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Date: Sat, 29 Sep 2007 22:49:27 +0200
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Subject: Re: [Qemu-devel] qcow2 vs. image file format --> pci device
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From: Dor Laor <dor.laor@gmail.com>
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To: qemu-devel@nongnu.org

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.