Re: [PATCH] Add /proc/pid_generation

On Fri 2018-11-23 11:14:17, David Laight wrote:

From: Kevin Easton

quoted

Sent: 22 November 2018 11:20

On Wed, Nov 21, 2018 at 12:14:44PM -0800, Daniel Colascione wrote:

quoted

This change adds a per-pid-namespace 64-bit generation number,
incremented on PID rollover, and exposes it via a new proc file
/proc/pid_generation. By examining this file before and after /proc
enumeration, user code can detect the potential reuse of a PID and
restart the task enumeration process, repeating until it gets a
coherent snapshot.

I see downthread this patch has been withdrawn, but nonetheless I'm
still curious - does this actually solve the problem?

It seems to me that a PID could be reused within a scan even if the
generation number remains the same at the beginning and end of a scan:

Why not allocate a 48bit generation number to each 16bit pid?
Then you have a 64bit 'extended-pid' that can be assumed to never be reused.
Provided enough interfaces are enhanced to support 'extended-pid' values
you'll never get reused values.

For the record, I really like this proposal.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
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