On Mon, 18 Jul 2022 at 12:10, Christian Kohlschütter <christian@xxxxxxxxxxxxxxxx> wrote: > > > Am 18.07.2022 um 11:14 schrieb Miklos Szeredi <miklos@xxxxxxxxxx>: > > > > On Mon, 4 Jul 2022 at 20:36, Christian Kohlschütter > > <christian@xxxxxxxxxxxxxxxx> wrote: > >> > >> overlayfs may fail to complete updates when a filesystem lacks > >> fileattr/xattr syscall support and responds with an ENOSYS error code, > >> resulting in an unexpected "Function not implemented" error. > > > > Issue seems to be with fuse: nothing should be returning ENOSYS to > > userspace except the syscall lookup code itself. ENOSYS means that > > the syscall does not exist. > > > > Fuse uses ENOSYS in the protocol to indicate that the filesystem does > > not support that operation, but that's not the value that the > > filesystem should be returning to userspace. > > > > The getxattr/setxattr implementations already translate ENOSYS to > > EOPNOTSUPP, but ioctl doesn't. > > > > The attached patch (untested) should do this. Can you please give it a try? > > > > Thanks, > > Miklos > > <fuse-ioctl-translate-enosys.patch> > > Yes, that change basically has the same effect for the demo use case,. > > However: it will change (and potentially) break assumptions in user space. We should never break user space. > > Example: lsattr /test/lower > Currently, fuse returns ENOSYS, e.g. > > lsattr: reading ./lost+found: Function not implemented > With your change, it would return ENOTTY > > lsattr: reading ./lost+found: Not a tty No, it would return success. > I also tried the setup (without patches) on a very old 4.4.176 system, and everything works fine. ovl introduced the regression, so it should also be fixed there. > It may affect other filing systems as well (I see some other fs also return ENOSYS on occasion). > > It's safe to say that adding the ENOSYS to the ovl code is probably the best move. Besides, you already have a workaround for ntfs-3g there as well. Flawed arguments. The change in overlayfs just made the preexisting bug in fuse visible. The bug should still be fixed in fuse. Thanks, Miklos
