[Qemu-devel] Re: [PATCH v3 1/1] Shared memory uio_pci driver

[Avi Kivity]

On 03/28/2010 10:48 PM, Cam Macdonell wrote:
> On Sat, Mar 27, 2010 at 11:48 AM, Avi Kivity<address@hidden>  wrote:
>    
> > On 03/26/2010 07:14 PM, Cam Macdonell wrote:
> >      
> > >        
> > > > I'm not familiar with the uio internals, but for the interface, an
> > > > ioctl()
> > > > on the fd to assign an eventfd to an MSI vector.  Similar to ioeventfd,
> > > > but
> > > > instead of mapping a doorbell to an eventfd, it maps a real MSI to an
> > > > eventfd.
> > > >
> > > >          
> > > uio will never support ioctls.
> > >        
> > Why not?
> >      
> Perhaps I spoke too strongly, but it was rejected before
>
> http://thread.gmane.org/gmane.linux.kernel/756481
>
> With a compelling case perhaps it could be added.
>    

Ah, the usual "ioctls are ugly, go away".

It could be done via sysfs:

  $ cat /sys/.../msix/max-interrupts
  256
  $ echo 4 > /sys/.../msix/allocate
  $ # subdirectories 0 1 2 3 magically appear
  $ # bind fd 13 to msix
  $ echo 13 > /sys/.../msix/2/bind-fd
  $ # from now on, msix interrupt 2 will call eventfd_signal() on fd 13

Call me old fashioned, but I prefer ioctls.

--
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.