Re: [Xen-devel] [PATCH 7/7] tools/hotplug: add wrapper to start xenstored

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Sep 10, 2015 at 03:19:35PM +0100, George Dunlap wrote:
> On Wed, Jan 7, 2015 at 9:40 AM, Olaf Hering <olaf@xxxxxxxxx> wrote:
> > On Tue, Jan 06, Ian Campbell wrote:
> >
> >> On Fri, 2014-12-19 at 12:25 +0100, Olaf Hering wrote:
> >> > The shell wrapper in xenstored.service does not handle XENSTORE_TRACE.
> >> >
> >> > Create a separate wrapper script which is used in the sysv runlevel
> >> > script and in systemd xenstored.service. It preserves existing
> >> > behaviour by handling the XENSTORE_TRACE boolean. It also implements
> >> > the handling of XENSTORED_ARGS=. This variable has to be added to
> >> > sysconfig/xencommons.
> >>
> >> Why don't we just drop XENSTORED_* in favour of XENSTORED_ARGS (with an
> >> example in the sysconfig file of enabling tracing if you like)?
> >
> > After having two weeks to think about this I came to the same
> > conclusion. I think whatever the outcome is, the boolean should be
> > removed. The sysconfig file should get a XENSTORED_ARGS="" along with a
> > help text which mentions "-T /path" and "xenstored --help" to get other
> > options because there is no man page.
> >
> >> Going to a wrapper script just to make some fairly uncommon debugging
> >> option marginally more convenient seems like overkill to me, plus
> >> XENSTORED_ARGS would allow for passing other useful options to
> >> xenstored.
> >
> > If I recall correctly the point of the current 'sh -c "exec ..."' stunt
> > was to expand the XENSTORE variable from the sysconfig file. But this
> > approach leads to failures with SELinux because the socket passing does
> > not work this way. Up to now I have not seen a success report for
> > selinux+systemd+xenstored. Maybe its already somewhere in the other
> > unread mails.
> >
> > In my cover letter I provided some possible ways to handle
> > selinux+systemd+xenstored. Ideally the approach "Exec=/usr/bin/env
> > $XENSTORED --no-fork $XENSTORED_ARGS" works because it means its
> > possible to select a binary via the sysconfig file. But it also means
> > the XENSTORE_TRACE boolean has to be removed in favour of the plain
> > XENSTORED_ARGS= approach mentioned above. Finally this would avoid the
> > need for a wrapper script.
> >
> > Hopefully someone with access to a SELinux enabled system will report
> > which approach actually works.
> 
> I can confirm that
> 
> ExecStart=/bin/sh -c "exec $XENSTORED --no-fork $XENSTORED_ARGS"
> 
> does not work on a CentOS7 system with selinux enabled, but that
> 
> ExecStart=/usr/bin/env $XENSTORED --no-fork $XENSTORED_ARGS
> 

And the difference between these two approaches is /usr/bin/env
preserves envars while sh -c doesn't?

Wei.

> does work.
> 
> A patch is on its way.
> 
>  -George

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