Re: [Qemu-devel] [PATCH] VirtIO Support for Memory Regions

[Avi Kivity <avi@redhat.com>]

On 02/24/2010 08:20 AM, Cam Macdonell wrote:
>
>> Virtio is really a DMA engine.  One of the nice things about it's design is
>> that you can do things like transparent bounce buffering if needed.  Adding
>> a mechanism like this breaks this abstract and turns virtio into something
>> that's more than I think it should be.
>>
>> For guest shared memory, what makes sense to me is to make use of uio_pci
>> within a guest to map bars in userspace.  The device can have the first bar
>> map a small MMIO region that is tied to a ioeventfd with KVM.  With just
>> qemu, it can be tied to a normal eventfd.  You can use irqfd with KVM to tie
>> an eventfd to the PCI irq.  Likewise, you can use a normal eventfd to
>> emulate that.  I'd suggest using a /dev/shm file to act as the shared memory
>> segment.  You'll need a little magic within qemu_ram_alloc() to use this
>> (maybe qemu_ram_alloc() should take a context parameter so this can be
>> setup).
>>      
> Part of my goal with this patch was to support systems without PCI.
> My previous patch
>    

Which?  The only one I know of is s390 (and it would be a pity not to 
have shared memory for that).

-- 
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