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    1: Introduction
    2: ============
    3: 
    4: [![[Xen
    5: screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](http://www.netbsd.org/gallery/in-Action/hubertf-xen.png)
    6: 
    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.
   16: 
   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.
   24: 
   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.
   29: 
   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.
   36: 
   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.)
   40: 
   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.
   46: 
   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.
   51: 
   52: NetBSD used to support Xen2; this has been removed.
   53: 
   54: Prerequisites
   55: -------------
   56: 
   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.
   62: 
   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](http://www.xenproject.org/).
   67: 
   68: Versions of Xen and NetBSD
   69: ==========================
   70: 
   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.
   75: 
   76: Xen
   77: ---
   78: 
   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.
   83: 
   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.
   87: 
   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.
   91: 
   92: xenkernel42 provides Xen 4.2.  This is maintained by Xen, but old as
   93: of 2014-12.
   94: 
   95: Ideally newer versions of Xen will be added to pkgsrc.
   96: 
   97: Note that NetBSD support is called XEN3.  It works with 3.1 through
   98: 4.2 because the hypercall interface has been stable.
   99: 
  100: Xen command program
  101: -------------------
  102: 
  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.  In 4.2 and later, "xl" is preferred.  4.4 is
  106: the last version that has "xm".
  107: 
  108: NetBSD
  109: ------
  110: 
  111: The netbsd-5, netbsd-6, netbsd-7, and -current branches are all
  112: reasonable choices, with more or less the same considerations for
  113: non-Xen use.  Therefore, netbsd-6 is recommended as the stable version
  114: of the most recent release for production use.  For those wanting to
  115: learn Xen or without production stability concerns, netbsd-7 is likely
  116: most appropriate.
  117: 
  118: As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
  119: no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
  120: need SMP; the lack of support is really a problem when using a dom0 as
  121: a normal computer.)
  122: 
  123: Architecture
  124: ------------
  125: 
  126: Xen itself can run on i386 or amd64 machines.  (Practically, almost
  127: any computer where one would want to run Xen supports amd64.)  If
  128: using an i386 NetBSD kernel for the dom0, PAE is required (PAE
  129: versions are built by default).  While i386 dom0 works fine, amd64 is
  130: recommended as more normal.
  131: 
  132: Xen 4.2 is the last version to support i386 as a host.  TODO: Clarify
  133: if this is about the CPU having to be amd64, or about the dom0 kernel
  134: having to be amd64.
  135: 
  136: One can then run i386 domUs and amd64 domUs, in any combination.  If
  137: running an i386 NetBSD kernel as a domU, the PAE version is required.
  138: (Note that emacs (at least) fails if run on i386 with PAE when built
  139: without, and vice versa, presumably due to bugs in the undump code.)
  140: 
  141: Recommendation
  142: --------------
  143: 
  144: Therefore, this HOWTO recommends running xenkernel42 (and xentools42),
  145: xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the
  146: dom0.  Either the i386 or amd64 of NetBSD may be used as domUs.
  147: 
  148: Build problems
  149: --------------
  150: 
  151: Ideally, all versions of Xen in pkgsrc would build on all versions of
  152: NetBSD on both i386 and amd64.  However, that isn't the case.  Besides
  153: aging code and aging compilers, qemu (included in xentools for HVM
  154: support) is difficult to build.  The following are known to work or FAIL:
  155: 
  156:         xenkernel3 netbsd-5 amd64
  157:         xentools3 netbsd-5 amd64
  158:         xentools3=hvm netbsd-5 amd64 ????
  159:         xenkernel33 netbsd-5 amd64
  160:         xentools33 netbsd-5 amd64
  161:         xenkernel41 netbsd-5 amd64
  162:         xentools41 netbsd-5 amd64
  163:         xenkernel42 netbsd-5 amd64
  164:         xentools42 netbsd-5 amd64
  165: 
  166:         xenkernel3 netbsd-6 i386 FAIL
  167:         xentools3 netbsd-6 i386
  168:         xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
  169:         xenkernel33 netbsd-6 i386
  170:         xentools33 netbsd-6 i386
  171:         xenkernel41 netbsd-6 i386
  172:         xentools41 netbsd-6 i386
  173:         xenkernel42 netbsd-6 i386
  174:         xentools42 netbsd-6 i386 *MIXED
  175: 
  176: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
  177: but it does not build for gdt.)
