File:  [NetBSD Developer Wiki] / wikisrc / ports / xen / howto.mdwn
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Sat Jan 17 13:11:49 2015 UTC (7 years, 4 months ago) by gdt
Branches: MAIN
CVS tags: HEAD
add xen/qemu example

    1: Introduction
    2: ============
    4: [![[Xen
    5: screenshot]](](
    7: Xen is a hypervisor (or virtual machine monitor) for x86 hardware
    8: (i686-class or higher), which supports running multiple guest
    9: operating systems on a single physical machine.  Xen is a Type 1 or
   10: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
   11: memory and console, a dom0 operating system which mediates access to
   12: other hardware (e.g., disks, network, USB), and one or more domU
   13: operating systems which operate in an unprivileged virtualized
   14: environment.  IO requests from the domU systems are forwarded by the
   15: hypervisor (Xen) to the dom0 to be fulfilled.
   17: Xen supports two styles of guests.  The original is Para-Virtualized
   18: (PV) which means that the guest OS does not attempt to access hardware
   19: directly, but instead makes hypercalls to the hypervisor.  This is
   20: analogous to a user-space program making system calls.  (The dom0
   21: operating system uses PV calls for some functions, such as updating
   22: memory mapping page tables, but has direct hardware access for disk
   23: and network.)   PV guests must be specifically coded for Xen.
   25: The more recent style is HVM, which means that the guest does not have
   26: code for Xen and need not be aware that it is running under Xen.
   27: Attempts to access hardware registers are trapped and emulated.  This
   28: style is less efficient but can run unmodified guests.
   30: Generally any amd64 machine will work with Xen and PV guests.  In
   31: theory i386 computers without amd64 support can be used for Xen <=
   32: 4.2, but we have no recent reports of this working (this is a hint).
   33: For HVM guests, the VT or VMX cpu feature (Intel) or SVM/HVM/VT
   34: (amd64) is needed; "cpuctl identify 0" will show this.  TODO: Clean up
   35: and check the above features.
   37: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   38: The dom0 can start one or more domUs.  (Booting is explained in detail
   39: in the dom0 section.)
   41: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
   42: and that Xen kernels and tools are available in pkgsrc.  This HOWTO
   43: attempts to address both the case of running a NetBSD dom0 on hardware
   44: and running domUs under it (NetBSD and other), and also running NetBSD
   45: as a domU in a VPS.
   47: Some versions of Xen support "PCI passthrough", which means that
   48: specific PCI devices can be made available to a specific domU instead
   49: of the dom0.  This can be useful to let a domU run X11, or access some
   50: network interface or other peripheral.
   52: NetBSD used to support Xen2; this has been removed.
   54: Prerequisites
   55: -------------
   57: Installing NetBSD/Xen is not extremely difficult, but it is more
   58: complex than a normal installation of NetBSD.
   59: In general, this HOWTO is occasionally overly restrictive about how
   60: things must be done, guiding the reader to stay on the established
   61: path when there are no known good reasons to stray.
   63: This HOWTO presumes a basic familiarity with the Xen system
   64: architecture.  This HOWTO presumes familiarity with installing NetBSD
   65: on i386/amd64 hardware and installing software from pkgsrc.
   66: See also the [Xen website](
   68: Versions of Xen and NetBSD
   69: ==========================
   71: Most of the installation concepts and instructions are independent
   72: of Xen version and NetBSD version.  This section gives advice on
   73: which version to choose.  Versions not in pkgsrc and older unsupported
   74: versions of NetBSD are intentionally ignored.
   76: Xen
   77: ---
   79: In NetBSD, xen is provided in pkgsrc, via matching pairs of packages
   80: xenkernel and xentools.  We will refer only to the kernel versions,
   81: but note that both packages must be installed together and must have
   82: matching versions.
   84: xenkernel3 and xenkernel33 provide Xen 3.1 and 3.3.  These no longer
   85: receive security patches and should not be used.  Xen 3.1 supports PCI
   86: passthrough.  Xen 3.1 supports non-PAE on i386.
   88: xenkernel41 provides Xen 4.1.  This is no longer maintained by Xen,
   89: but as of 2014-12 receives backported security patches.  It is a
   90: reasonable although trailing-edge choice.
   92: xenkernel42 provides Xen 4.2.  This is maintained by Xen, but old as
   93: of 2014-12.
   95: Ideally newer versions of Xen will be added to pkgsrc.
   97: Note that NetBSD support is called XEN3.  It works with 3.1 through
   98: 4.2 because the hypercall interface has been stable.
