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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: Versions of Xen, Styles, NetBSD
 hypervisor (Xen) to the dom0 to be fulfilled.  
   
 Xen supports two styles of guests.  The original is Para-Virtualized  
 (PV) which means that the guest OS does not attempt to access hardware  
 directly, but instead makes hypercalls to the hypervisor.  This is  
 analogous to a user-space program making system calls.  (The dom0  
 operating system uses PV calls for some functions, such as updating  
 memory mapping page tables, but has direct hardware access for disk  
 and network.)   PV guests must be specifically coded for Xen.  
   
 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.  
 Attempts to access hardware registers are trapped and emulated.  This  
 style is less efficient but can run unmodified guests.  
   
 Generally any machine that runs NetBSD/amd64 will work with Xen and PV  
 guests.  In theory i386 computers (without x86_64/amd64 support) can  
 be used for Xen <= 4.2, but we have no recent reports of this working  
 (this is a hint).  For HVM guests, hardware support is needed, but it  
 is common on recent machines.  For Intel CPUs, one needs the VT-x  
 extension, shown in "cpuctl identify 0" as VMX.  For AMD CPUs, one  
 needs the AMD-V extensions, shown in "cpuctl identify 0" as SVM.  
 There are further features for IOMMU virtualization, Intel's VT-d and  
 AMD's AMD-Vi.  TODO: Explain whether Xen on NetBSD makes use of these  
 features.  TODO: Review by someone who really understands this.  
   
 Note that a FreeBSD dom0 requires VT-x and VT-d (or equivalent); this  The basic concept of Xen is that the hypervisor (xenkernel) runs on
 is because the FreeBSD dom0 does not run in PV mode.  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.
   
   ## Guest Styles
   
   Xen supports different styles of guests.
   
   [[!table data="""
   Style of guest  |Supported by NetBSD
   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.  
   
 Xen 3.1 in pkgsrc supports "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 6 and earlier supported Xen 2; support was removed from NetBSD  
 7.  Xen 2 has been removed from pkgsrc.  
   
 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, with installing NetBSD on i386/amd64 hardware, and with  
 installing software from pkgsrc.  See also the [Xen  
 website](http://www.xenproject.org/).  
   
 Versions of Xen and NetBSD  There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
 ==========================  
   
 Most of the installation concepts and instructions are independent  The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
 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.
   
   ## 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,
 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 provides Xen 3.1.  It is no longer maintained by Xen, and the last applied security patch was in  Versions available in pkgsrc:
 2011. Thus, it should not be used.  It supports PCI passthrough,  
 which is why people use it anyway. Xen 3.1 supports i386, both PAE and  
 non-PAE.  
   
 xenkernel33 provides Xen 3.3.  It is no longer maintained by Xen, and  
 the last applied security patch was in 2012.  Thus, it should not be  
 used.  Xen 3.3 supports i386, but only in PAE mode.  There are no good  
 reasons to run this version.  
   
 xenkernel41 provides Xen 4.1.  It is no longer maintained by Xen, but  
 as of 2016-12 received backported security patches.  Xen 4.1 supports  
 i386, but only in PAE mode.  There are no good reasons to run this  
 version.  
   
 xenkernel42 provides Xen 4.2.  It is no longer maintained by Xen, but  
 as of 2016-12 received backported security patches.  Xen 4.2 supports  
 i386, but only in PAE mode.  The only reason to run this is if you  
 need to use xm instead of xl, or if you need to run an i386 dom0  
 (because your hardware is i386 only).  
   
 xenkernel45 provides Xen 4.5.  As of 2016-12, security patches were  
 released by Xen and applied to pkgsrc.  Xen 4.5 requires using a dom0  
 running NetBSD's amd64 port (Intel or AMD hardware is fine), but domUs  
 can be amd64 or i386 PAE.  While slightly old, n4.5 has been tested and  
 run by others, so it is the conservative choice.  
   
 xenkernel46 provides Xen 4.6.  It is new to pkgsrc as of 2016-05.  As  
 of 2016-12, security patches were released by Xen and applied to  
 pkgsrc.  Xen 4.6 similarly requires a NetBSD/amd64 dom0, but domUs can  
 be amd64 or i386 PAE.  For new installations, 4.6 is probably the  
 appropriate choice and it will likely soon be the standard approach.  
   
