Re: [PATCH v2 5/5] tools/xenstored: remove "-N" command line option

[Juergen Gross]

On 08.12.23 17:16, Anthony PERARD wrote:

On Fri, Dec 08, 2023 at 04:58:52PM +0100, Juergen Gross wrote:

On 08.12.23 16:46, Andrew Cooper wrote:

On 21/11/2023 11:40 am, Juergen Gross wrote:

The "-N" (do not daemonize) command line option is of questionable use:
its sole purpose seems to be to aid debugging of xenstored by making it
easier to start xenstored under gdb, or to see any debug messages
easily.

Debug messages can as well be sent to syslog(), while gdb can be
attached to the daemon easily. The only not covered case is an error
while initializing xenstored, but this could be handled e.g. by saving
a core dump, which can be analyzed later.

The call of talloc_enable_leak_report_full() done only with "-N"
specified is no longer needed, as the same can be achieved via
"xenstore-control memreport".

Signed-off-by: Juergen Gross <jgr...@suse.com>

Systemd wants daemons to not fork, because systemd can start them up in
a better-prescribed environment than deamonise() can make.

It was a lazy port to system which has caused us not to be using -N in
the first place.

So no - I think this option specifically wants to stay, and the systemd
integration improved.

The problem with this approach is that we have some functionality in the
launch-xenstore script relying on [o]xenstored coming back after having
forked off the daemon: we are setting the oom-score, which can be done

It's perfectly reasonable to bane the use of "-N" when using
`./launch-xenstore` to start xenstored. It doesn't mean that the option
needs to be removed from xenstored.

only when knowing the process id.

So we need a solution for this problem before we can really encourage
users to use the -N option.

Please note that setting the oom-score from within xenstored was rejected
back when I posted a patch in this regard, especially as it is specific to
Linux. Additionally this would mean we need to add this functionality to
xenstored AND oxenstored.

There's still a world where -N can be used, and oom-score can be set,
I'm pretty sure that can be done with an hand-crafted "systemd.service"
file. One probably need to have something like "OOMPolicy=" or
"OOMScoreAdjust=" in their service file, and start the `xenstored`
daemon of their choice directly, even with -N as systemd can detect when
the daemon is ready because we use sd_notify() (at least in cxenstored).


So, I think we should keep -N.

Okay, fair enough.

Lets drop the patch then.


Juergen

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