File:  [NetBSD Developer Wiki] / wikisrc / ports / xen / howto.mdwn
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Thu Jul 26 10:47:25 2018 UTC (2 years, 9 months ago) by maxv
Branches: MAIN
CVS tags: HEAD
reorg a little

    1: [[!meta title="Xen HowTo"]]
    3: Introduction
    4: ============
    6: [![[Xen
    7: screenshot]](](
    9: Xen is a hypervisor (or virtual machine monitor) for x86 hardware
   10: (i686-class or higher), which supports running multiple guest
   11: operating systems on a single physical machine.  Xen is a Type 1 or
   12: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
   13: memory and console, a dom0 operating system which mediates access to
   14: other hardware (e.g., disks, network, USB), and one or more domU
   15: operating systems which operate in an unprivileged virtualized
   16: environment.  IO requests from the domU systems are forwarded by the
   17: hypervisor (Xen) to the dom0 to be fulfilled.
   19: Xen supports two styles of guests.  The original is Para-Virtualized
   20: (PV) which means that the guest OS does not attempt to access hardware
   21: directly, but instead makes hypercalls to the hypervisor.  This is
   22: analogous to a user-space program making system calls.  (The dom0
   23: operating system uses PV calls for some functions, such as updating
   24: memory mapping page tables, but has direct hardware access for disk
   25: and network.)   PV guests must be specifically coded for Xen.
   27: The more recent style is HVM, which means that the guest does not have
   28: code for Xen and need not be aware that it is running under Xen.
   29: Attempts to access hardware registers are trapped and emulated.  This
   30: style is less efficient but can run unmodified guests.
   32: Generally any machine that runs NetBSD/amd64 will work with Xen and PV
   33: guests.  In theory i386 computers (without x86_64/amd64 support) can
   34: be used for Xen <= 4.2, but we have no recent reports of this working
   35: (this is a hint).  For HVM guests, hardware support is needed, but it
   36: is common on recent machines.  For Intel CPUs, one needs the VT-x
   37: extension, shown in "cpuctl identify 0" as VMX.  For AMD CPUs, one
   38: needs the AMD-V extensions, shown in "cpuctl identify 0" as SVM.
   39: There are further features for IOMMU virtualization, Intel's VT-d and
   40: AMD's AMD-Vi.  TODO: Explain whether Xen on NetBSD makes use of these
   41: features.  TODO: Review by someone who really understands this.
   43: Note that a FreeBSD dom0 requires VT-x and VT-d (or equivalent); this
   44: is because the FreeBSD dom0 does not run in PV mode.
   46: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   47: The dom0 can start one or more domUs.  (Booting is explained in detail
   48: in the dom0 section.)
   50: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
   51: and that Xen kernels and tools are available in pkgsrc.  This HOWTO
   52: attempts to address both the case of running a NetBSD dom0 on hardware
   53: and running domUs under it (NetBSD and other), and also running NetBSD
   54: as a domU in a VPS.
   56: Xen 3.1 in pkgsrc used to support "PCI passthrough", which means that
   57: specific PCI devices can be made available to a specific domU instead
   58: of the dom0.  This can be useful to let a domU run X11, or access some
   59: network interface or other peripheral.
   61: NetBSD 6 and earlier supported Xen 2; support was removed from NetBSD
   62: 7.  Xen 2 has been removed from pkgsrc.
   64: Prerequisites
   65: -------------
   67: Installing NetBSD/Xen is not extremely difficult, but it is more
   68: complex than a normal installation of NetBSD.
   69: In general, this HOWTO is occasionally overly restrictive about how
   70: things must be done, guiding the reader to stay on the established
   71: path when there are no known good reasons to stray.
   73: This HOWTO presumes a basic familiarity with the Xen system
   74: architecture, with installing NetBSD on i386/amd64 hardware, and with
   75: installing software from pkgsrc.  See also the [Xen
   76: website](
   78: Versions of Xen and NetBSD
   79: ==========================
   81: Most of the installation concepts and instructions are independent
   82: of Xen version and NetBSD version.  This section gives advice on
   83: which version to choose.  Versions not in pkgsrc and older unsupported
   84: versions of NetBSD are intentionally ignored.
   86: The term "amd64" is used to refer to both the NetBSD port and to the
   87: hardware architecture on which it runs.  (Such hardware is made by
   88: both Intel and AMD, and in 2016 a normal PC has this CPU
   89: architecture.)
   91: Xen versions
   92: ------------
   94: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   95: xenkernel and xentools.  We will refer only to the kernel versions,
   96: but note that both packages must be installed together and must have
   97: matching versions.
   99: Versions available in pkgsrc:
  101: [[!table data="""
  102: Xen Version	|Package Name	|Xen CPU Support	|EOL'ed By Upstream
  103: 4.2		|xenkernel42	|32bit, 64bit		|Yes
  104: 4.5		|xenkernel45	|64bit			|Yes
  105: 4.6		|xenkernel46	|64bit			|Partially
  106: 4.8		|xenkernel48	|64bit			|No
  107: 4.11		|xenkernel411	|64bit			|No
  108: """]]
  110: See also the [Xen Security Advisory page](
  112: Note: Xen 4.2 was the last version to support 32bit CPUs.