 Xen 4.7 (released 2016-06) and 4.8 (released 2016-12) are not yet in  [[!table data="""
 pkgsrc.  Xen Version     |Package Name   |Xen CPU Support        |xm?    |EOL'ed By Upstream
   4.11            |xenkernel411   |x86_64                 |       |No
   4.13            |xenkernel413   |x86_64                 |       |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 that NetBSD support is called XEN3.  It works with Xen 3 and Xen  Multiprocessor (SMP) support in NetBSD differs depending on the domain:
 4 because the hypercall interface has been stable.  
   
 Xen command program  [[!table data="""
 -------------------  Domain          |Supports SMP
   dom0            |No
   domU            |Yes
   """]]
   
 Early Xen used a program called xm to manipulate the system from the  Note: NetBSD support is called XEN3.  However, it does support Xen 4,
 dom0.  Starting in 4.1, a replacement program with similar behavior  because the hypercall interface has remained identical.
 called xl is provided, but it does not work well in 4.1.  In 4.2, both  
 xm and xl work fine.  4.4 is the last version that has xm.  
   
 You must make a global choice to use xm or xl, because it affects not  
 only which command you use, but the command used by rc.d scripts  
 (specifically xendomains) and which daemons should be run.  The  
 xentools packages provide xm for 3.1, 3.3 and 4.1 and xl for 4.2 and up.  
   
 In 4.2, you can choose to use xm by simply changing the ctl_command  
 variable.  
   
 With xl, virtual devices are configured in parallel, which can cause  
 problems if they are written assuming serial operation (e.g., updating  
 firewall rules without explicit locking).  There is now locking for  
 the provided scripts, which works for normal casses (e.g, file-backed  
 xbd, where a vnd must be allocated).  But, as of 201612, it has not  
 been adequately tested for a complex custom setup with a large number  
 of interfaces.  
   
 NetBSD  
 ------  
   
 The netbsd-6, netbsd-7, and -current branches are all reasonable  
 choices, with more or less the same considerations for non-Xen use.  
 Therefore, netbsd-7 is recommended as the stable version of the most  
 recent release for production use.  In addition, netbsd-7 and -current  
 have a important scheduler fix (in November of 2015) affecting  
 contention between dom0 and domUs; see  
 https://releng.netbsd.org/cgi-bin/req-7.cgi?show=1040 for a  
 description.  For those wanting to learn Xen or without production  
 stability concerns, netbsd-7 is still likely most appropriate, but  
 -current is also a reasonable choice.  (Xen runs ok on netbsd-5, but  
 the xentools packages are likely difficult to build, and netbsd-5 is  
 not supported.)  
   
 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 for dom0 functions; the lack of support is really a problem  
 when using a dom0 as a normal computer.)  
   
 Architecture  
 ------------  
   
 Xen itself can run on i386 (Xen < 3.1) or amd64 machines (all Xen  
 versions).  (Practically, almost any computer where one would want to  
 run Xen today supports amd64.)  
   
 Xen, the dom0 kernel, and each domU kernel can be either i386 or  
 amd64.  When building a xenkernel package, one obtains i386 on an i386  
 host, and amd64 on an amd64 host.  If the Xen kernel is i386, then the  
 dom0 kernel and all domU kernels must be i386.  With an amd64 Xen  
 kernel, an amd64 dom0 kernel is known to work, and an i386PAE dom0  
 kernel should in theory work.  An amd64 Xen/dom0 is known to support  
 both i386PAE and amd64 domUs.  
   
 i386 dom0 and domU kernels must be PAE (except for Xen 3.1); these are  
 built by default.  (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.)  
   
