Re: [PATCH] [GLIBC RFC] clone3: add CLONE3_RESET_SIGHAND

[Florian Weimer <fweimer@redhat.com>]

* Christian Brauner:

> I've been thinking about two things how to do this:
> - mask the flags that the kernel does not support

That doesn't look fully backwards-compatible to me.  The argument isn't
currently read/write, is it?  It would work for us though.

> - add another argument to struct clone_args that is "known_flags"
>   when the syscall returns it'll be set to all the flags this kernel
>   knows about

This needs some sort of protocol to detect whether the argument was
updated.  I suppose we could define CLONE3_INITIALLY_SUPPORTED_FLAGS
with all the flag bits currently supported and tell developers to
initialize struct clone_args with:

  .known_flags = CLONE3_INITIALLY_SUPPORTED_FLAGS,

Then the result would be correct whether or not known_flags is supported
by the kernel or not.  This too would work fine for glibc internal use.

By theway, I don't think we have a good userspace API story for
extensible *output* arguments yet.  Every system call does things a
little bit differently there.

Thanks,
Florian