Re: Guests networking using driver domain

[Felix Kuperjans <felix@xxxxxxxxxxxxxxxxxx>]

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)? 
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)?
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?

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, ...
Best Regards
Felix