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 [[!meta title="Xen HowTo"]]  [[!meta title="Xen HowTo"]]
   
 Introduction  Xen is a Type 1 hypervisor which supports running multiple guest operating
 ============  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 for x86 hardware, which supports running multiple guest  This HOWTO presumes a basic familiarity with the Xen system
 operating systems on a single physical machine.  Xen is a Type 1 or  architecture, with installing NetBSD on amd64 hardware, and with
 bare-metal hypervisor; one uses the Xen kernel to control the CPU,  installing software from pkgsrc.  See also the [Xen
 memory and console, a dom0 operating system which mediates access to  website](http://www.xenproject.org/).
 other hardware (e.g., disks, network, USB), and one or more domU  
 operating systems which operate in an unprivileged virtualized  [[!toc]]
 environment.  IO requests from the domU systems are forwarded by the  
 Xen hypervisor to the dom0 to be fulfilled.  # Overview
   
   The basic concept of Xen is that the hypervisor (xenkernel) runs on
   the hardware, and runs a privileged domain ("dom0") that can access
   disks/networking/etc.  One then runs additonal unprivileged domains
   (each a "domU"), presumably to do something useful.
   
   This HOWTO addresses how to run a NetBSD dom0 (and hence also build
   xen itself).  It also addresses how to run domUs in that environment,
   and how to deal with having a domU in a Xen environment run by someone
   else and/or not running NetBSD.
   
   There are many choices one can make; the HOWTO recommends the standard
   approach and limits discussion of alternatives in many cases.
   
 Xen supports different styles of guest:  ## Guest Styles
   
   Xen supports different styles of guests.
   
 [[!table data="""  [[!table data="""
 Style of guest  |Supported by NetBSD  Style of guest  |Supported by NetBSD
 PV              |Yes (dom0, domU)  PV              |Yes (dom0, domU)
 HVM             |Yes (domU)  HVM             |Yes (domU)
 PVHVM           |No  PVHVM           |current-only (domU)
 PVH             |No  PVH             |current-only (domU, dom0 not yet)
 """]]  """]]
   
 In Para-Virtualized (PV) mode, the guest OS does not attempt to access  In Para-Virtualized (PV) mode, the guest OS does not attempt to access
 hardware directly, but instead makes hypercalls to the hypervisor; PV  hardware directly, but instead makes hypercalls to the hypervisor; PV
 guests must be specifically coded for Xen. In HVM mode, no guest  guests must be specifically coded for Xen.
 modification is required; however, hardware support is required, such  See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
 as VT-x on Intel CPUs and SVM on AMD CPUs.  
   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.)
   
 This HOWTO presumes a basic familiarity with the Xen system  ## CPU Architecture
 architecture, with installing NetBSD on i386/amd64 hardware, and with  
 installing software from pkgsrc.  See also the [Xen  Xen runs on x86_64 hardware (the NetBSD amd64 port).
 website](http://www.xenproject.org/).  
   There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
   
 This HOWTO attempts to address both the case of running a NetBSD dom0  The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
 on hardware and running domUs under it (NetBSD and other), and also  
 running NetBSD as a domU in a VPS.  
   
 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.  
   
 The term "amd64" is used to refer to both the NetBSD port and to the  
 hardware architecture on which it runs.  Such hardware is generally  
 made by both Intel and AMD, and common on PC computers.  
   
 Xen versions  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.
   
   ## Xen Versions
   
 In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages  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,
Line 65  Versions available in pkgsrc: Line 89  Versions available in pkgsrc:
   
 [[!table data="""  [[!table data="""
 Xen Version     |Package Name   |Xen CPU Support        |EOL'ed By Upstream  Xen Version     |Package Name   |Xen CPU Support        |EOL'ed By Upstream
 4.2             |xenkernel42    |32bit, 64bit           |Yes  4.11            |xenkernel411   |x86_64                 |No
 4.5             |xenkernel45    |64bit                  |Yes  4.13            |xenkernel413   |x86_64                 |No
 4.6             |xenkernel46    |64bit                  |Partially  
 4.8             |xenkernel48    |64bit                  |No  
 4.11            |xenkernel411   |64bit                  |No  
 """]]  """]]
   
 See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).  See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
   
 Note: Xen 4.2 was the last version to support 32bit CPUs.  Older Xen had a python-based management tool called xm, now replaced
   by xl.
   
