On 2/3/2021 2:11 PM, Dave Hansen wrote:

On 2/3/21 1:54 PM, Yu, Yu-cheng wrote:

quoted

On 1/29/2021 10:56 AM, Yu, Yu-cheng wrote:

quoted

On 1/29/2021 9:07 AM, Dave Hansen wrote:

quoted

On 1/27/21 1:25 PM, Yu-cheng Yu wrote:

quoted

+    if (!IS_ENABLED(CONFIG_X86_CET))
+        return -EOPNOTSUPP;

Let's ignore glibc for a moment.  What error code *should* the kernel be
returning here?  errno(3) says:

         EOPNOTSUPP      Operation not supported on socket (POSIX.1)
...
         ENOTSUP         Operation not supported (POSIX.1)

Yeah, other places in kernel use ENOTSUPP.  This seems to be out of
line.  And since the issue is long-existing, applications already know
how to deal with it.  I should have made that argument.  Change it to
ENOTSUPP.

When I make the change, checkpatch says...

WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP
#128: FILE: arch/x86/kernel/cet_prctl.c:33:
+        return -ENOTSUPP;

Do we want to reconsider?

I'm not sure I trust checkpatch over manpages.  I had to google "SUSV4".
  I'm not sure it matters at *all* for a 100% Linux-specific interface.

ENOTSUPP does seem less popular lately:

quoted

$ git diff v5.0.. kernel/ arch/ drivers/ | grep ^+.*return.*E.*NO.*SUP.*\; | grep -o -- -E.*\; | sort | uniq -c | sort -n
... noise
      61 -EOPNOTSUPP);
     260 -ENOTSUPP;
    1577 -EOPNOTSUPP;

but far from unused.  That might be due to checkpatch spew more than
anything.

Maybe I will keep it ENOTSUPP for now.  If any logical reason should 
come up, I will be happy to change it again.  Thanks!

--
Yu-cheng