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POHow to use the in-qemu API for virtio serial device
 

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  1. POHow to use the in-qemu API for virtio serial device
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    <p>I want to exchange "complex" data (hierarchical structs) between the guest and the host in a KVM+Qemu setup. </p> <p>My idea was to use the virtio serial driver to do so. A guest application would use the normal I/O functions such as open(2), close(2), read(2) and write(2) to send the "buffer" (=the struct I want to send) to the virtio serial back-end. The back-end driver would run inside Qemu and receive the pointer to the struct through the in-qemu host API described here: <a href="http://www.linux-kvm.org/page/Virtio-serial_API" rel="nofollow">http://www.linux-kvm.org/page/Virtio-serial_API</a></p> <p>My question now may be relatively trivial, but I was looking around all over Google and couldn't find anything: How do I "hook into qemu" such that I can use the virtio serial host API?</p> <p>I understand that I have to provide an init function like <code>void my_init(void) { virtio_serial_port_qdev_register(&amp;myinfo); }</code> and register it with qemu using <code>device_init(&amp;my_init)</code>. However, I do not understand how I link my module with qemu? Do I have to add my source files to the qemu code base and makefiles and recompile qemu? Or can I compile it separately and use some magic qemu command line option to load it? Or something completely different?</p> <p>(Note: I know that I could optionally serialize my data, send it to a socket on the host, and de-serialize it there, but I wanted to avoid the serialization overhead. If there is a way to use a shared memory region instead of a socket with an out-of-the-box virtIO serial device, this could be an option, too).</p> <p>Thank you all for your help! Christoph</p>
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    1. COIn case somebody has the same problem: What I found so far is that the device_init() mechanism was replaced with type_init(). "Type" because Qemu internally now uses a class-based mechanism (the object orientation is realized in C as a set of conventions, macros, and helper functions). Also I think one actually must add new device sources to the Qemu make files, no dynamic modules. This is all good. But, the "Virtio-serial_API" info above is outdated: the virtio_serial_port_qdev_register() function doesn't exist any more which now opens the question: how do I register a new serial device?
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      1. POHow to use the in-qemu API for virtio serial device
      1. USChristoph
    2. COAnother find: the virtio_serial_port_qdev_register() function doesn't exist any more because the registration is now done natively through the Qemu Object Model (I think it is replaced by the type_register_static() calls). This happened in version 1.1.2 through commit 5ae1015 from 3 Feb 2012. So it seems that to do what I was planning you just create a class and register it, and the device should be available. I still leave the question open, however, in case somebody has a more educated opinion on this.
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      1. POHow to use the in-qemu API for virtio serial device
      1. USChristoph
 

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