Re: [PATCH] Add VirtIO Frame Buffer Support

From: Ondrej Zajicek <santiago@crfreenet.org>
To: Alexander Graf <agraf@suse.de>
Cc: linux-fbdev-devel@lists.sourceforge.net,
	qemu-devel <qemu-devel@nongnu.org>,
	Anthony Liguori <anthony@codemonkey.ws>,
	kvm list <kvm@vger.kernel.org>
Subject: Re: [PATCH] Add VirtIO Frame Buffer Support
Date: Tue, 3 Nov 2009 00:57:33 +0100	[thread overview]
Message-ID: <20091102235733.GB28292@localhost> (raw)
In-Reply-To: <5B01907D-86BE-4693-81BA-23CB81B8B047@suse.de>

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On Tue, Nov 03, 2009 at 12:24:15AM +0100, Alexander Graf wrote:
>> Also, we still need to keep the local frame buffer copy in sync so we
>> can mmap and read from it, right? So it's not really worth it
>> probably...
>
> But then again we could just try to be closer to a real graphics card.  
> What if we'd set up a memory region on the host that is basically our  
> graphics frame buffer? For S390 we could just append the graphics memory 
> to the guest's memory.
>
> We could use that as backing buffer in the qemu graphics frontend and as 
> frame buffer in the Linux fbdev layer, similar to what real graphics 
> cards set up.

Using shared memory pages between host and guest seems like a natural
way to implement paravirtualized graphics card. Most things are
straightforward, only a little problematic thing is when fbdev 
is mmaped from guest to userspace - you have to detect writes
and notify host that it changed.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago@crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."

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