  178: 
  179: NetBSD as a dom0
  180: ================
  181: 
  182: NetBSD can be used as a dom0 and works very well.  The following
  183: sections address installation, updating NetBSD, and updating Xen.
  184: Note that it doesn't make sense to talk about installing a dom0 OS
  185: without also installing Xen itself.  We first address installing
  186: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
  187: NetBSD install to a dom0 install by just changing the kernel and boot
  188: configuration.
  189: 
  190: For experimenting with Xen, a machine with as little as 1G of RAM and
  191: 100G of disk can work.  For running many domUs in productions, far
  192: more will be needed.
  193: 
  194: Styles of dom0 operation
  195: ------------------------
  196: 
  197: There are two basic ways to use Xen.  The traditional method is for
  198: the dom0 to do absolutely nothing other than providing support to some
  199: number of domUs.  Such a system was probably installed for the sole
  200: purpose of hosting domUs, and sits in a server room on a UPS.
  201: 
  202: The other way is to put Xen under a normal-usage computer, so that the
  203: dom0 is what the computer would have been without Xen, perhaps a
  204: desktop or laptop.  Then, one can run domUs at will.  Purists will
  205: deride this as less secure than the previous approach, and for a
  206: computer whose purpose is to run domUs, they are right.  But Xen and a
  207: dom0 (without domUs) is not meaingfully less secure than the same
  208: things running without Xen.  One can boot Xen or boot regular NetBSD
  209: alternately with little problems, simply refraining from starting the
  210: Xen daemons when not running Xen.
  211: 
  212: Note that NetBSD as dom0 does not support multiple CPUs.  This will
  213: limit the performance of the Xen/dom0 workstation approach.  In theory
  214: the only issue is that the "backend drivers" are not yet MPSAFE:
  215:   http://mail-index.netbsd.org/netbsd-users/2014/08/29/msg015195.html
  216: 
  217: Installation of NetBSD
  218: ----------------------
  219: 
  220: First,
  221: [install NetBSD/amd64](/guide/inst/)
  222: just as you would if you were not using Xen.
  223: However, the partitioning approach is very important.
  224: 
  225: If you want to use RAIDframe for the dom0, there are no special issues
  226: for Xen.  Typically one provides RAID storage for the dom0, and the
  227: domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
  228: over a RAID1 header to find /boot from a filesystem within a RAID
  229: partition; this is no different when booting Xen.
  230: 
  231: There are 4 styles of providing backing storage for the virtual disks
  232: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN,
  233: 
  234: With raw partitions, one has a disklabel (or gpt) partition sized for
  235: each virtual disk to be used by the domU.  (If you are able to predict
  236: how domU usage will evolve, please add an explanation to the HOWTO.
  237: Seriously, needs tend to change over time.)
  238: 
  239: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
  240: for domU disks.  This is almost as efficient as raw disk partitions
  241: and more flexible.  Hence raw disk partitions should typically not
  242: be used.
  243: 
  244: One can use files in the dom0 filesystem, typically created by dd'ing
  245: /dev/zero to create a specific size.  This is somewhat less efficient,
  246: but very convenient, as one can cp the files for backup, or move them
  247: between dom0 hosts.
  248: 
  249: Finally, in theory one can place the files backing the domU disks in a
  250: SAN.  (This is an invitation for someone who has done this to add a
  251: HOWTO page.)
  252: 
  253: Installation of Xen
  254: -------------------
  255: 
  256: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
  257: pkgsrc (or another matching pair).
  258: See [the pkgsrc
  259: documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with pkgsrc.
  260: 
  261: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm.  More
  262: recent versions have HVM support integrated in the main xentools
  263: package.  It is entirely reasonable to run only PV guests.
  264: 
  265: Next you need to install the selected Xen kernel itself, which is
  266: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz".  Copy it to /.
  267: For debugging, one may copy xen-debug.gz; this is conceptually similar
  268: to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
  269: useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
  270: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
  271: of a NetBSD build.  Both xen and NetBSD may be left compressed.  (If
  272: using i386, use releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.)
