RE: [RFC PATCH v4] ndctl: monitor: add ndctl monitor daemon

["Qi, Fuli" <qi.fuli@jp.fujitsu.com>]

> >
> > I prefer to add an EnvironmentFile like /etc/sysconfig/ndctl/monitor
> > to systemd rather than add a configuration file. According to [1],
> > environment variable substitution is supported in systemd.service, so
> > we can define the variables through
> "EnvironmentFile=/etc/sysconfig/ndctl/monitor".
> > In this fashion, we do not need to add any extra codes to parse the configuration
> file.
> >
> > In this case, [--conf-file] option is not necessary either.
> > According to [2], sytemd units can be instantiated from a template
> > file, thus we only need to add a template unit file in advance.
> > If user wants to run multiple monitors with different configurations,
> > they can differentiate them by adding multiple EnvironmentFiles, like
> /etc/sysconfig/ndctl/<monitor1...n>.
> > Then the monitors can be started by command like "# systemctl start
> > ndctl-monitor@<monitor1...n>.service".
> >
> > When the monitors started by hand, it will do not need any
> > configuration files, because we can add options and parameters directly.
> >
> > [1]https://www.freedesktop.org/software/systemd/man/systemd.service.ht
> > ml
> > [2]https://www.freedesktop.org/software/systemd/man/systemd.unit.html
> 
> This seems to needlessly tie ndctl to systemd, it should be able to operate without
> requiring systemd. I expect it would be straightforward to copy the configuration file
> implementation from git.

I have read the configuration file implementation of git, my understanding is that git daemon does not
have any options used to override default configuration. 
I want to confirm if the configuration file is only used for ndctl monitor.
If yes, I do not think copy the configuration file implementation from git is a good choice,
because only getting keys and values from configuration file is needed for us and the structure of
configuration file implementation in git is too complexity. 
I prefer to borrow from udev[1], because the implementation in udev is simpler and it seems ndctl also borrows a lot from udev.

[1] https://git.kernel.org/pub/scm/linux/hotplug/udev.git/tree/src/libudev.c
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