8 files changed, 292 insertions, 15 deletions

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index da6e9364a5e..9197e2e3340 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -1032,6 +1032,7 @@ continue_with_current_leaf_stack_frame:
                         struct btrfs_disk_key *disk_key;
                         u8 type;
                         u32 item_offset;
+                        u32 item_size;
 
                         if (disk_item_offset + sizeof(struct btrfs_item) >
                             sf->block_ctx->len) {
@@ -1047,6 +1048,7 @@ leaf_item_out_of_bounce_error:
                                                      disk_item_offset,
                                                      sizeof(struct btrfs_item));
                         item_offset = le32_to_cpu(disk_item.offset);
+                        item_size = le32_to_cpu(disk_item.size);
                         disk_key = &disk_item.key;
                         type = disk_key->type;
 
@@ -1057,14 +1059,13 @@ leaf_item_out_of_bounce_error:
 
                                 root_item_offset = item_offset +
                                         offsetof(struct btrfs_leaf, items);
-                                if (root_item_offset +
-                                    sizeof(struct btrfs_root_item) >
+                                if (root_item_offset + item_size >
                                     sf->block_ctx->len)
                                         goto leaf_item_out_of_bounce_error;
                                 btrfsic_read_from_block_data(
                                         sf->block_ctx, &root_item,
                                         root_item_offset,
-                                        sizeof(struct btrfs_root_item));
+                                        item_size);
                                 next_bytenr = le64_to_cpu(root_item.bytenr);
 
                                 sf->error =
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 8cfde9326dd..d5f6d745867 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -709,6 +709,36 @@ struct btrfs_root_item {
         struct btrfs_disk_key drop_progress;
         u8 drop_level;
         u8 level;
+
+        /*
+         * The following fields appear after subvol_uuids+subvol_times
+         * were introduced.
+         */
+
+        /*
+         * This generation number is used to test if the new fields are valid
+         * and up to date while reading the root item. Everytime the root item
+         * is written out, the "generation" field is copied into this field. If
+         * anyone ever mounted the fs with an older kernel, we will have
+         * mismatching generation values here and thus must invalidate the
+         * new fields. See btrfs_update_root and btrfs_find_last_root for
+         * details.
+         * the offset of generation_v2 is also used as the start for the memset
+         * when invalidating the fields.
+         */
+        __le64 generation_v2;
+        u8 uuid[BTRFS_UUID_SIZE];
+        u8 parent_uuid[BTRFS_UUID_SIZE];
+        u8 received_uuid[BTRFS_UUID_SIZE];
+        __le64 ctransid; /* updated when an inode changes */
+        __le64 otransid; /* trans when created */
+        __le64 stransid; /* trans when sent. non-zero for received subvol */
+        __le64 rtransid; /* trans when received. non-zero for received subvol */
+        struct btrfs_timespec ctime;
+        struct btrfs_timespec otime;
+        struct btrfs_timespec stime;
+        struct btrfs_timespec rtime;
+        __le64 reserved[8]; /* for future */
 } __attribute__ ((__packed__));
 
 /*
@@ -1416,6 +1446,8 @@ struct btrfs_root {
         dev_t anon_dev;
 
         int force_cow;
+
+        spinlock_t root_times_lock;
 };
 
 struct btrfs_ioctl_defrag_range_args {
@@ -2189,6 +2221,16 @@ BTRFS_SETGET_STACK_FUNCS(root_used, struct btrfs_root_item, bytes_used, 64);
 BTRFS_SETGET_STACK_FUNCS(root_limit, struct btrfs_root_item, byte_limit, 64);
 BTRFS_SETGET_STACK_FUNCS(root_last_snapshot, struct btrfs_root_item,
                          last_snapshot, 64);
+BTRFS_SETGET_STACK_FUNCS(root_generation_v2, struct btrfs_root_item,
+                         generation_v2, 64);
+BTRFS_SETGET_STACK_FUNCS(root_ctransid, struct btrfs_root_item,
+                         ctransid, 64);
+BTRFS_SETGET_STACK_FUNCS(root_otransid, struct btrfs_root_item,
+                         otransid, 64);
+BTRFS_SETGET_STACK_FUNCS(root_stransid, struct btrfs_root_item,
+                         stransid, 64);
+BTRFS_SETGET_STACK_FUNCS(root_rtransid, struct btrfs_root_item,
+                         rtransid, 64);
 
 static inline bool btrfs_root_readonly(struct btrfs_root *root)
 {
@@ -2822,6 +2864,9 @@ int __must_check btrfs_update_root(struct btrfs_trans_handle *trans,
                                    struct btrfs_root *root,
                                    struct btrfs_key *key,
                                    struct btrfs_root_item *item);
+void btrfs_read_root_item(struct btrfs_root *root,
+                         struct extent_buffer *eb, int slot,
+                         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);
 int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid);
@@ -2829,6 +2874,8 @@ int btrfs_find_orphan_roots(struct btrfs_root *tree_root);
 void btrfs_set_root_node(struct btrfs_root_item *item,
                          struct extent_buffer *node);
 void btrfs_check_and_init_root_item(struct btrfs_root_item *item);
+void btrfs_update_root_times(struct btrfs_trans_handle *trans,
+                             struct btrfs_root *root);
 
