On Sun, 2007-06-03 at 14:39 +0300, Avi Kivity wrote:
> Rusty Russell wrote:
> > Hmm... Perhaps I should move the used arrays into the "struct
> > virtio_device" and guarantee that the id (returned by add_*buf) is an
> > index into that. Then we can trivially add a corresponding bit array.
>
> That may force the virtio backend to do things it doesn't want to.
Well, I have two implementations, and both ids already fit this model so
I have some confidence. I just need to add the set_bit/clear_bit to the
read/write one, and use sync_clear_bit to the descriptor-based one
(which I suspect will actually get a little cleaner).
So I think this constraint is a reasonable thing to add anyway.
> > This also makes the "id" easier to use from the driver side: if we add a
> > "max_id" field it can size its own arrays if it wants to. Gets rid of
> > the linked-list in the block driver...
> >
>
> How about
>
> struct virtio_completion {
> unsigned long length;
> void *data;
> };
>
> int virtio_complete(struct virtio_completion *completions, int nr);
>
> where 'data' is an opaque pointer passed by the device during add_*buf()?
Other than the fact that the driver will look less like a normal driver,
it's actually harder to write the net driver if that complete call can
happen off an interrupt: we can't free skbs in interrupt context, which
is why the used-outbuf cleanup is currently done (inefficiently, but
that's orthogonal) in the xmit routine.
I'll code up the modifications now and check if I'm right about the
impact on the code. I might have to come up with something else...
Cheers,
Rusty.
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