 NetBSD versions  ## NetBSD versions
 ---------------  
   
 NetBSD 8 is recommended as the stable version of the most recent  Xen has been supported in NetBSD for a long time, at least since 2005.
 release for production use.  Initially Xen was PV only.
   
 For developing Xen, netbsd-current may be appropriate.  NetBSD 8 and up support PV and HVM modes.
   
 As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is  Support for PVHVM and PVH is available only in NetBSD-current.
 no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really  
 need SMP for dom0 functions; the lack of support is really a problem  
 when using a dom0 as a normal computer.)  
   
 Note: NetBSD support is called XEN3. However, it does support Xen 4,  NetBSD as a dom0 does not run SMP, because some drivers are not yet
 because the hypercall interface has remained identical.  safe for this.  \todo Link to more information about what needs work.
   
 Architecture  NetBSD, when run as a domU, can and does typically run SMP.
 ------------  
   
 Xen itself runs on amd64 hardware. Practically, almost any computer  Note: NetBSD support is called XEN3.  However, it does support Xen 4,
 where one would want to run Xen today supports amd64.  because the hypercall interface has remained identical.
   
 The dom0 system, plus each domU, can be either i386PAE or amd64.  # Creating a NetBSD dom0
 i386 without PAE is not supported.  
   
 The standard approach is to use NetBSD/amd64 for the dom0.  For domUs,  In order to install a NetBSD as a dom0, one must first install a normal
 NetBSD/i386 (PAE) and NetBSD/amd64 are in widespread use, and there is  NetBSD system, and then pivot the install to a dom0 install by changing
 little to no Xen-specific reason to prefer one over the other.  the kernel and boot configuration.
   
 Note that to use an i386 dom0 with Xen 4.5 or higher, one must build  
 (or obtain from pre-built packages) an amd64 Xen kernel and install  
 that on the system.  Almost no one in the NetBSD/Xen community does  
 this, and the standard, well-tested, approach is to use an amd64 dom0.  
   
 A [posting on  
 xen-devel](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html)  
 explained that PV system call overhead was higher on amd64, and thus  
 there is some notion that i386 guests are faster.  It goes on to  
 caution that the total situation is complex and not entirely  
 understood. On top of that caution, the post is about Linux, not  
 NetBSD.  
   
 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; e.g. 4-8G and 1T of disk is reasonable for a  
 half-dozen domUs of 512M and 32G each.  Basically, the RAM and disk  
 have to be bigger than the sum of the RAM/disk needs of the dom0 and  
 all the domUs.  
   
 In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with  In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
 512M it worked reliably.  This does not make sense, but if you see  512M it worked reliably.  This does not make sense, but if you see
 "not ELF" after Xen boots, try increasing dom0 RAM.  "not ELF" after Xen boots, try increasing dom0 RAM.
   
 Styles of dom0 operation  ## Installation of NetBSD
 ------------------------  
   
 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 meaningfully 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:  
   https://mail-index.netbsd.org/netbsd-users/2014/08/29/msg015195.html  
   
 Installation of NetBSD  [Install NetBSD/amd64](/guide/inst/)
 ----------------------  
   
 First,  
 [install NetBSD/amd64](/guide/inst/)  
 just as you would if you were not using Xen.  just as you would if you were not using Xen.
 However, the partitioning approach is very important.  Therefore, use the most recent release, or a build from the most recent stable branch.
   
   ## Installation of Xen
   
 If you want to use RAIDframe for the dom0, there are no special issues  Use the most recent version of Xen in pkgsrc, unless the DESCR says that it is not suitable.
 for Xen.  Typically one provides RAID storage for the dom0, and the  Therefore, choose 4.13.
 domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips  In the dom0, install xenkernel413 and xentools413 from pkgsrc.
 over a RAID1 header to find /boot from a file system 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 file system, 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  
 -------------------  
   
 We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as  
 dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.  
 Ensure that your packages are recent.  
   