  100: Xen command program
  101: -------------------
  103: Early Xen used a program called xm to manipulate the system from the
  104: dom0.  Starting in 4.1, a replacement program with similar behavior
  105: called xl is provided, but it does not work well in 4.1.  In 4.2, both
  106: xm and xl work fine.  4.4 is the last version that has xm.  You must
  107: choose one or the other, because it affects which daemons you run.
  109: NetBSD
  110: ------
  112: The netbsd-5, netbsd-6, netbsd-7, and -current branches are all
  113: reasonable choices, with more or less the same considerations for
  114: non-Xen use.  Therefore, netbsd-6 is recommended as the stable version
  115: of the most recent release for production use.  For those wanting to
  116: learn Xen or without production stability concerns, netbsd-7 is likely
  117: most appropriate.
  119: As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
  120: no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
  121: need SMP; the lack of support is really a problem when using a dom0 as
  122: a normal computer.)
  124: Architecture
  125: ------------
  127: Xen itself can run on i386 or amd64 machines.  (Practically, almost
  128: any computer where one would want to run Xen supports amd64.)  If
  129: using an i386 NetBSD kernel for the dom0, PAE is required (PAE
  130: versions are built by default).  While i386 dom0 works fine, amd64 is
  131: recommended as more normal.
  133: Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify
  134: if this is about the CPU having to be amd64, or about the dom0 kernel
  135: having to be amd64.
  137: One can then run i386 domUs and amd64 domUs, in any combination.  If
  138: running an i386 NetBSD kernel as a domU, the PAE version is required.
  139: (Note that emacs (at least) fails if run on i386 with PAE when built
  140: without, and vice versa, presumably due to bugs in the undump code.)
  142: Recommendation
  143: --------------
  145: Therefore, this HOWTO recommends running xenkernel42 (and xentools42),
  146: xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the
  147: dom0.  Either the i386 or amd64 of NetBSD may be used as domUs.
  149: Build problems
  150: --------------
  152: Ideally, all versions of Xen in pkgsrc would build on all versions of
  153: NetBSD on both i386 and amd64.  However, that isn't the case.  Besides
  154: aging code and aging compilers, qemu (included in xentools for HVM
  155: support) is difficult to build.  The following are known to work or FAIL:
  157:         xenkernel3 netbsd-5 amd64
  158:         xentools3 netbsd-5 amd64
  159:         xentools3=hvm netbsd-5 amd64 ????
  160:         xenkernel33 netbsd-5 amd64
  161:         xentools33 netbsd-5 amd64
  162:         xenkernel41 netbsd-5 amd64
  163:         xentools41 netbsd-5 amd64
  164:         xenkernel42 netbsd-5 amd64
  165:         xentools42 netbsd-5 amd64
  167:         xenkernel3 netbsd-6 i386 FAIL
  168:         xentools3 netbsd-6 i386
  169:         xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
  170:         xenkernel33 netbsd-6 i386
  171:         xentools33 netbsd-6 i386
  172:         xenkernel41 netbsd-6 i386
  173:         xentools41 netbsd-6 i386
  174:         xenkernel42 netbsd-6 i386
  175:         xentools42 netbsd-6 i386 *MIXED
  177: 	(all 3 and 33 seem to FAIL)
  178:         xenkernel41 netbsd-7 i386
  179:         xentools41 netbsd-7 i386
  180:         xenkernel42 netbsd-7 i386
  181:         xentools42 netbsd-7 i386 ??FAIL
  183: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
  184: but it does not build for gdt.)
  186: NetBSD as a dom0
  187: ================
  189: NetBSD can be used as a dom0 and works very well.  The following
  190: sections address installation, updating NetBSD, and updating Xen.
  191: Note that it doesn't make sense to talk about installing a dom0 OS
  192: without also installing Xen itself.  We first address installing
  193: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
  194: NetBSD install to a dom0 install by just changing the kernel and boot
  195: configuration.
  197: For experimenting with Xen, a machine with as little as 1G of RAM and
  198: 100G of disk can work.  For running many domUs in productions, far
  199: more will be needed.
  201: Styles of dom0 operation
  202: ------------------------
  204: There are two basic ways to use Xen.  The traditional method is for
  205: the dom0 to do absolutely nothing other than providing support to some
  206: number of domUs.  Such a system was probably installed for the sole
  207: purpose of hosting domUs, and sits in a server room on a UPS.
