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

[Avi Kivity]

On 03/31/2010 12:12 PM, Michael S. Tsirkin wrote:
> >    $ echo 4>  /sys/.../msix/allocate
> >    $ # subdirectories 0 1 2 3 magically appear
> >    $ # bind fd 13 to msix
> >      
> There's no way to know, when qemu starts, how many vectors will be used
> by driver.  So I think we can just go ahead and allocate as many vectors
> as supported by device at the moment when the first eventfd is bound.
>    

That will cause a huge amount of vectors to be allocated.  It's better 
to do this dynamically in response to guest programming.

> >    $ echo 13>  /sys/.../msix/2/bind-fd
> >      
> I think that this one can't work, both fd 13 and sysfs file will get
> closed when /bin/echo process exits.
>    

I meant figuratively.  It's pointless to bind an eventfd from a shell.  
You'd use fprintf() from qemu to bind the eventfd.

> >    $ # from now on, msix interrupt 2 will call eventfd_signal() on fd 13
> >
> > Call me old fashioned, but I prefer ioctls.
> >      
> I think we will have to use ioctl or irqcontrol because of lifetime
> issues outlines above.
>    

The lifetime issues don't exist if you do all that from qemu.  That's 
not to say I prefer sysfs to ioctl.

What's irqcontrol?

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