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    1: [[!meta title="Xen HowTo"]]
    2: 
    3: Introduction
    4: ============
    5: 
    6: Xen is a hypervisor for x86 hardware, which supports running multiple guest
    7: operating systems on a single physical machine.  Xen is a Type 1 or
    8: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
    9: memory and console, a dom0 operating system which mediates access to
   10: other hardware (e.g., disks, network, USB), and one or more domU
   11: operating systems which operate in an unprivileged virtualized
   12: environment.  IO requests from the domU systems are forwarded by the
   13: Xen hypervisor to the dom0 to be fulfilled.
   14: 
   15: Xen supports different styles of guest:
   16: 
   17: [[!table data="""
   18: Style of guest	|Supported by NetBSD
   19: PV		|Yes (dom0, domU)
   20: HVM		|Yes (domU)
   21: PVHVM		|No
   22: PVH		|No
   23: """]]
   24: 
   25: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
   26: hardware directly, but instead makes hypercalls to the hypervisor; PV
   27: guests must be specifically coded for Xen. In HVM mode, no guest
   28: modification is required; however, hardware support is required, such
   29: as VT-x on Intel CPUs and SVM on AMD CPUs.
   30: 
   31: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   32: The dom0 can start one or more domUs.  (Booting is explained in detail
   33: in the dom0 section.)
   34: 
   35: This HOWTO presumes a basic familiarity with the Xen system
   36: architecture, with installing NetBSD on i386/amd64 hardware, and with
   37: installing software from pkgsrc.  See also the [Xen
   38: website](http://www.xenproject.org/).
   39: 
   40: This HOWTO attempts to address both the case of running a NetBSD dom0
   41: on hardware and running domUs under it (NetBSD and other), and also
   42: running NetBSD as a domU in a VPS.
   43: 
   44: Versions of Xen and NetBSD
   45: ==========================
   46: 
   47: Most of the installation concepts and instructions are independent
   48: of Xen version and NetBSD version.  This section gives advice on
   49: which version to choose.  Versions not in pkgsrc and older unsupported
   50: versions of NetBSD are intentionally ignored.
   51: 
   52: The term "amd64" is used to refer to both the NetBSD port and to the
   53: hardware architecture on which it runs.  Such hardware is generally
   54: made by both Intel and AMD, and common on PC computers.
   55: 
   56: Xen versions
   57: ------------
   58: 
   59: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   60: xenkernel and xentools.  We will refer only to the kernel versions,
   61: but note that both packages must be installed together and must have
   62: matching versions.
   63: 
   64: Versions available in pkgsrc:
   65: 
   66: [[!table data="""
   67: Xen Version	|Package Name	|Xen CPU Support	|EOL'ed By Upstream
   68: 4.2		|xenkernel42	|32bit, 64bit		|Yes
   69: 4.5		|xenkernel45	|64bit			|Yes
   70: 4.6		|xenkernel46	|64bit			|Partially
   71: 4.8		|xenkernel48	|64bit			|No
   72: 4.11		|xenkernel411	|64bit			|No
   73: """]]
   74: 
   75: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
   76: 
   77: Note: Xen 4.2 was the last version to support 32bit CPUs.
   78: 
   79: NetBSD versions
   80: ---------------
   81: 
   82: NetBSD 8 is recommended as the stable version of the most recent
   83: release for production use.
   84: 
   85: For developing Xen, netbsd-current may be appropriate.
   86: 
   87: As of NetBSD 6, a NetBSD domU will support multiple vcpus.  There is
   88: no SMP support for NetBSD as dom0.  (The dom0 itself doesn't really
   89: need SMP for dom0 functions; the lack of support is really a problem
   90: when using a dom0 as a normal computer.)
   91: 
   92: Note: NetBSD support is called XEN3. However, it does support Xen 4,
   93: because the hypercall interface has remained identical.
   94: 
   95: Architecture
   96: ------------
   97: 
   98: Xen itself runs on amd64 hardware. Practically, almost any computer
   99: where one would want to run Xen today supports amd64.
  100: 
  101: The dom0 system, plus each domU, can be either i386PAE or amd64.
  102: i386 without PAE is not supported.
  103: 
  104: The standard approach is to use NetBSD/amd64 for the dom0.  For domUs,
  105: NetBSD/i386 (PAE) and NetBSD/amd64 are in widespread use, and there is
  106: little to no Xen-specific reason to prefer one over the other.
  107: 
  108: Note that to use an i386 dom0 with Xen 4.5 or higher, one must build
  109: (or obtain from pre-built packages) an amd64 Xen kernel and install
  110: that on the system.  Almost no one in the NetBSD/Xen community does
  111: this, and the standard, well-tested, approach is to use an amd64 dom0.
