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From:   Florian Weimer <fweimer@redhat.com>
To:     =?utf-8?Q?J=C3=BCrg?= Billeter <j@bitron.ch>
Cc:     Christian Brauner <christian@brauner.io>,
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Subject: Re: [PATCH v4] signal: add taskfd_send_signal() syscall
References: <20181206121858.12215-1-christian@brauner.io>
        <87h8fq7s84.fsf@oldenburg2.str.redhat.com>
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        <89a6b3a24412d385a816d7d981c60cb1e1bbc0ca.camel@bitron.ch>
Date:   Thu, 06 Dec 2018 14:20:21 +0100
In-Reply-To: <89a6b3a24412d385a816d7d981c60cb1e1bbc0ca.camel@bitron.ch>
 (=?utf-8?Q?=22J=C3=BCrg?=
        Billeter"'s message of "Thu, 06 Dec 2018 14:18:36 +0100")
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* Jürg Billeter:

> On Thu, 2018-12-06 at 14:12 +0100, Florian Weimer wrote:
>> * Jürg Billeter:
>> 
>> > On Thu, 2018-12-06 at 13:30 +0100, Florian Weimer wrote:
>> > > * Christian Brauner:
>> > > 
>> > > > /* zombies */
>> > > > Zombies can be signaled just as any other process. No special error will be
>> > > > reported since a zombie state is an unreliable state (cf. [3]).
>> > > 
>> > > I still disagree with this analysis.  If I know that the target process
>> > > is still alive, and it is not, this is a persistent error condition
>> > > which can be reliably reported.  Given that someone might send SIGKILL
>> > > to the process behind my back, detecting this error condition could be
>> > > useful.
>> > 
>> > As I understand it, kill() behaves the same way. I think it's good that
>> > this new syscall keeps the behavior as close as possible to kill().
>> 
>> No, kill does not behave in this way because the PID can be reused.
>> The error condition is not stable there.
>
> The PID can't be reused as long as it's a zombie. It can only be reused
> when it has been wait()ed for. Or am I misunderstanding something?

Hmm, that's a fair point.  So the original interface is just broken.

Florian