Re: Guests networking using driver domain

[Andrea Stevanato <andrea.stevanato@xxxxxxxxxxxxxxx>]

On 3/3/22 23:37, Felix Kuperjans wrote:
> Am 03.03.22 um 11:32 schrieb Andrea Stevanato:
> > Hi all,
> > I'm trying to configure two guests that can communicate with 
> > each other using a "virtual" network card exploiting the netback and 
> > netfront driver.
> > The first guest is created with the following configuration:
> >
> > name    = "guest0"
> > kernel  = "/media/sd-mmcblk0p1/Image"
> > ramdisk = "/media/sd-mmcblk0p1/rootfs.cpio.gz"
> > extra   = "console=hvc0 rdinit=/sbin/init root=/dev/ram0"
> > memory  = 1024
> > vcpus   = 2
> >
> > Once it is up and running, I create and setup the bridge:
> >
> > # brctl addbr xenbr0
> > # ip addr add 10.0.3.1/24 dev xenbr0
> > # ip link set dev xenbr0 up
> >
> > Then I configure the udhcpd server with the following configuration 
> > (/etc/udhcpd.conf):
> > start 10.0.3.15
> > end 10.0.3.254
> > interface xenbr0
> > option subnet 255.255.255.0
> >
> > And start it with: `# udhcpd`​.
> >
> > The second guest is created with the following configuration:
> >
> > name    = "guest1"
> > kernel  = "/media/sd-mmcblk0p1/Image"
> > ramdisk = "/media/sd-mmcblk0p1/rootfs.cpio.gz"
> > extra   = "console=hvc0 rdinit=/sbin/init root=/dev/ram0"
> > memory  = 1024
> > vcpus   = 2
> > vif = [ 'bridge=xenbr0, backend=guest0' ]
> >
> > Once it is up and running on the guest0 the new interface (vifX.0) is 
> > created correctly, however on the guest1 the eth0 interface is not 
> > present.
> > If I do the exact same thing on dom0, instead of guest0 (without 
> > attaching the eth0 to the bridge, since I do not need to reach 
> > outside), the eth0 on the guest is created correctly and get the 
> > 10.0.3.15 IP address.
> > What I'm doing wrong?
> >
> > Andrea
> Hi Andrea,
>
> I think this might be related to problems with the VIF hotplugging on 
> "guest0".
> Since the vifX.0 on guest0 is successfully created, some of the 
> hotplugging at least works, but maybe a failure to setup it correctly 
> leads to the problem in "guest1".
>
> A few questions for further investigation:
>
> Is the vifX.0 device up and having "master xenbr0" (see ip link show)?
The vifX.0 do not have "master xenbr0".

> If not, there is definitely a problem with the bridge hotplugging.
>
> Which daemon handles the vif hotplugging? xl devd? is /etc/xen/xl.conf 
> configured correctly (usually having vif.default.script="vif-bridge" and 
> run_hotplug_scripts=1)?
The configuration file is all commented, actually also in dom0 it is the
same.

> Do the hotplugging scripts exist, esp. /etc/xen/scripts/vif-bridge ? Can 
> you see any log messages from this script in /var/log/xen/xen-hotplug.log?
Yes, the vif-bridge script exists. No, the /var/log/xen directory is empty.

> Usually I would expect one of these to have a notable error causing the 
> script to not be called or not run properly.
> Otherwise, some more log output from guest0 would be helpful, dmesg, log 
> messages about the hotplugging, ...
Please have a look at 
https://lore.kernel.org/xen-devel/1d00a228-a699-5743-69ae-4dbadee5ebb9@xxxxxxxxxxxxxxx/T/#m50eed0b51f2fc8b0ac26bc269dd5119f83041dd0 
where I posted the full
log of xl -vvv devd -F executed on guest0.

> Best Regards
> Felix
Cheers,
Andrea