  114: Xen command program
  115: -------------------
  117: Early Xen used a program called xm to manipulate the system from the
  118: dom0.  Starting in 4.1, a replacement program with similar behavior
  119: called xl is provided, but it does not work well in 4.1.  In 4.2, both
  120: xm and xl work fine.  4.4 is the last version that has xm.
  122: You must make a global choice to use xm or xl, because it affects not
  123: only which command you use, but the command used by rc.d scripts
  124: (specifically xendomains) and which daemons should be run.  The
  125: xentools packages provide xl for 4.2 and up.
  127: In 4.2, you can choose to use xm by simply changing the ctl_command
  128: variable and setting xend=YES in rc.conf.
  130: With xl, virtual devices are configured in parallel, which can cause
  131: problems if they are written assuming serial operation (e.g., updating
  132: firewall rules without explicit locking).  There is now locking for
  133: the provided scripts, which works for normal casses (e.g, file-backed
  134: xbd, where a vnd must be allocated).  But, as of 201612, it has not
  135: been adequately tested for a complex custom setup with a large number
  136: of interfaces.
  138: NetBSD versions
  139: ---------------
  141: The netbsd-7, netbsd-8, and -current branches are all reasonable
  142: choices, with more or less the same considerations for non-Xen use.
  143: NetBSD 8 is recommended as the stable version of the most recent
  144: release for production use.
  146: For developing Xen, netbsd-current may be appropriate.
  148: As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
  149: no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
  150: need SMP for dom0 functions; the lack of support is really a problem
  151: when using a dom0 as a normal computer.)
  153: Note: NetBSD support is called XEN3. However, it does support Xen 4,
  154: because the hypercall interface has remained identical.
  156: Architecture
  157: ------------
  159: Xen itself can run on i386 (Xen < 4.2) or amd64 hardware (all Xen
  160: versions).  (Practically, almost any computer where one would want to
  161: run Xen today supports amd64.)
  163: Xen, the dom0 system, and each domU system can be either i386 or
  164: amd64.  When building a xenkernel package, one obtains an i386 Xen
  165: kernel on an i386 host, and an amd64 Xen kernel on an amd64 host.  If
  166: the Xen kernel is i386, then the dom0 kernel and all domU kernels must
  167: be i386.  With an amd64 Xen kernel, an amd64 dom0 kernel is known to
  168: work, and an i386 dom0 kernel should in theory work.  An amd64
  169: Xen/dom0 is known to support both i386 and amd64 domUs.
  171: i386 dom0 and domU kernels must be PAE (except for an i386 Xen 3.1
  172: kernel, where one can use non-PAE for dom0 and all domUs); PAE kernels
  173: are included in the NetBSD default build.  (Note that emacs (at least)
  174: fails if run on i386 with PAE when built without, and vice versa,
  175: presumably due to bugs in the undump code.)
  177: Because of the above, the standard approach is to use an amd64 Xen
  178: kernel and NetBSD/amd64 for the dom0.  For domUs, NetBSD/i386 (with
  179: the PAE kernel) and NetBSD/amd64 are in widespread use, and there is
  180: little to no Xen-specific reason to prefer one over the other.
  182: Note that to use an i386 dom0 with Xen 4.5 or higher, one must build
  183: (or obtain from pre-built packages) an amd64 Xen kernel and install
  184: that on the system.  (One must also use a PAE i386 kernel, but this is
  185: also required with an i386 Xen kernel.).  Almost no one in the
  186: NetBSD/Xen community does this, and the standard, well-tested,
  187: approach is to use an amd64 dom0.
  189: A [posting on
  190: xen-devel](
  191: explained that PV system call overhead was higher on amd64, and thus
  192: there is some notion that i386 guests are faster.  It goes on to
  193: caution that the total situation is complex and not entirely
  194: understood. On top of that caution, the post is about Linux, not
  195: NetBSD.  TODO: Include link to benchmarks, if someone posts them.
  197: Stability
  198: ---------
  200: Mostly, NetBSD as a dom0 or domU is quite stable. However, just like every
  201: other architecture, there are some open PRs indicating problems.
  203: Note also that there are issues with sparse vnd(4) instances, but
  204: these are not about Xen -- they just are noticed with sparse vnd(4)
  205: instances in support of virtual disks in a dom0.
  207: Recommendation
  208: --------------
  210: Therefore, this HOWTO recommends running xenkernel46, xl, the NetBSD 7
  211: stable branch, and therefore to use an amd64 kernel as the dom0.
  212: Either the i386PAE or amd64 version of NetBSD may be used as domUs.
  214: A tentative replacement recommendation is xenkernel48, xl, and NetBSD
  215: 8.
  217: Because bugs are fixed quite often, and because of Xen security
  218: advisories, it is good to stay up to date with NetBSD (tracking a
  219: stable branch), with the Xen kernel (tracking a Xen version via
  220: pkgsrc), and with the Xen tools.  Specifically, NetBSD (-7 and
  221: -current) got an important fix affecting dom0/domU timesharing in
  222: November, 2015, and xentools46 got a fix to enable Ubuntu guests to
  223: boot in December, 2016.
  225: NetBSD as a dom0
  226: ================
  228: NetBSD can be used as a dom0 and works very well.  The following
  229: sections address installation, updating NetBSD, and updating Xen.
  230: Note that it doesn't make sense to talk about installing a dom0 OS
  231: without also installing Xen itself.  We first address installing
  232: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
  233: NetBSD install to a dom0 install by just changing the kernel and boot
  234: configuration.
  236: For experimenting with Xen, a machine with as little as 1G of RAM and
  237: 100G of disk can work.  For running many domUs in productions, far
  238: more will be needed; e.g. 4-8G and 1T of disk is reasonable for a
  239: half-dozen domUs of 512M and 32G each.  Basically, the RAM and disk
  240: have to be bigger than the sum of the RAM/disk needs of the dom0 and
  241: all the domUs.
  243: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
  244: 512M it worked reliably.  This does not make sense, but if you see
  245: "not ELF" after Xen boots, try increasing dom0 RAM.
  247: Styles of dom0 operation
  248: ------------------------
  250: There are two basic ways to use Xen.  The traditional method is for
  251: the dom0 to do absolutely nothing other than providing support to some
  252: number of domUs.  Such a system was probably installed for the sole
  253: purpose of hosting domUs, and sits in a server room on a UPS.
  255: The other way is to put Xen under a normal-usage computer, so that the
  256: dom0 is what the computer would have been without Xen, perhaps a
  257: desktop or laptop.  Then, one can run domUs at will.  Purists will
  258: deride this as less secure than the previous approach, and for a
  259: computer whose purpose is to run domUs, they are right.  But Xen and a
  260: dom0 (without domUs) is not meaningfully less secure than the same
  261: things running without Xen.  One can boot Xen or boot regular NetBSD
  262: alternately with little problems, simply refraining from starting the
  263: Xen daemons when not running Xen.
  265: Note that NetBSD as dom0 does not support multiple CPUs.  This will
  266: limit the performance of the Xen/dom0 workstation approach.  In theory
  267: the only issue is that the "backend drivers" are not yet MPSAFE:
  270: Installation of NetBSD
  271: ----------------------
  273: First,
  274: [install NetBSD/amd64](/guide/inst/)
  275: just as you would if you were not using Xen.
  276: However, the partitioning approach is very important.
  278: If you want to use RAIDframe for the dom0, there are no special issues
  279: for Xen.  Typically one provides RAID storage for the dom0, and the
  280: domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
  281: over a RAID1 header to find /boot from a file system within a RAID
  282: partition; this is no different when booting Xen.
  284: There are 4 styles of providing backing storage for the virtual disks
  285: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
  287: With raw partitions, one has a disklabel (or gpt) partition sized for
  288: each virtual disk to be used by the domU.  (If you are able to predict
  289: how domU usage will evolve, please add an explanation to the HOWTO.
  290: Seriously, needs tend to change over time.)
  292: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
  293: for domU disks.  This is almost as efficient as raw disk partitions
  294: and more flexible.  Hence raw disk partitions should typically not
  295: be used.
  297: One can use files in the dom0 file system, typically created by dd'ing
  298: /dev/zero to create a specific size.  This is somewhat less efficient,
  299: but very convenient, as one can cp the files for backup, or move them
  300: between dom0 hosts.
  302: Finally, in theory one can place the files backing the domU disks in a
  303: SAN.  (This is an invitation for someone who has done this to add a
  304: HOWTO page.)
  306: Installation of Xen
  307: -------------------
  309: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
  310: pkgsrc (or another matching pair).  See [the pkgsrc
  311: documentation]( for help with
  312: pkgsrc.  Ensure that your packages are recent; the HOWTO does not
  313: contemplate old builds.
  316: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More
  317: recent versions have HVM support integrated in the main xentools
  318: package.  It is entirely reasonable to run only PV guests.
  320: Next you need to install the selected Xen kernel itself, which is
  321: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.
  322: For debugging, one may copy xen-debug.gz; this is conceptually similar
  323: to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
  324: useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
  325: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
  326: of a NetBSD build.  If using i386, use
  327: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen
  328: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you
  329: should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and
  330: typically are) left compressed.
  332: In a dom0, kernfs is mandatory for xend to communicate with the
  333: kernel, so ensure that /kern is in fstab.  (A standard NetBSD install
  334: should already mount /kern.)
  336: Because you already installed NetBSD, you have a working boot setup
  337: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
  338: beginning of your root file system, have /boot, and likely also
  339: /boot.cfg.  (If not, fix before continuing!)
  341: Add a line to to /boot.cfg to boot Xen.  See boot.cfg(5) for an
  342: example.  The basic line is
  344:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  346: which specifies that the dom0 should have 512M, leaving the rest to be
  347: allocated for domUs.  To use a serial console, use
  349:         menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  351: which will use the first serial port for Xen (which counts starting
  352: from 1, unlike NetBSD which counts starting from 0), forcing
  353: speed/parity.  Because the NetBSD command line lacks a
  354: "console=pc" argument, it will use the default "xencons" console device,
  355: which directs the console I/O through Xen to the same console device Xen
  356: itself uses (in this case, the serial port).
  358: In an attempt to add performance, one can also add
  360:         dom0_max_vcpus=1 dom0_vcpus_pin
  362: to force only one vcpu to be provided (since NetBSD dom0 can't use
  363: more) and to pin that vcpu to a physical CPU.  TODO: benchmark this.
  365: Xen has [many boot
  366: options](,
  367: and other than dom0 memory and max_vcpus, they are generally not
  368: necessary.
  370: As with non-Xen systems, you should have a line to boot /netbsd (a
  371: kernel that works without Xen).  Consider a line to boot /netbsd.ok (a
  372: fallback version of the non-Xen kernel, updated manually when you are
  373: sure /netbsd is ok).  Consider also a line to boot fallback versions
  374: of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used
  375: to resolve Xen booting issues.
  377: Probably you want a default=N line to choose Xen in the absence of
  378: intervention.
  380: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  381: than GENERIC without Xen.
  383: Using grub (historic)
  384: ---------------------
  386: Before NetBSD's native bootloader could support Xen, the use of
  387: grub was recommended.  If necessary, see the
  388: [old grub information](/ports/xen/howto-grub).
  390: The [HowTo on Installing into
  391: RAID-1](
  392: explains how to set up booting a dom0 with Xen using grub with
  393: NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
  394: boot.  Now, just create a system with RAID-1, and alter /boot.cfg as
  395: described above.)
  397: Configuring Xen
  398: ---------------
  400: Xen logs will be in /var/log/xen.
  402: Now, you have a system that will boot Xen and the dom0 kernel, but not
  403: do anything else special.  Make sure that you have rebooted into Xen.
  404: There will be no domUs, and none can be started because you still have
  405: to configure the dom0 daemons.
  407: The daemons which should be run vary with Xen version and with whether
  408: one is using xm or xl.  The Xen 3.1, 3.3 and 4.1 packages use xm.  Xen
  409: 4.2 and up packages use xl.  To use xm with 4.2, edit xendomains to
  410: use xm instead.
  412: For 3.1 and 3.3, you should enable xend and xenbackendd:
  414:         xend=YES
  415:         xenbackendd=YES
  417: For 4.1 and up, you should enable xencommons.  Not enabling xencommons
  418: will result in a hang; it is necessary to hit ^C on the console to let
  419: the machine finish booting.  If you are using xm (default in 4.1, or
  420: if you changed xendomains in 4.2), you should also enable xend:
  422:         xend=YES # only if using xm, and only installed <= 4.2
  423:         xencommons=YES
  425: TODO: Recommend for/against xen-watchdog.
  427: After you have configured the daemons and either started them (in the
  428: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
  429: available resources, and running domains.  An example with xl follows:
  431:         # xl dmesg
  432: 	[xen's boot info]
  433:         # xl info
  434: 	[available memory, etc.]
  435:         # xl list
  436:         Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  437:         Domain-0           0       64    0  r----     58.1
  439: ### Issues with xencommons
  441: xencommons starts xenstored, which stores data on behalf of dom0 and
  442: domUs.  It does not currently work to stop and start xenstored.
  443: Certainly all domUs should be shutdown first, following the sort order
  444: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  445: and is not notified when xenstored exits, leading to not recreating
  446: the state when the new xenstored starts.  Until there's a mechanism to
  447: make this work, one should not expect to be able to restart xenstored
  448: (and thus xencommons).  There is currently no reason to expect that
  449: this will get fixed any time soon.
  451: ### No-longer needed advice about devices
  453: The installation of NetBSD should already have created devices for xen
  454: (xencons, xenevt, xsd_kva), but if they are not present, create them:
  456:         cd /dev && sh MAKEDEV xen
  458: anita (for testing NetBSD)
  459: --------------------------
  461: With the setup so far (assuming 4.2/xl), one should be able to run
  462: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  463: root, because anita must create a domU):
  465:         anita --vmm=xl test file:///usr/obj/i386/
  467: Alternatively, one can use --vmm=xm to use xm-based domU creation
  468: instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.
  470: Xen-specific NetBSD issues
  471: --------------------------
  473: There are (at least) two additional things different about NetBSD as a
  474: dom0 kernel compared to hardware.
  476: One is that the module ABI is different because some of the #defines
  477: change, so one must build modules for Xen.  As of netbsd-7, the build
  478: system does this automatically.  TODO: check this.  (Before building
  479: Xen modules was added, it was awkward to use modules to the point
  480: where it was considered that it did not work.)
  482: The other difference is that XEN3_DOM0 does not have exactly the same
  483: options as GENERIC.  While it is debatable whether or not this is a
  484: bug, users should be aware of this and can simply add missing config
  485: items if desired.
  487: Updating NetBSD in a dom0
  488: -------------------------
  490: This is just like updating NetBSD on bare hardware, assuming the new
  491: version supports the version of Xen you are running.  Generally, one
  492: replaces the kernel and reboots, and then overlays userland binaries
  493: and adjusts /etc.
  495: Note that one must update both the non-Xen kernel typically used for
  496: rescue purposes and the DOM0 kernel used with Xen.
  498: Converting from grub to /boot
  499: -----------------------------
  501: These instructions were [TODO: will be] used to convert a system from
  502: grub to /boot.  The system was originally installed in February of
  503: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  504: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  505: 4.1 and grub, much like the message linked earlier in the grub
  506: section.
  508:         # Install MBR bootblocks on both disks. 
