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    SubjectRe: [PATCH RFC] pass write value to in_range pointers
    On Tue, Jun 23, 2009 at 07:41:12AM -0400, Gregory Haskins wrote:
    > Avi Kivity wrote:
    > > On 06/22/2009 07:08 PM, Michael S. Tsirkin wrote:
    > >> On Mon, Jun 22, 2009 at 11:45:00AM -0400, Gregory Haskins wrote:
    > >>
    > >>> Michael S. Tsirkin wrote:
    > >>>
    > >>>> It seems that a lot of complexity and trickiness with iosignalfd is
    > >>>> handling the group/item relationship, which comes about because kvm
    > >>>> does
    > >>>> not currently let a device on the bus claim a write transaction
    > >>>> based on the
    > >>>> value written. This could be greatly simplified if the value written
    > >>>> was passed to the in_range check for write operation. We could then
    > >>>> simply make each kvm_iosignalfd a device on the bus.
    > >>>>
    > >>>> What does everyone think of the following lightly tested patch?
    > >>>>
    > >>>>
    > >>> Hi Michael,
    > >>> Its interesting, but I am not convinced its necessary. We
    > >>> created the
    > >>> group/item layout because iosignalfds are unique in that they are
    > >>> probably the only IO device that wants to do some kind of address
    > >>> aliasing.
    > >>>
    > >>
    > >> We actually already have aliasing: is_write flag is used for this
    > >> purpose. Actually, it's possible to remove is_write by passing
    > >> a null pointer in write_val for reads. I like this a bit less as
    > >> the code generated is less compact ... Avi, what do you think?
    > >>
    > >
    > > Greg, won't Michael's patch eliminate a big chunk from your iosignalfd
    > > patches? Seems like a win to me.
    >
    > Well, it really just moves that hunk from eventfd.c to kvm_main.c, where
    > I don't think anyone else will use it by iosignalfd. But if that is
    > what everyone wants, I guess I have no choice.

    Wait a bit before you start rebasing though please.
    I just had a brainwave and is rewriting this patch.

    > >
    > >> One is enough :)
    > >> Seriously, do you see that this saves you all of RCU, linked lists and
    > >> counters? You don't need to keep track of iofds, you don't need to
    > >> implement your own lookup logic - you just use the kvm device
    > >> and that's it.
    > >>
    > >>
    > >
    > > Yup.
    > >
    >
    >




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