  209: The other way is to put Xen under a normal-usage computer, so that the
  210: dom0 is what the computer would have been without Xen, perhaps a
  211: desktop or laptop.  Then, one can run domUs at will.  Purists will
  212: deride this as less secure than the previous approach, and for a
  213: computer whose purpose is to run domUs, they are right.  But Xen and a
  214: dom0 (without domUs) is not meaingfully less secure than the same
  215: things running without Xen.  One can boot Xen or boot regular NetBSD
  216: alternately with little problems, simply refraining from starting the
  217: Xen daemons when not running Xen.
  219: Note that NetBSD as dom0 does not support multiple CPUs.  This will
  220: limit the performance of the Xen/dom0 workstation approach.  In theory
  221: the only issue is that the "backend drivers" are not yet MPSAFE:
  224: Installation of NetBSD
  225: ----------------------
  227: First,
  228: [install NetBSD/amd64](/guide/inst/)
  229: just as you would if you were not using Xen.
  230: However, the partitioning approach is very important.
  232: If you want to use RAIDframe for the dom0, there are no special issues
  233: for Xen.  Typically one provides RAID storage for the dom0, and the
  234: domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
  235: over a RAID1 header to find /boot from a filesystem within a RAID
  236: partition; this is no different when booting Xen.
  238: There are 4 styles of providing backing storage for the virtual disks
  239: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN,
  241: With raw partitions, one has a disklabel (or gpt) partition sized for
  242: each virtual disk to be used by the domU.  (If you are able to predict
  243: how domU usage will evolve, please add an explanation to the HOWTO.
  244: Seriously, needs tend to change over time.)
  246: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
  247: for domU disks.  This is almost as efficient as raw disk partitions
  248: and more flexible.  Hence raw disk partitions should typically not
  249: be used.
  251: One can use files in the dom0 filesystem, typically created by dd'ing
  252: /dev/zero to create a specific size.  This is somewhat less efficient,
  253: but very convenient, as one can cp the files for backup, or move them
  254: between dom0 hosts.
  256: Finally, in theory one can place the files backing the domU disks in a
  257: SAN.  (This is an invitation for someone who has done this to add a
  258: HOWTO page.)
  260: Installation of Xen
  261: -------------------
  263: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
  264: pkgsrc (or another matching pair).
  265: See [the pkgsrc
  266: documentation]( for help with pkgsrc.
  268: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More
  269: recent versions have HVM support integrated in the main xentools
  270: package.  It is entirely reasonable to run only PV guests.
  272: Next you need to install the selected Xen kernel itself, which is
  273: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.
  274: For debugging, one may copy xen-debug.gz; this is conceptually similar
  275: to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
  276: useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
  277: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
  278: of a NetBSD build.  If using i386, use
  279: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen
  280: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you
  281: should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and
  282: typically are) left compressed.
  284: In a dom0 kernel, kernfs is mandatory for xend to comunicate with the
  285: kernel, so ensure that /kern is in fstab.  TODO: Say this is default,
  286: or file a PR and give a reference.
  288: Because you already installed NetBSD, you have a working boot setup
  289: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
  290: beginning of your root filesystem, /boot present, and likely
  291: /boot.cfg.  (If not, fix before continuing!)
  293: Add a line to to /boot.cfg to boot Xen.  See boot.cfg(5) for an
  294: example.  The basic line is
  296:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  298: which specifies that the dom0 should have 256M, leaving the rest to be
  299: allocated for domUs.  To use a serial console, use
  301:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
  303: which will use the first serial port for Xen (which counts starting
  304: from 1), forcing speed/parity, and also for NetBSD (which counts
  305: starting at 0).  In an attempt to add performance, one can also add
  307:         dom0_max_vcpus=1 dom0_vcpus_pin
  309: to force only one vcpu to be provided (since NetBSD dom0 can't use
  310: more) and to pin that vcpu to a physical cpu.  TODO: benchmark this.
  312: As with non-Xen systems, you should have a line to boot /netbsd (a
  313: kernel that works without Xen) and fallback versions of the non-Xen
  314: kernel, Xen, and the dom0 kernel.
  316: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  317: than GENERIC without Xen.
  319: Using grub (historic)
  320: ---------------------
  322: Before NetBSD's native bootloader could support Xen, the use of
  323: grub was recommended.  If necessary, see the
  324: [old grub information](/ports/xen/howto-grub/).
  326: The [HowTo on Installing into
  327: RAID-1](
  328: explains how to set up booting a dom0 with Xen using grub with
  329: NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
  330: boot.)
  332: Configuring Xen
  333: ---------------
  335: Xen logs will be in /var/log/xen.
  337: Now, you have a system that will boot Xen and the dom0 kernel, but not
  338: do anything else special.  Make sure that you have rebooted into Xen.
