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Re: [Xen-devel] [patch] xen udev rule interfering with openvpn

On Fri, 2012-04-20 at 16:26 +0100, Teck Choon Giam wrote:
> On Fri, Apr 20, 2012 at 9:21 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Fri, 2012-04-20 at 12:04 +0100, Ian Jackson wrote:
> >> Ian Campbell writes ("Re: [Xen-devel] [patch] xen udev rule interfering 
> >> with openvpn"):
> >> > On Fri, 2012-04-20 at 11:55 +0100, Ian Jackson wrote:
> >> > > I'm not quite up to speed with all the context here but is the reason
> >> > > that you're not suggesting "xen-" is that that's already used for
> >> > > something else ?
> >> >
> >> > This is to distinguish the vif device from the associated tap device,
> >> > which would otherwise both be called whatever the user gave as "vifname"
> >> > in their config, so for vifname=foo you would get foo (the PV one) and
> >> > xen-foo (the EMU one) which does the job but doesn't really distinguish
> >> > them.
> >>
> >> Ah, I see.  This sounds like more a job for a suffix than a prefix so
> >> if we can spare 4 chars I would suggest foo-emu.
> So what is the final prefix/suffix here?  Is it "emu-"?  Sorry, need
> to counter check :p

I think we have agreed on a "-emu" suffix.

> Question... vifname is limited to 16 characters?  If so, does the
> configuration for xm/xl check for its allowable length?  I mean if a
> user set vifname more than its allowable length in the domU
> configuration, would xm/xl show error?

I can't see any existing check for the length of the vif name.

It's a bit hard for us to do, consider a network driver domain running a
kernel which has a different, or no, limit here. libxl might not have
any idea what that name limit should be. We could pick an arbitrary
limit which is the smallest we know of, e.g. 12 chars (to allow +4), I

BTW, the failure if your name is too long will be that the vif hotplug
script will fail to rename the device.

This limit has long existed and I don't recall ever having seen a report
about it, maybe the failure case is so obvious that people just fix it
and move on. I also expect that setting such a long name is rare...

> Sorry for asking as it isn't clear in manual... ...
> http://xenbits.xen.org/docs/unstable/misc/xl-network-configuration.html
> ================================
> vifname
> This keyword is valid for HVM guest devices with type=ioemu only.
> Specifies the backend device name for an emulated device. The default
> is tapDOMID.DEVID where DOMID is the guest domain ID and DEVID is the
> device number.
> ================================
> >
> > I agree.
> >
> > This patch interacts a bit with Roger's hotplug series, I'll rebase on
> > top of his with this change when he reposts it.
> Looking forward for your reports ;)
> >
> > Ian.
> >
> Thanks.
> Kindest regards,
> Giam Teck Choon

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