--- wikisrc/ports/xen/howto.mdwn	2014/12/24 16:06:38	1.37
+++ wikisrc/ports/xen/howto.mdwn	2014/12/26 13:04:31	1.41
@@ -330,13 +330,43 @@ For 4.2 with xl (preferred), add to rc.c
 TODO: Recommend for/against xen-watchdog.
 
 After you have configured the daemons and rebooted, run the following
-to inspect Xen's boot messages, available resources, and running
-domains:
+(or use xl) to inspect Xen's boot messages, available resources, and
+running domains:
 
         xm dmesg
         xm info
         xm list
 
+anita (for testing NetBSD)
+--------------------------
+
+With the setup so far, one should be able to run anita (see
+pkgsrc/sysutils/py-anita) to test NetBSD releases, by doing (as root,
+because anita must create a domU):
+
+        anita --vmm=xm test file:///usr/obj/i386/
+
+Alternatively, one can use --vmm=xl to use xl-based domU creation instead.
+TODO: check this.
+
+Xen-specific NetBSD issues
+--------------------------
+
+There are (at least) two additional things different about NetBSD as a
+dom0 kernel compared to hardware.
+
+One is that modules are not usable in DOM0 kernels, so one must
+compile in what's needed.  It's not really that modules cannot work,
+but that modules must be built for XEN3_DOM0 because some of the
+defines change and the normal module builds don't do this.  Basically,
+enabling Xen changes the kernel ABI, and the module build system
+doesn't cope with this.
+
+The other difference is that XEN3_DOM0 does not have exactly the same
+options as GENERIC.  While it is debatable whether or not this is a
+bug, users should be aware of this and can simply add missing config
+items if desired.
+
 Updating NetBSD in a dom0
 -------------------------
 
@@ -411,7 +441,10 @@ improves performance.  The other is that
 failed to work.  TODO: give working/notworking NetBSD versions for
 sparse vnd.  Note that the use of file/vnd for Xen is not really
 different than creating a file-backed virtual disk for some other
-purpose, except that xentools handles the vnconfig commands.
+purpose, except that xentools handles the vnconfig commands.  To
+create an empty 4G virtual disk, simply do
+
+        dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
 
 With the lvm style, one creates logical devices.  They are then used
 similarly to vnds.
@@ -444,6 +477,22 @@ create a new file and vnconfig it (or lv
 just like updating physical disks, but without having to be there and
 without those pesky connectors.
 
+domU kernels
+------------
+
+On a physical computer, the BIOS reads sector 0, and a chain of boot
+loaders finds and loads a kernel.  Normally this comes from the root
+filesystem.  With Xen domUs, the process is totally different.  The
+normal path is for the domU kernel to be a file in the dom0's
+filesystem.  At the request of the dom0, Xen loads that kernel into a
+new domU instance and starts execution.  While domU kernels can be
+anyplace, reasonable places to store domU kernels on the dom0 are in /
+(so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
+config files), or in /u0/xen (where the vdisks are).
+
+See the VPS section near the end for discussion of alternate ways to
+obtain domU kernels.
+
 Config files
 ------------
 
@@ -608,7 +657,7 @@ working vif-bridge is also provided with
 
     #!/bin/sh
     #============================================================================
-    # $NetBSD: howto.mdwn,v 1.36 2014/12/24 16:02:49 gdt Exp $
+    # $NetBSD: howto.mdwn,v 1.40 2014/12/26 13:00:23 gdt Exp $
     #
     # /usr/pkg/etc/xen/vif-bridge
     #