2014-02-08 23:46 GMT+08:00 Wang Shilong <wangshilong1991@xxxxxxxxx>: > From: Wang Shilong <wangsl.fnst@xxxxxxxxxxxxxx> > > This reverts commit 41ce9970a8a6a362ae8df145f7a03d789e9ef9d2. > Previously i was thinking we can use readonly root's commit root > safely while it is not true, readonly root may be cowed with the > following cases. > > 1.snapshot send root will cow source root. > 2.balance,device operations will also cow readonly send root > to relocate. > > So i have two ideas to make us safe to use commit root. > > -->approach 1: > make it protected by transaction and end transaction properly and we research > next item from root node(see btrfs_search_slot_for_read()). > > -->approach 2: > add another counter to local root structure to sync snapshot with send. > and add a global counter to sync send with exclusive device operations. > > So with approach 2, send can use commit root safely, because we make sure > send root can not be cowed during send. Unfortunately, it make codes *ugly* > and more complex to maintain. > > To make snapshot and send exclusively, device operations and send operation > exclusively with each other is a little confusing for common users. > > So why not drop into previous way. > > Cc: Josef Bacik <jbacik@xxxxxx> > Signed-off-by: Wang Shilong <wangsl.fnst@xxxxxxxxxxxxxx> > --- > Josef, if we reach agreement to adopt this approach, please revert > Filipe's patch(Btrfs: make some tree searches in send.c more efficient) > from btrfs-next. Oops, this patch guarantee searching commit roots are all protected by transaction, Filipe's patch is ok, we need update Josef's previous patch. Wang -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
