Messages in this thread | | | Subject | Re: [PATCH 14/38] fallthru: ext2 fallthru support | From | Miklos Szeredi <> | Date | Thu, 05 Aug 2010 13:13:55 +0200 |
| |
On Wed, 4 Aug 2010, Valerie Aurora wrote: > > Another idea is to use an internal inode and make all fallthroughs be > > hard links to that. > > > > I think the same would work for whiteouts as well. I don't like the > > fact that whiteouts are invisible even when not mounted as part of a > > union. > > I don't know if this helps, but I just wrote support for removing ext2 > whiteouts and fallthrus using tune2fs and e2fsck. I think this does > what people want from a "visible" whiteout feature without adding more > complexity to the VFS. It also takes away all consideration of race > conditions and dentry conversion that happens with online removal of > whiteouts and fallthrus. > > What are your thoughts on what a visible whiteout/fallthru would look > like?
Best would be if it didn't need any modification to filesystems. All this having to upgrade util-linux, e2fsprogs, having incompatible filesystem features is a pain for users (just been through that).
What we already have in most filesystems:
- extended attributes, e.g. use the system.union.* namespace and denote whiteouts and falltroughs with such an attribute
- hard links to make sure a separate inode is not necessary for each whiteout/fallthrough entry
- some way for the user to easily identify such files when not mounted as part of a union e.g. make it a symlink pointing to "(deleted)" or whatever
Later the extended attributes can also be used for other things like e.g. chmod()/chown() only copying up metadata, not data, and indicating that data is still found on the lower layers.
Miklos
| |