Re: [PATCH] pidfd: add NSpid entries to fdinfo

On Mon, Oct 14, 2019 at 12:32 PM Christian Brauner
[off-list ref] wrote:

On Mon, Oct 14, 2019 at 11:43:01AM +0200, Christian Kellner wrote:

quoted

On Sat, 2019-10-12 at 12:21 +0200, Christian Brauner wrote:

quoted

I tried to think of cases where the first entry of Pid is not
identical
to the first entry of NSpid but I came up with none. Maybe you do,
Jann?

Yeah, I don't think that can be the case. By looking at the source of
'pid_nr_ns(pid, ns)' a non-zero return means that a) 'pid' valid, ie.
non-null and b) 'ns' is in the pid namespace hierarchy of 'pid' (at
pid->level, i.e. "pid->numbers[ns->level].ns == ns").

Agreed.

You could probably do:

#ifdef CONFIG_PID_NS
seq_put_decimal_ull(m, "\nNSpid:\t", nr);
for (i = ns->level + 1; i <= pid->level && nr; i++)
        seq_put_decimal_ull(m, "\t", pid->numbers[i].nr);
#endif

Personally, I dislike hiding the precondition for running the loop in
the loop statement like that. While it makes the code more concise, it
somewhat obfuscates the high-level logic at a first glance.