Re: [PATCH 2/4] clone: add CLONE_PIDFD

[Daniel Colascione]

On Mon, Apr 15, 2019 at 10:15 AM Jonathan Kowalski <bl0pbl33p@xxxxxxxxx> wrote:
> > Why else do we want pidfd?
>
> Apart from what others have already pointed out, there are two other
> things I am looking forward to:

Everything that Christian, Joel, and Jonathan have said is right.

If I can wax philosophical for a bit (as I've been accused to doing
:-)), there's a lot of value in consistency itself, a "more than the
sum of its parts" effect that arises from modeling all kernel-resource
handles as file descriptors. You get lifecycle consistency, API
consistency (e.g., dup, close), introspection consistency (via
/proc/pid/fd and friends), wait consistency, IPC consistency, and tons
of other benefits from using a file descriptor. The alternatives tend
to be very ugly: one of SysV IPC's* biggest mistakes, for example, was
having users manage its resources via non-file-descriptor kernel
handles. The process is, I think, the last major class of kernel
resource that users can't manipulate via file descriptor. Even if
using pidfds didn't provide strong immediate and direct benefits, it'd
*still* be worth moving to a file descriptor resource handle model for
the sake of making the system interface regular and uniform.

* Does anyone know *why* the SysV people didn't use FDs? The
consistency argument I'm making was just as relevant then as it is
now.