Btrfs: introduce subvol uuids and times

This patch introduces uuids for subvolumes. Each
subvolume has it's own uuid. In case it was snapshotted,
it also contains parent_uuid. In case it was received,
it also contains received_uuid.

It also introduces subvolume ctime/otime/stime/rtime. The
first two are comparable to the times found in inodes. otime
is the origin/creation time and ctime is the change time.
stime/rtime are only valid on received subvolumes.
stime is the time of the subvolume when it was
sent. rtime is the time of the subvolume when it was
received.

Additionally to the times, we have a transid for each
time. They are updated at the same place as the times.

btrfs receive uses stransid and rtransid to find out
if a received subvolume changed in the meantime.

If an older kernel mounts a filesystem with the
extented fields, all fields become invalid. The next
mount with a new kernel will detect this and reset the
fields.

Signed-off-by: Alexander Block <ablock84@googlemail.com>
Reviewed-by: David Sterba <dave@jikos.cz>
Reviewed-by: Arne Jansen <sensille@gmx.net>
Reviewed-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Reviewed-by: Alex Lyakas <alex.bolshoy.btrfs@gmail.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index b72b068183ec..a21f3085a334 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) {