 Because of the above, the standard approach is to use amd64 for the  Older Xen had a python-based management tool called xm, now replaced
 dom0.  by xl.
   
   # Creating a dom0
   
 Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify  In order to install a NetBSD as a dom0, one must first install a normal
 if this is about the CPU, the Xen kernel, or the dom0 kernel having to  NetBSD system, and then pivot the install to a dom0 install by changing
 be amd64.  the kernel and boot configuration.
   
   
 Stability  
 ---------  
   
 Mostly, NetBSD as a dom0 or domU is quite stable.  
 However, there are some open PRs indicating problems.  
   
  - [PR 48125](http://gnats.netbsd.org/48125)  
  - [PR 47720](http://gnats.netbsd.org/47720)  
   
 Note also that there are issues with sparse vnd(4) instances, but  
 these are not about Xen -- they just are noticed with sparse vnd(4)  
 instances in support of virtual disks in a dom0.  
   
 Recommendation  
 --------------  
   
 Therefore, this HOWTO recommends running xenkernel45 or xenkernel46,  
 xl, the NetBSD 7 stable branch, and to use an amd64 kernel as the  
 dom0.  Either the i386PAE or amd64 version of NetBSD may be used as  
 domUs.  
   
 Status  
 ------  
   
 Ideally, all versions of Xen in pkgsrc would build on all supported  
 versions of NetBSD/amd64, to the point where this section would be  
 silly.  However, that has not always been the case.  Besides aging  
 code and aging compilers, qemu (included in xentools for HVM support)  
 is difficult to build.  Note that there is intentionally no data for  
 4.5+ up for i386, and often omits xentools info if the corresponding  
 kernel fails.  
   
 The following table gives status, with the date last checked  
 (generally on the most recent quarterly branch).  The first code is  
 "builds" if it builds ok, and "FAIL" for a failure to build.  The  
 second code/date only appears for xenkernel* and is "works" if it runs  
 ok as a dom0, and "FAIL" if it won't boot or run a domU.  
   
         xenkernel3 netbsd-6 i386 FAIL 201612  
         xenkernel33 netbsd-6 i386 FAIL 201612  
         xenkernel41 netbsd-6 i386 builds 201612  
         xenkernel42 netbsd-6 i386 builds 201612  
         xentools3 netbsd-6 i386 FAIL 201612  
         xentools33 netbsd-6 i386 FAIL 201612  
         xentools41 netbsd-6 i386 builds 201612  
         xentools42 netbsd-6 i386 FAIL 201612  
   
         xenkernel3 netbsd-7 i386 FAIL 201412  
         xenkernel33 netbsd-7 i386 FAIL 201412  
         xenkernel41 netbsd-7 i386 builds 201412  
         xenkernel42 netbsd-7 i386 builds 201412  
         xentools41 netbsd-7 i386 builds 201412  
         xentools42 netbsd-7 i386 ??FAIL 201412  
   
         xenkernel3 netbsd-6 amd64 FAIL 201612  
         xenkernel33 netbsd-6 amd64 FAIL 201612  
         xenkernel41 netbsd-6 amd64 builds 201612 works 201612  
         xenkernel42 netbsd-6 amd64 builds 201612 works 201612  
         xenkernel45 netbsd-6 amd64 builds 201612  
         xenkernel46 netbsd-6 amd64 builds 201612  
         xentools41 netbsd-6 amd64 builds 201612  
         xentools42 netbsd-6 amd64 builds 201612  
         xentools45 netbsd-6 amd64 builds 201612  
         xentools46 netbsd-6 amd64 FAIL 201612  
   
         xenkernel3 netbsd-7 amd64 builds 201612  
         xenkernel33 netbsd-7 amd64 builds 201612  
         xenkernel41 netbsd-7 amd64 builds 201612  
         xenkernel42 netbsd-7 amd64 builds 201612  
         xenkernel45 netbsd-7 amd64 builds 201612  
         xenkernel46 netbsd-7 amd64 builds 201612  
         xentools3 netbsd-7 amd64 builds 201612  
         xentools3-hvm netbsd-7 amd64 builds 201612  
         xentools33 netbsd-7 amd64 FAIL 201612  
         xentools41 netbsd-7 amd64 builds 201612  
         xentools42 netbsd-7 amd64 builds 201612  
         xentools45 netbsd-7 amd64 builds 201612  
         xentools46 netbsd-7 amd64 builds 201612  
   
