fuse: ioctl: translate ENOSYS
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. This bug may occur with FUSE filesystems, such as davfs2. Steps to reproduce: # install davfs2, e.g., apk add davfs2 mkdir /test mkdir /test/lower /test/upper /test/work /test/mnt yes '' | mount -t davfs -o ro http://some-web-dav-server/path \ /test/lower mount -t overlay -o upperdir=/test/upper,lowerdir=/test/lower \ -o workdir=/test/work overlay /test/mnt # when "some-file" exists in the lowerdir, this fails with "Function # not implemented", with dmesg showing "overlayfs: failed to retrieve # lower fileattr (/some-file, err=-38)" touch /test/mnt/some-file The underlying cause of this regresion is actually in FUSE, which fails to translate the ENOSYS error code returned by userspace filesystem (which means that the ioctl operation is not supported) to ENOTTY. Reported-by:Christian Kohlschütter <christian@kohlschutter.com> Fixes: 72db8211 ("ovl: copy up sync/noatime fileattr flags") Fixes: 59efec7b ("fuse: implement ioctl support") Cc: <stable@vger.kernel.org> Signed-off-by: