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 Introduction  [[!meta title="Xen HowTo"]]
 ============  
   
 [![[Xen  Xen is a Type 1 hypervisor which supports running multiple guest operating
 screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](http://www.netbsd.org/gallery/in-Action/hubertf-xen.png)  systems on a single physical machine. 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 Xen hypervisor to the dom0 to be
   fulfilled.
   
 Xen is a hypervisor (or virtual machine monitor) for x86 hardware  This HOWTO presumes a basic familiarity with the Xen system
 (i686-class or higher), which supports running multiple guest  architecture, with installing NetBSD on amd64 hardware, and with
 operating systems on a single physical machine.  Xen is a Type 1 or  installing software from pkgsrc.  See also the [Xen
 bare-metal hypervisor; one uses the Xen kernel to control the CPU,  website](http://www.xenproject.org/).
 memory and console, a dom0 operating system which mediates access to  
 other hardware (e.g., disks, network, USB), and one or more domU  [[!toc]]
 operating systems which operate in an unprivileged virtualized  
 environment.  IO requests from the domU systems are forwarded by the  # Overview
 hypervisor (Xen) to the dom0 to be fulfilled.  
   The basic concept of Xen is that the hypervisor (xenkernel) runs on
 Xen supports two styles of guests.  The original is Para-Virtualized  the hardware, and runs a privileged domain ("dom0") that can access
 (PV) which means that the guest OS does not attempt to access hardware  disks/networking/etc.  One then runs additonal unprivileged domains
 directly, but instead makes hypercalls to the hypervisor.  This is  (each a "domU"), presumably to do something useful.
 analogous to a user-space program making system calls.  (The dom0  
 operating system uses PV calls for some functions, such as updating  This HOWTO addresses how to run a NetBSD dom0 (and hence also build
 memory mapping page tables, but has direct hardware access for disk  xen itself).  It also addresses how to run domUs in that environment,
 and network.)   PV guests must be specifically coded for Xen.  and how to deal with having a domU in a Xen environment run by someone
   else and/or not running NetBSD.
 The more recent style is HVM, which means that the guest does not have  
 code for Xen and need not be aware that it is running under Xen.  There are many choices one can make; the HOWTO recommends the standard
 Attempts to access hardware registers are trapped and emulated.  This  approach and limits discussion of alternatives in many cases.
 style is less efficient but can run unmodified guests.  
   ## Guest Styles
 Generally any amd64 machine will work with Xen and PV guests.  In  
 theory i386 computers without amd64 support can be used for Xen <=  Xen supports different styles of guests.
 4.2, but we have no recent reports of this working (this is a hint).  
 For HVM guests, the VT or VMX cpu feature (Intel) or SVM/HVM/VT  [[!table data="""
 (amd64) is needed; "cpuctl identify 0" will show this.  TODO: Clean up  Style of guest  |Supported by NetBSD
 and check the above features.  PV              |Yes (dom0, domU)
   HVM             |Yes (domU)
   PVHVM           |current-only (domU)
   PVH             |current-only (domU, dom0 not yet)
   """]]
   
   In Para-Virtualized (PV) mode, the guest OS does not attempt to access
   hardware directly, but instead makes hypercalls to the hypervisor; PV
   guests must be specifically coded for Xen.
   See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
   
   In HVM mode, no guest modification is required; however, hardware
   support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
   The dom0 runs qemu to emulate hardware.
   
   In PVHVM mode, the guest runs as HVM, but additionally can use PV
   drivers for efficiency.
   See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
   
   There have been two PVH modes: original PVH and PVHv2.  Original PVH
   was based on PV mode and is no longer relevant at all.  PVHv2 is
   basically lightweight HVM with PV drivers.  A critical feature of it
   is that qemu is not needed; the hypervisor can do the emulation that
   is required.  Thus, a dom0 can be PVHv2.
   The source code uses PVH and config files use pvh; this refers to PVHv2.
   See [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).
   
 At boot, the dom0 kernel is loaded as a module with Xen as the kernel.  At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
 The dom0 can start one or more domUs.  (Booting is explained in detail  The dom0 can start one or more domUs.  (Booting is explained in detail
 in the dom0 section.)  in the dom0 section.)
   
 NetBSD supports Xen in that it can serve as dom0, be used as a domU,  ## CPU Architecture
 and that Xen kernels and tools are available in pkgsrc.  This HOWTO  
 attempts to address both the case of running a NetBSD dom0 on hardware  
 and running domUs under it (NetBSD and other), and also running NetBSD  
 as a domU in a VPS.  
   
 Some versions of Xen support "PCI passthrough", which means that  
 specific PCI devices can be made available to a specific domU instead  
 of the dom0.  This can be useful to let a domU run X11, or access some  
 network interface or other peripheral.  
   
 NetBSD used to support Xen2; this has been removed.  
   
 Prerequisites  
 -------------  
   
 Installing NetBSD/Xen is not extremely difficult, but it is more  
 complex than a normal installation of NetBSD.  
 In general, this HOWTO is occasionally overly restrictive about how  
 things must be done, guiding the reader to stay on the established  
 path when there are no known good reasons to stray.  
   
 This HOWTO presumes a basic familiarity with the Xen system  Xen runs on x86_64 hardware (the NetBSD amd64 port).
 architecture.  This HOWTO presumes familiarity with installing NetBSD  
 on i386/amd64 hardware and installing software from pkgsrc.  There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
 See also the [Xen website](http://www.xenproject.org/).  
   The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
 Versions of Xen and NetBSD  
 ==========================  
   
 Most of the installation concepts and instructions are independent  
 of Xen version and NetBSD version.  This section gives advice on  
 which version to choose.  Versions not in pkgsrc and older unsupported  
 versions of NetBSD are intentionally ignored.  
   
 Xen  The domU can be i386PAE or amd64.
 ---  i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
   
 In NetBSD, xen is provided in pkgsrc, via matching pairs of packages  ## Xen Versions
   
   In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
 xenkernel and xentools.  We will refer only to the kernel versions,  xenkernel and xentools.  We will refer only to the kernel versions,
 but note that both packages must be installed together and must have  but note that both packages must be installed together and must have
 matching versions.  matching versions.
   
 xenkernel3 and xenkernel33 provide Xen 3.1 and 3.3.  These no longer  Versions available in pkgsrc:
 receive security patches and should not be used.  Xen 3.1 supports PCI  
 passthrough.  Xen 3.1 supports non-PAE on i386.  
   
 xenkernel41 provides Xen 4.1.  This is no longer maintained by Xen,  
 but as of 2014-12 receives backported security patches.  It is a  
 reasonable although trailing-edge choice.  
   
 xenkernel42 provides Xen 4.2.  This is maintained by Xen, but old as  
 of 2014-12.  
   