 /* dir-item.c */
 int btrfs_insert_dir_item(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 2936ca49b3b..c39eb71fae3 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1182,6 +1182,8 @@ static void __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
         root->defrag_running = 0;
         root->root_key.objectid = objectid;
         root->anon_dev = 0;
+
+        spin_lock_init(&root->root_times_lock);
 }
 
 static int __must_check find_and_setup_root(struct btrfs_root *tree_root,
@@ -1326,6 +1328,7 @@ struct btrfs_root *btrfs_read_fs_root_no_radix(struct btrfs_root *tree_root,
         u64 generation;
         u32 blocksize;
         int ret = 0;
+        int slot;
 
         root = btrfs_alloc_root(fs_info);
         if (!root)
@@ -1352,9 +1355,8 @@ struct btrfs_root *btrfs_read_fs_root_no_radix(struct btrfs_root *tree_root,
         ret = btrfs_search_slot(NULL, tree_root, location, path, 0, 0);
         if (ret == 0) {
                 l = path->nodes[0];
-                read_extent_buffer(l, &root->root_item,
-                                btrfs_item_ptr_offset(l, path->slots[0]),
-                                sizeof(root->root_item));
+                slot = path->slots[0];
+                btrfs_read_root_item(tree_root, l, slot, &root->root_item);
                 memcpy(&root->root_key, location, sizeof(*location));
         }
         btrfs_free_path(path);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a7d1921ac76..4ffc8738954 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2734,6 +2734,8 @@ noinline int btrfs_update_inode(struct btrfs_trans_handle *trans,
          */
         if (!btrfs_is_free_space_inode(root, inode)
             && root->root_key.objectid != BTRFS_DATA_RELOC_TREE_OBJECTID) {
+                btrfs_update_root_times(trans, root);
+
                 ret = btrfs_delayed_update_inode(trans, root, inode);
                 if (!ret)
                         btrfs_set_inode_last_trans(trans, inode);
@@ -4723,6 +4725,8 @@ static struct inode *btrfs_new_inode(struct btrfs_trans_handle *trans,
         trace_btrfs_inode_new(inode);
         btrfs_set_inode_last_trans(trans, inode);
 
+        btrfs_update_root_times(trans, root);
+
         return inode;
 fail:
         if (dir)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 7011871c45b..99fe2ce7f72 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -41,6 +41,7 @@
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
+#include <linux/uuid.h>
 #include "compat.h"
 #include "ctree.h"
 #include "disk-io.h"
@@ -346,11 +347,13 @@ static noinline int create_subvol(struct btrfs_root *root,
         struct btrfs_root *new_root;
         struct dentry *parent = dentry->d_parent;
         struct inode *dir;
+        struct timespec cur_time = CURRENT_TIME;
         int ret;
         int err;
         u64 objectid;
         u64 new_dirid = BTRFS_FIRST_FREE_OBJECTID;
         u64 index = 0;
+        uuid_le new_uuid;
 
         ret = btrfs_find_free_objectid(root->fs_info->tree_root, &objectid);
         if (ret)
@@ -389,8 +392,9 @@ static noinline int create_subvol(struct btrfs_root *root,
                             BTRFS_UUID_SIZE);
         btrfs_mark_buffer_dirty(leaf);
 
+        memset(&root_item, 0, sizeof(root_item));
+
         inode_item = &root_item.inode;
-        memset(inode_item, 0, sizeof(*inode_item));
         inode_item->generation = cpu_to_le64(1);
         inode_item->size = cpu_to_le64(3);
         inode_item->nlink = cpu_to_le32(1);
@@ -408,8 +412,15 @@ static noinline int create_subvol(struct btrfs_root *root,
         btrfs_set_root_used(&root_item, leaf->len);
         btrfs_set_root_last_snapshot(&root_item, 0);
 
