On Tue, Feb 9, 2010 at 9:48 AM, Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote: > Greg Freemyer <greg.freemyer@xxxxxxxxx> writes: > >> On Tue, Feb 9, 2010 at 8:53 AM, Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote: >>> 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 */ >>> } >> >> Conceptually agreed. >> >> But you'd still be limited to one subtree_entry per inode with that right? >> >> Another option would be more like >> >> #define EXT4_SUBTREE_MAX_SERVICE_GROUPS 1 >> #define EXT4_SUBTREE_MAX_SERVICE_GROUP_QUOTA 0 >> >> // OHSM would patch the above when its ready to submit >> >> subtree_entry[EXT4_SUBTREE_MAX_SERVICE_GROUPS] >> { >> __le16 sbe_flags /* entry flags */ >> __le32 sbe_id /* subtree id */ >> } >> >> (Clearly that won't actually work as is, but you get the idea. Each >> service group gets its own flags and id.) >> >> Another option would be separate xattr entries for each subtree group. >> >> Regardless, it looks very doable and its just a matter of figuring out >> the best way to support multiple subtree service groups. > Off course i mean that. In fact i'm plan to pack entries in to one > xattr data block because each xattr has significant space overhead. > Sounds great. Does xfs support multiple service groups with its current offering? 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