Re: [Qemu-devel] Assigning an eth port to a guest VM

[Yehuda Yitschak]

> >
> >  Eric, Alex,  Thank you very much for all your answers and details.
> > From your answers it sounds like I need to extended vfio's resource query 
> > mechanism to enable flagging
> > certain resources as NO_MAP and then make VFIO in QEMU act accordingly.
> > That looks like the easier part. The more complex part in my view is to 
> > manage the trap to vfio-platform driver and emulate the access.
> >
> > In any way, I will take some time to process all this into a solution and 
> > fill in some gaps in my knowledge.
> 
> TBH, I don't see any need to extend VFIO based on your needs so far.
> VFIO already has the ability to describe whether a region supports mmap.
> If it doesn't support mmap, QEMU has no choice but to use an I/O memory
> region and translate VM accesses into reads and writes.  vfio-pci
> already makes extensive use of this capability today.  I/O port regions
> don't support mmap on x86, so those regions never expose an mmap capable
> flag.  We also require page alignment for mmap, so regions that are not
> page aligned don't expose mmap for MMIO regions.  PCI config space also
> does not support mmap because of the emulation and virtualization we do
> in that space.  So not supporting mmap is really not uncommon.  You
> might want to look at my slides from KVM Forum 2013 [1] which shows how
> VFIO can really be thought of as a conduit for decomposing a device
> through a file descriptor.  QEMU then recomposes it back into a device
> through the QEMU driver model.  Since platform devices have no standard
> like PCI to provide self discovery, there are device specific drivers on
> both ends with vfio-platform.  Thanks,

Ok...it looks like i need dig in some more into the code :)
This is very helpful.
Thanks 

Yehuda 

> 
> Alex
> 
> [1] http://www.linux-kvm.org/images/e/ed/Kvm-forum-2013-VFIO-VGA.pdf