-        memset(&root_item.drop_progress, 0, sizeof(root_item.drop_progress));
-        root_item.drop_level = 0;
+        btrfs_set_root_generation_v2(&root_item,
+                        btrfs_root_generation(&root_item));
+        uuid_le_gen(&new_uuid);
+        memcpy(root_item.uuid, new_uuid.b, BTRFS_UUID_SIZE);
+        root_item.otime.sec = cpu_to_le64(cur_time.tv_sec);
+        root_item.otime.nsec = cpu_to_le64(cur_time.tv_nsec);
+        root_item.ctime = root_item.otime;
+        btrfs_set_root_ctransid(&root_item, trans->transid);
+        btrfs_set_root_otransid(&root_item, trans->transid);
 
         btrfs_tree_unlock(leaf);
         free_extent_buffer(leaf);
@@ -3395,6 +3406,87 @@ out:
         return ret;
 }
 
+static long btrfs_ioctl_set_received_subvol(struct file *file,
+                                            void __user *arg)
+{
+        struct btrfs_ioctl_received_subvol_args *sa = NULL;
+        struct inode *inode = fdentry(file)->d_inode;
+        struct btrfs_root *root = BTRFS_I(inode)->root;
+        struct btrfs_root_item *root_item = &root->root_item;
+        struct btrfs_trans_handle *trans;
+        struct timespec ct = CURRENT_TIME;
+        int ret = 0;
+
+        ret = mnt_want_write_file(file);
+        if (ret < 0)
+                return ret;
+
+        down_write(&root->fs_info->subvol_sem);
+
+        if (btrfs_ino(inode) != BTRFS_FIRST_FREE_OBJECTID) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        if (btrfs_root_readonly(root)) {
+                ret = -EROFS;
+                goto out;
+        }
+
+        if (!inode_owner_or_capable(inode)) {
+                ret = -EACCES;
+                goto out;
+        }
+
+        sa = memdup_user(arg, sizeof(*sa));
+        if (IS_ERR(sa)) {
+                ret = PTR_ERR(sa);
+                sa = NULL;
+                goto out;
+        }
+
+        trans = btrfs_start_transaction(root, 1);
+        if (IS_ERR(trans)) {
+                ret = PTR_ERR(trans);
+                trans = NULL;
+                goto out;
+        }
+
+        sa->rtransid = trans->transid;
+        sa->rtime.sec = ct.tv_sec;
+        sa->rtime.nsec = ct.tv_nsec;
+
+        memcpy(root_item->received_uuid, sa->uuid, BTRFS_UUID_SIZE);
+        btrfs_set_root_stransid(root_item, sa->stransid);
+        btrfs_set_root_rtransid(root_item, sa->rtransid);
+        root_item->stime.sec = cpu_to_le64(sa->stime.sec);
+        root_item->stime.nsec = cpu_to_le32(sa->stime.nsec);
+        root_item->rtime.sec = cpu_to_le64(sa->rtime.sec);
+        root_item->rtime.nsec = cpu_to_le32(sa->rtime.nsec);
+
+        ret = btrfs_update_root(trans, root->fs_info->tree_root,
+                                &root->root_key, &root->root_item);
+        if (ret < 0) {
+                btrfs_end_transaction(trans, root);
+                trans = NULL;
+                goto out;
+        } else {
+                ret = btrfs_commit_transaction(trans, root);
+                if (ret < 0)
+                        goto out;
+        }
+
+        ret = copy_to_user(arg, sa, sizeof(*sa));
+        if (ret)
+                ret = -EFAULT;
+
+out:
+        kfree(sa);
+        up_write(&root->fs_info->subvol_sem);
+        mnt_drop_write_file(file);
+        return ret;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
                 cmd, unsigned long arg)
 {
@@ -3477,6 +3569,8 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_balance_ctl(root, arg);
         case BTRFS_IOC_BALANCE_PROGRESS:
                 return btrfs_ioctl_balance_progress(root, argp);
+        case BTRFS_IOC_SET_RECEIVED_SUBVOL:
+                return btrfs_ioctl_set_received_subvol(file, argp);
         case BTRFS_IOC_GET_DEV_STATS:
                 return btrfs_ioctl_get_dev_stats(root, argp, 0);
         case BTRFS_IOC_GET_AND_RESET_DEV_STATS:
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index e440aa653c3..0c505d7ff8e 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -295,6 +295,21 @@ struct btrfs_ioctl_get_dev_stats {
         __u64 unused[128 - 2 - BTRFS_DEV_STAT_VALUES_MAX]; /* pad to 1k */
 };
 