  273: 
  274: With Xen as the kernel, you must provide a dom0 NetBSD kernel to be
  275: used as a module; place this in /.  Suitable kernels are provided in
  276: releasedir/binary/kernel:
  277: 
  278:         i386 XEN3_DOM0
  279:         i386 XEN3PAE_DOM0
  280: 	amd64 XEN3_DOM0
  281: 
  282: The first one is only for use with Xen 3.1 and i386-mode Xen (and you
  283: should not do this).  Current Xen always uses PAE on i386, but you
  284: should generally use amd64 for the dom0.  In a dom0 kernel, kernfs is
  285: mandatory for xend to comunicate with the kernel, so ensure that /kern
  286: is in fstab.  TODO: Say this is default, or file a PR and give a
  287: reference.
  288: 
  289: Because you already installed NetBSD, you have a working boot setup
  290: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
  291: beginning of your root filesystem, /boot present, and likely
  292: /boot.cfg.  (If not, fix before continuing!)
  293: 
  294: See boot.cfg(5) for an example.  The basic line is
  295: 
  296:         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  297: 
  298: which specifies that the dom0 should have 256M, leaving the rest to be
  299: allocated for domUs.  In an attempt to add performance, one can also
  300: add
  301: 
  302:         dom0_max_vcpus=1 dom0_vcpus_pin
  303: 
  304: to force only one vcpu to be provided (since NetBSD dom0 can't use
  305: more) and to pin that vcpu to a physical cpu.  TODO: benchmark this.
  306: 
  307: As with non-Xen systems, you should have a line to boot /netbsd (a
  308: kernel that works without Xen) and fallback versions of the non-Xen
  309: kernel, Xen, and the dom0 kernel.
  310: 
  311: Using grub (historic)
  312: ---------------------
  313: 
  314: Before NetBSD's native bootloader could support Xen, the use of
  315: grub was recommended.  If necessary, see the
  316: [old grub information](/ports/xen/howto-grub/).
  317: 
  318: The [HowTo on Installing into
  319: RAID-1](http://mail-index.NetBSD.org/port-xen/2006/03/01/0010.html)
  320: explains how to set up booting a dom0 with Xen using grub with
  321: NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
  322: boot.)
  323: 
  324: Configuring Xen
  325: ---------------
  326: 
  327: Xen logs will be in /var/log/xen.
  328: 
  329: Now, you have a system that will boot Xen and the dom0 kernel, and
  330: just run the dom0 kernel.  There will be no domUs, and none can be
  331: started because you still have to configure the dom0 tools.  The
  332: daemons which should be run vary with Xen version and with whether one
  333: is using xm or xl.  Note that xend is for supporting "xm", and should
  334: only be used if you plan on using "xm".  Do NOT enable xend if you
  335: plan on using "xl" as it will cause problems.
  336: 
  337: The installation of NetBSD should already have created devices for xen
  338: (xencons, xenevt), but if they are not present, create them:
  339: 
  340:         cd /dev && sh MAKEDEV xen
  341: 
  342: TODO: Give 3.1 advice (or remove it from pkgsrc).
  343: 
  344: For 3.3 (and thus xm), add to rc.conf (but note that you should have
  345: installed 4.1 or 4.2):
  346: 
  347:         xend=YES
  348:         xenbackendd=YES
  349: 
  350: For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
  351: 
  352:         xencommons=YES
  353:         xend=YES
  354: 
  355: (If you are using xentools41 from before 2014-12-26, change
  356: rc.d/xendomains to use xm rather than xl.)
  357: 
  358: For 4.2 with xm, add to rc.conf
  359: 
  360:         xencommons=YES
  361:         xend=YES
  362: 
  363: For 4.2 with xl (preferred), add to rc.conf:
  364: 
  365:         xencommons=YES
  366:         TODO: explain if there is a xend replacement
  367: 
  368: TODO: Recommend for/against xen-watchdog.
  369: 
  370: After you have configured the daemons and either started them (in the
  371: order given) or rebooted, run the following (or use xl) to inspect
  372: Xen's boot messages, available resources, and running domains:
  373: 
  374:         # xm dmesg
  375: 	[xen's boot info]
  376:         # xm info
  377: 	[available memory, etc.]
