I'm wondering if there is a way to remove a file from the upper directory without leaving a whiteout behind, but instead let the file (if any, of course) in the lower file system become visible? Obviously this can be done by unmounting the overlay, removing the file (or whiteout) from the upper dir, then mounting again, but I'd like to be able to do this to a live system. Essentially, having a way to revert changes done to an existing file. I briefly looked into dir.c, and it seems that ovl_remove_upper would actually do the right thing, but there doesn't seem to be any way to get there via normal VFS operations. RENAME_WHITEOUT is the exact opposite, and even if there was a RENAME_NOWHITEOUT, that would have a lot of problems (probably wouldn't work if the file is a whiteout (src dentry lookup would fail), requires coming up with a tmp name to rename to and then unlink that as a second step, semantics if the file only exists in the lower layer). Maybe an AT_REMOVEUPPER flag for unlinkat could be implemented (which would fail with ENOENT unless the file is in the upper part of an overlay file system)? Or, as an overlayfs specific ioctl on the containing directory? Thanks, Rasmus
