btrfs: pass fs_info to trace_btrfs_transaction_commit

The root on the trans->root can be anything, and generally we're
committing from the transaction kthread so it's usually the tree_root.
Change this to just take an fs_info, and to maintain compatibility
simply put the ROOT_TREE_OBJECTID as the root objectid for the
tracepoint.  This will allow use to remove trans->root.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -4989,7 +4989,7 @@ static int btrfs_cleanup_transaction(struct btrfs_fs_info *fs_info)
 		spin_unlock(&fs_info->trans_lock);
 
 		btrfs_put_transaction(t);
-		trace_btrfs_transaction_commit(fs_info->tree_root);
+		trace_btrfs_transaction_commit(fs_info);
 		spin_lock(&fs_info->trans_lock);
 	}
 	spin_unlock(&fs_info->trans_lock);

fs/btrfs/transaction.c

@@ -1956,7 +1956,7 @@ static void cleanup_transaction(struct btrfs_trans_handle *trans, int err)
 	btrfs_put_transaction(cur_trans);
 	btrfs_put_transaction(cur_trans);
 
-	trace_btrfs_transaction_commit(trans->root);
+	trace_btrfs_transaction_commit(fs_info);
 
 	if (current->journal_info == trans)
 		current->journal_info = NULL;
@@ -2361,7 +2361,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 	if (trans->type & __TRANS_FREEZABLE)
 		sb_end_intwrite(fs_info->sb);
 
-	trace_btrfs_transaction_commit(trans->root);
+	trace_btrfs_transaction_commit(fs_info);
 
 	btrfs_scrub_continue(fs_info);
 

include/trace/events/btrfs.h

@@ -182,18 +182,18 @@ FLUSH_STATES
 
 TRACE_EVENT(btrfs_transaction_commit,
 
-	TP_PROTO(const struct btrfs_root *root),
+	TP_PROTO(const struct btrfs_fs_info *fs_info),
 
-	TP_ARGS(root),
+	TP_ARGS(fs_info),
 
 	TP_STRUCT__entry_btrfs(
 		__field(	u64,  generation		)
 		__field(	u64,  root_objectid		)
 	),
 
-	TP_fast_assign_btrfs(root->fs_info,
-		__entry->generation	= root->fs_info->generation;
-		__entry->root_objectid	= root->root_key.objectid;
+	TP_fast_assign_btrfs(fs_info,
+		__entry->generation	= fs_info->generation;
+		__entry->root_objectid	= BTRFS_ROOT_TREE_OBJECTID;
 	),
 
 	TP_printk_btrfs("root=%llu(%s) gen=%llu",