+struct btrfs_ioctl_timespec {
+        __u64 sec;
+        __u32 nsec;
+};
+
+struct btrfs_ioctl_received_subvol_args {
+        char    uuid[BTRFS_UUID_SIZE];  /* in */
+        __u64   stransid;               /* in */
+        __u64   rtransid;               /* out */
+        struct btrfs_ioctl_timespec stime; /* in */
+        struct btrfs_ioctl_timespec rtime; /* out */
+        __u64   flags;                  /* in */
+        __u64   reserved[16];           /* in */
+};
+
 #define BTRFS_IOC_SNAP_CREATE _IOW(BTRFS_IOCTL_MAGIC, 1, \
                                    struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_DEFRAG _IOW(BTRFS_IOCTL_MAGIC, 2, \
@@ -359,6 +374,8 @@ struct btrfs_ioctl_get_dev_stats {
                                         struct btrfs_ioctl_ino_path_args)
 #define BTRFS_IOC_LOGICAL_INO _IOWR(BTRFS_IOCTL_MAGIC, 36, \
                                         struct btrfs_ioctl_ino_path_args)
+#define BTRFS_IOC_SET_RECEIVED_SUBVOL _IOWR(BTRFS_IOCTL_MAGIC, 37, \
+                                struct btrfs_ioctl_received_subvol_args)
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
                                       struct btrfs_ioctl_get_dev_stats)
 #define BTRFS_IOC_GET_AND_RESET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 53, \
diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
index 24fb8ce4e07..6bb465cca20 100644
--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -16,12 +16,55 @@
  * Boston, MA 021110-1307, USA.
  */
 
+#include <linux/uuid.h>
 #include "ctree.h"
 #include "transaction.h"
 #include "disk-io.h"
 #include "print-tree.h"
 
 /*
+ * Read a root item from the tree. In case we detect a root item smaller then
+ * sizeof(root_item), we know it's an old version of the root structure and
+ * initialize all new fields to zero. The same happens if we detect mismatching
+ * generation numbers as then we know the root was once mounted with an older
+ * kernel that was not aware of the root item structure change.
+ */
+void btrfs_read_root_item(struct btrfs_root *root,
+                         struct extent_buffer *eb, int slot,
+                         struct btrfs_root_item *item)
+{
+        uuid_le uuid;
+        int len;
+        int need_reset = 0;
+
+        len = btrfs_item_size_nr(eb, slot);
+        read_extent_buffer(eb, item, btrfs_item_ptr_offset(eb, slot),
+                        min_t(int, len, (int)sizeof(*item)));
+        if (len < sizeof(*item))
+                need_reset = 1;
+        if (!need_reset && btrfs_root_generation(item)
+                != btrfs_root_generation_v2(item)) {
+                if (btrfs_root_generation_v2(item) != 0) {
+                        printk(KERN_WARNING "btrfs: mismatching "
+                                        "generation and generation_v2 "
+                                        "found in root item. This root "
+                                        "was probably mounted with an "
+                                        "older kernel. Resetting all "
+                                        "new fields.\n");
+                }
+                need_reset = 1;
+        }
+        if (need_reset) {
+                memset(&item->generation_v2, 0,
+                        sizeof(*item) - offsetof(struct btrfs_root_item,
+                                        generation_v2));
+
+                uuid_le_gen(&uuid);
+                memcpy(item->uuid, uuid.b, BTRFS_UUID_SIZE);
+        }
+}
+
+/*
  * lookup the root with the highest offset for a given objectid.  The key we do
  * find is copied into 'key'.  If we find something return 0, otherwise 1, < 0
  * on error.
@@ -61,10 +104,10 @@ int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
                 goto out;
         }
         if (item)
-                read_extent_buffer(l, item, btrfs_item_ptr_offset(l, slot),
-                                   sizeof(*item));
+                btrfs_read_root_item(root, l, slot, item);
         if (key)
                 memcpy(key, &found_key, sizeof(found_key));
+
         ret = 0;
 out:
         btrfs_free_path(path);
@@ -91,16 +134,15 @@ int btrfs_update_root(struct btrfs_trans_handle *trans, struct btrfs_root
         int ret;
         int slot;
         unsigned long ptr;
+        int old_len;
 
         path = btrfs_alloc_path();
         if (!path)
                 return -ENOMEM;
 
         ret = btrfs_search_slot(trans, root, key, path, 0, 1);
-        if (ret < 0) {
-                btrfs_abort_transaction(trans, root, ret);
-                goto out;
-        }
+        if (ret < 0)
+                goto out_abort;
 
