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Re: [Qemu-devel] qemu virtIO blocking operation - question

From: Sinha, Ani
Subject: Re: [Qemu-devel] qemu virtIO blocking operation - question
Date: Tue, 13 Sep 2011 12:35:28 -0500

>> We are trying to paravirtualize the IPMI device (/dev/ipmi0).
> From http://en.wikipedia.org/wiki/Intelligent_Platform_Management_Interface:
> "An implementation of IPMI version 1.5 can communicate via a direct
> serial connection or via a side-band local area network (LAN)
> connection to a remote client."
> Why do you need a new virtio device?  Can't you use virtio-serial?
> This is what other management channels are using for host<->guest
> agents.

It might be possible. However, we are doing it this way because :

(a) I am not sure of the interactions with the real ipmi device on the host 
when the device is shared with multiple guests (we are not using pci 
passthrough to attach the device to a single guest).  The device itself is 
stateless - that is, it can not handle multiple requests at one time. When 
multiple users use the device, the driver has to serialize the requests and 
send it to the device. The existing ipmi driver within Linux 
(drivers/char/ipmi)  does that now.  But this driver on one guest would not 
know the existence of another guest. May be it might have to be reworked to 
work with virtio-serial. Dunno.

So, we wanted to keep this driver as is in the host and build a lightweight 
interface layer in the guest that can talk to the real driver on the host. 
Multiple guests would then be like multiple processes accessing the device.

(b) We wanted to gain some experience paravirtualizing devices this way through 
virtio since we have other proprietary hardware that needs to be 

Makes sense?


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