Re: [Xen-devel] Question: Redirect guest kernel's message via serial port to a file on dom0

[Meng Xu <xumengpanda@xxxxxxxxx>]

Hi Andrew,

Thank you so much for your suggestion! I tried but have some questions.

2015-08-24 4:10 GMT-04:00 Andrew Cooper <andrew.cooper3@xxxxxxxxxx>:
>
> On 24/08/2015 04:01, Meng Xu wrote:
>
> Hi,
>
> I'm trying to use a PV guest VM on Xen to help debug Linux.
> I was using VirtualBox to help debug Linux kernel by redirecting the output 
> of the serial port of the VM to a file in the host. I can do it in VirtualBox.
>
> [Why do I want to achieve this?]
> It is much faster to reboot a VM than rebooting the physical machine.
> I don't need another machine to physically connect to the serial port of the 
> development machine.
> I want to use Xen for as many things as possible. ;-)
>
> I tried to google a tutorial or manual about how to configure it, but didn't 
> find any. :-(
>
> In my understanding, I need to do the following things:
> 1) I need to add a line (something like "serial=") in the guest's 
> configuration file to specify the serial port device to the VM;
> 2) I need some configuration to redirect the output of the serial device to a 
> file in domU;
> 3) After that, I can configure the kernel command line in the VM to dump the 
> kernel message via the serial port of the VM. (I know how to do this step.)
>
> Did anyone have tried this before and have some configuration I can refer to? 
> or
> Could anyone give me some references that describes how to configure the 
> above three steps?
>
> I really appreciate any help or suggestion or comment.
>
>
> Configure xenconsoled to log guest consoles to file "--log=guest" at which 
> point anything sent to hvc0 will be logged to files in 
> /var/log/xen/guest/console (configurable with "--log-dir=")


I set "XENCONSOLED_TRACE=guest" under /etc/default/xencommons ,
because in /etc/init.d/xencommons, it has: test -z
"$XENCONSOLED_TRACE" || XENCONSOLED_ARGS=" --log=$XENCONSOLED_TRACE"

So I think this is what you mean by "--log=guest"; After I set this
variable and restart the xencommons by "service xencommons restart" on
dom0 (Ubuntu 12.04LTS), I still couldn't find the file in
/var/log/xen/guest/console when I reboot the VM.
Actually, "find /var -name console" returns no result.

**My question is:**
Is there anything else I need to configure to get the
/var/log/xen/guest/console?

I don't see the folder under /var/log/xen. :-(

BTW, I also tried "find /etc |grep -i "log-dir"", but find no file has
the keyword "log-dir".


>
>
> There is usually XENCONSOLED_ARGS= in a configuration file somewhere in /etc.


Yes, I think I found it in /etc/init.d/xencommons.


---I attached the config file for the VM just in case it is helpful:--

name = "vm1"

memory = 8192

disk = ['file:/images/vm1.img,xvda,w']

vif = ['bridge=xenbr0']

extra = "debian-installer/exit/always_halt=true --console=hvc0"

bootloader = "pygrub"


Thank you very much for your help!

Best regards,

Meng

-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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