 Once this is done, install the Xen kernel itself:  Once this is done, copy the Xen kernel from where pkgsrc puts it to
   where the boot process will be able to find it:
   
 [[!template id=programlisting text="""  [[!template id=programlisting text="""
 # cp /usr/pkg/xen48-kernel/xen.gz /  # cp -p /usr/pkg/xen413-kernel/xen.gz /
 """]]  """]]
   
 Then, place a NetBSD XEN3_DOM0 kernel in /, copied from  Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
 releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz of a NetBSD build.  can either be compiled manually, or downloaded from the NetBSD FTP, for
   example at:
   
   [[!template id=programlisting text="""
   ftp.netbsd.org/pub/NetBSD/NetBSD-9.1/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
   """]]
   
 Add a line to /boot.cfg to boot Xen:  Add a line to /boot.cfg to boot Xen:
   
 [[!template id=programlisting text="""  [[!template id=filecontent name="/boot.cfg" text="""
 menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M  menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
 """]]  """]]
   
 which specifies that the dom0 should have 512MB of ram, leaving the rest  This specifies that the dom0 should have 512MB of ram, leaving the rest
 to be allocated for domUs.  To use a serial console, use  to be allocated for domUs.
   
 [[!template id=programlisting text="""  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.
   
   To use a serial console, add settings as follows:
   
   [[!template id=filecontent name="/boot.cfg" text="""
 menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1  menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
 """]]  """]]
   
Line 235  speed/parity.  Because the NetBSD comman Line 178  speed/parity.  Because the NetBSD comman
 which directs the console I/O through Xen to the same console device Xen  which directs the console I/O through Xen to the same console device Xen
 itself uses (in this case, the serial port).  itself uses (in this case, the serial port).
   
 In an attempt to add performance, one can also add:  In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
   
 [[!template id=programlisting text="""  
 dom0_max_vcpus=1 dom0_vcpus_pin  
 """]]  
   
 to force only one vcpu to be provided (since NetBSD dom0 can't use  to force only one vcpu to be provided (since NetBSD dom0 can't use
 more) and to pin that vcpu to a physical CPU.  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),
 Xen has [many boot  
 options](http://xenbits.xenproject.org/docs/4.5-testing/misc/xen-command-line.html),  
 and other than dom0 memory and max_vcpus, they are generally not  and other than dom0 memory and max_vcpus, they are generally not
 necessary.  necessary.
   
 As with non-Xen systems, you should have a line to boot /netbsd (a  Ensure that the boot scripts installed in
 kernel that works without Xen).  `/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,
 Now, reboot so that you are running a DOM0 kernel under Xen, rather  but a normal part of pkgsrc usage.)
 than GENERIC without Xen.  
   
 Using grub (historic)  
 ---------------------  
   
 Before NetBSD's native bootloader could support Xen, the use of  Set `xencommons=YES` in rc.conf:
 grub was recommended.  If necessary, see the  
 [old grub information](/ports/xen/howto-grub).  
   
 The [HowTo on Installing into  
 RAID-1](https://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.  Now, just create a system with RAID-1, and alter /boot.cfg as  
 described above.)  
   
 Configuring Xen  
 ---------------  
   
 Now, you have a system that will boot Xen and the dom0 kernel, but not  
 do anything else special.  Make sure that you have rebooted into Xen.  
 There will be no domUs, and none can be started because you still have  
 to configure the dom0 daemons.  
   
 The daemons which should be run vary with Xen version and with whether  
 one is using xm or xl. Xen 4.2 and up packages use xl. To use xm with 4.2,  
 edit xendomains to use xm instead.  
   
 For 4.1 and up, you should enable xencommons.  Not enabling xencommons  
 will result in a hang; it is necessary to hit ^C on the console to let  
 the machine finish booting.  If you are using xm (default in 4.1, or  
 if you changed xendomains in 4.2), you should also enable xend:  
   
 [[!template id=programlisting text="""  [[!template id=filecontent name="/etc/rc.conf" text="""
 xend=YES # only if using xm, and only installed <= 4.2  
 xencommons=YES  xencommons=YES
 """]]  """]]
   
 TODO: Recommend for/against xen-watchdog.  \todo Recommend for/against xen-watchdog.
   
   Now, reboot so that you are running a DOM0 kernel under Xen, rather
   than GENERIC without Xen.
   
 After you have configured the daemons and either started them (in the  Once the reboot is done, use `xl` to inspect Xen's boot messages,
 order given) or rebooted, use xm or xl to inspect Xen's boot messages,  available resources, and running domains.  For example:
 available resources, and running domains.  An example with xl follows:  
   
 [[!template id=programlisting text="""  [[!template id=programlisting text="""
 # xl dmesg  # xl dmesg
Line 311  Xen logs will be in /var/log/xen. Line 218  Xen logs will be in /var/log/xen.
   
 ### Issues with xencommons  ### Issues with xencommons
   
 xencommons starts xenstored, which stores data on behalf of dom0 and  `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
 domUs.  It does not currently work to stop and start xenstored.  domUs.  It does not currently work to stop and start xenstored.
 Certainly all domUs should be shutdown first, following the sort order  Certainly all domUs should be shutdown first, following the sort order
 of the rc.d scripts.  However, the dom0 sets up state with xenstored,  of the rc.d scripts.  However, the dom0 sets up state with xenstored,
Line 320  the state when the new xenstored starts. Line 227  the state when the new xenstored starts.
 make this work, one should not expect to be able to restart xenstored  make this work, one should not expect to be able to restart xenstored
 (and thus xencommons).  There is currently no reason to expect that  (and thus xencommons).  There is currently no reason to expect that
 this will get fixed any time soon.  this will get fixed any time soon.
   \todo Confirm if this is still true in 2020.
   
 ### No-longer needed advice about devices  ## Xen-specific NetBSD issues
   
 The installation of NetBSD should already have created devices for xen  
 (xencons, xenevt, xsd_kva), but if they are not present, create them:  
   
 [[!template id=programlisting text="""  
 cd /dev && sh MAKEDEV xen  
 """]]  
   
 anita (for testing NetBSD)  
 --------------------------  
   
 With the setup so far (assuming 4.2/xl), 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/  
 """]]  
   
 Alternatively, one can use --vmm=xm to use xm-based domU creation  
 instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.  
       
 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 the module ABI is different because some of the #defines  One is that the module ABI is different because some of the #defines
 change, so one must build modules for Xen.  As of netbsd-7, the build  change, so one must build modules for Xen.  As of netbsd-7, the build
 system does this automatically.  TODO: check this.  (Before building  system does this automatically.
 Xen modules was added, it was awkward to use modules to the point  
 where it was considered that it did not work.)  
   
 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 boot.cfg following earlier guidance:  cp -p /usr/mdec/boot /
         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M  # Create boot.cfg following earlier guidance:
         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M  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.  """]]
   
 Upgrading Xen versions  
 ---------------------  
   
 Minor version upgrades are trivial.  Just rebuild/replace the  
 xenkernel version and copy the new xen.gz to / (where /boot.cfg  
 references it), and reboot.  
   
 Major version upgrades are 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.  Specifically,  
 they must match the package you just installed and not be left over  
 from some previous installation.  
   
 Enable the correct set of daemons; see the configuring section above.  
 (Upgrading from 3.x to 4.x without doing this will result in a hang.)  
   
 Ensure that the domU config files are valid for the new version.  
 Specifically, for 4.x remove autorestart=True, and ensure that disks  
 are specified with numbers as the second argument, as the examples  
 above show, and not NetBSD device names.  
   
 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.
   
Line 444  mediated by Xen, and configured in the d Line 321  mediated by Xen, and configured in the d
 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  See /usr/pkg/share/examples/xen/xlexample*
 surrounding what is being configured.  We first show an example config  for a small number of well-commented examples, mostly for running
 file, and then in the various sections give details.  
   
 See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,  
 for a large 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 treats 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  
         xm create -c foo  
         xm shutdown foo  
         xm list  
   
 Typing ^] will exit the console session.  Shutting down a domain is  [[!template id=programlisting text="""
   xl create /usr/pkg/etc/xen/foo
   xl console domU-id
   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
 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
 file system.  With Xen domUs, the process is totally different.  The  
 normal path is for the domU kernel to be a file in the dom0's  
 file system.  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 527  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 and gnats reference.  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  
   
 Do not use qemu-img-xen, because this will create sparse file.  There  
 have been recent (2015) reports of sparse vnd(4) devices causing  
 lockups, but there is apparently no PR.  
   
