--- wikisrc/ports/xen/howto.mdwn	2014/12/27 00:15:40	1.55
+++ wikisrc/ports/xen/howto.mdwn	2014/12/27 15:46:47	1.59
@@ -2,17 +2,17 @@ Introduction
 ============
 
 [![[Xen
-screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](../../gallery/in-Action/hubertf-xen.png)
+screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](http://www.netbsd.org/gallery/in-Action/hubertf-xen.png)
 
-Xen is a virtual machine monitor or hypervisor for x86 hardware
+Xen is a hypervisor (or virtual machine monitor) for x86 hardware
 (i686-class or higher), which supports running multiple guest
-operating systems on a single physical machine.  With Xen, one uses
-the Xen kernel to control the CPU, memory and console, a dom0
-operating system which mediates access to other hardware (e.g., disks,
-network, USB), and one or more domU operating systems which operate in
-an unprivileged virtualized environment.  IO requests from the domU
-systems are forwarded by the hypervisor (Xen) to the dom0 to be
-fulfilled.
+operating systems on a single physical machine.  Xen is a Type 1 or
+bare-metal hypervisor; one uses the Xen kernel to control the CPU,
+memory and console, a dom0 operating system which mediates access to
+other hardware (e.g., disks, network, USB), and one or more domU
+operating systems which operate in an unprivileged virtualized
+environment.  IO requests from the domU systems are forwarded by the
+hypervisor (Xen) to the dom0 to be fulfilled.
 
 Xen supports two styles of guests.  The original is Para-Virtualized
 (PV) which means that the guest OS does not attempt to access hardware
@@ -339,8 +339,8 @@ For 4.1 (and thus xm; xl is believed not
         xencommons=YES
         xend=YES
 
-TODO: Explain why if xm is preferred on 4.1, rc.d/xendomains has xl.
-Or fix the package.
+(If you are using xentools41 from before 2014-12-26, change
+rc.d/xendomains to use xm rather than xl.)
 
 For 4.2 with xm, add to rc.conf
 
@@ -531,6 +531,8 @@ anyplace, reasonable places to store dom
 (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
 config files), or in /u0/xen (where the vdisks are).
 
+Note that loading the domU kernel from the dom0 implies that boot
+blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
 See the VPS section near the end for discussion of alternate ways to
 obtain domU kernels.
 
@@ -866,19 +868,37 @@ npf, run IPsec, or any other reason why 
 their kernel.
 
 One approach is to have an adminstrative interface to upload a kernel,
-or to select from a prepopulated list.
+or to select from a prepopulated list.  Other approaches are py-grub
+(deprecated) and pvgrub, which are ways to have a bootloader obtain a
+kernel from the domU filesystem.  This is closer to a regular physical
+computer, where someone who controls a machine can replace the kernel.
+
+py-grub
+-------
+
+py-grub runs in the dom0 and looks into the domU filesystem.  This
+implies that the domU must have a kernel in a filesystem in a format
+known to py-grub.  As of 2014, py-grub seems to be of mostly historical interest.
 
-Otehr approaches are pvgrub and py-grub, which are ways to start a
-bootloader from the dom0 instead of the actual domU kernel, and for
-that loader to then load a kernel from the domU filesystem.  This is
-closer to a regular physical computer, where someone who controls a
-machine can replace the kernel.
+pvgrub
+------
+
+pvgrub is a version of grub that uses PV operations instead of BIOS
+calls.  It is booted from the dom0 as the domU kernel, and then reads
+/grub/menu.lst and loads a kernel from the domU filesystem.
+
+[prgmr.com](http://prgmr.com/) uses this approach to let users choose
+their own operating system and kernel.  See then [prgmr.com NetBSD
+HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU).
+
+Typically one has an ext2 or FAT partition for the kernel, so that
+grub can understand it, which leads to /netbsd not being the actual
+kernel.  One must remember to update the special boot partiion.
 
-prmgr and pvgrub
-----------------
+Amazon
+------
 
-TODO: Perhaps reference panix, prmgr, amazon as interesting examples.
-Explain what prmgr does.
+TODO: add link to NetBSD amazon howto.
 
 Using npf
 ---------
@@ -886,5 +906,6 @@ Using npf
 In standard kernels, npf is a module, and thus cannot be loadeed in a
 DOMU kernel.
 
-TODO: explain how to compile npf into a custom kernel, answering:
+TODO: explain how to compile npf into a custom kernel, answering (but
+note that the problem was caused by not booting the right kernel):
 http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html