 Ideally newer versions of Xen will be added to pkgsrc.  
   
 Note that NetBSD support is called XEN3.  It works with 3.1 through  
 4.2 because the hypercall interface has been stable.  
   
 Xen command program  
 -------------------  
   
 Early Xen used a program called "xm" to manipulate the system from the  
 dom0.  Starting in 4.1, a replacement program with similar behavior  
 called "xl" is provided.  In 4.2 and later, "xl" is preferred.  4.4 is  
 the last version that has "xm".  
   
 NetBSD  
 ------  
   
 The netbsd-5, netbsd-6, netbsd-7, and -current branches are all  
 reasonable choices, with more or less the same considerations for  
 non-Xen use.  Therefore, netbsd-6 is recommended as the stable version  
 of the most recent release for production use.  For those wanting to  
 learn Xen or without production stability concerns, netbsd-7 is likely  
 most appropriate.  
   
 As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is  
 no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really  
 need SMP; the lack of support is really a problem when using a dom0 as  
 a normal computer.)  
   
 Architecture  
 ------------  
   
 Xen itself can run on i386 or amd64 machines.  (Practically, almost  
 any computer where one would want to run Xen supports amd64.)  If  
 using an i386 NetBSD kernel for the dom0, PAE is required (PAE  
 versions are built by default).  While i386 dom0 works fine, amd64 is  
 recommended as more normal.  
   
 Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify  
 if this is about the CPU having to be amd64, or about the dom0 kernel  
 having to be amd64.  
   
 One can then run i386 domUs and amd64 domUs, in any combination.  If  
 running an i386 NetBSD kernel as a domU, the PAE version is required.  
 (Note that emacs (at least) fails if run on i386 with PAE when built  
 without, and vice versa, presumably due to bugs in the undump code.)  
   
 Recommendation  
 --------------  
   
 Therefore, this HOWTO recommends running xenkernel42 (and xentools42),  
 xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the  
 dom0.  Either the i386 or amd64 of NetBSD may be used as domUs.  
   
 Build problems  
 --------------  
   
 Ideally, all versions of Xen in pkgsrc would build on all versions of  
 NetBSD on both i386 and amd64.  However, that isn't the case.  Besides  
 aging code and aging compilers, qemu (included in xentools for HVM  
 support) is difficult to build.  The following are known to fail:  
   
         xenkernel3 netbsd-6 i386  
         xentools42 netbsd-6 i386   
   
 The following are known to work:  
   
         xenkernel41 netbsd-5 amd64  
         xentools41 netbsd-5 amd64  
         xenkernel41 netbsd-6 i386  
         xentools41 netbsd-6 i386  
   
 NetBSD as a dom0  
 ================  
   
 NetBSD can be used as a dom0 and works very well.  The following  
 sections address installation, updating NetBSD, and updating Xen.  
 Note that it doesn't make sense to talk about installing a dom0 OS  
 without also installing Xen itself.  We first address installing  
 NetBSD, which is not yet a dom0, and then adding Xen, pivoting the  
 NetBSD install to a dom0 install by just changing the kernel and boot  
 configuration.  
   
 For experimenting with Xen, a machine with as little as 1G of RAM and  
 100G of disk can work.  For running many domUs in productions, far  
 more will be needed.  
   
 Styles of dom0 operation  
 ------------------------  
   
 There are two basic ways to use Xen.  The traditional method is for  
 the dom0 to do absolutely nothing other than providing support to some  
 number of domUs.  Such a system was probably installed for the sole  
 purpose of hosting domUs, and sits in a server room on a UPS.  
   
 The other way is to put Xen under a normal-usage computer, so that the  
 dom0 is what the computer would have been without Xen, perhaps a  
 desktop or laptop.  Then, one can run domUs at will.  Purists will  
 deride this as less secure than the previous approach, and for a  
 computer whose purpose is to run domUs, they are right.  But Xen and a  
 dom0 (without domUs) is not meaingfully less secure than the same  
 things running without Xen.  One can boot Xen or boot regular NetBSD  
 alternately with little problems, simply refraining from starting the  
 Xen daemons when not running Xen.  
   
 Note that NetBSD as dom0 does not support multiple CPUs.  This will  
 limit the performance of the Xen/dom0 workstation approach.  In theory  
 the only issue is that the "backend drivers" are not yet MPSAFE:  
   http://mail-index.netbsd.org/netbsd-users/2014/08/29/msg015195.html  
   
 Installation of NetBSD  [[!table data="""
 ----------------------  Xen Version     |Package Name   |Xen CPU Support        |EOL'ed By Upstream
   4.11            |xenkernel411   |x86_64                 |No
   4.13            |xenkernel413   |x86_64                 |No
   """]]
   
 First,  See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
 [install NetBSD/amd64](/guide/inst/)  
 just as you would if you were not using Xen.  
 However, the partitioning approach is very important.  
   
 If you want to use RAIDframe for the dom0, there are no special issues  Older Xen had a python-based management tool called xm, now replaced
 for Xen.  Typically one provides RAID storage for the dom0, and the  by xl.
 domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips  
 over a RAID1 header to find /boot from a filesystem within a RAID  
 partition; this is no different when booting Xen.  
   
 There are 4 styles of providing backing storage for the virtual disks  
 used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN,  
   
 With raw partitions, one has a disklabel (or gpt) partition sized for  
 each virtual disk to be used by the domU.  (If you are able to predict  
 how domU usage will evolve, please add an explanation to the HOWTO.  
 Seriously, needs tend to change over time.)  
   
 One can use [lvm(8)](/guide/lvm/) to create logical devices to use  
 for domU disks.  This is almost as efficient as raw disk partitions  
 and more flexible.  Hence raw disk partitions should typically not  
 be used.  
   
 One can use files in the dom0 filesystem, typically created by dd'ing  
 /dev/zero to create a specific size.  This is somewhat less efficient,  
 but very convenient, as one can cp the files for backup, or move them  
 between dom0 hosts.  
   
 Finally, in theory one can place the files backing the domU disks in a  
 SAN.  (This is an invitation for someone who has done this to add a  
 HOWTO page.)  
   
