[Qemu-devel] view qemu output/console

[Qemu-devel] view qemu output/console

[Clemens Kolbitsch]

hi!
i'm having a problem that could have a very easy answer:

my i386 linx system crashes due to a module error and i have to find out where 
it crashes exactly.... i have the module source code.

when the kernel crashes, it displayes the message, however as it is way much 
more information that can be displayed in the qemu window, i only see the 
last 20-something lines. as the crash is fatal, no entries are made to the 
log-files and i have not succeeded redirecting output to my console (using 
the -nographic option) as my linux does not boot correctly then.

i have also tried attaching a debugger, however i neither have a unzipped 
image of my kernel nor are the breakpoints hit correctly as the crash happens 
inside a module that is loaded on system-startup (i.e. is not part of the 
kernel).

can someone give me a hint on how i am able to read the whole output of 
the "kernel-oops"?

thanks!!

Re: [Qemu-devel] view qemu output/console

[Johannes Schindelin]

Hi,

On Mon, 24 Sep 2007, Clemens Kolbitsch wrote:

> when the kernel crashes, it displayes the message, however as it is way 
> much more information that can be displayed in the qemu window, i only 
> see the last 20-something lines. as the crash is fatal, no entries are 
> made to the log-files and i have not succeeded redirecting output to my 
> console (using the -nographic option) as my linux does not boot 
> correctly then.

If your host is not windows, you can use the "-monitor stdio" option to 
output monitor information on the console you start QEmu in.

Hth,
Dscho

Re: [Qemu-devel] view qemu output/console

[andrzej zaborowski]

On 24/09/2007, Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> On Mon, 24 Sep 2007, Clemens Kolbitsch wrote:
>
> > when the kernel crashes, it displayes the message, however as it is way
> > much more information that can be displayed in the qemu window, i only
> > see the last 20-something lines. as the crash is fatal, no entries are
> > made to the log-files and i have not succeeded redirecting output to my
> > console (using the -nographic option) as my linux does not boot
> > correctly then.
>
> If your host is not windows, you can use the "-monitor stdio" option to
> output monitor information on the console you start QEmu in.

AIUI Clemens wants to redirect the VGA console output, not QEmu
monitor. One idea is to dig out my ncurses interface patch (I believe
debian has a version that applies to post-9.0 qemu, and if you're on
debian just use the "-curses" switch), then GNU screen would let you
log all VGA console output to a file. Another idea is to set a
breakpoint at the guest printk() address.

Regards

Re: [Qemu-devel] view qemu output/console

[Clemens Kolbitsch]

On Monday 24 September 2007 18:11:04 andrzej zaborowski wrote:
> On 24/09/2007, Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> > On Mon, 24 Sep 2007, Clemens Kolbitsch wrote:
> > > when the kernel crashes, it displayes the message, however as it is way
> > > much more information that can be displayed in the qemu window, i only
> > > see the last 20-something lines. as the crash is fatal, no entries are
> > > made to the log-files and i have not succeeded redirecting output to my
> > > console (using the -nographic option) as my linux does not boot
> > > correctly then.
> >
> > If your host is not windows, you can use the "-monitor stdio" option to
> > output monitor information on the console you start QEmu in.
>
> AIUI Clemens wants to redirect the VGA console output, not QEmu
> monitor.

exactly...

> One idea is to dig out my ncurses interface patch (I believe 
> debian has a version that applies to post-9.0 qemu, and if you're on
> debian just use the "-curses" switch), then GNU screen would let you
> log all VGA console output to a file.

ok... i'll give it a try!! thanks :-)

> Another idea is to set a 
> breakpoint at the guest printk() address.

that was my first approach.. however as I don't have the uncompressed linux 
image, i don't know what to connect gdb to :-(

can i simply uncompress the kernel-file??

[Qemu-devel] qcow2 vs. image file format --> pci device

[Clemens Kolbitsch]

hi everyone!
i have a strange problem (at least to me it seems strange :-)  ):

i have implemented a pci device (Network IC) and it works just fine when using 
a standard image. however i now want to support snapshotting...

i started to convert my image into the qcow2 format and suddenly my code does 
not work any more... even if i uncomment everything that has to do with 
snapshotting in my code, it still blocks during qemu startup.

the thing that could cause this: i use 2 additional threads in my NIC code ... 
each is working with semaphores that might cause problems.

is there something in particular i have to be careful of when using qcow2 file 
format?

thanks!!

