On Tue, Apr 17, 2007 at 10:35:50AM -0400, Shaya Potter wrote: > Bharata B Rao wrote: > >Hi, > > > >Here is an attempt towards vfs based union mount implementation. > >Union mount provides the filesytem namespace unification feature. > >Unlike the traditional mounts which hide the contents of the mount point, > >the union mount presents the merged view of the mount point and the > >mounted filesytem. > > does this approach allow one to add directories to the union and have it > behave normally. namely when imagine one has the situation > > dir-b > dir-a/ (contains file foo) > > > if one unions this and deletes foo, that will create a whiteout entry in > dir-a (I guess you mean to say that this creates a whiteout in dir-b) > > now, what happens if one does > > dir-c > dir-b (now contains whiteout, from previous union). > dir-a (contains file foo) > > will one see foo or not. i.e. are whiteouts only looked for in the > topmost dir, or in every dir? No. foo is not visible. While looking for a file in a union mounted directory, the lookup starts from the topmost directory and proceeds downwards if the file isn't present the top layers. If a whiteout is found in any of the top layers, the lookup is abondoned and -ENOENT is removed. Thus until a whiteout exists in any upper layer for a corresponding file in the lower layer, the lower layer file remains hidden until the whiteout is removed. However in the case of dir-c containing foo, the foo(from dir-c) will become visible after union mounting dir-c on top of dir-b and dir-a. Regards, Bharata. - 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
