Re: [PATCH 1/2] tools: remove systemd xenstore socket definitions

[Juergen Gross <jgross@suse.com>]

On 29/06/16 15:31, Ross Lagerwall wrote:
> On 06/29/2016 02:00 PM, Juergen Gross wrote:
>> On 29/06/16 14:52, Andrew Cooper wrote:
>>> On 29/06/16 13:44, Juergen Gross wrote:
>>>> @@ -2068,13 +1964,6 @@ int main(int argc, char *argv[])
>>>>      /* Tell the kernel we're up and running. */
>>>>      xenbus_notify_running();
>>>>
>>>> -#if defined(XEN_SYSTEMD_ENABLED)
>>>> -    if (systemd) {
>>>> -        sd_notify(1, "READY=1");
>>>> -        fprintf(stderr, SD_NOTICE "xenstored is ready\n");
>>>> -    }
>>>> -#endif
>>>
>>> Getting rid of the socket configuration for systemd is ok, but we should
>>> keep the sd_notify() calls for when the daemon is started by systemd.
>>>
>>> Socket activiation and sd_notify() are orthogonal, and sd_notify() is
>>> still required if we don't want systemd to treat xenstored as a legacy
>>> unix daemon.
>>
>> So what is the downside of xenstored being treated as a legacy daemon?
>> This question is especially interesting for the case of patch 2 being
>> considered: xenstored is no longer started by systemd, but by a wrapper
>> script which might decide to start the xenstore domain instead.
>>
>> Another problem: today xenstored decides whether to call sd_notify()
>> by testing the xenstore sockets being specified via systemd. This will
>> no longer work. So how to do it now?
>>
>>
> 
> One problem with the patch as it currently is implemented is that the
> service type is not correct for when xenstored is a daemon. This makes
> it difficult to manage with systemd and difficult for other services to
> depend on it in a sensible fashion. The end result is subtle races and
> occasional failures.

Could you please educate me what's wrong? I'm no systemd expert.

> How about:
> * Maintain the existing service for xenstored
> * Have a separate service (with different a service type) for starting
> the xenstore domain
> * Switch between the two services

How could I specify e.g. in xendomains.service the dependency to
xenstore?

> Personally I think it is better and more uniform for the administrator
> to enable and disable services in the normal fashion, but if you want to

The two services would be mutually exclusive. Can I tell systemd this
is the case?

> make it configurable with /etc/sysconfig/xencommons, then you can add
> something like this to xenstored.service:
> 
> ExecStartPre=/bin/grep -q XENSTORETYPE=daemon /etc/sysconfig/xencommons
> 
> and to xenstore-domain.service:
> 
> ExecStartPre=/bin/grep -q XENSTORETYPE=domain /etc/sysconfig/xencommons

That's no good idea. Someone commenting out the old line and adding the
other option would end in both variants to be tried. This would have to
be a little bit more sophisticated. :-)


Juergen

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