libxl/xend: name tap devices vifX.Y-emu

This prevents the udev scripts from operating on other tap devices (e.g.
openvpn etc)

Correct the documentation for the "vifname" option which suggested it applied
to HVM tap devices only, which is not the case.

Reported by Michael Young.

Also fix the use of vifname with emulated devices. This is slightly complex.
The current hotplug scripts rely on being able to parse the "tapX.Y" (now
"vifX.Y-emu") name in order to locate the xenstore backend dir relating to the
corresponding vif. This is because we cannot inject our own environment vars
into the tap hotplug events. However this means that if the tap is initially
named with a user specified name (which will not match the expected scheme) we
fail to do anything useful with the device. So now we create the initial tap
device with the standard "vifX.Y-emu" name and the hotplug script will handle
the rename to the desired name. This is also how PV vif devices work -- they
are always created by netback with the name vifX.Y and renamed in the script.

Lastly also move libxl__device_* to a better place in the header, otherwise the
comment about evgen stuff isn't next to the associated functions (noticed jsut
because I was going to add nic_devname near to the setdefault functions)

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/docs/misc/xl-network-configuration.markdown b/docs/misc/xl-network-configuration.markdown
index e2a5bc60c5..b36d6c89c9 100644
--- a/docs/misc/xl-network-configuration.markdown
+++ b/docs/misc/xl-network-configuration.markdown
@@ -93,11 +93,14 @@ are:
 
 ### vifname
 
-This keyword is valid for HVM guest devices with `type=ioemu` only.
+Specifies the backend device name for the virtual device.
+
+If the domain is an HVM domain then the associated emulated (tap)
+device will have a "-emu" suffice added.
 
-Specifies the backend device name for an emulated device. The default
-is `tapDOMID.DEVID` where `DOMID` is the guest domain ID and `DEVID`
-is the device number.
+The default name for the virtual device is `vifDOMID.DEVID` where
+`DOMID` is the guest domain ID and `DEVID` is the device
+number. Likewise the default tap name is `vifDOMID.DEVID-emu`.
 
 ### script