Re: [PATCH] clone.2: Fix the erroneous statement about CLONE_NEWPID

Alejandro Colomar
2023-08-12T17:48:43Z

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Hello Sargun,

On 2023-08-10 04:26, Sargun Dhillon wrote:
> It appears like the documentation is based on out of date information in
> regards to using CLONE_NEWPID and CLONE_PARENT together.
>
> For example, in this test program, one can see that it works:
>
> static pid_t sys_clone3(struct clone_args *args)
> {
> fflush(stdout);
> fflush(stderr);
> return syscall(__NR_clone3, args, sizeof(*args));
> }
>
> int main() {
> struct clone_args args = {
> .flags = CLONE_PARENT | CLONE_NEWPID,
> };
> int ret;
>
> printf("The main program is running with pid: %d, and ppid: %d\n", getpid(), getppid());
> ret = sys_clone3(&args);
> assert(ret != -1);
> if (ret == 0) {
> printf("This is the child, running with pid: %d, and ppid: %d\n", getpid(), getppid());
> _exit(0);

Do we really need _exit(3)? Why not exit(3)? There are no atexit(3)
or on_exit(3) handlers registered, so the only difference I expect is
the flushing of stdio(3) streams, which _exit(3) doesn't perform but
exit(3) does. So exit(3) seems more appropriate, isn't it?

> }
>
> return 0;
> }

Thanks for the example program! It helps a lot with the review. :)

>
> This test program (successfully) outputs:
> The main program is running with pid: 648411, and ppid: 648397
> This is the child, running with pid: 1, and ppid: 0
>
> Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> ---
> man2/clone.2 | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/man2/clone.2 b/man2/clone.2
> index 4c5b4ac6b..96ad24b95 100644
> --- a/man2/clone.2
> +++ b/man2/clone.2
> @@ -736,9 +736,7 @@ Only a privileged process
> can employ
> .BR CLONE_NEWPID .
> This flag can't be specified in conjunction with
> -.B CLONE_THREAD
> -or
> -.BR CLONE_PARENT .
> +.B CLONE_THREAD.

You'll need BR here, and the space before the period; otherwise,
the period will be in bold, which we don't want (as it's not part
of the identifier).

Thanks,
Alex

> .TP
> .B CLONE_NEWUSER
> (This flag first became meaningful for

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