 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 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:  
   http://mail-index.netbsd.org/netbsd-users/2014/08/29/msg015195.html  
   
 Installation of NetBSD  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
   "not ELF" after Xen boots, try increasing dom0 RAM.
   
 First,  ## Installation of NetBSD
 [install NetBSD/amd64](/guide/inst/)  
   [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.  
   
 If you want to use RAIDframe for the dom0, there are no special issues  ## Installation of Xen
 for Xen.  Typically one provides RAID storage for the dom0, and the  
 domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips  
 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  
 -------------------  
   
 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.  Ensure that your packages are recent; the HOWTO does not  
 contemplate old builds.  
   
   
 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.  If using i386, use  
 releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen  
 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you  
 should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and  
 typically are) left compressed.  
   
 In a dom0 kernel, kernfs is mandatory for xend to communicate 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 file system, /boot present, and likely  
 /boot.cfg.  (If not, fix before continuing!)  
   
 Add a line to to /boot.cfg to boot Xen.  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  We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
   dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
   
 which specifies that the dom0 should have 256M, leaving the rest to be  Once this is done, install the Xen kernel itself:
 allocated for domUs.  To use a serial console, use  
   
         menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1  [[!template id=programlisting text="""
   # cp /usr/pkg/xen48-kernel/xen.gz /
   """]]
   
 which will use the first serial port for Xen (which counts starting  Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
 from 1), forcing speed/parity, and also for NetBSD (which counts  can either be compiled manually, or downloaded from the NetBSD FTP, for
 starting at 0).  In an attempt to add performance, one can also add  example at:
   
         dom0_max_vcpus=1 dom0_vcpus_pin  [[!template id=programlisting text="""
   ftp.netbsd.org/pub/NetBSD/NetBSD-8.0/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
   """]]
   
 to force only one vcpu to be provided (since NetBSD dom0 can't use  Add a line to /boot.cfg to boot Xen:
 more) and to pin that vcpu to a physical CPU.  TODO: benchmark this.  
   
 Xen has [many boot  [[!template id=filecontent name="/boot.cfg" text="""
 options](http://xenbits.xenproject.org/docs/4.5-testing/misc/xen-command-line.html),  menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
 and other than dom0 memory and max_vcpus, they are generally not  """]]
 necessary.  
   
 As with non-Xen systems, you should have a line to boot /netbsd (a  This specifies that the dom0 should have 512MB of ram, leaving the rest
 kernel that works without Xen).  Consider a line to boot /netbsd.ok (a  to be allocated for domUs.  To use a serial console, use:
 fallback version of the non-Xen kernel, updated manually when you are  
 sure /netbsd is ok).  Consider also a line to boot fallback versions  
 of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used  
 to resolve Xen booting issues.  
   
 Probably you want a default=N line to choose Xen in the absence of  [[!template id=filecontent name="/boot.cfg" text="""
 intervention.  menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
   """]]
   
 Now, reboot so that you are running a DOM0 kernel under Xen, rather  which will use the first serial port for Xen (which counts starting
 than GENERIC without Xen.  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).
   
 Using grub (historic)  In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
 ---------------------  to force only one vcpu to be provided (since NetBSD dom0 can't use
   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.
   
 Before NetBSD's native bootloader could support Xen, the use of  Copy the boot scripts into `/etc/rc.d`:
 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  [[!template id=programlisting text="""
 ---------------  # cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/
   """]]
   
 Xen logs will be in /var/log/xen.  Enable `xencommons`:
   
 Now, you have a system that will boot Xen and the dom0 kernel, but not  [[!template id=filecontent name="/etc/rc.conf" text="""
 do anything else special.  Make sure that you have rebooted into Xen.  xencommons=YES
 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.  The Xen 3.1, 3.3 and 4.1 packages use xm.  Xen  
 4.2 and up packages use xl.  To use xm with 4.2, edit xendomains to  
 use xm instead.  
   