  339: There will be no domUs, and none can be started because you still have
  340: to configure the dom0 tools.  The daemons which should be run vary
  341: with Xen version and with whether one is using xm or xl.  Note that
  342: xend is for supporting "xm", and should only be used if you plan on
  343: using "xm".  Do NOT enable xend if you plan on using "xl" as it will
  344: cause problems.
  346: The installation of NetBSD should already have created devices for xen
  347: (xencons, xenevt), but if they are not present, create them:
  349:         cd /dev && sh MAKEDEV xen
  351: TODO: Give 3.1 advice (or remove it from pkgsrc).
  353: For 3.3 (and thus xm), add to rc.conf (but note that you should have
  354: installed 4.1 or 4.2):
  356:         xend=YES
  357:         xenbackendd=YES
  359: For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
  361:         xencommons=YES
  362:         xend=YES
  364: (If you are using xentools41 from before 2014-12-26, change
  365: rc.d/xendomains to use xm rather than xl.)
  367: For 4.2 with xm, add to rc.conf
  369:         xencommons=YES
  370:         xend=YES
  372: For 4.2 with xl, add to rc.conf:
  374:         xencommons=YES
  375:         TODO: explain if there is a xend replacement
  377: TODO: Recommend for/against xen-watchdog.
  379: After you have configured the daemons and either started them (in the
  380: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
  381: available resources, and running domains.  An example with xm follows:
  383:         # xm dmesg
  384: 	[xen's boot info]
  385:         # xm info
  386: 	[available memory, etc.]
  387:         # xm list
  388:         Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  389:         Domain-0           0       64    0  r----     58.1
  391: With xl, the commands are the same, and the output may be slightly
  392: different.  TODO: add example output for xl, after confirming on 4.2
  393: and resolving the TODO about rc.conf.
  395: anita (for testing NetBSD)
  396: --------------------------
  398: With the setup so far (assuming 4.2/xl), one should be able to run
  399: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  400: root, because anita must create a domU):
  402:         anita --vmm=xl test file:///usr/obj/i386/
  404: Alternatively, one can use --vmm=xm to use xm-based domU creation
  405: instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.
  407: Xen-specific NetBSD issues
  408: --------------------------
  410: There are (at least) two additional things different about NetBSD as a
  411: dom0 kernel compared to hardware.
  413: One is that modules are not usable in DOM0 kernels, so one must
  414: compile in what's needed.  It's not really that modules cannot work,
  415: but that modules must be built for XEN3_DOM0 because some of the
  416: defines change and the normal module builds don't do this.  Basically,
  417: enabling Xen changes the kernel ABI, and the module build system
  418: doesn't cope with this.
  420: The other difference is that XEN3_DOM0 does not have exactly the same
  421: options as GENERIC.  While it is debatable whether or not this is a
  422: bug, users should be aware of this and can simply add missing config
  423: items if desired.
  425: Updating NetBSD in a dom0
  426: -------------------------
  428: This is just like updating NetBSD on bare hardware, assuming the new
  429: version supports the version of Xen you are running.  Generally, one
  430: replaces the kernel and reboots, and then overlays userland binaries
  431: and adjusts /etc.
  433: Note that one must update both the non-Xen kernel typically used for
  434: rescue purposes and the DOM0 kernel used with Xen.
  436: Converting from grub to /boot
  437: -----------------------------
  439: These instructions were [TODO: will be] used to convert a system from
  440: grub to /boot.  The system was originally installed in February of
  441: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  442: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  443: 4.1 and grub, much like the message linked earlier in the grub
  444: section.
  446:         # Install mbr bootblocks on both disks. 
  447:         fdisk -i /dev/rwd0d
  448:         fdisk -i /dev/rwd1d
  449:         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  450:         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  451:         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  452:         # Install secondary boot loader
  453:         cp -p /usr/mdec/boot /
  454:         # Create boog.cfg following earlier guidance:
  455:         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  456:         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
  457:         menu=GENERIC:boot
  458:         menu=GENERIC single-user:boot -s
  459:         menu=GENERIC.ok:boot netbsd.ok
  460:         menu=GENERIC.ok single-user:boot netbsd.ok -s
  461:         menu=Drop to boot prompt:prompt
  462:         default=1
  463:         timeout=30
  465: TODO: actually do this and fix it if necessary.
  467: Updating Xen versions
  468: ---------------------
  470: Updating Xen is conceptually not difficult, but can run into all the
  471: issues found when installing Xen.  Assuming migration from 4.1 to 4.2,
  472: remove the xenkernel41 and xentools41 packages and install the
  473: xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz to /.
  475: Ensure that the contents of /etc/rc.d/xen* are correct.  Enable the
  476: correct set of daemons.  Ensure that the domU config files are valid
  477: for the new version.
