Re: [PATCH 1/5] vring: Replace mmap() interface with ioctl()

[Rusty Russell <rusty@rustcorp.com.au>]

On Friday 13 June 2008 23:57:57 Mark McLoughlin wrote:
> /dev/vring's mmap() interface is a strange creature. It
> serves as a way for userland to supply the address of the
> already allocated ring descriptors, but causes those pages
> to be re-maped as a natural side effect of the mmap()
>
> This is not an issue for lguest because it does the mmap()
> before even starting the guest. However, in the case of kvm,
> the guest allocates the ring and informs the host of its
> addresss. If we then mmap() it, we cause it to be remapped
> to new pages which the vring driver will then use.

Yeah, ugly, huh?  I didn't like it either, but my ioctl aversion forced me to 
consider mmap.  Then my aversion to rewriting the mmap code lead me to 
this "simply replace the user pages" hack :)

Fix the couple of minor issues reported here and I'll happily apply it.

BTW, including base and limit makes sense.  I didn't do this to start since 
Avi doesn't want to guarentee kvm's guest mapping linear (of course he's only 
doing this so he can fix it later).

Cheers,
Rusty.