  378:         # xm list
  379:         Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  380:         Domain-0           0       64    0  r----     58.1
  381: 
  382: anita (for testing NetBSD)
  383: --------------------------
  384: 
  385: With the setup so far, one should be able to run anita (see
  386: pkgsrc/sysutils/py-anita) to test NetBSD releases, by doing (as root,
  387: because anita must create a domU):
  388: 
  389:         anita --vmm=xm test file:///usr/obj/i386/
  390: 
  391: Alternatively, one can use --vmm=xl to use xl-based domU creation instead.
  392: TODO: check this.
  393: 
  394: Xen-specific NetBSD issues
  395: --------------------------
  396: 
  397: There are (at least) two additional things different about NetBSD as a
  398: dom0 kernel compared to hardware.
  399: 
  400: One is that modules are not usable in DOM0 kernels, so one must
  401: compile in what's needed.  It's not really that modules cannot work,
  402: but that modules must be built for XEN3_DOM0 because some of the
  403: defines change and the normal module builds don't do this.  Basically,
  404: enabling Xen changes the kernel ABI, and the module build system
  405: doesn't cope with this.
  406: 
  407: The other difference is that XEN3_DOM0 does not have exactly the same
  408: options as GENERIC.  While it is debatable whether or not this is a
  409: bug, users should be aware of this and can simply add missing config
  410: items if desired.
  411: 
  412: Updating NetBSD in a dom0
  413: -------------------------
  414: 
  415: This is just like updating NetBSD on bare hardware, assuming the new
  416: version supports the version of Xen you are running.  Generally, one
  417: replaces the kernel and reboots, and then overlays userland binaries
  418: and adjusts /etc.
  419: 
  420: Note that one must update both the non-Xen kernel typically used for
  421: rescue purposes and the DOM0 kernel used with Xen.
  422: 
  423: Converting from grub to /boot
  424: -----------------------------
  425: 
  426: These instructions were [TODO: will be] used to convert a system from
  427: grub to /boot.  The system was originally installed in February of
  428: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  429: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  430: 4.1 and grub, much like the message linked earlier in the grub
  431: section.
  432: 
  433:         # Install mbr bootblocks on both disks. 
  434:         fdisk -i /dev/rwd0d
  435:         fdisk -i /dev/rwd1d
  436:         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  437:         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  438:         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  439:         # Install secondary boot loader
  440:         cp -p /usr/mdec/boot /
  441:         # Create boog.cfg following earlier guidance:
  442:         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
  443:         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
  444:         menu=GENERIC:boot
  445:         menu=GENERIC single-user:boot -s
  446:         menu=GENERIC.ok:boot netbsd.ok
  447:         menu=GENERIC.ok single-user:boot netbsd.ok -s
  448:         menu=Drop to boot prompt:prompt
  449:         default=1
  450:         timeout=30
  451: 
  452: TODO: actually do this and fix it if necessary.
  453: 
  454: Updating Xen versions
  455: ---------------------
  456: 
  457: Updating Xen is conceptually not difficult, but can run into all the
  458: issues found when installing Xen.  Assuming migration from 4.1 to 4.2,
  459: remove the xenkernel41 and xentools41 packages and install the
  460: xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz to /.
  461: 
  462: Ensure that the contents of /etc/rc.d/xen* are correct.  Enable the
  463: correct set of daemons.  Ensure that the domU config files are valid
  464: for the new version.
  465: 
  466: 
  467: Unprivileged domains (domU)
  468: ===========================
  469: 
  470: This section describes general concepts about domUs.  It does not
  471: address specific domU operating systems or how to install them.  The
  472: config files for domUs are typically in /usr/pkg/etc/xen, and are
  473: typically named so that the file name, domU name and the domU's host
  474: name match.
  475: 
  476: The domU is provided with cpu and memory by Xen, configured by the
  477: dom0.  The domU is provided with disk and network by the dom0,
  478: mediated by Xen, and configured in the dom0.
  479: 
  480: Entropy in domUs can be an issue; physical disks and network are on
  481: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  482: 
  483: Config files
  484: ------------
  485: 
  486: There is no good order to present config files and the concepts
  487: surrounding what is being configured.  We first show an example config
  488: file, and then in the various sections give details.
  489: 
  490: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
  491: for a large number of well-commented examples, mostly for running
  492: GNU/Linux.
