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    SubjectRe: [KVM-RFC PATCH 0/2] irqfd: use POLLHUP notification for close()
    On Tue, Jun 02, 2009 at 12:14:15PM -0400, Gregory Haskins wrote:
    > Michael S. Tsirkin wrote:
    > > On Tue, Jun 02, 2009 at 11:15:28AM -0400, Gregory Haskins wrote:
    > >
    > >> (Applies to kvm.git/master:25deed73)
    > >>
    > >> Please see the header for 2/2 for a description. This patch series has
    > >> been fully tested and appears to be working correctly. I have it as an RFC
    > >> for now because it needs Davide's official submission/SOB for patch 1/2, and
    > >> it should get some eyeballs/acks on my SRCU usage before going in.
    > >>
    > >> I will submit the updated irqfd userspace which eschews the deassign() verb
    > >> since we can now just use the close(fd) method alone. I will also address
    > >> the userspace review comments from Avi.
    > >>
    > >
    > >
    > > We are not killing the deassign though, do we?
    > >
    >
    > Yes, it is not needed any more now that we have proper
    > release-notification from eventfd.
    >
    > > It's good to have that option e.g. for when we pass
    > > the fd to another process.
    > >
    >
    > Passing the fd to another app should up the underlying file reference
    > count. If the producer app wants to "deassign" it simply calls
    > close(fd) (as opposed to today where it calls DEASSIGN+close), but the
    > reference count will allow the consuming app to leave the eventfd's file
    > open. Or am I misunderstanding you?
    >
    > -Greg
    >
    >

    I think we want to keep supporting the deassign ioctl. This, even though
    close overlaps with it functionally somewhat.

    This allows qemu to pass eventfd to another process/device, and then
    block/unblock interrupts as seen by that process by
    assigning/deassigning irq to it. This is much easier and lightweight
    than asking another process to close the fd and passing another fd
    later.

    --
    MST


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