  509:         fdisk -i /dev/rwd0d
  510:         fdisk -i /dev/rwd1d
  511:         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  512:         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  513:         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  514:         # Install secondary boot loader
  515:         cp -p /usr/mdec/boot /
  516:         # Create boot.cfg following earlier guidance:
  517:         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  518:         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  519:         menu=GENERIC:boot
  520:         menu=GENERIC single-user:boot -s
  521:         menu=GENERIC.ok:boot netbsd.ok
  522:         menu=GENERIC.ok single-user:boot netbsd.ok -s
  523:         menu=Drop to boot prompt:prompt
  524:         default=1
  525:         timeout=30
  527: TODO: actually do this and fix it if necessary.
  529: Upgrading Xen versions
  530: ---------------------
  532: Minor version upgrades are trivial.  Just rebuild/replace the
  533: xenkernel version and copy the new xen.gz to / (where /boot.cfg
  534: references it), and reboot.
  536: Major version upgrades are conceptually not difficult, but can run
  537: into all the issues found when installing Xen.  Assuming migration
  538: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
  539: install the xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz
  540: to /.
  542: Ensure that the contents of /etc/rc.d/xen* are correct.  Specifically,
  543: they must match the package you just installed and not be left over
  544: from some previous installation.
  546: Enable the correct set of daemons; see the configuring section above.
  547: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
  549: Ensure that the domU config files are valid for the new version.
  550: Specifically, for 4.x remove autorestart=True, and ensure that disks
  551: are specified with numbers as the second argument, as the examples
  552: above show, and not NetBSD device names.
  554: Hardware known to work
  555: ----------------------
  557: Arguably, this section is misplaced, and there should be a page of
  558: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
  559: assumption that NetBSD/xen runs fine on any modern hardware that
  560: NetBSD/amd64 runs well on.  Until then, we give motherboard/CPU (and
  561: sometimes RAM) pairs/triples to aid those choosing a motherboard.
  562: Note that Xen systems usually do not run X, so a listing here does not
  563: imply that X works at all.
  565:         Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
  566:         Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
  567:         ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
  569: Older hardware:
  571:         Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
  572:         INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU     E6850  @ 3.00GHz"
  573:         INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU     E8400  @ 3.00GHz"
  575: Running Xen under qemu
  576: ----------------------
  578: The astute reader will note that this section is somewhat twisted.
  579: However, it can be useful to run Xen under qemu either because the
  580: version of NetBSD as a dom0 does not run on the hardware in use, or to
  581: generate automated test cases involving Xen.
  583: In 2015-01, the following combination was reported to mostly work:
  585:         host OS: NetBSD/amd64 6.1.4
  586:         qemu: 2.2.0 from pkgsrc
  587:         Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
  588:         dom0 kernel: NetBSD/amd64 6.1.5
  589:         Xen tools: xentools42-4.2.5 from pkgsrc
  591: See [PR 47720]( for a problem with dom0
  592: shutdown.
  594: Unprivileged domains (domU)
  595: ===========================
  597: This section describes general concepts about domUs.  It does not
  598: address specific domU operating systems or how to install them.  The
  599: config files for domUs are typically in /usr/pkg/etc/xen, and are
  600: typically named so that the file name, domU name and the domU's host
  601: name match.
  603: The domU is provided with CPU and memory by Xen, configured by the
  604: dom0.  The domU is provided with disk and network by the dom0,
  605: mediated by Xen, and configured in the dom0.
  607: Entropy in domUs can be an issue; physical disks and network are on
  608: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  610: Config files
  611: ------------
  613: There is no good order to present config files and the concepts
  614: surrounding what is being configured.  We first show an example config
  615: file, and then in the various sections give details.
  617: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
  618: for a large number of well-commented examples, mostly for running
  619: GNU/Linux.
  621: The following is an example minimal domain configuration file
  622: "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual
  623: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
  624: i386 domU).  The domU serves as a network file server.
  626:         # -*- mode: python; -*-
  628:         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  629:         memory = 1024
  630:         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  631:         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  632:                  'file:/n0/xen/foo-wd1,0x1,w' ]
  634: The domain will have the same name as the file.  The kernel has the
  635: host/domU name in it, so that on the dom0 one can update the various
  636: domUs independently.  The vif line causes an interface to be provided,
  637: with a specific mac address (do not reuse MAC addresses!), in bridge
  638: mode.  Two disks are provided, and they are both writable; the bits
  639: are stored in files and Xen attaches them to a vnd(4) device in the
  640: dom0 on domain creation.  The system treats xbd0 as the boot device
  641: without needing explicit configuration.
  643: By default xm looks for domain config files in /usr/pkg/etc/xen.  Note
  644: that "xm create" takes the name of a config file, while other commands
  645: take the name of a domain.  To create the domain, connect to the
  646: console, create the domain while attaching the console, shutdown the
  647: domain, and see if it has finished stopping, do (or xl with Xen >=
  648: 4.2):
  650:         xm create foo
  651:         xm console foo
  652:         xm create -c foo
  653:         xm shutdown foo
  654:         xm list
  656: Typing ^] will exit the console session.  Shutting down a domain is
  657: equivalent to pushing the power button; a NetBSD domU will receive a
  658: power-press event and do a clean shutdown.  Shutting down the dom0
  659: will trigger controlled shutdowns of all configured domUs.
