Re: [PATCH] ovl: Handle ENOSYS when fileattr support is missing in lower/upper fs

[Miklos Szeredi]

On Mon, 18 Jul 2022 at 12:56, Christian Kohlschütter
<christian@xxxxxxxxxxxxxxxx> wrote:

> However, users of fuse that have no business with overlayfs suddenly see their ioctl return ENOTTY instead of ENOSYS.

And returning ENOTTY is the correct behavior.  See this comment in
<asm-generic/errrno.h>:

/*
 * This error code is special: arch syscall entry code will return
 * -ENOSYS if users try to call a syscall that doesn't exist.  To keep
 * failures of syscalls that really do exist distinguishable from
 * failures due to attempts to use a nonexistent syscall, syscall
 * implementations should refrain from returning -ENOSYS.
 */
#define ENOSYS 38 /* Invalid system call number */

Thanks,
Miklos