  112: 
  113: A [posting on
  114: xen-devel](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html)
  115: explained that PV system call overhead was higher on amd64, and thus
  116: there is some notion that i386 guests are faster.  It goes on to
  117: caution that the total situation is complex and not entirely
  118: understood. On top of that caution, the post is about Linux, not
  119: NetBSD.
  120: 
  121: NetBSD as a dom0
  122: ================
  123: 
  124: NetBSD can be used as a dom0 and works very well.  The following
  125: sections address installation, updating NetBSD, and updating Xen.
  126: Note that it doesn't make sense to talk about installing a dom0 OS
  127: without also installing Xen itself.  We first address installing
  128: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
  129: NetBSD install to a dom0 install by just changing the kernel and boot
  130: configuration.
  131: 
  132: For experimenting with Xen, a machine with as little as 1G of RAM and
  133: 100G of disk can work.  For running many domUs in productions, far
  134: more will be needed; e.g. 4-8G and 1T of disk is reasonable for a
  135: half-dozen domUs of 512M and 32G each.  Basically, the RAM and disk
  136: have to be bigger than the sum of the RAM/disk needs of the dom0 and
  137: all the domUs.
  138: 
  139: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
  140: 512M it worked reliably.  This does not make sense, but if you see
  141: "not ELF" after Xen boots, try increasing dom0 RAM.
  142: 
  143: Styles of dom0 operation
  144: ------------------------
  145: 
  146: There are two basic ways to use Xen.  The traditional method is for
  147: the dom0 to do absolutely nothing other than providing support to some
  148: number of domUs.  Such a system was probably installed for the sole
  149: purpose of hosting domUs, and sits in a server room on a UPS.
  150: 
  151: The other way is to put Xen under a normal-usage computer, so that the
  152: dom0 is what the computer would have been without Xen, perhaps a
  153: desktop or laptop.  Then, one can run domUs at will.  Purists will
  154: deride this as less secure than the previous approach, and for a
  155: computer whose purpose is to run domUs, they are right.  But Xen and a
  156: dom0 (without domUs) is not meaningfully less secure than the same
  157: things running without Xen.  One can boot Xen or boot regular NetBSD
  158: alternately with little problems, simply refraining from starting the
  159: Xen daemons when not running Xen.
  160: 
  161: Note that NetBSD as dom0 does not support multiple CPUs.  This will
  162: limit the performance of the Xen/dom0 workstation approach.  In theory
  163: the only issue is that the "backend drivers" are not yet MPSAFE:
  164:   https://mail-index.netbsd.org/netbsd-users/2014/08/29/msg015195.html
  165: 
  166: Installation of NetBSD
  167: ----------------------
  168: 
  169: First,
  170: [install NetBSD/amd64](/guide/inst/)
  171: just as you would if you were not using Xen.
  172: However, the partitioning approach is very important.
  173: 
  174: If you want to use RAIDframe for the dom0, there are no special issues
  175: for Xen.  Typically one provides RAID storage for the dom0, and the
  176: domU systems are unaware of RAID.  The 2nd-stage loader bootxx_* skips
  177: over a RAID1 header to find /boot from a file system within a RAID
  178: partition; this is no different when booting Xen.
  179: 
  180: There are 4 styles of providing backing storage for the virtual disks
  181: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
  182: 
  183: With raw partitions, one has a disklabel (or gpt) partition sized for
  184: each virtual disk to be used by the domU.  (If you are able to predict
  185: how domU usage will evolve, please add an explanation to the HOWTO.
  186: Seriously, needs tend to change over time.)
  187: 
  188: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
  189: for domU disks.  This is almost as efficient as raw disk partitions
  190: and more flexible.  Hence raw disk partitions should typically not
  191: be used.
  192: 
  193: One can use files in the dom0 file system, typically created by dd'ing
  194: /dev/zero to create a specific size.  This is somewhat less efficient,
  195: but very convenient, as one can cp the files for backup, or move them
  196: between dom0 hosts.
  197: 
  198: Finally, in theory one can place the files backing the domU disks in a
  199: SAN.  (This is an invitation for someone who has done this to add a
  200: HOWTO page.)
  201: 
  202: Installation of Xen
  203: -------------------
  204: 
  205: We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as
  206: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
  207: Ensure that your packages are recent.
  208: 
  209: Once this is done, install the Xen kernel itself:
  210: 
  211: [[!template id=programlisting text="""
  212: # cp /usr/pkg/xen48-kernel/xen.gz /
  213: """]]
  214: 
  215: Then, place a NetBSD XEN3_DOM0 kernel in /, copied from
  216: releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz of a NetBSD build.