 Installation of Xen  
 -------------------  
   
 In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from  
 pkgsrc (or another matching pair).  
 See [the pkgsrc  
 documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with pkgsrc.  
   
 For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More  
 recent versions have HVM support integrated in the main xentools  
 package.  It is entirely reasonable to run only PV guests.  
   
 Next you need to install the selected Xen kernel itself, which is  
 installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.  
 For debugging, one may copy xen-debug.gz; this is conceptually similar  
 to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only  
 useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel  
 in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz  
 of a NetBSD build.  Both xen and NetBSD may be left compressed.  (If  
 using i386, use releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.)  
   
 With Xen as the kernel, you must provide a dom0 NetBSD kernel to be  
 used as a module; place this in /.  Suitable kernels are provided in  
 releasedir/binary/kernel:  
   
         i386 XEN3_DOM0  
         i386 XEN3PAE_DOM0  
         amd64 XEN3_DOM0  
   
 The first one is only for use with Xen 3.1 and i386-mode Xen (and you  
 should not do this).  Current Xen always uses PAE on i386, but you  
 should generally use amd64 for the dom0.  In a dom0 kernel, kernfs is  
 mandatory for xend to comunicate with the kernel, so ensure that /kern  
 is in fstab.  TODO: Say this is default, or file a PR and give a  
 reference.  
   
 Because you already installed NetBSD, you have a working boot setup  
 with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the  
 beginning of your root filesystem, /boot present, and likely  
 /boot.cfg.  (If not, fix before continuing!)  
   
 See boot.cfg(5) for an example.  The basic line is  
   
         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M  
   
 which specifies that the dom0 should have 256M, leaving the rest to be  
 allocated for domUs.  In an attempt to add performance, one can also  
 add  
   
         dom0_max_vcpus=1 dom0_vcpus_pin  ## NetBSD versions
   
 to force only one vcpu to be provided (since NetBSD dom0 can't use  Xen has been supported in NetBSD for a long time, at least since 2005.
 more) and to pin that vcpu to a physical cpu.  TODO: benchmark this.  Initially Xen was PV only.
   
 As with non-Xen systems, you should have a line to boot /netbsd (a  NetBSD 8 and up support PV and HVM modes.
 kernel that works without Xen) and fallback versions of the non-Xen  
 kernel, Xen, and the dom0 kernel.  
   
 Using grub (historic)  
 ---------------------  
   
 Before NetBSD's native bootloader could support Xen, the use of  
 grub was recommended.  If necessary, see the  
 [old grub information](/ports/xen/howto-grub/).  
   
 The [HowTo on Installing into  
 RAID-1](http://mail-index.NetBSD.org/port-xen/2006/03/01/0010.html)  
 explains how to set up booting a dom0 with Xen using grub with  
 NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native  
 boot.)  
   
 Configuring Xen  Support for PVHVM and PVH is available only in NetBSD-current.
 ---------------  
   
 Xen logs will be in /var/log/xen.  NetBSD as a dom0 does not run SMP, because some drivers are not yet
   safe for this.  \todo Link to more information about what needs work.
   
 Now, you have a system that will boot Xen and the dom0 kernel, and  NetBSD, when run as a domU, can and does typically run SMP.
 just run the dom0 kernel.  There will be no domUs, and none can be  
 started because you still have to configure the dom0 tools.  The  
 daemons which should be run vary with Xen version and with whether one  
 is using xm or xl.  Note that xend is for supporting "xm", and should  
 only be used if you plan on using "xm".  Do NOT enable xend if you  
 plan on using "xl" as it will cause problems.  
   
 The installation of NetBSD should already have created devices for xen  Note: NetBSD support is called XEN3.  However, it does support Xen 4,
 (xencons, xenevt), but if they are not present, create them:  because the hypercall interface has remained identical.
   
         cd /dev && sh MAKEDEV xen  # Creating a NetBSD dom0
   
 TODO: Give 3.1 advice (or remove it from pkgsrc).  In order to install a NetBSD as a dom0, one must first install a normal
   NetBSD system, and then pivot the install to a dom0 install by changing
   the kernel and boot configuration.
   
 For 3.3 (and thus xm), add to rc.conf (but note that you should have  In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
 installed 4.1 or 4.2):  512M it worked reliably.  This does not make sense, but if you see
   "not ELF" after Xen boots, try increasing dom0 RAM.
   
         xend=YES  ## Installation of NetBSD
         xenbackendd=YES  
   
 For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:  [Install NetBSD/amd64](/guide/inst/)
   just as you would if you were not using Xen.
   Therefore, use the most recent release, or a build from the most recent stable branch.
   
   ## Installation of Xen
   
   Use the most recent version of Xen in pkgsrc, unless the DESCR says that it is not suitable.
   Therefore, choose 4.13.
   In the dom0, install xenkernel413 and xentools413 from pkgsrc.
   
   Once this is done, copy the Xen kernel from where pkgsrc puts it to
   where the boot process will be able to find it:
   
         xencommons=YES  [[!template id=programlisting text="""
         xend=YES  # cp -p /usr/pkg/xen413-kernel/xen.gz /
   """]]
   
 (If you are using xentools41 from before 2014-12-26, change  Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
 rc.d/xendomains to use xm rather than xl.)  can either be compiled manually, or downloaded from the NetBSD FTP, for
   example at:
   
 For 4.2 with xm, add to rc.conf  [[!template id=programlisting text="""
   ftp.netbsd.org/pub/NetBSD/NetBSD-9.1/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
   """]]
   
         xencommons=YES  Add a line to /boot.cfg to boot Xen:
         xend=YES  
   
 For 4.2 with xl (preferred), add to rc.conf:  [[!template id=filecontent name="/boot.cfg" text="""
   menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
   """]]
   
         xencommons=YES  This specifies that the dom0 should have 512MB of ram, leaving the rest
         TODO: explain if there is a xend replacement  to be allocated for domUs.
   
 TODO: Recommend for/against xen-watchdog.  NB: This says add, not replace, so that you will be able to boot a
   NetBSD kernel without Xen.  Once Xen boots ok, you may want to set it
   as default.
   
