vmm: Add iommu=on|off option for --device

Having the virtual IOMMU created with --iommu is one thing, but we also
need a way to decide if a VFIO device should be attached to the virtual
IOMMU or not. That's why we introduce an extra option "iommu" with the
value "on" or "off". By default, the device is not attached, which means
"iommu=off".

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

src/main.rs

@@ -198,6 +198,10 @@ fn main() {
             Arg::with_name("device")
                 .long("device")
                 .help("Direct device assignment parameter")
+                .help(
+                    "Direct device assignment parameters \
+                     \"path=<device_path>,iommu=on|off\"",
+                )
                 .takes_value(true)
                 .min_values(1)
                 .group("vm-config"),