On Mon, 4 Jul 2022 at 20:36, Christian Kohlschütter
<christian@kohlschutter.com> 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