  480: Running Xen under qemu
  481: ----------------------
  483: The astute reader will note that this section is somewhat twisted.
  484: However, it can be useful to run Xen under qemu either because the
  485: version of NetBSD as a dom0 does not run on the hardware in use, or to
  486: generate automated test cases involving Xen.
  488: In 2015-01, the following combination was reported to work:
  490:         host OS: NetBSD/amd64 6.1.4
  491:         qemu: 2.2.0 from pkgsrc
  492:         Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
  493:         dom0 kernel: NetBSD/amd64 6.1.5
  494:         Xen tools: xentools42-4.2.5 from pkgsrc
  496: Unprivileged domains (domU)
  497: ===========================
  499: This section describes general concepts about domUs.  It does not
  500: address specific domU operating systems or how to install them.  The
  501: config files for domUs are typically in /usr/pkg/etc/xen, and are
  502: typically named so that the file name, domU name and the domU's host
  503: name match.
  505: The domU is provided with cpu and memory by Xen, configured by the
  506: dom0.  The domU is provided with disk and network by the dom0,
  507: mediated by Xen, and configured in the dom0.
  509: Entropy in domUs can be an issue; physical disks and network are on
  510: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  512: Config files
  513: ------------
  515: There is no good order to present config files and the concepts
  516: surrounding what is being configured.  We first show an example config
  517: file, and then in the various sections give details.
  519: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
  520: for a large number of well-commented examples, mostly for running
  521: GNU/Linux.
  523: The following is an example minimal domain configuration file
  524: "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual
  525: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
  526: i386 domU).  The domU serves as a network file server.
  528:         # -*- mode: python; -*-
  530:         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  531:         memory = 1024
  532:         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  533:         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  534:                  'file:/n0/xen/foo-wd1,0x1,w' ]
  536: The domain will have the same name as the file.  The kernel has the
  537: host/domU name in it, so that on the dom0 one can update the various
  538: domUs independently.  The vif line causes an interface to be provided,
  539: with a specific mac address (do not reuse MAC addresses!), in bridge
  540: mode.  Two disks are provided, and they are both writable; the bits
  541: are stored in files and Xen attaches them to a vnd(4) device in the
  542: dom0 on domain creation.  The system treates xbd0 as the boot device
  543: without needing explicit configuration.
  545: By default xm looks for domain config files in /usr/pkg/etc/xen.  Note
  546: that "xm create" takes the name of a config file, while other commands
  547: take the name of a domain.  To create the domain, connect to the
  548: console, create the domain while attaching the console, shutdown the
  549: domain, and see if it has finished stopping, do (or xl with Xen >=
  550: 4.2):
  552:         xm create foo
  553:         xm console foo
  554:         xm create -c foo
  555:         xm shutdown foo
  556: 	xm list
  558: Typing ^] will exit the console session.  Shutting down a domain is
  559: equivalent to pushing the power button; a NetBSD domU will receive a
  560: power-press event and do a clean shutdown.  Shutting down the dom0
  561: will trigger controlled shutdowns of all configured domUs.
  563: domU kernels
  564: ------------
  566: On a physical computer, the BIOS reads sector 0, and a chain of boot
  567: loaders finds and loads a kernel.  Normally this comes from the root
  568: filesystem.  With Xen domUs, the process is totally different.  The
  569: normal path is for the domU kernel to be a file in the dom0's
  570: filesystem.  At the request of the dom0, Xen loads that kernel into a
  571: new domU instance and starts execution.  While domU kernels can be
  572: anyplace, reasonable places to store domU kernels on the dom0 are in /
  573: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
  574: config files), or in /u0/xen (where the vdisks are).
  576: Note that loading the domU kernel from the dom0 implies that boot
  577: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  578: See the VPS section near the end for discussion of alternate ways to
  579: obtain domU kernels.
  581: CPU and memory
  582: --------------
  584: A domain is provided with some number of vcpus, less than the number
  585: of cpus seen by the hypervisor.  (For a dom0, this is controlled by
  586: the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled
  587: from the config file by the "vcpus = N" directive.
  589: A domain is provided with memory; this is controlled in the config
  590: file by "memory = N" (in megabytes).  In the straightforward case, the
  591: sum of the the memory allocated to the dom0 and all domUs must be less
  592: than the available memory.
  594: Xen also provides a "balloon" driver, which can be used to let domains
  595: use more memory temporarily.  TODO: Explain better, and explain how
  596: well it works with NetBSD.