  493: 
  494: The following is an example minimal domain configuration file
  495: "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual
  496: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
  497: i386 domU).  The domU serves as a network file server.
  498: 
  499:         # -*- mode: python; -*-
  500: 
  501:         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  502:         memory = 1024
  503:         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  504:         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  505:                  'file:/n0/xen/foo-wd1,0x1,w' ]
  506: 
  507: The domain will have the same name as the file.  The kernel has the
  508: host/domU name in it, so that on the dom0 one can update the various
  509: domUs independently.  The vif line causes an interface to be provided,
  510: with a specific mac address (do not reuse MAC addresses!), in bridge
  511: mode.  Two disks are provided, and they are both writable; the bits
  512: are stored in files and Xen attaches them to a vnd(4) device in the
  513: dom0 on domain creation.  The system treates xbd0 as the boot device
  514: without needing explicit configuration.
  515: 
  516: By default xm looks for domain config files in /usr/pkg/etc/xen.  Note
  517: that "xm create" takes the name of a config file, while other commands
  518: take the name of a domain.  To create the domain, connect to the
  519: console, create the domain while attaching the console, shutdown the
  520: domain, and see if it has finished stopping, do (or xl with Xen >=
  521: 4.2):
  522: 
  523:         xm create foo
  524:         xm console foo
  525:         xm create -c foo
  526:         xm shutdown foo
  527: 	xm list
  528: 
  529: Typing ^] will exit the console session.  Shutting down a domain is
  530: equivalent to pushing the power button; a NetBSD domU will receive a
  531: power-press event and do a clean shutdown.  Shutting down the dom0
  532: will trigger controlled shutdowns of all configured domUs.
  533: 
  534: domU kernels
  535: ------------
  536: 
  537: On a physical computer, the BIOS reads sector 0, and a chain of boot
  538: loaders finds and loads a kernel.  Normally this comes from the root
  539: filesystem.  With Xen domUs, the process is totally different.  The
  540: normal path is for the domU kernel to be a file in the dom0's
  541: filesystem.  At the request of the dom0, Xen loads that kernel into a
  542: new domU instance and starts execution.  While domU kernels can be
  543: anyplace, reasonable places to store domU kernels on the dom0 are in /
  544: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
  545: config files), or in /u0/xen (where the vdisks are).
  546: 
  547: Note that loading the domU kernel from the dom0 implies that boot
  548: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  549: See the VPS section near the end for discussion of alternate ways to
  550: obtain domU kernels.
  551: 
  552: CPU and memory
  553: --------------
  554: 
  555: A domain is provided with some number of vcpus, less than the number
  556: of cpus seen by the hypervisor.  (For a dom0, this is controlled by
  557: the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled
  558: from the config file by the "vcpus = N" directive.
  559: 
  560: A domain is provided with memory; this is controlled in the config
  561: file by "memory = N" (in megabytes).  In the straightforward case, the
  562: sum of the the memory allocated to the dom0 and all domUs must be less
  563: than the available memory.
  564: 
  565: Xen also provides a "balloon" driver, which can be used to let domains
  566: use more memory temporarily.  TODO: Explain better, and explain how
  567: well it works with NetBSD.
  568: 
  569: Virtual disks
  570: -------------
  571: 
  572: With the file/vnd style, typically one creates a directory,
  573: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  574: domUs.  Then, for each domU disk, one writes zeros to a file that then
  575: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  576: for the first virtual disk for the domU called foo.  Writing zeros to
  577: the file serves two purposes.  One is that preallocating the contents
  578: improves performance.  The other is that vnd on sparse files has
  579: failed to work.  TODO: give working/notworking NetBSD versions for
  580: sparse vnd.  Note that the use of file/vnd for Xen is not really
  581: different than creating a file-backed virtual disk for some other
  582: purpose, except that xentools handles the vnconfig commands.  To
  583: create an empty 4G virtual disk, simply do
  584: 
  585:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  586: 
  587: With the lvm style, one creates logical devices.  They are then used
  588: similarly to vnds.  TODO: Add an example with lvm.
  589: 
  590: In domU config files, the disks are defined as a sequence of 3-tuples.
  591: The first element is "method:/path/to/disk".  Common methods are
  592: "file:" for file-backed vnd. and "phy:" for something that is already
  593: a (TODO: character or block) device.