 After you have configured the daemons and either started them (in the  To use a serial console, add settings as follows:
 order given) or rebooted, run the following (or use xl) to inspect  
 Xen's boot messages, available resources, and running domains:  
   
         # xm dmesg  [[!template id=filecontent name="/boot.cfg" text="""
         [xen's boot info]  menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
         # xm info  """]]
         [available memory, etc.]  
         # xm list  
         Name              Id  Mem(MB)  CPU  State  Time(s)  Console  
         Domain-0           0       64    0  r----     58.1  
   
 anita (for testing NetBSD)  which will use the first serial port for Xen (which counts starting
 --------------------------  from 1, unlike NetBSD which counts starting from 0), forcing
   speed/parity.  Because the NetBSD command line lacks a
   "console=pc" argument, it will use the default "xencons" console device,
   which directs the console I/O through Xen to the same console device Xen
   itself uses (in this case, the serial port).
   
 With the setup so far, one should be able to run anita (see  In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
 pkgsrc/sysutils/py-anita) to test NetBSD releases, by doing (as root,  to force only one vcpu to be provided (since NetBSD dom0 can't use
 because anita must create a domU):  more) and to pin that vcpu to a physical CPU. Xen has
   [many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
   and other than dom0 memory and max_vcpus, they are generally not
   necessary.
   
   Ensure that the boot scripts installed in
   `/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
   have `PKG_RCD_SCRIPTS=yes`, or manually.  (This is not special to Xen,
   but a normal part of pkgsrc usage.)
   
   Set `xencommons=YES` in rc.conf:
   
   [[!template id=filecontent name="/etc/rc.conf" text="""
   xencommons=YES
   """]]
   
   \todo Recommend for/against xen-watchdog.
   
   Now, reboot so that you are running a DOM0 kernel under Xen, rather
   than GENERIC without Xen.
   
   Once the reboot is done, use `xl` to inspect Xen's boot messages,
   available resources, and running domains.  For example:
   
   [[!template id=programlisting text="""
   # xl dmesg
   ... xen's boot info ...
   # xl info
   ... available memory, etc ...
   # xl list
   Name              Id  Mem(MB)  CPU  State  Time(s)  Console
   Domain-0           0       64    0  r----     58.1
   """]]
   
   Xen logs will be in /var/log/xen.
   
         anita --vmm=xm test file:///usr/obj/i386/  ### Issues with xencommons
   
 Alternatively, one can use --vmm=xl to use xl-based domU creation instead.  `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
 TODO: check this.  domUs.  It does not currently work to stop and start xenstored.
   Certainly all domUs should be shutdown first, following the sort order
   of the rc.d scripts.  However, the dom0 sets up state with xenstored,
   and is not notified when xenstored exits, leading to not recreating
   the state when the new xenstored starts.  Until there's a mechanism to
   make this work, one should not expect to be able to restart xenstored
   (and thus xencommons).  There is currently no reason to expect that
   this will get fixed any time soon.
   \todo Confirm if this is still true in 2020.
   
 Xen-specific NetBSD issues  ## Xen-specific NetBSD issues
 --------------------------  
   
 There are (at least) two additional things different about NetBSD as a  There are (at least) two additional things different about NetBSD as a
 dom0 kernel compared to hardware.  dom0 kernel compared to hardware.
   
 One is that modules are not usable in DOM0 kernels, so one must  One is that the module ABI is different because some of the #defines
 compile in what's needed.  It's not really that modules cannot work,  change, so one must build modules for Xen.  As of netbsd-7, the build
 but that modules must be built for XEN3_DOM0 because some of the  system does this automatically.
 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  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  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  bug, users should be aware of this and can simply add missing config
 items if desired.  items if desired.
   
 Updating NetBSD in a dom0  Finally, there have been occasional reports of trouble with X11
 -------------------------  servers in NetBSD as a dom0.
   
   ## Updating Xen in a dom0
   
   Basically, update the xenkernel and xentools packages and copy the new
   Xen kernel into place, and reboot.  This procedure should be usable to
   update to a new Xen release, but the reader is reminded that having a
   non-Xen boot methods was recommended earlier.
   
   ## Updating NetBSD in a dom0
   
 This is just like updating NetBSD on bare hardware, assuming the new  This is just like updating NetBSD on bare hardware, assuming the new
 version supports the version of Xen you are running.  Generally, one  version supports the version of Xen you are running.  Generally, one
 replaces the kernel and reboots, and then overlays userland binaries  replaces the kernel and reboots, and then overlays userland binaries
 and adjusts /etc.  and adjusts `/etc`.
   
 Note that one must update both the non-Xen kernel typically used for  Note that one must update both the non-Xen kernel typically used for
 rescue purposes and the DOM0 kernel used with Xen.  rescue purposes and the DOM0 kernel used with Xen.
   
 Converting from grub to /boot  ## anita (for testing NetBSD)
 -----------------------------  
   With a NetBSD dom0, even without any domUs, one should be able to run
   anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
   root, because anita must create a domU):
   
   [[!template id=programlisting text="""
   anita --vmm=xl test file:///usr/obj/i386/
   """]]
   
   ## Converting from grub to /boot (historical note)
   
   These instructions are provided only to help people using grub, which
   used to be the normal approach.
   
 These instructions were [TODO: will be] used to convert a system from  These instructions were used to convert a system from
 grub to /boot.  The system was originally installed in February of  grub to /boot.  The system was originally installed in February of
 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated  2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
 over time.  Before these commands, it was running NetBSD 6 i386, Xen  over time.  Before these commands, it was running NetBSD 6 i386, Xen
 4.1 and grub, much like the message linked earlier in the grub  4.1 and grub, much like the message linked earlier in the grub
 section.  section.
   
         # Install mbr bootblocks on both disks.   [[!template id=programlisting text="""
         fdisk -i /dev/rwd0d  # Install MBR bootblocks on both disks.
         fdisk -i /dev/rwd1d  fdisk -i /dev/rwd0d
         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.  fdisk -i /dev/rwd1d
         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1  # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1  installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
         # Install secondary boot loader  installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
         cp -p /usr/mdec/boot /  # Install secondary boot loader
         # Create boog.cfg following earlier guidance:  cp -p /usr/mdec/boot /
         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M  # Create boot.cfg following earlier guidance:
         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M  menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
         menu=GENERIC:boot  menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
         menu=GENERIC single-user:boot -s  menu=GENERIC:boot
         menu=GENERIC.ok:boot netbsd.ok  menu=GENERIC single-user:boot -s
         menu=GENERIC.ok single-user:boot netbsd.ok -s  menu=GENERIC.ok:boot netbsd.ok
         menu=Drop to boot prompt:prompt  menu=GENERIC.ok single-user:boot netbsd.ok -s
         default=1  menu=Drop to boot prompt:prompt
         timeout=30  default=1
   timeout=30
 TODO: actually do this and fix it if necessary.  """]]
   
 Updating Xen versions  
 ---------------------  
   
 Updating Xen is conceptually not difficult, but can run into all the  
 issues found when installing Xen.  Assuming migration from 4.1 to 4.2,  
 remove the xenkernel41 and xentools41 packages and install the  
 xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz to /.  
   
