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    SubjectRe: [KVM-RFC PATCH 0/2] irqfd: use POLLHUP notification for close()
    On Tue, Jun 02, 2009 at 01:41:05PM -0400, Gregory Haskins wrote:
    > > And having close not clean up the state unless you do an ioctl first is
    > > very messy IMO - I don't think you'll find any such examples in kernel.
    > >
    > >
    > I agree, and that is why I am advocating this POLLHUP solution. It was
    > only this other way to begin with because the technology didn't exist
    > until Davide showed me the light.
    > Problem with your request is that I already looked into what is
    > essentially a bi-directional reference problem (for a different reason)
    > when I started the POLLHUP series. Its messy to do this in a way that
    > doesn't negatively impact the fast path (introducing locking, etc) or
    > make my head explode making sure it doesn't race. Afaict, we would need
    > to solve this problem to do what you are proposing (patches welcome).
    > If this hybrid decoupled-deassign + unified-close is indeed an important
    > feature set, I suggest that we still consider this POLLHUP series for
    > inclusion, and then someone can re-introduce DEASSIGN support in the
    > future as a CAP bit extension. That way we at least get the desirable
    > close() properties that we both seem in favor of, and get this advanced
    > use case when we need it (and can figure out the locking design).

    FWIW, I took a look and yes, it is non-trivial.
    I concur, we can always add the deassign ioctl later.


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