On Sat, Apr 10, 2021 at 2:30 PM Christian Brauner <christian.brauner@xxxxxxxxxx> wrote: > > On Sat, Apr 10, 2021 at 12:31:02AM +0000, Al Viro wrote: > > On Fri, Apr 09, 2021 at 06:24:21PM +0200, Christian Brauner wrote: > > > > > Reading through the codebase of ecryptfs it currently takes path->mnt > > > and then retrieves that path whenever it needs to perform operations in > > > the underlying filesystem. Simply drop the old path->mnt once we've > > > created a private mount and place the new private mnt into path->mnt. > > > This should be all that is needed to make this work since ecryptfs uses > > > the same lower path's vfsmount to construct the paths it uses to operate > > > on the underlying filesystem. > > > > > + mnt = clone_private_mount(&path); > > > > Incidentally, why is that thing anything other than a trivial wrapper > > for mnt_clone_internal() (if that - I'm not convinced that the check of > > unbindable is the right thing to do here). Miklos? > > The unbindable check is irrelevant at least for both ecryptfs and for > the corresponding cachefiles change I sent out since they don't care > about it. > In practice it doesn't matter to be honest. MS_UNBINDABLE is wildly > esoteric in userspace (We had a glaring bug with that some time ago that > went completely unnoticed for years.). Especially unlikely to be used > for a users home directory (ecryptfs) or /var/cache/fscache > (cachefiles). So even by leaving this check in it's very unlikely for > any regressions to appear. > > I hadn't seen mnt_clone_internal() but it's different in so far as it > sets MNT_INTERNAL whereas clone_private_mount() uses MNT_NS_INTERNAL. > Which points me to another potential problem here: > clone_private_mount() seems to want kern_unmount() to be called instead > of just a simple mntput()? Yes, that's stated in a comment in the clone_private_mount() helper. The difference is that short term mounts take a small penalty on each mntput(), while longterm mounts take a fairly large penalty on kern_unmount(). It's just a performance thing, AFAIK. As for MS_UNBINDABLE, my recollection is that it was copy-pasted from regular bind mount. I agree that it can be moved to overlayfs (or removed altogether, with some thought into what MS_UNBINDABLE actually is used for). Thanks, Miklos