 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' ]
   """]]
   
 Note that NetBSD by default creates only vnd[0123].  If you need more  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  than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
 dom0.  dom0.
   
 Note that NetBSD by default creates only xbd[0123].  If you need more  ## Virtual Networking
 virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.  
   
 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
 adapters 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 604  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 616  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  
 512M 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:
   
 Note that earlier versions of the xentools41 xendomains rc.d script  [[!template id=filecontent name="/etc/rc.conf" text="""
 used xl, when one should use xm with 4.1.  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.  Of course, this section presumes that you have a working dom0.
   
 Creating an unprivileged NetBSD domain (domU)  ## 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 file system, 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 XEN3PAE_DOMU          i386 XEN3PAE_DOMU
         amd64 XEN3_DOMU          amd64 XEN3_DOMU
   
 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 674  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 684  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 709  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.
   
 It is not strictly necessary to have a kernel (as /netbsd) in the domU  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  file system.  However, various programs (e.g. netstat) will use that
Line 719  not really a Xen-specific issue, but bec Line 538  not really a Xen-specific issue, but bec
 obtained from the dom0, it is far more likely to be out of sync or  obtained from the dom0, it is far more likely to be out of sync or
 missing with Xen.)  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 763  To get the Linux console right, you need Line 584  To get the Linux console right, you need
 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 840  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
Line 868  A second issue is multiple CPUs.  With N Line 719  A second issue is multiple CPUs.  With N
 multiple vcpus, and it is typical for VPS providers to enable multiple  multiple vcpus, and it is typical for VPS providers to enable multiple
 CPUs for NetBSD domUs.  CPUs for NetBSD domUs.
   
 pygrub  ## Complexities due to Xen changes
 -------  
   
 pygrub runs in the dom0 and looks into the domU file system.  This  Xen has many security advisories and people running Xen systems make
 implies that the domU must have a kernel in a file system in a format  different choices.
 known to pygrub.  As of 2014, pygrub seems to be of mostly historical  
 interest.  ### stub domains
   
   Some (Linux only?) dom0 systems use something called "stub domains" to
   isolate qemu from the dom0 system, as a security and reliabilty
   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.
   
   ### Grant tables
   
   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
 ------  
   
 pvgrub is a version of grub that uses PV operations instead of BIOS  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  calls.  It is booted from the dom0 as the domU kernel, and then reads
Line 902  partition for the kernel with the intent Line 769  partition for the kernel with the intent
 which leads to /netbsd not being the actual kernel.  One must remember  which leads to /netbsd not being the actual kernel.  One must remember
 to update the special boot partition.  to update the special boot partition.
   
 Amazon  ### pygrub
 ------  
   
 See the [Amazon EC2 page](/amazon_ec2/).  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 items for improving NetBSD/xen  As of 2014, pygrub seems to be of mostly historical
 ===================================  interest. New DomUs should use pvgrub.
   
 * Make the NetBSD dom0 kernel work with SMP.  ## Specific Providers
 * Test the Xen 4.5 packages adequately to be able to recommend them as  
   the standard approach.  ### Amazon
 * Get PCI passthrough working on Xen 4.5  
 * Get pvgrub into pkgsrc, either via xentools or separately.  See the [Amazon EC2 page](/amazon_ec2/).
 * grub  
   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary  
     fragsize/blocksize (UFS2 support may be present; the point is to  
     make it so that with any UFS1/UFS2 file system setup that works  
     with NetBSD grub will also work).  
     See [pkg/40258](https://gnats.netbsd.org/40258).  
   * Push patches upstream.  
   * Get UFS2 patches into pvgrub.  
 * Add support for PV ops to a version of /boot, and make it usable as  
   a kernel in Xen, similar to pvgrub.  
   
 Random pointers  
 ===============  
   
 This section contains links from elsewhere not yet integrated into the  
 HOWTO, and other guides.  
   
 * http://www.lumbercartel.ca/library/xen/  
 * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html  
 * https://gmplib.org/~tege/xen.html  
Removed from v.1.155  
changed lines
  Added in v.1.189

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