Re: [Qemu-devel] Questions regarding ivshmem spec

[Sasha Levin]

On Thu, 2011-08-25 at 17:00 +0300, Avi Kivity wrote:
> On 08/25/2011 04:29 PM, Sasha Levin wrote:
> > 2. The spec describes DOORBELL as an array of DWORDs, when one guest
> > wants to poke a different guest it would write something into the offset
> > of the other guest in the DOORBELL array.
> > Looking at the implementation in QEMU, DOORBELL is one DWORD, when
> > writing to it the upper WORD is the guest id and the lower WORD is the
> > value.
> > What am I missing here?
> >
> 
> The spec in qemu.git is accurate.  The intent is to use an ioeventfd 
> bound into an irqfd so a write into the doorbell injects an interrupt 
> directly into the other guest, without going through qemu^Wkvm tool.
> 

But the doorbell is a single DWORD, so if a guest writes to it we'd
still need to figure out which guest/vector he wants to poke from
userspace, no?

If it was an array of doorbells then yes, we could assign an ioeventfd
to each offset - but now I don't quite see how we can avoid passing
through the userspace.

-- 

Sasha.