  661: domU kernels
  662: ------------
  664: On a physical computer, the BIOS reads sector 0, and a chain of boot
  665: loaders finds and loads a kernel.  Normally this comes from the root
  666: file system.  With Xen domUs, the process is totally different.  The
  667: normal path is for the domU kernel to be a file in the dom0's
  668: file system.  At the request of the dom0, Xen loads that kernel into a
  669: new domU instance and starts execution.  While domU kernels can be
  670: anyplace, reasonable places to store domU kernels on the dom0 are in /
  671: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
  672: config files), or in /u0/xen (where the vdisks are).
  674: Note that loading the domU kernel from the dom0 implies that boot
  675: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  676: See the VPS section near the end for discussion of alternate ways to
  677: obtain domU kernels.
  679: CPU and memory
  680: --------------
  682: A domain is provided with some number of vcpus, less than the number
  683: of CPUs seen by the hypervisor.  (For a dom0, this is controlled by
  684: the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled
  685: from the config file by the "vcpus = N" directive.
  687: A domain is provided with memory; this is controlled in the config
  688: file by "memory = N" (in megabytes).  In the straightforward case, the
  689: sum of the the memory allocated to the dom0 and all domUs must be less
  690: than the available memory.
  692: Xen also provides a "balloon" driver, which can be used to let domains
  693: use more memory temporarily.  TODO: Explain better, and explain how
  694: well it works with NetBSD.
  696: Virtual disks
  697: -------------
  699: With the file/vnd style, typically one creates a directory,
  700: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  701: domUs.  Then, for each domU disk, one writes zeros to a file that then
  702: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  703: for the first virtual disk for the domU called foo.  Writing zeros to
  704: the file serves two purposes.  One is that preallocating the contents
  705: improves performance.  The other is that vnd on sparse files has
  706: failed to work.  TODO: give working/notworking NetBSD versions for
  707: sparse vnd and gnats reference.  Note that the use of file/vnd for Xen
  708: is not really different than creating a file-backed virtual disk for
  709: some other purpose, except that xentools handles the vnconfig
  710: commands.  To create an empty 4G virtual disk, simply do
  712:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  714: Do not use qemu-img-xen, because this will create sparse file.  There
  715: have been recent (2015) reports of sparse vnd(4) devices causing
  716: lockups, but there is apparently no PR.
  718: With the lvm style, one creates logical devices.  They are then used
  719: similarly to vnds.  TODO: Add an example with lvm.
  721: In domU config files, the disks are defined as a sequence of 3-tuples.
  722: The first element is "method:/path/to/disk".  Common methods are
  723: "file:" for file-backed vnd. and "phy:" for something that is already
  724: a (TODO: character or block) device.
  726: The second element is an artifact of how virtual disks are passed to
  727: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  728: are given a device name to associate with the disk, and values like
  729: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  730: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  731: second argument.  The name given is converted to a major/minor by
  732: calling stat(2) on the name in /dev and this is passed to the domU.
  733: In the general case, the dom0 and domU can be different operating
  734: systems, and it is an unwarranted assumption that they have consistent
  735: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  736: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  737: for the second works fine and avoids this issue.  For a GNU/Linux
  738: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  739: /dev/hda1.
  741: The third element is "w" for writable disks, and "r" for read-only
  742: disks.
  744: Note that NetBSD by default creates only vnd[0123].  If you need more
  745: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  746: dom0.
  748: Note that NetBSD by default creates only xbd[0123].  If you need more
  749: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  751: Virtual Networking
  752: ------------------
  754: Xen provides virtual Ethernets, each of which connects the dom0 and a
  755: domU.  For each virtual network, there is an interface "xvifN.M" in
  756: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  757: name).  The interfaces behave as if there is an Ethernet with two
  758: adapters connected.  From this primitive, one can construct various
  759: configurations.  We focus on two common and useful cases for which
  760: there are existing scripts: bridging and NAT.
  762: With bridging (in the example above), the domU perceives itself to be
  763: on the same network as the dom0.  For server virtualization, this is
  764: usually best.  Bridging is accomplished by creating a bridge(4) device
  765: and adding the dom0's physical interface and the various xvifN.0
  766: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  767: config file.  The bridge must be set up already in the dom0; an
  768: example /etc/ifconfig.bridge0 is:
  770:         create
  771:         up
  772:         !brconfig bridge0 add wm0
  774: With NAT, the domU perceives itself to be behind a NAT running on the
  775: dom0.  This is often appropriate when running Xen on a workstation.
  776: TODO: NAT appears to be configured by "vif = [ '' ]".
  778: The MAC address specified is the one used for the interface in the new
  779: domain.  The interface in dom0 will use this address XOR'd with
  780: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  782: Sizing domains
  783: --------------
  785: Modern x86 hardware has vast amounts of resources.  However, many
  786: virtual servers can function just fine on far less.  A system with
  787: 512M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  788: far easier to adjust virtual resources than physical ones.  For
  789: memory, it's just a config file edit and a reboot.  For disk, one can
  790: create a new file and vnconfig it (or lvm), and then dump/restore,
  791: just like updating physical disks, but without having to be there and
  792: without those pesky connectors.
  794: Starting domains automatically
  795: ------------------------------
  797: To start domains foo at bar at boot and shut them down cleanly on dom0
  798: shutdown, in rc.conf add:
  800:         xendomains="foo bar"
  802: Note that earlier versions of the xentools41 xendomains rc.d script
  803: used xl, when one should use xm with 4.1.
