Initially i've posted RFC patch-set which add subtree support for ext4. http://marc.info/?l=linux-ext4&m=126563931215496&w=2 But in fact this is rather generic feature which may be implemented in vfs layer similar to namespace or security feature. 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 assumptions: * Each inode has subtree id (this id is stored inside inode). * Subtree id is inherent from parent directory if corresponding flag is set * Inode can not belongs to different subtrees i've ommit subtree_type feature in order to simplify brief explanation. Subtree with id == 0 has special meaning. It may contains roots of other subtrees (this feature is used for cross subtree renames) This feature has much in common with XFS project_id. There are many usecases for such subtrees 1) Choroot environment or Containers on common file-system administrator creates a subtree,and setup quota #mkdir chroot-env #chattr -Q ${subtree_id} chroot-env #tar jxf /tmp/fedora-x86_64.tar.bz2 -C chroot-env #### as soon as subtree id inherented from parent untared content #### automatically belongs to ${subtree_id} #quotactl --type=subtree --id=${subtree_id} --bsoft=1000000 --bhard=1000000 ### #chroot chroot-env /bin/bash 2) NFS quota on server side Administrator perform exactly the same stages, but instead of chroot hi just export result subtree to nfs server One may imagine it's own usecase. Usually we already have some content which we want to see as subtree In this case we have to in-depth traverse it from the subtree root. add_to_subtree(dir, subtree_id) /* in-depth tree traversal */ { while(de = getdents(dir)) { if (IS_DIR(de)) add_to_subtree(de, subtree_id) else set_subtree_id(de, subtree); } set_subtree_id(de, subtree); } It is possible to manipulate subtree content For example we have following hierarchy /root/subtree-1/a/b/c/d/e/f/g /root/subtree-2/dir/ want rename /root/subtree-1/a to /root/subtree-2/dir/AA first we have to move "a" to default tree "root" #rename /root/subtree-1/a /root/a-1 Then we have assign to default subtree. Do it in width traverse order Because otherwise this result in subtree assumptions violation. #walk_in_width(/root/AA, 0 /* default subtree */) Then assign target subtree_id #walk_in_depth(/root/AA, 2) Ok now all content from /root/a-1 belongs to subtree_id == 2 so it is possible rename it in to target place #rename /root/a-1 /root/subtree-2/dir/AA -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