 Ensure that the contents of /etc/rc.d/xen* are correct.  Enable the  
 correct set of daemons.  Ensure that the domU config files are valid  
 for the new version.  
   
   # Unprivileged domains (domU)
 Unprivileged domains (domU)  
 ===========================  
   
 This section describes general concepts about domUs.  It does not  This section describes general concepts about domUs.  It does not
 address specific domU operating systems or how to install them.  The  address specific domU operating systems or how to install them.  The
 config files for domUs are typically in /usr/pkg/etc/xen, and are  config files for domUs are typically in `/usr/pkg/etc/xen`, and are
 typically named so that the file name, domU name and the domU's host  typically named so that the file name, domU name and the domU's host
 name match.  name match.
   
 The domU is provided with cpu and memory by Xen, configured by the  The domU is provided with CPU and memory by Xen, configured by the
 dom0.  The domU is provided with disk and network by the dom0,  dom0.  The domU is provided with disk and network by the dom0,
 mediated by Xen, and configured in the dom0.  mediated by Xen, and configured in the dom0.
   
 Entropy in domUs can be an issue; physical disks and network are on  Entropy in domUs can be an issue; physical disks and network are on
 the dom0.  NetBSD's /dev/random system works, but is often challenged.  the dom0.  NetBSD's /dev/random system works, but is often challenged.
   
 Config files  ## Config files
 ------------  
   
 There is no good order to present config files and the concepts  
 surrounding what is being configured.  We first show an example config  
 file, and then in the various sections give details.  
   
 See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,  See /usr/pkg/share/examples/xen/xlexample*
 for a large number of well-commented examples, mostly for running  for a small number of well-commented examples, mostly for running
 GNU/Linux.  GNU/Linux.
   
 The following is an example minimal domain configuration file  The following is an example minimal domain configuration file. The domU
 "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual  serves as a network file server.
 known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5  
 i386 domU).  The domU serves as a network file server.  
   
         # -*- mode: python; -*-  
   
         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"  
         memory = 1024  
         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]  
         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',  
                  'file:/n0/xen/foo-wd1,0x1,w' ]  
   
 The domain will have the same name as the file.  The kernel has the  [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
   name = "domU-id"
   kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
   memory = 1024
   vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
   disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
            'file:/n0/xen/foo-wd1,0x1,w' ]
   """]]
   
   The domain will have name given in the `name` setting.  The kernel has the
 host/domU name in it, so that on the dom0 one can update the various  host/domU name in it, so that on the dom0 one can update the various
 domUs independently.  The vif line causes an interface to be provided,  domUs independently.  The `vif` line causes an interface to be provided,
 with a specific mac address (do not reuse MAC addresses!), in bridge  with a specific mac address (do not reuse MAC addresses!), in bridge
 mode.  Two disks are provided, and they are both writable; the bits  mode.  Two disks are provided, and they are both writable; the bits
 are stored in files and Xen attaches them to a vnd(4) device in the  are stored in files and Xen attaches them to a vnd(4) device in the
 dom0 on domain creation.  The system treates xbd0 as the boot device  dom0 on domain creation.  The system treats xbd0 as the boot device
 without needing explicit configuration.  without needing explicit configuration.
   
 By default xm looks for domain config files in /usr/pkg/etc/xen.  Note  There is not type line; that implicitly defines a pv domU.
 that "xm create" takes the name of a config file, while other commands  
 take the name of a domain.  To create the domain, connect to the  By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
 console, create the domain while attaching the console, shutdown the  that "xl create" takes the name of a config file, while other commands
 domain, and see if it has finished stopping, do (or xl with Xen >=  take the name of a domain.
 4.2):  
   Examples of commands:
         xm create foo  
         xm console foo  [[!template id=programlisting text="""
         xm create -c foo  xl create /usr/pkg/etc/xen/foo
         xm shutdown foo  xl console domU-id
         xm list  xl create -c /usr/pkg/etc/xen/foo
   xl shutdown domU-id
   xl list
   """]]
   
 Typing ^] will exit the console session.  Shutting down a domain is  Typing `^]` will exit the console session.  Shutting down a domain is
 equivalent to pushing the power button; a NetBSD domU will receive a  equivalent to pushing the power button; a NetBSD domU will receive a
 power-press event and do a clean shutdown.  Shutting down the dom0  power-press event and do a clean shutdown.  Shutting down the dom0
 will trigger controlled shutdowns of all configured domUs.  will trigger controlled shutdowns of all configured domUs.
   
 domU kernels  ## CPU and memory
 ------------  
   
 On a physical computer, the BIOS reads sector 0, and a chain of boot  A domain is provided with some number of vcpus, up to the number
 loaders finds and loads a kernel.  Normally this comes from the root  of CPUs seen by the hypervisor. For a domU, it is controlled
 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).  
   
 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.  
   
 CPU and memory  
 --------------  
   
 A domain is provided with some number of vcpus, less than the number  
 of cpus seen by the hypervisor.  (For a dom0, this is controlled by  
 the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled  
 from the config file by the "vcpus = N" directive.  from the config file by the "vcpus = N" directive.
   
 A domain is provided with memory; this is controlled in the config  A domain is provided with memory; this is controlled in the config
Line 550  sum of the the memory allocated to the d Line 381  sum of the the memory allocated to the d
 than the available memory.  than the available memory.
   
 Xen also provides a "balloon" driver, which can be used to let domains  Xen also provides a "balloon" driver, which can be used to let domains
 use more memory temporarily.  TODO: Explain better, and explain how  use more memory temporarily.
 well it works with NetBSD.  
   
