Messages in this thread | | | Date | Tue, 06 Nov 2007 17:05:53 -0600 | From | Anthony Liguori <> | Subject | Re: virtio config_ops refactoring |
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Rusty Russell wrote: > On Wednesday 07 November 2007 04:48:35 Anthony Liguori wrote: >> Semantically, find requires that a field have both a type and a length. >> With the exception of the VIRTQUEUE field used internally by lguest, >> type is always a unique identifier. Since virtqueue information is not >> a required part of the config space, it seems to me that type really >> should be treated as a unique identifier. > > Hi Anthony, > > Not sure I get this. It is a unique identifier. You need the length > to handle unknown fields.
It's not a unique identifier since it can be used for multiple items (like it is for virtqueues configs).
>> find_vq also is curious in that it is stateful in it's enumeration. > > Well, they're *all* stateful. This gives a simple method of knowing what > fields the guest understands: it marks the fields as it finds them. Then it > sets the status, which allows the host to know when it's completed > configuration reads.
But PCI device configuration is not stateful. If you care about letting the host know what features a guest understands, I think something more explicit and stateful should be used. For instance, a feature register that stores a bitmap.
Otherwise, the host has to infer based on what fields that guest has read what features the guest actually supports. That seems error prone to me.
> I like enumerating the virtqueues: it's not necessary but it's clearer. > >> This adds seemingly unnecessary complexity. > > I'd be happy for a simpler mechanism...
What do you think of what I proposed? It seems simpler to me.
Regards,
Anthony Liguori
> Cheers, > Rusty.
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