Re: [PATCH v2] vfio-ccw: Permit missing IRQs

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 21 Apr 2021 17:20:53 +0200
Eric Farman <farman@linux.ibm.com> wrote:

> Commit 690e29b91102 ("vfio-ccw: Refactor ccw irq handler") changed
> one of the checks for the IRQ notifier registration from saying
> "the host needs to recognize the only IRQ that exists" to saying
> "the host needs to recognize ANY IRQ that exists."
> 
> And this worked fine, because the subsequent change to support the
> CRW IRQ notifier doesn't get into this code when running on an older
> kernel, thanks to a guard by a capability region. The later addition
> of the REQ(uest) IRQ by commit b2f96f9e4f5f ("vfio-ccw: Connect the
> device request notifier") broke this assumption because there is no
> matching capability region. Thus, running new QEMU on an older
> kernel fails with:
> 
>   vfio: unexpected number of irqs 2
> 
> Let's adapt the message here so that there's a better clue of what
> IRQ is missing.
> 
> Furthermore, let's make the REQ(uest) IRQ not fail when attempting
> to register it, to permit running vfio-ccw on a newer QEMU with an
> older kernel.
> 
> Fixes: b2f96f9e4f5f ("vfio-ccw: Connect the device request notifier")
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
> 
> Notes:
>     v1->v2:
>      - Keep existing "invalid number of IRQs" message with adapted text [CH]
>      - Move the "is this an error" test to the registration of the IRQ in
>        question, rather than making it allowable for any IRQ mismatch [CH]
>      - Drop Fixes tag for initial commit [EF]
>     
>     v1: https://lore.kernel.org/qemu-devel/20210419184906.2847283-1-farman@linux.ibm.com/
> 
>  hw/vfio/ccw.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)

Thanks, applied.