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

[Meng Xu <xumengpanda@xxxxxxxxx>]

2015-09-01 6:52 GMT-04:00 Ian Campbell <ian.campbell@xxxxxxxxxx>:
> On Tue, 2015-08-25 at 09:04 -0400, Meng Xu wrote:
>> 2015-08-25 3:42 GMT-04:00 Andrew Cooper <andrew.cooper3@xxxxxxxxxx>:
>> > On 25/08/2015 03:48, Meng Xu wrote:
>> > > 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. :-(
>> >
>> > You probably need to mkdir it then, or extend the args list with
>> > --log-dir=/var/log/xen
>>
>> I tried both, but neither of them works. :-(
>>
>> I'm wondering if anyone has some document about how to do this?
>> If there is some document about how to debug this configuration issue,
>> it could also be helpful...
>> But I didn't find it after googling and trying for 2 hours...:-(
>>
>> Below is the detail of what I tried:
>>
>> I tried to mkdir /var/log/xen/guest
>
> The correct (default) path is /var/log/xen/console I think.
>
>>  and restart the xencommons by
>> "service xencommons restart",
>
> Are you using sysvinit or systemd?

I'm using sysvinit, since "pidof /sbin/init " shows that init process
has pid = 1.

> If the latter are you using the systemd
> units of the sysvinit scripts via systemd's LSB compat mode?
>
> If you are using the systemd units then I think they might be configured
> elsewhere.

Do I have to explicitly configure a virtual serial device to the PV
VM, in order to make Xen  create the /var/log/xen/console file?

Right now, when I ssh into the PV VM and issue the command #echo 1 >
/dev/ttyS0, it returns error "echo: write error: Input/output error".
I'm guessing maybe it's because the VM has no serial port configured?

Thank you very much for your time and help in this issue!

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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