  598: Virtual disks
  599: -------------
  601: With the file/vnd style, typically one creates a directory,
  602: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  603: domUs.  Then, for each domU disk, one writes zeros to a file that then
  604: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  605: for the first virtual disk for the domU called foo.  Writing zeros to
  606: the file serves two purposes.  One is that preallocating the contents
  607: improves performance.  The other is that vnd on sparse files has
  608: failed to work.  TODO: give working/notworking NetBSD versions for
  609: sparse vnd.  Note that the use of file/vnd for Xen is not really
  610: different than creating a file-backed virtual disk for some other
  611: purpose, except that xentools handles the vnconfig commands.  To
  612: create an empty 4G virtual disk, simply do
  614:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  616: With the lvm style, one creates logical devices.  They are then used
  617: similarly to vnds.  TODO: Add an example with lvm.
  619: In domU config files, the disks are defined as a sequence of 3-tuples.
  620: The first element is "method:/path/to/disk".  Common methods are
  621: "file:" for file-backed vnd. and "phy:" for something that is already
  622: a (TODO: character or block) device.
  624: The second element is an artifact of how virtual disks are passed to
  625: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  626: are given a device name to associate with the disk, and values like
  627: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  628: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  629: second argument.  The name given is converted to a major/minor by
  630: calling stat(2) on the name in /dev and this is passed to the domU.
  631: In the general case, the dom0 and domU can be different operating
  632: systems, and it is an unwarranted assumption that they have consistent
  633: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  634: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  635: for the second works fine and avoids this issue.  For a GNU/Linux
  636: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  637: /dev/hda1.
  639: The third element is "w" for writable disks, and "r" for read-only
  640: disks.
  642: Virtual Networking
  643: ------------------
  645: Xen provides virtual ethernets, each of which connects the dom0 and a
  646: domU.  For each virtual network, there is an interface "xvifN.M" in
  647: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  648: name).  The interfaces behave as if there is an Ethernet with two
  649: adaptors connected.  From this primitive, one can construct various
  650: configurations.  We focus on two common and useful cases for which
  651: there are existing scripts: bridging and NAT.
  653: With bridging (in the example above), the domU perceives itself to be
  654: on the same network as the dom0.  For server virtualization, this is
  655: usually best.  Bridging is accomplished by creating a bridge(4) device
  656: and adding the dom0's physical interface and the various xvifN.0
  657: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  658: config file.  The bridge must be set up already in the dom0; an
  659: example /etc/ifconfig.bridge0 is:
  661:         create
  662:         up
  663:         !brconfig bridge0 add wm0
  665: With NAT, the domU perceives itself to be behind a NAT running on the
  666: dom0.  This is often appropriate when running Xen on a workstation.
  667: TODO: NAT appears to be configured by "vif = [ '' ]".
  669: The MAC address specified is the one used for the interface in the new
  670: domain.  The interface in dom0 will use this address XOR'd with
  671: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  673: Sizing domains
  674: --------------
  676: Modern x86 hardware has vast amounts of resources.  However, many
  677: virtual servers can function just fine on far less.  A system with
  678: 256M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  679: far easier to adjust virtual resources than physical ones.  For
  680: memory, it's just a config file edit and a reboot.  For disk, one can
  681: create a new file and vnconfig it (or lvm), and then dump/restore,
  682: just like updating physical disks, but without having to be there and
  683: without those pesky connectors.
  685: Starting domains automatically
  686: ------------------------------
  688: To start domains foo at bar at boot and shut them down cleanly on dom0
  689: shutdown, in rc.conf add:
  691:         xendomains="foo bar"
  693: TODO: Explain why 4.1 rc.d/xendomains has xl, when one should use xm
  694: on 4.1.  Or fix the xentools41 package to have xm
  696: Creating specific unprivileged domains (domU)
  697: =============================================
  699: Creating domUs is almost entirely independent of operating system.  We
  700: have already presented the basics of config files.  Note that you must
  701: have already completed the dom0 setup so that "xl list" (or "xm list")
  702: works.
  704: Creating an unprivileged NetBSD domain (domU)
  705: ---------------------------------------------
  707: See the earlier config file, and adjust memory.  Decide on how much
  708: storage you will provide, and prepare it (file or lvm).
  710: While the kernel will be obtained from the dom0 filesystem, the same
  711: file should be present in the domU as /netbsd so that tools like
  712: savecore(8) can work.   (This is helpful but not necessary.)
  714: The kernel must be specifically for Xen and for use as a domU.  The
  715: i386 and amd64 provide the following kernels:
  717:         i386 XEN3_DOMU
  718:         i386 XEN3PAE_DOMU
  719: 	amd64 XEN3_DOMU
  721: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
  722: use the PAE version of the i386 kernel.