 Virtual disks  ## Virtual disks
 -------------  
   
 With the file/vnd style, typically one creates a directory,  In domU config files, the disks are defined as a sequence of 3-tuples:
 e.g. /u0/xen, on a disk large enough to hold virtual disks for all  
 domUs.  Then, for each domU disk, one writes zeros to a file that then  
 serves to hold the virtual disk's bits; a suggested name is foo-xbd0  
 for the first virtual disk for the domU called foo.  Writing zeros to  
 the file serves two purposes.  One is that preallocating the contents  
 improves performance.  The other is that vnd on sparse files has  
 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.  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.  TODO: Add an example with lvm.  
   
 In domU config files, the disks are defined as a sequence of 3-tuples.  
 The first element is "method:/path/to/disk".  Common methods are  
 "file:" for file-backed vnd. and "phy:" for something that is already  
 a (TODO: character or block) device.  
   
 The second element is an artifact of how virtual disks are passed to  
 Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs  
 are given a device name to associate with the disk, and values like  
 "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears  
 as xbd0, the second as xbd1, and so on.  However, xm/xl demand a  
 second argument.  The name given is converted to a major/minor by  
 calling stat(2) on the name in /dev and this is passed to the domU.  
 In the general case, the dom0 and domU can be different operating  
 systems, and it is an unwarranted assumption that they have consistent  
 numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD  
 as both dom0 and domU, using values of 0x0 for the first disk and 0x1  
 for the second works fine and avoids this issue.  For a GNU/Linux  
 guest, one can create /dev/hda1 in /dev, or to pass 0x301 for  
 /dev/hda1.  
   
 The third element is "w" for writable disks, and "r" for read-only   * The first element is "method:/path/to/disk". Common methods are
 disks.     "file:" for a file-backed vnd, and "phy:" for something that is already
      a device, such as an LVM logical volume.
   
    * The second element is an artifact of how virtual disks are passed to
      Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
      are given a device name to associate with the disk, and values like
      "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
      as xbd0, the second as xbd1, and so on.  However, xl demands a
      second argument.  The name given is converted to a major/minor by
      calling stat(2) on the name in /dev and this is passed to the domU.
      In the general case, the dom0 and domU can be different operating
      systems, and it is an unwarranted assumption that they have consistent
      numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
      as both dom0 and domU, using values of 0x0 for the first disk and 0x1
      for the second works fine and avoids this issue.  For a GNU/Linux
      guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
      /dev/hda1.
   
    * The third element is "w" for writable disks, and "r" for read-only
      disks.
   
   Example:
   [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
   disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
   """]]
   
 Virtual Networking  Note that NetBSD by default creates only vnd[0123].  If you need more
 ------------------  than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
   dom0.
   
   ## Virtual Networking
   
 Xen provides virtual ethernets, each of which connects the dom0 and a  Xen provides virtual Ethernets, each of which connects the dom0 and a
 domU.  For each virtual network, there is an interface "xvifN.M" in  domU.  For each virtual network, there is an interface "xvifN.M" in
 the dom0, and in domU index N, a matching interface xennetM (NetBSD  the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
 name).  The interfaces behave as if there is an Ethernet with two  The interfaces behave as if there is an Ethernet with two
 adaptors connected.  From this primitive, one can construct various  adapters connected.  From this primitive, one can construct various
 configurations.  We focus on two common and useful cases for which  configurations.  We focus on two common and useful cases for which
 there are existing scripts: bridging and NAT.  there are existing scripts: bridging and NAT.
   
Line 616  interfaces to the bridge.  One specifies Line 436  interfaces to the bridge.  One specifies
 config file.  The bridge must be set up already in the dom0; an  config file.  The bridge must be set up already in the dom0; an
 example /etc/ifconfig.bridge0 is:  example /etc/ifconfig.bridge0 is:
   
         create  [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
         up  create
         !brconfig bridge0 add wm0  up
   !brconfig bridge0 add wm0
   """]]
   
 With NAT, the domU perceives itself to be behind a NAT running on the  With NAT, the domU perceives itself to be behind a NAT running on the
 dom0.  This is often appropriate when running Xen on a workstation.  dom0.  This is often appropriate when running Xen on a workstation.
Line 628  The MAC address specified is the one use Line 450  The MAC address specified is the one use
 domain.  The interface in dom0 will use this address XOR'd with  domain.  The interface in dom0 will use this address XOR'd with
 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.  00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
   
 Sizing domains  ## Starting domains automatically
 --------------  
   
 Modern x86 hardware has vast amounts of resources.  However, many  
 virtual servers can function just fine on far less.  A system with  
 256M of RAM and a 4G disk can be a reasonable choice.  Note that it is  
 far easier to adjust virtual resources than physical ones.  For  
 memory, it's just a config file edit and a reboot.  For disk, one can  
 create a new file and vnconfig it (or lvm), and then dump/restore,  
 just like updating physical disks, but without having to be there and  
 without those pesky connectors.  
   
 Starting domains automatically  
 ------------------------------  
   
 To start domains foo at bar at boot and shut them down cleanly on dom0  
 shutdown, in rc.conf add:  
   
         xendomains="foo bar"  To start domains `domU-netbsd` and `domU-linux` at boot and shut them
   down cleanly on dom0 shutdown, add the following in rc.conf:
   
 TODO: Explain why 4.1 rc.d/xendomains has xl, when one should use xm  [[!template id=filecontent name="/etc/rc.conf" text="""
 on 4.1.  Or fix the xentools41 package to have xm  xendomains="domU-netbsd domU-linux"
   """]]
   
 Creating specific unprivileged domains (domU)  # domU setup for specific systems
 =============================================  
   
 Creating domUs is almost entirely independent of operating system.  We  Creating domUs is almost entirely independent of operating system.  We
 have already presented the basics of config files.  Note that you must  have already presented the basics of config files in the previous system.
 have already completed the dom0 setup so that "xl list" (or "xm list")  
 works.  
   
 Creating an unprivileged NetBSD domain (domU)  Of course, this section presumes that you have a working dom0.
 ---------------------------------------------  
   ## Creating a NetBSD PV domU
   
 See the earlier config file, and adjust memory.  Decide on how much  See the earlier config file, and adjust memory.  Decide on how much
 storage you will provide, and prepare it (file or lvm).  storage you will provide, and prepare it (file or LVM).
   
 While the kernel will be obtained from the dom0 filesystem, the same  While the kernel will be obtained from the dom0 file system, the same
 file should be present in the domU as /netbsd so that tools like  file should be present in the domU as /netbsd so that tools like
 savecore(8) can work.   (This is helpful but not necessary.)  savecore(8) can work.   (This is helpful but not necessary.)
   
