Andreas Dilger <adilger@xxxxxxx> writes: > On 2010-02-08, at 06:28, Dmitry Monakhov wrote: >> 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. > > > Presumably this would need e2fsck support, in order to ensure that > inodes in a given directory have the same subtree ID as the parent > directory. Yes i'm working on this, I've already prepared ioctl support for chattr/lsattr. > Also, how are the subtree IDs generated, to ensure that they are > unique between subtrees? This is user responsibility. There is possible situation where set of subtrees may has same ID. The main idea it that each of such subtrees is a *full* subtree (it includes all nodes starting from the subtree root) About isolation: currently there is a discussion about this feature some people state that subtrees may exist without a isolation requirement. Let's wait where it goes. > > Cheers, Andreas > -- > Andreas Dilger > Sr. Staff Engineer, Lustre Group > Sun Microsystems of Canada, Inc. -- 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