  724: This will boot NetBSD, but this is not that useful if the disk is
  725: empty.  One approach is to unpack sets onto the disk outside of xen
  726: (by mounting it, just as you would prepare a physical disk for a
  727: system you can't run the installer on).
  729: A second approach is to run an INSTALL kernel, which has a miniroot
  730: and can load sets from the network.  To do this, copy the INSTALL
  731: kernel to / and change the kernel line in the config file to:
  733:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  735: Then, start the domain as "xl create -c configname".
  737: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  738: line should be used in the config file.
  740:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  742: After booting the domain, the option to install via CDROM may be
  743: selected.  The CDROM device should be changed to `xbd1d`.
  745: Once done installing, "halt -p" the new domain (don't reboot or halt,
  746: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  747: config file), switch the config file back to the XEN3_DOMU kernel,
  748: and start the new domain again. Now it should be able to use "root on
  749: xbd0a" and you should have a, functional NetBSD domU.
  751: TODO: check if this is still accurate.
  752: When the new domain is booting you'll see some warnings about *wscons*
  753: and the pseudo-terminals. These can be fixed by editing the files
  754: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  755: `/etc/ttys`, except *console*, like this:
  757:     console "/usr/libexec/getty Pc"         vt100   on secure
  758:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  759:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  760:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  761:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  763: Finally, all screens must be commented out from `/etc/wscons.conf`.
  765: It is also desirable to add
  767:         powerd=YES
  769: in rc.conf. This way, the domain will be properly shut down if
  770: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  772: Your domain should be now ready to work, enjoy.
  774: Creating an unprivileged Linux domain (domU)
  775: --------------------------------------------
  777: Creating unprivileged Linux domains isn't much different from
  778: unprivileged NetBSD domains, but there are some details to know.
  780: First, the second parameter passed to the disk declaration (the '0x1' in
  781: the example below)
  783:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  785: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  786: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  787: So, hda1 which has major 3 and minor 1 on a Linux system will have
  788: device number 0x301.  Alternatively, devices names can be used (hda,
  789: hdb, ...)  as xentools has a table to map these names to devices
  790: numbers.  To export a partition to a Linux guest we can use:
  792:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  793:         root = "/dev/hda1 ro"
  795: and it will appear as /dev/hda on the Linux system, and be used as root
  796: partition.
  798: To install the Linux system on the partition to be exported to the
  799: guest domain, the following method can be used: install
  800: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  801: that will be the root partition of your Linux domain, and mount it.
  802: Then copy the files from a working Linux system, make adjustments in
  803: `/etc` (fstab, network config).  It should also be possible to extract
  804: binary packages such as .rpm or .deb directly to the mounted partition
  805: using the appropriate tool, possibly running under NetBSD's Linux
  806: emulation.  Once the filesystem has been populated, umount it.  If
  807: desirable, the filesystem can be converted to ext3 using tune2fs -j.
  808: It should now be possible to boot the Linux guest domain, using one of
  809: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  811: To get the linux console right, you need to add:
  813:     extra = "xencons=tty1"
  815: to your configuration since not all linux distributions auto-attach a
  816: tty to the xen console.
  818: Creating an unprivileged Solaris domain (domU)
  819: ----------------------------------------------
  821: See possibly outdated
  822: [Solaris domU instructions](/ports/xen/howto-solaris/).
  825: PCI passthrough: Using PCI devices in guest domains
  826: ---------------------------------------------------
  828: The dom0 can give other domains access to selected PCI
  829: devices. This can allow, for example, a non-privileged domain to have
  830: access to a physical network interface or disk controller.  However,
  831: keep in mind that giving a domain access to a PCI device most likely
  832: will give the domain read/write access to the whole physical memory,
  833: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  834: device.  Also, it's not possible to export ISA devices to non-dom0
  835: domains, which means that the primary VGA adapter can't be exported.
  836: A guest domain trying to access the VGA registers will panic.
  838: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  839: not been ported to later versions at this time.
  841: For a PCI device to be exported to a domU, is has to be attached to
  842: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  843: pciback.hide boot parameter will attach to "pciback" instead of the
  844: usual driver.  The list of devices is specified as "(bus:dev.func)",
  845: where bus and dev are 2-digit hexadecimal numbers, and func a
  846: single-digit number:
  848:         pciback.hide=(00:0a.0)(00:06.0)
  850: pciback devices should show up in the dom0's boot messages, and the
  851: devices should be listed in the `/kern/xen/pci` directory.