  594: 
  595: The second element is an artifact of how virtual disks are passed to
  596: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  597: are given a device name to associate with the disk, and values like
  598: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  599: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  600: second argument.  The name given is converted to a major/minor by
  601: calling stat(2) on the name in /dev and this is passed to the domU.
  602: In the general case, the dom0 and domU can be different operating
  603: systems, and it is an unwarranted assumption that they have consistent
  604: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  605: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  606: for the second works fine and avoids this issue.  For a GNU/Linux
  607: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  608: /dev/hda1.
  609: 
  610: The third element is "w" for writable disks, and "r" for read-only
  611: disks.
  612: 
  613: Virtual Networking
  614: ------------------
  615: 
  616: Xen provides virtual ethernets, each of which connects the dom0 and a
  617: domU.  For each virtual network, there is an interface "xvifN.M" in
  618: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  619: name).  The interfaces behave as if there is an Ethernet with two
  620: adaptors connected.  From this primitive, one can construct various
  621: configurations.  We focus on two common and useful cases for which
  622: there are existing scripts: bridging and NAT.
  623: 
  624: With bridging (in the example above), the domU perceives itself to be
  625: on the same network as the dom0.  For server virtualization, this is
  626: usually best.  Bridging is accomplished by creating a bridge(4) device
  627: and adding the dom0's physical interface and the various xvifN.0
  628: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  629: config file.  The bridge must be set up already in the dom0; an
  630: example /etc/ifconfig.bridge0 is:
  631: 
  632:         create
  633:         up
  634:         !brconfig bridge0 add wm0
  635: 
  636: With NAT, the domU perceives itself to be behind a NAT running on the
  637: dom0.  This is often appropriate when running Xen on a workstation.
  638: TODO: NAT appears to be configured by "vif = [ '' ]".
  639: 
  640: The MAC address specified is the one used for the interface in the new
  641: domain.  The interface in dom0 will use this address XOR'd with
  642: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  643: 
  644: Sizing domains
  645: --------------
  646: 
  647: Modern x86 hardware has vast amounts of resources.  However, many
  648: virtual servers can function just fine on far less.  A system with
  649: 256M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  650: far easier to adjust virtual resources than physical ones.  For
  651: memory, it's just a config file edit and a reboot.  For disk, one can
  652: create a new file and vnconfig it (or lvm), and then dump/restore,
  653: just like updating physical disks, but without having to be there and
  654: without those pesky connectors.
  655: 
  656: Starting domains automatically
  657: ------------------------------
  658: 
  659: To start domains foo at bar at boot and shut them down cleanly on dom0
  660: shutdown, in rc.conf add:
  661: 
  662:         xendomains="foo bar"
  663: 
  664: TODO: Explain why 4.1 rc.d/xendomains has xl, when one should use xm
  665: on 4.1.  Or fix the xentools41 package to have xm
  666: 
  667: Creating specific unprivileged domains (domU)
  668: =============================================
  669: 
  670: Creating domUs is almost entirely independent of operating system.  We
  671: have already presented the basics of config files.  Note that you must
  672: have already completed the dom0 setup so that "xl list" (or "xm list")
  673: works.
  674: 
  675: Creating an unprivileged NetBSD domain (domU)
  676: ---------------------------------------------
  677: 
  678: See the earlier config file, and adjust memory.  Decide on how much
  679: storage you will provide, and prepare it (file or lvm).
  680: 
  681: While the kernel will be obtained from the dom0 filesystem, the same
  682: file should be present in the domU as /netbsd so that tools like
  683: savecore(8) can work.   (This is helpful but not necessary.)
  684: 
  685: The kernel must be specifically for Xen and for use as a domU.  The
  686: i386 and amd64 provide the following kernels:
  687: 
  688:         i386 XEN3_DOMU
  689:         i386 XEN3PAE_DOMU
  690: 	amd64 XEN3_DOMU
  691: 
  692: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
  693: use the PAE version of the i386 kernel.
  694: 
  695: This will boot NetBSD, but this is not that useful if the disk is
  696: empty.  One approach is to unpack sets onto the disk outside of xen
  697: (by mounting it, just as you would prepare a physical disk for a
  698: system you can't run the installer on).
