Greg Freemyer <greg.freemyer@xxxxxxxxx> writes: > On Tue, Feb 9, 2010 at 5:06 AM, Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote: >> Greg Freemyer <greg.freemyer@xxxxxxxxx> writes: >> >>> On Mon, Feb 8, 2010 at 8:28 AM, Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote: >>>> * Abstract >>>> A subtree of a directory tree T is a tree consisting of a directory >>>> (the subtree root) in T and all of its descendants in T. >>>> >>>> Subtree feature allows to create an isolated (from user point of view) >>>> trees. >>>> >>>> Subtree assumptions: >>>> (1) Each inode has subtree id. This id is persistently stored inside >>>> inode (xattr, usually inside ibody) >>>> (2) Subtree id is inherent from parent directory >>>> (3) Inode can not belongs to different subtree >>>> Otherwise changes in one subtree result in changes in other subtree >>>> which contradict to isolation criteria. >>>> >>>> This feature is similar to project-id in XFS. One may assign some id to >>>> a subtree. Each entry from the subtree may be accounted in directory >>>> subtree quota. Will appear in later patches. >>>> >>>> * Disk layout >>>> Subtree id is stored on disk inside xattr usually inside ibody. >>>> Xattr is used only as a data storage, It has not user visiable xattr >>>> interface. >>>> >>>> Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx> >>> >>> Dmitry, >>> >>> I think the idea of subtrees is useful, but I'm curious about other >>> use cases than just quota. >>> >>> At first glance you are attempting to create a generic subtree >>> functionality for ext4, but criteria 3) above says a inode can only be >>> in one subtree at a time. >> Theoretically this is possible, but this dramatically complicate things >> Just think about this. If inode belongs to different subtrees then >> it must have several tree-dquota objects attached to it. This means >> that quota require great quota redesign. >> Obviously i don't know any use case for this feature. do you know any? > > Maybe we're talking about different things. I working with the OHSM > project <http://ohsm.sourceforge.net/> > > We haven't submitted any patches yet, but for one of our features we > have something fairly close to your subtree patch. If we were to > leverage your patch and drop that part of ours we would be in the > unhappy situation that quota and ohsm could not both be enabled on the > same filesystem because the ohsm subtree geography is not likely to be > consistent with the quota subtree geography. > > If we call quota and ohsm services then my desire would be to see your > subtree patches support orthoganal subtree groups. One group per > service. > > I haven't looked into the actual implementation, but from an API > perspective it is just a matter of adding a service parameter to the > various calls. For a given subtree service group, a given inode could > only be part of one subtree, but a single inode could participate in > multiple subtree service groups. Ok now i think i understand what you are talking about. one subtree <=> one service is the main rule i'm standing. If you wan to support several services, no problem I can easily extend xattr to support different services something like this subtree_entry { __le16 sbe_flags /* entry flags */ __le16 sbe_type /* service type */ __le32 sbe_id /* subtree id */ } /* subtree entry flags enum { SUBTREE_FL_VALID = 1, /* entry contains valid data */ SUBTREE_FL_INHERENT = 2, /* inherent id from parent on create * SUBTREE_FL_ISOLATE = 4 /* Isolated subtree */ /* and soon */ }; > > Greg -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
