Re: [Qemu-devel] [PATCH 19/38] ivshmem: Assert interrupts are set up once

[Marc-André Lureau]

Hi

On Mon, Feb 29, 2016 at 7:40 PM, Markus Armbruster <address@hidden> wrote:
> An interrupt is set up when the interrupt's file descriptor is
> received.  Each message applies to the next interrupt vector.
> Therefore, each vector cannot be set up more than once.
>
> ivshmem_add_kvm_msi_virq() half-heartedly tries not to rely on this by
> doing nothing then, but that's not going to recover from this error
> should it become possible in the future.  watch_vector_notifier()
> doesn't even try.
>
> Simply assert what is the case, so we get alerted if we ever screw it
> up.
>
> Signed-off-by: Markus Armbruster <address@hidden>
> ---
>  hw/misc/ivshmem.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> index fc37feb..9d2209d 100644
> --- a/hw/misc/ivshmem.c
> +++ b/hw/misc/ivshmem.c
> @@ -349,7 +349,7 @@ static void watch_vector_notifier(IVShmemState *s, 
> EventNotifier *n,
>  {
>      int eventfd = event_notifier_get_fd(n);
>
> -    /* if MSI is supported we need multiple interrupts */
> +    assert(!s->msi_vectors[vector].pdev);

ok, why not

>      s->msi_vectors[vector].pdev = PCI_DEVICE(s);
>
>      qemu_set_fd_handler(eventfd, ivshmem_vector_notify,
> @@ -535,10 +535,7 @@ static int ivshmem_add_kvm_msi_virq(IVShmemState *s, int 
> vector)
>      int ret;
>
>      IVSHMEM_DPRINTF("ivshmem_add_kvm_msi_virq vector:%d\n", vector);
> -
> -    if (s->msi_vectors[vector].pdev != NULL) {
> -        return 0;
> -    }
> +    assert(!s->msi_vectors[vector].pdev);

that one is more tricky, since irqfd may be enabled/disabled
dynamically from ivshmem_write_config(), and
ivshmem_add_kvm_msi_virq() may be called at different times. However,
I think an assert is correct as there shouldn't be a valid state where
add_kvm_msi_virq() is called with the same vector when irqfd is
enabled.

Reviewed-by: Marc-André Lureau <address@hidden>