  699: 
  700: A second approach is to run an INSTALL kernel, which has a miniroot
  701: and can load sets from the network.  To do this, copy the INSTALL
  702: kernel to / and change the kernel line in the config file to:
  703: 
  704:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  705: 
  706: Then, start the domain as "xl create -c configname".
  707: 
  708: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  709: line should be used in the config file.
  710: 
  711:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  712: 
  713: After booting the domain, the option to install via CDROM may be
  714: selected.  The CDROM device should be changed to `xbd1d`.
  715: 
  716: Once done installing, "halt -p" the new domain (don't reboot or halt,
  717: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  718: config file), switch the config file back to the XEN3_DOMU kernel,
  719: and start the new domain again. Now it should be able to use "root on
  720: xbd0a" and you should have a, functional NetBSD domU.
  721: 
  722: TODO: check if this is still accurate.
  723: When the new domain is booting you'll see some warnings about *wscons*
  724: and the pseudo-terminals. These can be fixed by editing the files
  725: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  726: `/etc/ttys`, except *console*, like this:
  727: 
  728:     console "/usr/libexec/getty Pc"         vt100   on secure
  729:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  730:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  731:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  732:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  733: 
  734: Finally, all screens must be commented out from `/etc/wscons.conf`.
  735: 
  736: It is also desirable to add
  737: 
  738:         powerd=YES
  739: 
  740: in rc.conf. This way, the domain will be properly shut down if
  741: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  742: 
  743: Your domain should be now ready to work, enjoy.
  744: 
  745: Creating an unprivileged Linux domain (domU)
  746: --------------------------------------------
  747: 
  748: Creating unprivileged Linux domains isn't much different from
  749: unprivileged NetBSD domains, but there are some details to know.
  750: 
  751: First, the second parameter passed to the disk declaration (the '0x1' in
  752: the example below)
  753: 
  754:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  755: 
  756: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  757: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  758: So, hda1 which has major 3 and minor 1 on a Linux system will have
  759: device number 0x301.  Alternatively, devices names can be used (hda,
  760: hdb, ...)  as xentools has a table to map these names to devices
  761: numbers.  To export a partition to a Linux guest we can use:
  762: 
  763:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  764:         root = "/dev/hda1 ro"
  765: 
  766: and it will appear as /dev/hda on the Linux system, and be used as root
  767: partition.
  768: 
  769: To install the Linux system on the partition to be exported to the
  770: guest domain, the following method can be used: install
  771: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  772: that will be the root partition of your Linux domain, and mount it.
  773: Then copy the files from a working Linux system, make adjustments in
  774: `/etc` (fstab, network config).  It should also be possible to extract
  775: binary packages such as .rpm or .deb directly to the mounted partition
  776: using the appropriate tool, possibly running under NetBSD's Linux
  777: emulation.  Once the filesystem has been populated, umount it.  If
  778: desirable, the filesystem can be converted to ext3 using tune2fs -j.
  779: It should now be possible to boot the Linux guest domain, using one of
  780: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  781: 
  782: To get the linux console right, you need to add:
  783: 
  784:     extra = "xencons=tty1"
  785: 
  786: to your configuration since not all linux distributions auto-attach a
  787: tty to the xen console.
  788: 
  789: Creating an unprivileged Solaris domain (domU)
  790: ----------------------------------------------
  791: 
  792: See possibly outdated
  793: [Solaris domU instructions](/ports/xen/howto-solaris/).
  794: 
  795: 
  796: PCI passthrough: Using PCI devices in guest domains
  797: ---------------------------------------------------
  798: 
  799: The dom0 can give other domains access to selected PCI
  800: devices. This can allow, for example, a non-privileged domain to have
  801: access to a physical network interface or disk controller.  However,
  802: keep in mind that giving a domain access to a PCI device most likely
  803: will give the domain read/write access to the whole physical memory,
  804: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  805: device.  Also, it's not possible to export ISA devices to non-dom0
  806: domains, which means that the primary VGA adapter can't be exported.
  807: A guest domain trying to access the VGA registers will panic.
  808: 
  809: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  810: not been ported to later versions at this time.
