_set_root_objectid(info + 1, 2);
+        btrfs_set_root_tree_root(info + 1, 18);
 
-        info[1].blocknr = 16;
-        info[1].objectid = 2;
-        info[1].tree_root = 18;
         ret = pwrite(fd, info, sizeof(info),
                      BTRFS_SUPER_INFO_OFFSET(BTRFS_BLOCKSIZE));
         if (ret != sizeof(info))
@@ -81,3 +196,4 @@ int mkfs(int fd)
                 return -1;
         return 0;
 }
+#endif
diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c
index c95c85640aa9..64829b6b90f9 100644
--- a/fs/btrfs/print-tree.c
+++ b/fs/btrfs/print-tree.c
@@ -11,6 +11,7 @@ void btrfs_print_leaf(struct btrfs_leaf *l)
         u32 nr = btrfs_header_nritems(&l->header);
         struct btrfs_item *item;
         struct btrfs_extent_item *ei;
+        struct btrfs_root_item *ri;
         printf("leaf %Lu total ptrs %d free space %d\n",
                 btrfs_header_blocknr(&l->header), nr, btrfs_leaf_free_space(l));
         fflush(stdout);
@@ -23,13 +24,15 @@ void btrfs_print_leaf(struct btrfs_leaf *l)
                         btrfs_key_offset(&item->key),
                         btrfs_item_offset(item),
                         btrfs_item_size(item));
-                fflush(stdout);
                 printf("\t\titem data %.*s\n", btrfs_item_size(item),
                         l->data + btrfs_item_offset(item));
                 ei = (struct btrfs_extent_item *)(l->data +
                                                   btrfs_item_offset(item));
-                printf("\t\textent data refs %u owner %Lu\n", ei->refs,
-                        ei->owner);
+                printf("\t\textent data refs %u owner %Lu\n",
+                        btrfs_extent_refs(ei), btrfs_extent_owner(ei));
+                ri = (struct btrfs_root_item *)ei;
+                printf("\t\troot data blocknr %Lu refs %u\n",
+                        btrfs_root_blocknr(ri), btrfs_root_refs(ri));
                 fflush(stdout);
         }
 }
@@ -71,6 +74,5 @@ void btrfs_print_tree(struct btrfs_root *root, struct btrfs_buffer *t)
                 btrfs_print_tree(root, next_buf);
                 btrfs_block_release(root, next_buf);
         }
-
 }
 
diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
new file mode 100644
index 000000000000..0ab90cfea98f
--- /dev/null
+++ b/fs/btrfs/root-tree.c
@@ -0,0 +1,88 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "kerncompat.h"
+#include "radix-tree.h"
+#include "ctree.h"
+#include "disk-io.h"
+#include "print-tree.h"
+
+int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
+                        struct btrfs_root_item *item, struct btrfs_key *key)
+{
+        struct btrfs_path path;
+        struct btrfs_key search_key;
+        struct btrfs_leaf *l;
+        int ret;
+        int slot;
+
+        search_key.objectid = objectid;
+        search_key.flags = (u32)-1;
+        search_key.offset = (u32)-1;
+
+        btrfs_init_path(&path);
+        ret = btrfs_search_slot(root, &search_key, &path, 0, 0);
+        if (ret < 0)
+                goto out;
+        BUG_ON(ret == 0);
+        l = &path.nodes[0]->leaf;
+        BUG_ON(path.slots[0] == 0);
+        slot = path.slots[0] - 1;
+        if (btrfs_key_objectid(&l->items[slot].key) != objectid) {
+                ret = 1;
+                goto out;
+        }
+        memcpy(item, l->data + btrfs_item_offset(l->items + slot),
+                sizeof(*item));
+        btrfs_disk_key_to_cpu(key, &l->items[slot].key);
+        btrfs_release_path(root, &path);
+        ret = 0;
+out:
+        return ret;
+}
+
+int btrfs_update_root(struct btrfs_root *root, struct btrfs_key *key,
+                      struct btrfs_root_item *item)
+{
+        struct btrfs_path path;
+        struct btrfs_leaf *l;
+        int ret;
+        int slot;
+
+        btrfs_init_path(&path);
+        ret = btrfs_search_slot(root, key, &path, 0, 1);
+        if (ret < 0)
+                goto out;
+        BUG_ON(ret != 0);
+        l = &path.nodes[0]->leaf;
+        slot = path.slots[0];
+        memcpy(l->data + btrfs_item_offset(l->items + slot), item,
+                sizeof(*item));
+out:
+        btrfs_release_path(root, &path);
+        return ret;
+}
+
+int btrfs_insert_root(struct btrfs_root *root, struct btrfs_key *key,
+                      struct btrfs_root_item *item)
+{
+        int ret;
+        ret = btrfs_insert_item(root, key, item, sizeof(*item));
+        BUG_ON(ret);
+        return ret;
+}
+
+int btrfs_del_root(struct btrfs_root *root, struct btrfs_key *key)
+{
+        struct btrfs_path path;
+        int ret;
+
+        btrfs_init_path(&path);
+        ret = btrfs_search_slot(root, key, &path, -1, 1);
+        if (ret < 0)
+                goto out;
+        BUG_ON(ret != 0);
+        ret = btrfs_del_item(root, &path);
+out:
+        btrfs_release_path(root, &path);
+        return ret;
+}