On 04/08, Eric W. Biederman wrote:
> Oleg Nesterov <[email protected]> writes:
>
> > For review only.
> >
> > To implement for-in-kerenl-use-only CLONE_ flags, we need to filter out them
> > in sys_clone().
>
> Nack
>
> The current clone_flags field is for user space consumption and we
> have proposed users for all or almost all of the remaining bits.
OK.
> If we are going to have kernel only flags please use an additional
> argument to do_fork and copy_process.
Yes, we can do this. But we have a number of architectures which use
sys_clone() to implement kernel_thread(). It would be nice to have an
architecture neutral kernel_thread() implementation as you proposed.
We should change all of them if we want to add a new parameter to
do_fork().
Perhaps it is better to add reparent_kthread() (next patch) to kthread()
and forget about CLONE_KERNEL_THREAD.
Anyway, re-parenting to swapper breaks pstree, it doesn't show kernel
threads. And if ->parent == /sbin/init, we can't remove us from ->children
(unless we forbid sub-thread-of-init exec). So the only safe change is
set ->exit_state = -1.
> Your current scheme also has the bad side that if user space supplied
> a kernel flag it is hard to detect it and return -EINVAL. Which
> limits future expansion. Silently dropping clone flags is a real
> pain, if you are trying to detect if a new flag has been implemented.
Yes. But that is what we are doing now. copy_process() just ignores
unknown flags.
Oleg.
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