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    SubjectRe: [PATCH] virtio: make PCI devices take a virtio_pci module ref
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    Hi Rusty,

    On Fri, 2008-12-05 at 10:43 +1030, Rusty Russell wrote:
    > On Thursday 04 December 2008 23:14:31 Mark McLoughlin wrote:
    > > Nothing takes a ref on virtio_pci, so even if you have
    > > devices in use, rmmod will attempt to unload the module.
    > >
    > > Fix by simply making each device take a ref on the module.
    >
    > Hi Mark,
    >
    > Taking a reference to oneself is almost always wrong.

    Yeah, it certainly seems fairly unorthodox, alright. But then again,
    virtio_pci is an odd creature anyway :-)

    My thinking was that the virtio abstraction is preventing there being an
    explicit dependency between e.g. virtio_net and virtio_pci. If we didn't
    have the abstraction, virtio_net would be calling directly into
    virtio_pci and we'd have an explicit dep. So, I was just trying to
    artificially mimic that.

    Another example of a lack of an explicit dependency causing problems is
    Fedora's mkinitrd having this hack:

    if echo $PWD | grep -q /virtio-pci/ ; then
    findmodule virtio_pci
    fi

    which basically says "if this is a virtio device, don't forget to
    include virtio_pci in the initrd too!". Now, mkinitrd is full of hacks,
    but this is a particularly unusual one.

    Í'm thinking that maybe we should default to having virtio_pci built-in
    if e.g. CONFIG_KVM_GUEST is set.

    > I'm a little surprised that a successful call to pci_device->probe
    > doesn't bump the module count though.

    Nah, removing a module for device should actually work fine.

    Anyway, with the root cause of Michael's traceback fixed, rmmod-ing
    virtio_pci and re-loading it works just fine, so ...

    Cheers,
    Mark.

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