On Sat, Feb 04, 2017 at 11:19:32AM -0800, James Bottomley wrote: > This allows any subtree to be uid/gid shifted and bound elsewhere. It > does this by operating simlarly to overlayfs. Its primary use is for > shifting the underlying uids of filesystems used to support > unpriviliged (uid shifted) containers. The usual use case here is > that the container is operating with an uid shifted unprivileged root > but sometimes needs to make use of or work with a filesystem image > that has root at real uid 0. > > The mechanism is to allow any subordinate mount namespace to mount a > shiftfs filesystem (by marking it FS_USERNS_MOUNT) but only allowing > it to mount marked subtrees (using the -o mark option as root). Once > mounted, the subtree is mapped via the super block user namespace so > that the interior ids of the mounting user namespace are the ids > written to the filesystem. Please move this into VFS instead of a stackable fs. We might need addtional parameters to getattr/setattr to specify the ID translation, but that's why better than a horrible hack like this.