  805: Creating specific unprivileged domains (domU)
  806: =============================================
  808: Creating domUs is almost entirely independent of operating system.  We
  809: have already presented the basics of config files.  Note that you must
  810: have already completed the dom0 setup so that "xl list" (or "xm list")
  811: works.
  813: Creating an unprivileged NetBSD domain (domU)
  814: ---------------------------------------------
  816: See the earlier config file, and adjust memory.  Decide on how much
  817: storage you will provide, and prepare it (file or lvm).
  819: While the kernel will be obtained from the dom0 file system, the same
  820: file should be present in the domU as /netbsd so that tools like
  821: savecore(8) can work.   (This is helpful but not necessary.)
  823: The kernel must be specifically for Xen and for use as a domU.  The
  824: i386 and amd64 provide the following kernels:
  826:         i386 XEN3_DOMU
  827:         i386 XEN3PAE_DOMU
  828:         amd64 XEN3_DOMU
  830: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
  831: use the PAE version of the i386 kernel.
  833: This will boot NetBSD, but this is not that useful if the disk is
  834: empty.  One approach is to unpack sets onto the disk outside of xen
  835: (by mounting it, just as you would prepare a physical disk for a
  836: system you can't run the installer on).
  838: A second approach is to run an INSTALL kernel, which has a miniroot
  839: and can load sets from the network.  To do this, copy the INSTALL
  840: kernel to / and change the kernel line in the config file to:
  842:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  844: Then, start the domain as "xl create -c configname".
  846: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  847: line should be used in the config file.
  849:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  851: After booting the domain, the option to install via CDROM may be
  852: selected.  The CDROM device should be changed to `xbd1d`.
  854: Once done installing, "halt -p" the new domain (don't reboot or halt,
  855: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  856: config file), switch the config file back to the XEN3_DOMU kernel,
  857: and start the new domain again. Now it should be able to use "root on
  858: xbd0a" and you should have a, functional NetBSD domU.
  860: TODO: check if this is still accurate.
  861: When the new domain is booting you'll see some warnings about *wscons*
  862: and the pseudo-terminals. These can be fixed by editing the files
  863: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  864: `/etc/ttys`, except *console*, like this:
  866:     console "/usr/libexec/getty Pc"         vt100   on secure
  867:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  868:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  869:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  870:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  872: Finally, all screens must be commented out from `/etc/wscons.conf`.
  874: It is also desirable to add
  876:         powerd=YES
  878: in rc.conf. This way, the domain will be properly shut down if
  879: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  881: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  882: file system.  However, various programs (e.g. netstat) will use that
  883: kernel to look up symbols to read from kernel virtual memory.  If
  884: /netbsd is not the running kernel, those lookups will fail.  (This is
  885: not really a Xen-specific issue, but because the domU kernel is
  886: obtained from the dom0, it is far more likely to be out of sync or
  887: missing with Xen.)
  889: Creating an unprivileged Linux domain (domU)
  890: --------------------------------------------
  892: Creating unprivileged Linux domains isn't much different from
  893: unprivileged NetBSD domains, but there are some details to know.
  895: First, the second parameter passed to the disk declaration (the '0x1' in
  896: the example below)
  898:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  900: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  901: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  902: So, hda1 which has major 3 and minor 1 on a Linux system will have
  903: device number 0x301.  Alternatively, devices names can be used (hda,
  904: hdb, ...)  as xentools has a table to map these names to devices
  905: numbers.  To export a partition to a Linux guest we can use:
  907:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  908:         root = "/dev/hda1 ro"
  910: and it will appear as /dev/hda on the Linux system, and be used as root
  911: partition.
  913: To install the Linux system on the partition to be exported to the
  914: guest domain, the following method can be used: install
  915: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  916: that will be the root partition of your Linux domain, and mount it.
  917: Then copy the files from a working Linux system, make adjustments in
  918: `/etc` (fstab, network config).  It should also be possible to extract
  919: binary packages such as .rpm or .deb directly to the mounted partition
  920: using the appropriate tool, possibly running under NetBSD's Linux
  921: emulation.  Once the file system has been populated, umount it.  If
  922: desirable, the file system can be converted to ext3 using tune2fs -j.
  923: It should now be possible to boot the Linux guest domain, using one of
  924: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  926: To get the Linux console right, you need to add:
  928:     extra = "xencons=tty1"
  930: to your configuration since not all Linux distributions auto-attach a
  931: tty to the xen console.
  933: Creating an unprivileged Solaris domain (domU)
  934: ----------------------------------------------
  936: See possibly outdated
  937: [Solaris domU instructions](/ports/xen/howto-solaris/).
  940: PCI passthrough: Using PCI devices in guest domains
  941: ---------------------------------------------------
  943: The dom0 can give other domains access to selected PCI
  944: devices. This can allow, for example, a non-privileged domain to have
  945: access to a physical network interface or disk controller.  However,
  946: keep in mind that giving a domain access to a PCI device most likely
  947: will give the domain read/write access to the whole physical memory,
  948: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  949: device.  Also, it's not possible to export ISA devices to non-dom0
  950: domains, which means that the primary VGA adapter can't be exported.
  951: A guest domain trying to access the VGA registers will panic.
  953: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  954: not been ported to later versions at this time.
