Al Viro: > Umm... I would prefer it to go through vfs.git, with serious modifications. > I really don't like the idea of xattr-based whiteouts, for example. I'd ask you how do you think another whiteout approach? Here is a part of a posts which describes about aufs2 in 2009 <http://marc.info/?l=linux-kernel&m=123934927611907&w=2> ::: +- whiteout is hardlinked in order to reduce the consumption of inodes + on branch ::: +- kernel thread for removing the dir who has a plenty of whiteouts ::: +The whiteout is for hiding files on lower branches. Also it is applied +to stop readdir going lower branches. +The latter case is called \[oq]opaque directory.\[cq] Any +whiteout is an empty file, it means whiteout is just an mark. +In the case of hiding lower files, the name of whiteout is +\[oq]\*[AUFS_WH_PFX]<filename>.\[cq] +And in the case of stopping readdir, the name is +\[oq]\*[AUFS_WH_PFX]\*[AUFS_WH_PFX].opq\[cq] or +\[oq]\*[AUFS_WH_PFX]__dir_opaque.\[cq] The name depends upon your compile +configuration +CONFIG_AUFS_COMPAT. +.\" All of newly created or renamed directory will be opaque. +All whiteouts are hardlinked, +including \[oq]<writable branch top dir>/\*[AUFS_WH_BASE].\[cq] ::: +The whiteout in aufs is very similar to Unionfs's. That is represented +by its filename. UnionMount takes an approach of a file mode, but I am +afraid several utilities (find(1) or something) will have to support it. + +Basically the whiteout represents "logical deletion" which stops aufs to +lookup further, but also it represents "dir is opaque" which also stop +lookup. + +In aufs, rmdir(2) and rename(2) for dir uses whiteout alternatively. +In order to make several functions in a single systemcall to be +revertible, aufs adopts an approach to rename a directory to a temporary +unique whiteouted name. +For example, in rename(2) dir where the target dir already existed, aufs +renames the target dir to a temporary unique whiteouted name before the +actual rename on a branch and then handles other actions (make it opaque, +update the attributes, etc). If an error happens in these actions, aufs +simply renames the whiteouted name back and returns an error. If all are +succeeded, aufs registers a function to remove the whiteouted unique +temporary name completely and asynchronously to the system global +workqueue. ::: Latest version is aufs3 (for linux-3.x series), there is no essential changes about whiteout since aufs2. J. R. Okajima -- 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
