[PATCH 6/6] kernel: add a kernel_wait helper

[Luis Chamberlain]

On Thu, Jun 18, 2020 at 04:46:27PM +0200, Christoph Hellwig wrote:
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1626,6 +1626,22 @@ long kernel_wait4(pid_t upid, int __user *stat_addr, int options,
>  	return ret;
>  }
>  
> +int kernel_wait(pid_t pid, int *stat)
> +{
> +	struct wait_opts wo = {
> +		.wo_type	= PIDTYPE_PID,
> +		.wo_pid		= find_get_pid(pid),
> +		.wo_flags	= WEXITED,
> +	};
> +	int ret;
> +
> +	ret = do_wait(&wo);
> +	if (ret > 0 && wo.wo_stat)
> +		*stat = wo.wo_stat;

Since all we care about is WEXITED, that could be simplified
to something like this:

if (ret > 0 && KWIFEXITED(wo.wo_stat)
 	*stat = KWEXITSTATUS(wo.wo_stat)

Otherwise callers have to use W*() wrappers.

> +	put_pid(wo.wo_pid);
> +	return ret;
> +}

Then we don't get *any* in-kernel code dealing with the W*() crap.
I just unwrapped this for the umh [0], given that otherwise we'd
have to use KW*() callers elsewhere. Doing it upshot one level
further would be even better.

[0] https://lkml.kernel.org/r/20200610154923.27510-1-mcgrof@kernel.org              

  Luis