 For "xm", you should enable xend and xenbackendd:  
   
         xend=YES  
         xenbackendd=YES  
   
 For "xl", you should enable xend and xencommons (xenstored).  Trying  
 to use xl without xencommons=YES will result in a hang; it is  
 necessary to hit ^C on the console to let the machine finish booting.  
 TODO: Check if xend really should be used, and if not why it is  
 installed.  
   
         xend=YES  Now, reboot so that you are running a DOM0 kernel under Xen, rather
         xencommons=YES  than GENERIC without Xen.
   
 TODO: Recommend for/against xen-watchdog.  TODO: Recommend for/against xen-watchdog.
   
 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="""
         # xl dmesg  # xl dmesg
         [xen's boot info]  ... xen's boot info ...
         # xl info  # xl info
         [available memory, etc.]  ... available memory, etc ...
         # xl list  # xl list
         Name              Id  Mem(MB)  CPU  State  Time(s)  Console  Name              Id  Mem(MB)  CPU  State  Time(s)  Console
         Domain-0           0       64    0  r----     58.1  Domain-0           0       64    0  r----     58.1
   """]]
   
   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 496  make this work, one should not expect to Line 212  make this work, one should not expect to
 (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.
   
 ### No-longer needed advice about devices  ## anita (for testing NetBSD)
   
 The installation of NetBSD should already have created devices for xen  
 (xencons, xenevt, xsd_kva), but if they are not present, create them:  
   
         cd /dev && sh MAKEDEV xen  With the setup so far, one should be able to run
   
 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  anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
 root, because anita must create a domU):  root, because anita must create a domU):
   
         anita --vmm=xl test file:///usr/obj/i386/  [[!template id=programlisting text="""
   anita --vmm=xl test file:///usr/obj/i386/
   """]]
   
 Alternatively, one can use --vmm=xm to use xm-based domU creation  ## Xen-specific NetBSD issues
 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  ## 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  ## Converting from grub to /boot
 -----------------------------  
   
 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=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.  ## Upgrading Xen versions
   
 Upgrading Xen versions  
 ---------------------  
   
 Minor version upgrades are trivial.  Just rebuild/replace the  Minor version upgrades are trivial.  Just rebuild/replace the
 xenkernel version and copy the new xen.gz to / (where /boot.cfg  xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
 references it), and reboot.  references it), and reboot.
   
 Major version upgrades are conceptually not difficult, but can run  #Unprivileged domains (domU)
 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.  
   
 Hardware known to work  
 ----------------------  
   
 Arguably, this section is misplaced, and there should be a page of  
 hardware that runs NetBSD/amd64 well, with the mostly-well-founded  
 assumption that NetBSD/xen runs fine on any modern hardware that  
 NetBSD/amd64 runs well on.  Until then, we give motherboard/CPU (and  
 sometimes RAM) pairs/triples to aid those choosing a motherboard.  
 Note that Xen systems usually do not run X, so a listing here does not  
 imply that X works at all.  
   
         Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC  
         Supermicro ??, Atom C2758 (8 core), 32 GiB ECC  
         ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC  
   
 Older hardware:  
   
         Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2  
         INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU     E6850  @ 3.00GHz"  
         INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU     E8400  @ 3.00GHz"  
   
 Running Xen under qemu  
 ----------------------  
   
 The astute reader will note that this section is somewhat twisted.  
 However, it can be useful to run Xen under qemu either because the  
 version of NetBSD as a dom0 does not run on the hardware in use, or to  
 generate automated test cases involving Xen.  
   