 The kernel must be specifically for Xen and for use as a domU.  The  The kernel must be specifically built for Xen, to use PV interfacesas
 i386 and amd64 provide the following kernels:  a domU.  NetBSD release builds provide the following kernels:
   
         i386 XEN3_DOMU  
         i386 XEN3PAE_DOMU          i386 XEN3PAE_DOMU
         amd64 XEN3_DOMU          amd64 XEN3_DOMU
   
 Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must  
 use the PAE version of the i386 kernel.  
   
 This will boot NetBSD, but this is not that useful if the disk is  This will boot NetBSD, but this is not that useful if the disk is
 empty.  One approach is to unpack sets onto the disk outside of xen  empty.  One approach is to unpack sets onto the disk outside of Xen
 (by mounting it, just as you would prepare a physical disk for a  (by mounting it, just as you would prepare a physical disk for a
 system you can't run the installer on).  system you can't run the installer on).
   
Line 690  kernel to / and change the kernel line i Line 492  kernel to / and change the kernel line i
   
         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"          kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
   
 Then, start the domain as "xl create -c configname".  Then, start the domain as "xl create -c configfile".
   
 Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following  Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
 line should be used in the config file.  line should be used in the config file.
Line 700  line should be used in the config file. Line 502  line should be used in the config file.
 After booting the domain, the option to install via CDROM may be  After booting the domain, the option to install via CDROM may be
 selected.  The CDROM device should be changed to `xbd1d`.  selected.  The CDROM device should be changed to `xbd1d`.
   
 Once done installing, "halt -p" the new domain (don't reboot or halt,  Once done installing, "halt -p" the new domain (don't reboot or halt:
 it would reload the INSTALL_XEN3_DOMU kernel even if you changed the  it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
 config file), switch the config file back to the XEN3_DOMU kernel,  config file), switch the config file back to the XEN3_DOMU kernel,
 and start the new domain again. Now it should be able to use "root on  and start the new domain again. Now it should be able to use "root on
 xbd0a" and you should have a, functional NetBSD domU.  xbd0a" and you should have a functional NetBSD domU.
   
 TODO: check if this is still accurate.  TODO: check if this is still accurate.
 When the new domain is booting you'll see some warnings about *wscons*  When the new domain is booting you'll see some warnings about *wscons*
Line 725  It is also desirable to add Line 527  It is also desirable to add
         powerd=YES          powerd=YES
   
 in rc.conf. This way, the domain will be properly shut down if  in rc.conf. This way, the domain will be properly shut down if
 `xm shutdown -R` or `xm shutdown -H` is used on the dom0.  `xl shutdown -R` or `xl shutdown -H` is used on the dom0.
   \todo Check the translation to xl.
   
 Your domain should be now ready to work, enjoy.  It is not strictly necessary to have a kernel (as /netbsd) in the domU
   file system.  However, various programs (e.g. netstat) will use that
   kernel to look up symbols to read from kernel virtual memory.  If
   /netbsd is not the running kernel, those lookups will fail.  (This is
   not really a Xen-specific issue, but because the domU kernel is
   obtained from the dom0, it is far more likely to be out of sync or
   missing with Xen.)
   
 Creating an unprivileged Linux domain (domU)  Note that NetBSD by default creates only xbd[0123].  If you need more
 --------------------------------------------  virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
   
   ## Creating a Linux domU
   
 Creating unprivileged Linux domains isn't much different from  Creating unprivileged Linux domains isn't much different from
 unprivileged NetBSD domains, but there are some details to know.  unprivileged NetBSD domains, but there are some details to know.
Line 761  Then copy the files from a working Linux Line 572  Then copy the files from a working Linux
 `/etc` (fstab, network config).  It should also be possible to extract  `/etc` (fstab, network config).  It should also be possible to extract
 binary packages such as .rpm or .deb directly to the mounted partition  binary packages such as .rpm or .deb directly to the mounted partition
 using the appropriate tool, possibly running under NetBSD's Linux  using the appropriate tool, possibly running under NetBSD's Linux
 emulation.  Once the filesystem has been populated, umount it.  If  emulation.  Once the file system has been populated, umount it.  If
 desirable, the filesystem can be converted to ext3 using tune2fs -j.  desirable, the file system can be converted to ext3 using tune2fs -j.
 It should now be possible to boot the Linux guest domain, using one of  It should now be possible to boot the Linux guest domain, using one of
 the vmlinuz-\*-xenU kernels available in the Xen binary distribution.  the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
   
 To get the linux console right, you need to add:  To get the Linux console right, you need to add:
   
     extra = "xencons=tty1"      extra = "xencons=tty1"
   
 to your configuration since not all linux distributions auto-attach a  to your configuration since not all Linux distributions auto-attach a
 tty to the xen console.  tty to the xen console.
   
 Creating an unprivileged Solaris domain (domU)  ## Creating a NetBSD HVM domU
 ----------------------------------------------  
   Use type='hmv', probably.  Use a GENERIC kernel within the disk image.
   
   ## Creating a NetBSD PVH domU
   
   Use type='pvh'.
   
   \todo Explain where the kernel comes from.
   
   
   ## Creating a Solaris domU
   
 See possibly outdated  See possibly outdated
 [Solaris domU instructions](/ports/xen/howto-solaris/).  [Solaris domU instructions](/ports/xen/howto-solaris/).
   
   
 PCI passthrough: Using PCI devices in guest domains  ## PCI passthrough: Using PCI devices in guest domains
 ---------------------------------------------------  
   NB: PCI passthrough only works on some Xen versions and as of 2020 it
   is not clear that it works on any version in pkgsrc.  Reports
   confirming or denying this notion should be sent to port-xen@.
   
 The dom0 can give other domains access to selected PCI  The dom0 can give other domains access to selected PCI
 devices. This can allow, for example, a non-privileged domain to have  devices. This can allow, for example, a non-privileged domain to have
Line 814  the domU's config file, with the format  Line 638  the domU's config file, with the format 
         pci = [ '0000:00:06.0', '0000:00:0a.0' ]          pci = [ '0000:00:06.0', '0000:00:0a.0' ]
   
 In the domU an "xpci" device will show up, to which one or more pci  In the domU an "xpci" device will show up, to which one or more pci
 busses will attach.  Then the PCI drivers will attach to PCI busses as  buses will attach.  Then the PCI drivers will attach to PCI buses as
 usual.  Note that the default NetBSD DOMU kernels do not have "xpci"  usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
 or any PCI drivers built in by default; you have to build your own  or any PCI drivers built in by default; you have to build your own
 kernel to use PCI devices in a domU.  Here's a kernel config example;  kernel to use PCI devices in a domU.  Here's a kernel config example;
Line 822  note that only the "xpci" lines are unus Line 646  note that only the "xpci" lines are unus
   
         include         "arch/i386/conf/XEN3_DOMU"          include         "arch/i386/conf/XEN3_DOMU"
   
         # Add support for PCI busses to the XEN3_DOMU kernel          # Add support for PCI buses to the XEN3_DOMU kernel
         xpci* at xenbus ?          xpci* at xenbus ?
         pci* at xpci ?          pci* at xpci ?
   