Re: [Qemu-devel] qcow2 vs. image file format --> pci device

[Dor Laor]

Clemens Kolbitsch wrote:
> hi everyone!
> i have a strange problem (at least to me it seems strange :-)  ):
>
> i have implemented a pci device (Network IC) and it works just fine when using 
> a standard image. however i now want to support snapshotting...
>
> i started to convert my image into the qcow2 format and suddenly my code does 
> not work any more... even if i uncomment everything that has to do with 
> snapshotting in my code, it still blocks during qemu startup.
>
> the thing that could cause this: i use 2 additional threads in my NIC code ... 
> each is working with semaphores that might cause problems.
>
> is there something in particular i have to be careful of when using qcow2 file 
> format?
>
> thanks!!
>
>
>   
Qcow2 uses async io which triggers io completion with SIGIO signal.
If you use threads you must mask this (and also SIGALARM, ..) so your 
thread won't
take over the main threads handling.
Anyway, using threads is not the standard qemu guideline.
Dor.

Re: Re: [Qemu-devel] qcow2 vs. image file format --> pci device

[Clemens Kolbitsch]

> Clemens Kolbitsch wrote:
> > hi everyone!
> > i have a strange problem (at least to me it seems strange :-)  ):
> >
> > i have implemented a pci device (Network IC) and it works just fine when
> > using a standard image. however i now want to support snapshotting...
> >
> > i started to convert my image into the qcow2 format and suddenly my code
> > does not work any more... even if i uncomment everything that has to do
> > with snapshotting in my code, it still blocks during qemu startup.
> >
> > the thing that could cause this: i use 2 additional threads in my NIC
> > code ... each is working with semaphores that might cause problems.
> >
> > is there something in particular i have to be careful of when using qcow2
> > file format?
> >
> > thanks!!
>
> Qcow2 uses async io which triggers io completion with SIGIO signal.
> If you use threads you must mask this (and also SIGALARM, ..) so your
> thread won't
> take over the main threads handling.
> Anyway, using threads is not the standard qemu guideline.

Hi,
Ok.. thanks! How do I tell Qemu that I use threads (in this case I don't see 
an easy way around using them... although there is one obviously ;-) )??

In what other HW example can I see how to use the SIGIO completion stuff?
Clemens

Re: [Qemu-devel] qcow2 vs. image file format --> pci device

[Dor Laor]

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Clemens Kolbitsch wrote:
>> Clemens Kolbitsch wrote:
>>     
>>> hi everyone!
>>> i have a strange problem (at least to me it seems strange :-)  ):
>>>
>>> i have implemented a pci device (Network IC) and it works just fine when
>>> using a standard image. however i now want to support snapshotting...
>>>
>>> i started to convert my image into the qcow2 format and suddenly my code
>>> does not work any more... even if i uncomment everything that has to do
>>> with snapshotting in my code, it still blocks during qemu startup.
>>>
>>> the thing that could cause this: i use 2 additional threads in my NIC
>>> code ... each is working with semaphores that might cause problems.
>>>
>>> is there something in particular i have to be careful of when using qcow2
>>> file format?
>>>
>>> thanks!!
>>>       
>> Qcow2 uses async io which triggers io completion with SIGIO signal.
>> If you use threads you must mask this (and also SIGALARM, ..) so your
>> thread won't
>> take over the main threads handling.
>> Anyway, using threads is not the standard qemu guideline.
>>     
>
> Hi,
> Ok.. thanks! How do I tell Qemu that I use threads (in this case I don't see 
> an easy way around using them... although there is one obviously ;-) )??
>
>   
All other NIC emulation work without threads. They use select 
(qemu_set_fd_handler)
> In what other HW example can I see how to use the SIGIO completion stuff?
>   
Actually I had a mistake, qemu use SIGUSR2 for async io and SIGIO for 
timer management.
> Clemens
>
>   


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