On Sat, Apr 19, 2008 at 6:11 PM, Glauber Costa <[EMAIL PROTECTED]> wrote:
>
> On Fri, Apr 18, 2008 at 1:27 PM, Avi Kivity <[EMAIL PROTECTED]> wrote:
> >
> > Glauber de Oliveira Costa wrote:
> >
> > > Hi,
> > > I've got some qemu crashes while trying to passthrough an ide device
> > > to a kvm guest. After some investigation, it turned out that
> > register_ioport_{read/write} will abort on errors instead of returning
> > > a meaningful error.
> > >
> > > However, even if we do return an error, the asynchronous nature of pci
> > > config space mapping updates makes it a little bit hard to treat.
> > >
> > > This series of patches basically treats errors in the mapping functions
> in
> > > the pci layer. If anything goes wrong, we unregister the pci device,
> > unmapping
> > > any mappings that happened to be sucessfull already.
> > >
> > > After these patches are applied, a lot of warnings appears. And, you
> know,
> > > everytime there is a warning, god kills a kitten. But I'm not planning on
> > > touching the other pieces of qemu code for this until we set up (or not)
> > in
> > > this solution
> > >
> > > Comments are very welcome, specially from qemu folks (since it is a bit
> > invasive)
> > >
> > >
> > >
> >
> > Have you considered, instead of rolling back the changes you already made
> > before the failure, to have a function which checks if an ioport
> > registration will be successful? This may simplify the code.
> >
> Yes, I did.
>
> Basic problem is that I basically could not find this information
> handy until we were deep in the stack, right before calling the update
> mapping functions. I turned out preferring this option. I can,
> however, take a fresh look at that.
>
Looked at this again, and it does seem to me that we don't have too
much to gain from a "test-before" solution. We definitely can't test
it reliably until update_mappings arrive, (since the mapping can
change) and by this time, the pci device is already registered, and we
would have to de-register it anyway. There is room for "improvement"
(with a wide definition of improvement) if we test all the ports of a
device in advance (inside update_mappings) instead of a port-by-port
basis. We could get rid of the flag, but it would be traded off by
another complexities.
So unless someone have a very direct alternate solution for this I'm
failing to see, I do advocate for those humble patches.
--
Glauber Costa.
"Free as in Freedom"
http://glommer.net
"The less confident you are, the more serious you have to act."
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