  956: For a PCI device to be exported to a domU, is has to be attached to
  957: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  958: pciback.hide boot parameter will attach to "pciback" instead of the
  959: usual driver.  The list of devices is specified as "(bus:dev.func)",
  960: where bus and dev are 2-digit hexadecimal numbers, and func a
  961: single-digit number:
  963:         pciback.hide=(00:0a.0)(00:06.0)
  965: pciback devices should show up in the dom0's boot messages, and the
  966: devices should be listed in the `/kern/xen/pci` directory.
  968: PCI devices to be exported to a domU are listed in the "pci" array of
  969: the domU's config file, with the format "0000:bus:dev.func".
  971:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  973: In the domU an "xpci" device will show up, to which one or more pci
  974: buses will attach.  Then the PCI drivers will attach to PCI buses as
  975: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  976: or any PCI drivers built in by default; you have to build your own
  977: kernel to use PCI devices in a domU.  Here's a kernel config example;
  978: note that only the "xpci" lines are unusual.
  980:         include         "arch/i386/conf/XEN3_DOMU"
  982:         # Add support for PCI buses to the XEN3_DOMU kernel
  983:         xpci* at xenbus ?
  984:         pci* at xpci ?
  986:         # PCI USB controllers
  987:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  989:         # USB bus support
  990:         usb*    at uhci?
  992:         # USB Hubs
  993:         uhub*   at usb?
  994:         uhub*   at uhub? port ? configuration ? interface ?
  996:         # USB Mass Storage
  997:         umass*  at uhub? port ? configuration ? interface ?
  998:         wd*     at umass?
  999:         # SCSI controllers
 1000:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
 1002:         # SCSI bus support (for both ahc and umass)
 1003:         scsibus* at scsi?
 1005:         # SCSI devices
 1006:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
 1007:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
 1010: NetBSD as a domU in a VPS
 1011: =========================
 1013: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
 1014: hardware.  This section explains how to deal with Xen in a domU as a
 1015: virtual private server where you do not control or have access to the
 1016: dom0.  This is not intended to be an exhaustive list of VPS providers;
 1017: only a few are mentioned that specifically support NetBSD.
 1019: VPS operators provide varying degrees of access and mechanisms for
 1020: configuration.  The big issue is usually how one controls which kernel
 1021: is booted, because the kernel is nominally in the dom0 file system (to
 1022: which VPS users do not normally have access).  A second issue is how
 1023: to install NetBSD.
 1024: A VPS user may want to compile a kernel for security updates, to run
 1025: npf, run IPsec, or any other reason why someone would want to change
 1026: their kernel.
 1028: One approach is to have an administrative interface to upload a kernel,
 1029: or to select from a prepopulated list.  Other approaches are pygrub
 1030: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
 1031: kernel from the domU file system.  This is closer to a regular physical
 1032: computer, where someone who controls a machine can replace the kernel.
 1034: A second issue is multiple CPUs.  With NetBSD 6, domUs support
 1035: multiple vcpus, and it is typical for VPS providers to enable multiple
 1036: CPUs for NetBSD domUs.
 1038: pygrub
 1039: -------
 1041: pygrub runs in the dom0 and looks into the domU file system.  This
 1042: implies that the domU must have a kernel in a file system in a format
 1043: known to pygrub.  As of 2014, pygrub seems to be of mostly historical
 1044: interest.
 1046: pvgrub
 1047: ------
 1049: pvgrub is a version of grub that uses PV operations instead of BIOS
 1050: calls.  It is booted from the dom0 as the domU kernel, and then reads
 1051: /grub/menu.lst and loads a kernel from the domU file system.
 1053: [Panix]( lets users use pvgrub.  Panix reports
 1054: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
 1055: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
 1056: page](, which describes only
 1057: Linux but should be updated to cover NetBSD :-).
 1059: []( also lets users with pvgrub to boot
 1060: their own kernel.  See then [ NetBSD
 1061: HOWTO](
 1062: (which is in need of updating).
 1064: It appears that [grub's FFS
 1065: code](
 1066: does not support all aspects of modern FFS, but there are also reports
 1067: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
 1068: partition for the kernel with the intent that grub can understand it,
 1069: which leads to /netbsd not being the actual kernel.  One must remember
 1070: to update the special boot partition.
 1072: Amazon
 1073: ------
 1075: See the [Amazon EC2 page](/amazon_ec2/).
 1077: TODO items for improving NetBSD/xen
 1078: ===================================
 1080: * Make the NetBSD dom0 kernel work with SMP.
 1081: * Test the Xen 4.5 packages adequately to be able to recommend them as
 1082:   the standard approach.
 1083: * Get PCI passthrough working on Xen 4.5
 1084: * Get pvgrub into pkgsrc, either via xentools or separately.
 1085: * grub
 1086:   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
 1087:     fragsize/blocksize (UFS2 support may be present; the point is to
 1088:     make it so that with any UFS1/UFS2 file system setup that works
 1089:     with NetBSD grub will also work).
 1090:     See [pkg/40258](
 1091:   * Push patches upstream.
 1092:   * Get UFS2 patches into pvgrub.
 1093: * Add support for PV ops to a version of /boot, and make it usable as
 1094:   a kernel in Xen, similar to pvgrub.
 1096: Random pointers
 1097: ===============
 1099: This section contains links from elsewhere not yet integrated into the
 1100: HOWTO, and other guides.
 1102: *
 1103: *
 1104: *

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