On 10.03.2013 05:21, Shilong Wang wrote: > Hello, Arne > > Steps to reproduce: > > > mkfs.btrfs <disk> > mount <disk> <mnt> > btrfs quota enable <mnt> > > btrfs sub create <mnt>/sub > btrfs qgroup create 1/1 <mnt> > btrfs qgroup assign sub_qgroupid 1/1 <mnt> > > > dd if=/dev/zero of=<mnt>/sub/data bs=1M count=1 > sync > btrfs qgroup show <mnt> > #until now, every thing goes well, however, if snapshot > happens > #the quota accounting will go wrong > > btrfs sub snapshot <mnt>/sub <mnt>/snap > sync > btrfs qgroup show <mnt> > #the accounting information of group(1/1) is not expected > #here exclusive of group (1/1) do not change as expected. > > So i took a close look at the algorithm of quota accounting, the 3 > steps of algorithm don't > consider some cases like the above example. > > In fact, i think you try to put some work on users, especially when > snapshot happens. > It is complex to track all the group's accounting when having > snapshots..See the following > commands. > > btrfs sub snapshot -c src_qgroupid:dst_qgroupid <mnt> > btrfs sub snapshot -x src_qgroupid:dst_qgroupid <mnt> > > > Are these commands designed for some cases regarding to > snapshots/subvolume cases?
Yes, these commands would have helped you in the above case. You need to create an empty qgroup and copy the exclusive from there on snapshot creation. > If so, i think it really confusing and too complex for users to do > such work, is't it?... It is complex. That is why I always point anyone asking to do some work on btrfs or qgroups to writing an enhanced interface to simplify this task for the user. I don't think the kernel should handle this. And that's why I took the effort to write a pdf to explain the concepts :) But the current interface is not only complex, it also is very powerful. You can solve problems with it that no other quota system I know of can solve. > > BTW, i have a question about the function btrfs_qgroup_inherit(), > when copying exclusive value from src_qgroup to dst_qgroup: > > dst_qgroup->exclusive = src_qgroup->exclusive + level_size > > while copying referenced value from src_qgroup to dot_qgroup: > > dst_qgroup->referenced = src_qgroup->referenced -level_size > > I can't really figure out...~_~ level_size is just a small correction for the space the tree root occupies. The tree root is never shared between subvolumes. -Arne > > Thanks, > Wang -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
