Re: [Xen-devel] Xen on ARM basic questions

[Vaibhav Bedia <vaibhav.bedia@xxxxxxxxx>]

Hi Ian,

Sorry for the delayed response. Juggling between different thing in grad school.

On Tue, Nov 26, 2013 at 4:34 AM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Fri, 2013-11-22 at 14:20 -0500, Vaibhav Bedia wrote:
>> >> >> Right now i have an OMAP5 dom0 with network+usb support and i am
>> >> >> trying to figure out how to get these things in domU and hence the
>> >> >> questions.
>> >> >
>> >> > You need blkback and netback in dom0 and blkfront and netfront in domU
>> >> > (all in mainline Linux). Then you need to add vif and disk options to
>> >> > your guest configuration.
>> >> >
>> >>
>> >> I enabled both of the options and can get a ramdisk based domU running 
>> >> fine.
>> >> I tried a Ubuntu based fs for domU but can't get to the login prompt
>> >> for some reason.
>> >> I tried out the various options mentioned @
>> >> http://wiki.xen.org/wiki/Xen_Common_Problems#Console
>> >> and some other things mentioned on various forums but nothing seems to 
>> >> work :(
>> >> Any hints on where things could be going wrong? I have hvc0.conf under
>> >> /etc/init/
>> >
>> > Do you have CONFIG_HVC_XEN enabled in the guest kernel config? Is the
>> > guest detecting that it is running under Xen? Can you post a guest dmesg
>> > please.
>> >
>>
>> Yes. It's enabled. I can get the same image to the login prompt using a 
>> minimal
>> ramdisk so it should be something to do with the Ubuntu filesystem, right?
>
> You may need to configure Ubuntu to start a getty on hvc0 (the console
> device). This involves adding an upstart configuration file, copying an
> existing tty one and changing the device I guess? I don't know the
> details. Hopefully there's enough keywords there to let you do a search.
>

Thanks. I got this sorted out now (more below).

> Oh, I see further back in the thread that you have this. I'm afraid I
> don't know enough about Ubuntu to diagnose what may be going wrong.
> Perhaps post your hvc.conf and maybe someone can spot what is going
> wrong.
>
>> The IP address is via DHCP. Once i get the login prompt using the
>> minimal ramdisk i run
>> $ ifconfig eth0 up
>> <eth0 mac address is what i assign in the config file>
>> $ udhcpc
>> Guest gets an IP address now.
>
> Do you know where the DHCP server is? It is worth checking the logs in
> case udhcpc has actually failed and used a previously successful lease
> which it has cached. I don't know about udhcpc but other DHCP clients
> tend to log when they do this.
>

I doubt i'll get anywhere the campus server :)
I had to go through a few hoops just to get the ssh port enabled.

>> The above sequence doesn't work always but when it does get an IP
>> address i can't
>> ping domU or have it ping some other host. I didn't setup any firewall
>> explicitly - just
>> using plain ubuntu 13.04.
>
> I don't know if Ubuntu ships with a firewall enabled or not -- you
> should certainly confirm!
>

I learnt a bit about iptables and tcpdump and can now confirm that
there's no firewall enabled.

>> I do see that the vif is added to the bridge.
>
> In "brctl show" I suppose?
>

Yes.

>>  I also noticed that the
>> errrors under eth0
>> starts going up when i create a guest and eventually the network in dom0 
>> becomes
>> completely unresponsive.
>
> That's quite, er, interesting. I've never heard of that before.
>
> I see you have two vifs, are they on the same bridge? Do they have
> different mac addresses?
>
> Can you post your guest cfg file please.
>
> I'd suggest taking the second vif out and working to get a single one
> working, just to eliminate variables etc.
>
>> P.S. Apologies for the flood of seemingly random datapoints.
>> As you can see i am right now a total newbie to xen and trying to find
>> my way around :)
>
> That's ok. I'm a bit perplexed to be honest...
>
>>
>> =================
>>
>> Guest bootlog with Ubuntu fs:
>> ===
>>
>> root@arm:~# xl console domU-xen
>> [    0.000000] Booting Linux on physical CPU 0x0
>> [    0.000000] Linux version 3.12.0-01110-g0c72f67-dirty
>> (vaibhav@vaibhav-VirtualBox) (gcc version 4.7.3 (Ubuntu/Linaro
>> 4.7.3-1ubuntu1) ) #13
>> [    0.000000] CPU: ARMv7 Processor [412fc0f2] revision 2 (ARMv7), 
>> cr=10c5387d
>> [    0.000000] CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction 
>> cache
>> [    0.000000] Machine: Dummy Virtual Machine, model: XENVM-4.2
>> [    0.000000] cma: CMA: reserved 16 MiB at 87000000
>> [    0.000000] Memory policy: ECC disabled, Data cache writealloc
>> [    0.000000] PERCPU: Embedded 9 pages/cpu @c0ff4000 s15232 r8192 d13440 
>> u36864
>> [    0.000000] Built 1 zonelists in Zone order, mobility grouping on.
>> Total pages: 32512
>> [    0.000000] Kernel command line: console=hvc0 root=/dev/xvda
>> mem=128M xencons=tty
>
> How much mem did you give the guest in its configuration file? What
> about in the DTB? I'd recommend leaving off this instance of mem= for
> now.
>
>

>
> This is the point at which I would expect to start seeing userspace/init
> system (e.g. upstart) output. You have a correct console= line so I
> can't think where this might be going.
>
> Perhaps try booting with init=/bin/sh?
>
> Ian.
>

I seem to have the console mystery sorted out. I was using a standard
ubuntu filesystem and after reading some more blogs related to xen
usage realized that i had not never updated the /etc/fstab file to point
it to /dev/xvda1! Once i did that i got the console fine.

Thanks,
Vaibhav

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