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. -- 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
