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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 24 Jul 2019 10:45:38 -0700
Message-ID: <CAHk-=whZPKzbPQftNGFB=iaSZGTSXNkhUASWF2V53MwB+A4zAQ@mail.gmail.com>
Subject: Re: [PATCH 2/5] pidfd: add pidfd_wait()
To:     Christian Brauner <christian@brauner.io>
Cc:     Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Tejun Heo <tj@kernel.org>, David Howells <dhowells@redhat.com>,
        Jann Horn <jannh@google.com>,
        Andrew Lutomirski <luto@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Android Kernel Team <kernel-team@android.com>,
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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.

               Linus