         if (ret != 0) {
                 btrfs_print_leaf(root, path->nodes[0]);
@@ -113,16 +155,56 @@ int btrfs_update_root(struct btrfs_trans_handle *trans, struct btrfs_root
         l = path->nodes[0];
         slot = path->slots[0];
         ptr = btrfs_item_ptr_offset(l, slot);
+        old_len = btrfs_item_size_nr(l, slot);
+
+        /*
+         * If this is the first time we update the root item which originated
+         * from an older kernel, we need to enlarge the item size to make room
+         * for the added fields.
+         */
+        if (old_len < sizeof(*item)) {
+                btrfs_release_path(path);
+                ret = btrfs_search_slot(trans, root, key, path,
+                                -1, 1);
+                if (ret < 0)
+                        goto out_abort;
+                ret = btrfs_del_item(trans, root, path);
+                if (ret < 0)
+                        goto out_abort;
+                btrfs_release_path(path);
+                ret = btrfs_insert_empty_item(trans, root, path,
+                                key, sizeof(*item));
+                if (ret < 0)
+                        goto out_abort;
+                l = path->nodes[0];
+                slot = path->slots[0];
+                ptr = btrfs_item_ptr_offset(l, slot);
+        }
+
+        /*
+         * Update generation_v2 so at the next mount we know the new root
+         * fields are valid.
+         */
+        btrfs_set_root_generation_v2(item, btrfs_root_generation(item));
+
         write_extent_buffer(l, item, ptr, sizeof(*item));
         btrfs_mark_buffer_dirty(path->nodes[0]);
 out:
         btrfs_free_path(path);
         return ret;
+
+out_abort:
+        btrfs_abort_transaction(trans, root, ret);
+        goto out;
 }
 
 int btrfs_insert_root(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                       struct btrfs_key *key, struct btrfs_root_item *item)
 {
+        /*
+         * Make sure generation v1 and v2 match. See update_root for details.
+         */
+        btrfs_set_root_generation_v2(item, btrfs_root_generation(item));
         return btrfs_insert_item(trans, root, key, item, sizeof(*item));
 }
 
@@ -454,3 +536,16 @@ void btrfs_check_and_init_root_item(struct btrfs_root_item *root_item)
                 root_item->byte_limit = 0;
         }
 }
+
+void btrfs_update_root_times(struct btrfs_trans_handle *trans,
+                             struct btrfs_root *root)
+{
+        struct btrfs_root_item *item = &root->root_item;
+        struct timespec ct = CURRENT_TIME;
+
+        spin_lock(&root->root_times_lock);
+        item->ctransid = trans->transid;
+        item->ctime.sec = cpu_to_le64(ct.tv_sec);
+        item->ctime.nsec = cpu_to_le64(ct.tv_nsec);
+        spin_unlock(&root->root_times_lock);
+}
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index b72b068183e..a21f3085a33 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -22,6 +22,7 @@
 #include <linux/writeback.h>
 #include <linux/pagemap.h>
 #include <linux/blkdev.h>
+#include <linux/uuid.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
@@ -926,11 +927,13 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
         struct dentry *dentry;
         struct extent_buffer *tmp;
         struct extent_buffer *old;
+        struct timespec cur_time = CURRENT_TIME;
         int ret;
         u64 to_reserve = 0;
         u64 index = 0;
         u64 objectid;
         u64 root_flags;
+        uuid_le new_uuid;
 
         rsv = trans->block_rsv;
 
@@ -1016,6 +1019,20 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
                 root_flags &= ~BTRFS_ROOT_SUBVOL_RDONLY;
         btrfs_set_root_flags(new_root_item, root_flags);
 
+        btrfs_set_root_generation_v2(new_root_item,
+                        trans->transid);
+        uuid_le_gen(&new_uuid);
+        memcpy(new_root_item->uuid, new_uuid.b, BTRFS_UUID_SIZE);
+        memcpy(new_root_item->parent_uuid, root->root_item.uuid,
+                        BTRFS_UUID_SIZE);
+        new_root_item->otime.sec = cpu_to_le64(cur_time.tv_sec);
+        new_root_item->otime.nsec = cpu_to_le64(cur_time.tv_nsec);
+        btrfs_set_root_otransid(new_root_item, trans->transid);
+        memset(&new_root_item->stime, 0, sizeof(new_root_item->stime));
+        memset(&new_root_item->rtime, 0, sizeof(new_root_item->rtime));
+        btrfs_set_root_stransid(new_root_item, 0);
+        btrfs_set_root_rtransid(new_root_item, 0);
+
         old = btrfs_lock_root_node(root);
         ret = btrfs_cow_block(trans, root, old, NULL, 0, &old);
         if (ret) {