 In 2015-01, the following combination was reported to mostly work:  
   
         host OS: NetBSD/amd64 6.1.4  
         qemu: 2.2.0 from pkgsrc  
         Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc  
         dom0 kernel: NetBSD/amd64 6.1.5  
         Xen tools: xentools42-4.2.5 from pkgsrc  
   
 See [PR 47720](http://gnats.netbsd.org/47720) for a problem with dom0  
 shutdown.  
   
 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 655  mediated by Xen, and configured in the d Line 297  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  
 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 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  By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
 that "xm create" takes the name of a config file, while other commands  that "xl create" takes the name of a config file, while other commands
 take the name of a domain.  To create the domain, connect to the  take the name of a domain.
 console, create the domain while attaching the console, shutdown the  
 domain, and see if it has finished stopping, do (or xl with Xen >=  Examples of commands:
 4.2):  
   [[!template id=programlisting text="""
         xm create foo  xl create /usr/pkg/etc/xen/foo
         xm console foo  xl console domU-id
         xm create -c foo  xl create -c /usr/pkg/etc/xen/foo
         xm shutdown foo  xl shutdown domU-id
         xm list  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
 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 738  sum of the the memory allocated to the d Line 355  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
Line 801  Virtual Networking Line 400  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 815  interfaces to the bridge.  One specifies Line 414  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 827  The MAC address specified is the one use Line 428  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  
 --------------  
   
 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  Starting domains automatically
 ------------------------------  ------------------------------
   
 To start domains foo at bar at boot and shut them down cleanly on dom0  To start domains `domU-netbsd` and `domU-linux` at boot and shut them
 shutdown, in rc.conf add:  down cleanly on dom0 shutdown, add the following in rc.conf:
   
         xendomains="foo bar"  
   
 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)  # Creating a domU
 =============================================  
   
 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.  Note that you must
 have already completed the dom0 setup so that "xl list" (or "xm list")  have already completed the dom0 setup so that "xl list" works.
 works.  
   
 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
Line 871  savecore(8) can work.   (This is helpful Line 457  savecore(8) can work.   (This is helpful
 The kernel must be specifically for Xen and for use as a domU.  The  The kernel must be specifically for Xen and for use as a domU.  The
 i386 and amd64 provide the following kernels:  i386 and amd64 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
Line 889  kernel to / and change the kernel line i Line 471  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 934  not really a Xen-specific issue, but bec Line 516  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)  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 978  To get the Linux console right, you need Line 560  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/).
Line 988  See possibly outdated Line 581  See possibly outdated
 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
 access to a physical network interface or disk controller.  However,  access to a physical network interface or disk controller.  However,
Line 1055  note that only the "xpci" lines are unus Line 652  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  # Specific Issues
 =========================  
   ## 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 1083  A second issue is multiple CPUs.  With N Line 686  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
   
 pvgrub  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  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 1117  partition for the kernel with the intent Line 736  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
 ------  
   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.
   
   As of 2014, pygrub seems to be of mostly historical
   interest. New DomUs should use pvgrub.
   
 See the [Amazon EC2 page](../amazon_ec2/).  ## Specific Providers
   
 Using npf  ### Amazon
 ---------  
   
 In standard kernels, npf is a module, and thus cannot be loaded in a  See the [Amazon EC2 page](/amazon_ec2/).
 DOMU kernel.  
   
 TODO: Explain how to compile npf into a custom kernel, answering (but  
 note that the problem was caused by not booting the right kernel)  
 [this email to  
 netbsd-users](http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html).  
   
 TODO items for improving NetBSD/xen  
 ===================================  
   
 * Make the NetBSD dom0 kernel work with SMP.  
 * Test the Xen 4.5 packages adequately to be able to recommend them as  
   the standard approach.  
 * Get PCI passthrough working on Xen 4.5  
 * Get pvgrub into pkgsrc, either via xentools or separately.  
 * 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](http://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.  
 * Solve somehow the issue with modules for GENERIC not being loadable  
   in a Xen dom0 or domU kernel.  
   
 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.1.131  
changed lines
  Added in v.1.182

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