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

[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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