Line 850  note that only the "xpci" lines are unus Line 674  note that only the "xpci" lines are unus
         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives          cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
   
   
 NetBSD as a domU in a VPS  # Miscellaneous Information
 =========================  
   ## Nesting under Linux KVM
   
   It is possible to run a Xen and a NetBSD dom0 under Linux KVM.  One
   can enable virtio in the dom0 for greater speed.
   
   ## Other nesting
   
   In theory, any full emulation should be able to run Xen and a NetBSD
   dom0.  The HOWTO does not currently have information about Xen XVM
   mode, nvmm, qemu, Virtualbox, etc.
   
   ## NetBSD 5 as domU
   
   [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
   (However, NetBSD 5 systems should be updated to a supported version.)
   
   # NetBSD as a domU in a VPS
   
 The bulk of the HOWTO is about using NetBSD as a dom0 on your own  The bulk of the HOWTO is about using NetBSD as a dom0 on your own
 hardware.  This section explains how to deal with Xen in a domU as a  hardware.  This section explains how to deal with Xen in a domU as a
 virtual private server where you do not control or have access to the  virtual private server where you do not control or have access to the
 dom0.  dom0.  This is not intended to be an exhaustive list of VPS providers;
   only a few are mentioned that specifically support NetBSD.
   
 VPS operators provide varying degrees of access and mechanisms for  VPS operators provide varying degrees of access and mechanisms for
 configuration.  The big issue is usually how one controls which kernel  configuration.  The big issue is usually how one controls which kernel
 is booted, because the kernel is nominally in the dom0 filesystem (to  is booted, because the kernel is nominally in the dom0 file system (to
 which VPS users do not normally have acesss).  which VPS users do not normally have access).  A second issue is how
   to install NetBSD.
 A VPS user may want to compile a kernel for security updates, to run  A VPS user may want to compile a kernel for security updates, to run
 npf, run IPsec, or any other reason why someone would want to change  npf, run IPsec, or any other reason why someone would want to change
 their kernel.  their kernel.
   
 One approach is to have an adminstrative interface to upload a kernel,  One approach is to have an administrative interface to upload a kernel,
 or to select from a prepopulated list.  Other approaches are py-grub  or to select from a prepopulated list.  Other approaches are pygrub
 (deprecated) and pvgrub, which are ways to have a bootloader obtain a  (deprecated) and pvgrub, which are ways to have a bootloader obtain a
 kernel from the domU filesystem.  This is closer to a regular physical  kernel from the domU file system.  This is closer to a regular physical
 computer, where someone who controls a machine can replace the kernel.  computer, where someone who controls a machine can replace the kernel.
   
 py-grub  A second issue is multiple CPUs.  With NetBSD 6, domUs support
 -------  multiple vcpus, and it is typical for VPS providers to enable multiple
   CPUs for NetBSD domUs.
   
 py-grub runs in the dom0 and looks into the domU filesystem.  This  ## Complexities due to Xen changes
 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.  
   
 pvgrub  Xen has many security advisories and people running Xen systems make
 ------  different choices.
   
 pvgrub is a version of grub that uses PV operations instead of BIOS  ### stub domains
 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  Some (Linux only?) dom0 systems use something called "stub domains" to
 their own operating system and kernel.  See then [prgmr.com NetBSD  isolate qemu from the dom0 system, as a security and reliabilty
 HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU).  mechanism when running HVM domUs.  Somehow, NetBSD's GENERIC kernel
   ends up using PIO for disks rather than DMA.  Of course, all of this
   is emulated, but emulated PIO is unusably slow.  This problem is not
   currently understood.
   
 Typically one has an ext2 or FAT partition for the kernel, so that  ### Grant tables
 grub can understand it, which leads to /netbsd not being the actual  
 kernel.  One must remember to update the special boot partiion.  There are multiple versions of using grant tables, and some security
   advisories have suggested disabling some versions.  Some versions of
   NetBSD apparently only use specific versions and this can lead to
   "NetBSD current doesn't run on hosting provider X" situations.
   
   \todo Explain better.
   
   ## Boot methods
   
   ### 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 file system.
   
 Amazon  [Panix](http://www.panix.com/) lets users use pvgrub.  Panix reports
 ------  that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
   (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
   page](http://www.panix.com/v-colo/grub.html), which describes only
   Linux but should be updated to cover NetBSD :-).
   
   [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
   their own kernel.  See then [prgmr.com NetBSD
   HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
   (which is in need of updating).
   
   It appears that [grub's FFS
   code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
   does not support all aspects of modern FFS, but there are also reports
   that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
   partition for the kernel with the intent that grub can understand it,
   which leads to /netbsd not being the actual kernel.  One must remember
   to update the special boot partition.
   
   ### pygrub
   
   pygrub runs in the dom0 and looks into the domU file system.  This
   implies that the domU must have a kernel in a file system in a format
   known to pygrub.
   
   pygrub doesn't seem to work to load Linux images under NetBSD dom0,
   and is inherently less secure than pvgrub due to running inside dom0. For both these
   reasons, pygrub should not be used, and is only still present so that
   historical DomU images using it still work.
   
 TODO: add link to NetBSD amazon howto.  As of 2014, pygrub seems to be of mostly historical
   interest. New DomUs should use pvgrub.
   
 Using npf  ## Specific Providers
 ---------  
   
 In standard kernels, npf is a module, and thus cannot be loadeed in a  ### Amazon
 DOMU kernel.  
   
 TODO: explain how to compile npf into a custom kernel, answering (but  See the [Amazon EC2 page](/amazon_ec2/).
 note that the problem was caused by not booting the right kernel):  
 http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html  
Removed from v.1.60  
changed lines
  Added in v.1.189

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