  811: 
  812: For a PCI device to be exported to a domU, is has to be attached to
  813: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  814: pciback.hide boot parameter will attach to "pciback" instead of the
  815: usual driver.  The list of devices is specified as "(bus:dev.func)",
  816: where bus and dev are 2-digit hexadecimal numbers, and func a
  817: single-digit number:
  818: 
  819:         pciback.hide=(00:0a.0)(00:06.0)
  820: 
  821: pciback devices should show up in the dom0's boot messages, and the
  822: devices should be listed in the `/kern/xen/pci` directory.
  823: 
  824: PCI devices to be exported to a domU are listed in the "pci" array of
  825: the domU's config file, with the format "0000:bus:dev.func".
  826: 
  827:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  828: 
  829: In the domU an "xpci" device will show up, to which one or more pci
  830: busses will attach.  Then the PCI drivers will attach to PCI busses as
  831: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  832: or any PCI drivers built in by default; you have to build your own
  833: kernel to use PCI devices in a domU.  Here's a kernel config example;
  834: note that only the "xpci" lines are unusual.
  835: 
  836:         include         "arch/i386/conf/XEN3_DOMU"
  837: 
  838:         # Add support for PCI busses to the XEN3_DOMU kernel
  839:         xpci* at xenbus ?
  840:         pci* at xpci ?
  841: 
  842:         # PCI USB controllers
  843:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  844: 
  845:         # USB bus support
  846:         usb*    at uhci?
  847: 
  848:         # USB Hubs
  849:         uhub*   at usb?
  850:         uhub*   at uhub? port ? configuration ? interface ?
  851: 
  852:         # USB Mass Storage
  853:         umass*  at uhub? port ? configuration ? interface ?
  854:         wd*     at umass?
  855:         # SCSI controllers
  856:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  857: 
  858:         # SCSI bus support (for both ahc and umass)
  859:         scsibus* at scsi?
  860: 
  861:         # SCSI devices
  862:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  863:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  864: 
  865: 
  866: NetBSD as a domU in a VPS
  867: =========================
  868: 
  869: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  870: hardware.  This section explains how to deal with Xen in a domU as a
  871: virtual private server where you do not control or have access to the
  872: dom0.
  873: 
  874: VPS operators provide varying degrees of access and mechanisms for
  875: configuration.  The big issue is usually how one controls which kernel
  876: is booted, because the kernel is nominally in the dom0 filesystem (to
  877: which VPS users do not normally have acesss).
  878: 
  879: A VPS user may want to compile a kernel for security updates, to run
  880: npf, run IPsec, or any other reason why someone would want to change
  881: their kernel.
  882: 
  883: One approach is to have an adminstrative interface to upload a kernel,
  884: or to select from a prepopulated list.  Other approaches are py-grub
  885: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  886: kernel from the domU filesystem.  This is closer to a regular physical
  887: computer, where someone who controls a machine can replace the kernel.
  888: 
  889: py-grub
  890: -------
  891: 
  892: py-grub runs in the dom0 and looks into the domU filesystem.  This
  893: implies that the domU must have a kernel in a filesystem in a format
  894: known to py-grub.  As of 2014, py-grub seems to be of mostly historical interest.
  895: 
  896: pvgrub
  897: ------
  898: 
  899: pvgrub is a version of grub that uses PV operations instead of BIOS
  900: calls.  It is booted from the dom0 as the domU kernel, and then reads
  901: /grub/menu.lst and loads a kernel from the domU filesystem.
  902: 
  903: [prgmr.com](http://prgmr.com/) uses this approach to let users choose
  904: their own operating system and kernel.  See then [prgmr.com NetBSD
  905: HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU).
  906: 
  907: Because [grub's FFS code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
  908: appears not to support all aspects of modern FFS,
  909: typically one has an ext2 or FAT partition for the kernel, so that
  910: grub can understand it, which leads to /netbsd not being the actual
  911: kernel.  One must remember to update the special boot partiion.
  912: 
  913: Amazon
  914: ------
  915: 
  916: TODO: add link to NetBSD amazon howto.
  917: 
  918: Using npf
  919: ---------
  920: 
  921: In standard kernels, npf is a module, and thus cannot be loadeed in a
  922: DOMU kernel.
  923: 
  924: TODO: explain how to compile npf into a custom kernel, answering (but
  925: note that the problem was caused by not booting the right kernel):
  926: http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html

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