  853: PCI devices to be exported to a domU are listed in the "pci" array of
  854: the domU's config file, with the format "0000:bus:dev.func".
  856:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  858: In the domU an "xpci" device will show up, to which one or more pci
  859: busses will attach.  Then the PCI drivers will attach to PCI busses as
  860: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  861: or any PCI drivers built in by default; you have to build your own
  862: kernel to use PCI devices in a domU.  Here's a kernel config example;
  863: note that only the "xpci" lines are unusual.
  865:         include         "arch/i386/conf/XEN3_DOMU"
  867:         # Add support for PCI busses to the XEN3_DOMU kernel
  868:         xpci* at xenbus ?
  869:         pci* at xpci ?
  871:         # PCI USB controllers
  872:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  874:         # USB bus support
  875:         usb*    at uhci?
  877:         # USB Hubs
  878:         uhub*   at usb?
  879:         uhub*   at uhub? port ? configuration ? interface ?
  881:         # USB Mass Storage
  882:         umass*  at uhub? port ? configuration ? interface ?
  883:         wd*     at umass?
  884:         # SCSI controllers
  885:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  887:         # SCSI bus support (for both ahc and umass)
  888:         scsibus* at scsi?
  890:         # SCSI devices
  891:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  892:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  895: NetBSD as a domU in a VPS
  896: =========================
  898: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  899: hardware.  This section explains how to deal with Xen in a domU as a
  900: virtual private server where you do not control or have access to the
  901: dom0.  This is not intended to be an exhaustive list of VPS providers;
  902: only a few are mentioned that specifically support NetBSD.
  904: VPS operators provide varying degrees of access and mechanisms for
  905: configuration.  The big issue is usually how one controls which kernel
  906: is booted, because the kernel is nominally in the dom0 filesystem (to
  907: which VPS users do not normally have acesss).  A second issue is how
  908: to install NetBSD.
  909: A VPS user may want to compile a kernel for security updates, to run
  910: npf, run IPsec, or any other reason why someone would want to change
  911: their kernel.
  913: One approach is to have an adminstrative interface to upload a kernel,
  914: or to select from a prepopulated list.  Other approaches are pygrub
  915: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  916: kernel from the domU filesystem.  This is closer to a regular physical
  917: computer, where someone who controls a machine can replace the kernel.
  919: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  920: multiple vcpus, and it is typical for VPS providers to enable multiple
  921: CPUs for NetBSD domUs.
  923: pygrub
  924: -------
  926: pygrub runs in the dom0 and looks into the domU filesystem.  This
  927: implies that the domU must have a kernel in a filesystem in a format
  928: known to pygrub.  As of 2014, pygrub seems to be of mostly historical
  929: interest.
  931: pvgrub
  932: ------
  934: pvgrub is a version of grub that uses PV operations instead of BIOS
  935: calls.  It is booted from the dom0 as the domU kernel, and then reads
  936: /grub/menu.lst and loads a kernel from the domU filesystem.
  938: [Panix]( lets users use pvgrub.  Panix reports
  939: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  940: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  941: page](, which describes only
  942: Linux but should be updated to cover NetBSD :-).
  944: []( also lets users with pvgrub to boot
  945: their own kernel.  See then [ NetBSD
  946: HOWTO](
  947: (which is in need of updating).
  949: It appears that [grub's FFS
  950: code](
  951: does not support all aspects of modern FFS, but there are also reports
  952: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  953: partition for the kernel with the intent that grub can understand it,
  954: which leads to /netbsd not being the actual kernel.  One must remember
  955: to update the special boot partiion.
  957: Amazon
  958: ------
  960: TODO: add link to NetBSD amazon howto.
  962: Using npf
  963: ---------
  965: In standard kernels, npf is a module, and thus cannot be loaded in a
  966: DOMU kernel.
  968: TODO: explain how to compile npf into a custom kernel, answering (but
  969: note that the problem was caused by not booting the right kernel):
  972: TODO items for improving NetBSD/xen
  973: ===================================
  975: * Package Xen 4.4.
  976: * Get PCI passthrough working on Xen 4.2 (or 4.4).
  977: * Get pvgrub into pkgsrc, either via xentools or separately.
  978: * grub
  979:   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
  980:     fragsize/blocksize (UFS2 support may be present; the point is to
  981:     make it so that with any UFS1/UFS2 filesystem setup that works
  982:     with NetBSD grub will also work).
  983:     See [pkg/40258](
  984:   * Push patches upstream.
  985:   * Get UFS2 patches into pvgrub.
  986: * Add support for PV ops to a version of /boot, and make it usable as
  987:   a kernel in Xen, similar to pvgrub.

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