Re: [Xen-devel] [PATCH for-4.6 v2] tools/hotplug: Add an initscript to start "xl devd" in a driver domain

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-07-20 at 16:16 +0200, Roger Pau Monnà wrote:
> El 16/07/15 a les 18.58, Ian Campbell ha escrit:
> > The removal of the udev rules highlighted that although it has been
> > replaced by "xl devd" there isn't an initscript to replace it.
> > 
> > To enable this add a --pidfile option to xl devd.
> > 
> > Tested on Linux by running the script in dom0 and checking the daemon
> > was started/stopped, but not in an actual driver domain environment
> > since I don't have one conveniently available. I also checked that
> > running without the --pidfile option still works.
> > 
> > Scripts mainly cribbed from the xencommons for each platform.
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Cc: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
> > Cc: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
> > Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> > ---
> > For 4.6: I think having removed the udev rules we ought to include
> > this, it's basically zero risk to normal operation.
> > 
> > Nothing seems to start xl devd for domain 0 in *BSD, nor is xenbackend
> > started. Is that correct?
> > 
> > v2: Check in Linux script that we don't start on dom0. I don't know
> > the equivalent for *BSD.
> 
> At least on FreeBSD there's no easy way to know if we are running on
> Dom0 from userspace (unless we start using hypercalls with privcmd).
> 
> I could add a dummy device (let's say /dev/xen/control) that's only
> present if we are running on Dom0, does that sound reasonable?

FWIW on Linux there is a capabilities "device" (actually procfs thing,
close enough) which contains "control_d" in dom0. Not sure if that is
helpful to follow?

> Another option would be to add a small C program that can use hypercalls
> and privcmd to detect if we are running on Dom0 or not, but that seems
> over engineering it.

Agreed.

> [...]
> 
> > diff --git a/tools/hotplug/FreeBSD/rc.d/xendriverdomain.in 
> > b/tools/hotplug/FreeBSD/rc.d/xendriverdomain.in
> > new file mode 100644
> > index 0000000..25e3edd
> > --- /dev/null
> > +++ b/tools/hotplug/FreeBSD/rc.d/xendriverdomain.in
> > @@ -0,0 +1,48 @@
> > +#!/bin/sh
> > +#
> > +# PROVIDE: xendriverdomain
> > +# REQUIRE: DAEMON
> > +#
> > +# Should be run in a driver domain, but not in domain 0.
> > +
> > +. /etc/rc.subr
> > +
> > +. /etc/xen/scripts/hotplugpath.sh
> 
> This should have been:
> 
> . @XEN_SCRIPT_DIR@/hotplugpath.sh
> 
> I will send a patch ASAP to fix it.

Sorry, and please do, thanks.

> [...]

> > +        if ( close(fd) < 0 ) {
> 
> <pedantic>
> The line above doesn't follow libxl coding style.
> </pedantic>

Damn, sorry.

Ian.


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