Re: [PATCH v2 2/5] clone: add CLONE_PIDFD

[Oleg Nesterov <oleg@redhat.com>]

On 04/18, Christian Brauner wrote:
>
> @@ -1674,13 +1729,14 @@ static __latent_entropy struct task_struct *copy_process(
>  					unsigned long clone_flags,
>  					unsigned long stack_start,
>  					unsigned long stack_size,
> +					int __user *parent_tidptr,
>  					int __user *child_tidptr,
>  					struct pid *pid,
>  					int trace,
>  					unsigned long tls,
>  					int node)
>  {
> -	int retval;
> +	int pidfd = -1, retval;

it seems that initialization is unneeded, but this is cosmetic.

I see no technical problems, feel free to add my reviewed-by.


But let me ask a couple of questions...


Why O_CLOEXEC? I am just curious, I do not really care.


Should we allow CLONE_THREAD | CLONE_PIDFD ?


Are you sure we will never need to extend this interface? If not, then perhaps it
make sense to add something like

	if (CLONE_PIDFD) {
		unsigned long not_used_yet;
		if (get_user(not_used_yet, parent_tidptr) ||
		    not_used_yet != 0)
			return -EINVAL;
	}

this way we can easily add more arguments in future or even turn CLONE_PIDFD into
CLONE_MORE_ARGS_IN_PARENT_TIDPTR.

Not that I think this is really good idea, sys_clone2() makes more sense, but still.

Oleg.