Re: [PATCH 2/5] pidfd: add pidfd_wait()

[ebiederm@xmission.com (Eric W. Biederman)]

Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Wed, Jul 24, 2019 at 7:47 AM Christian Brauner <christian@brauner.io> wrote:
>>
>> This adds the pidfd_wait() syscall.
>
> I despise this patch.
>
> Why can't this just be a new P_PIDFD flag, and then use
> "waitid(P_PIDFD, pidfd, ...);"
>
> Yes, yes, yes, I realize that "pidfd" is of type "int", and waitid()
> takes an argument of type pid_t, but it's the same type in the end,
> and it does seem like the whole *point* of "waitid()" is that
> "idtype_t idtype" which tells you what kind of ID you're passing it.

Just to emphasize this point.

The posix declaration of waitid is:
>int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);

Where id_t is defined as:
> id_t - Used as a general identifier; can be used to contain at least a pid_t, uid_t, or gid_t.

And the BSDs at least have defined P_UID and P_GID.  So that flexibility
has been used.

So it looks entirely reasonable to have P_PIDFD that just waits for a
specified child.

Eric