  217: 
  218: Add a line to /boot.cfg to boot Xen:
  219: 
  220: [[!template id=programlisting text="""
  221: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  222: """]]
  223: 
  224: which specifies that the dom0 should have 512MB of ram, leaving the rest
  225: to be allocated for domUs.  To use a serial console, use
  226: 
  227: [[!template id=programlisting text="""
  228: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  229: """]]
  230: 
  231: which will use the first serial port for Xen (which counts starting
  232: from 1, unlike NetBSD which counts starting from 0), forcing
  233: speed/parity.  Because the NetBSD command line lacks a
  234: "console=pc" argument, it will use the default "xencons" console device,
  235: which directs the console I/O through Xen to the same console device Xen
  236: itself uses (in this case, the serial port).
  237: 
  238: In an attempt to add performance, one can also add:
  239: 
  240: [[!template id=programlisting text="""
  241: dom0_max_vcpus=1 dom0_vcpus_pin
  242: """]]
  243: 
  244: to force only one vcpu to be provided (since NetBSD dom0 can't use
  245: more) and to pin that vcpu to a physical CPU.
  246: 
  247: Xen has [many boot
  248: options](http://xenbits.xenproject.org/docs/4.5-testing/misc/xen-command-line.html),
  249: and other than dom0 memory and max_vcpus, they are generally not
  250: necessary.
  251: 
  252: As with non-Xen systems, you should have a line to boot /netbsd (a
  253: kernel that works without Xen).
  254: 
  255: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  256: than GENERIC without Xen.
  257: 
  258: Using grub (historic)
  259: ---------------------
  260: 
  261: Before NetBSD's native bootloader could support Xen, the use of
  262: grub was recommended.  If necessary, see the
  263: [old grub information](/ports/xen/howto-grub).
  264: 
  265: The [HowTo on Installing into
  266: RAID-1](https://mail-index.NetBSD.org/port-xen/2006/03/01/0010.html)
  267: explains how to set up booting a dom0 with Xen using grub with
  268: NetBSD's RAIDframe.  (This is obsolete with the use of NetBSD's native
  269: boot.  Now, just create a system with RAID-1, and alter /boot.cfg as
  270: described above.)
  271: 
  272: Configuring Xen
  273: ---------------
  274: 
  275: Now, you have a system that will boot Xen and the dom0 kernel, but not
  276: do anything else special.  Make sure that you have rebooted into Xen.
  277: There will be no domUs, and none can be started because you still have
  278: to configure the dom0 daemons.
  279: 
  280: The daemons which should be run vary with Xen version and with whether
  281: one is using xm or xl. Xen 4.2 and up packages use xl. To use xm with 4.2,
  282: edit xendomains to use xm instead.
  283: 
  284: For 4.1 and up, you should enable xencommons.  Not enabling xencommons
  285: will result in a hang; it is necessary to hit ^C on the console to let
  286: the machine finish booting.  If you are using xm (default in 4.1, or
  287: if you changed xendomains in 4.2), you should also enable xend:
  288: 
  289: [[!template id=programlisting text="""
  290: xend=YES # only if using xm, and only installed <= 4.2
  291: xencommons=YES
  292: """]]
  293: 
  294: TODO: Recommend for/against xen-watchdog.
  295: 
  296: After you have configured the daemons and either started them (in the
  297: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
  298: available resources, and running domains.  An example with xl follows:
  299: 
  300: [[!template id=programlisting text="""
  301: # xl dmesg
  302: ... xen's boot info ...
  303: # xl info
  304: ... available memory, etc ...
  305: # xl list
  306: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  307: Domain-0           0       64    0  r----     58.1
  308: """]]
  309: 
  310: Xen logs will be in /var/log/xen.
  311: 
  312: ### Issues with xencommons
  313: 
  314: xencommons starts xenstored, which stores data on behalf of dom0 and
  315: domUs.  It does not currently work to stop and start xenstored.
  316: Certainly all domUs should be shutdown first, following the sort order
  317: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  318: and is not notified when xenstored exits, leading to not recreating
  319: the state when the new xenstored starts.  Until there's a mechanism to
  320: make this work, one should not expect to be able to restart xenstored
  321: (and thus xencommons).  There is currently no reason to expect that
  322: this will get fixed any time soon.
  323: 
  324: ### No-longer needed advice about devices
  325: 
  326: The installation of NetBSD should already have created devices for xen
  327: (xencons, xenevt, xsd_kva), but if they are not present, create them:
  328: 
  329: [[!template id=programlisting text="""
  330: cd /dev && sh MAKEDEV xen
  331: """]]
  332: 
  333: anita (for testing NetBSD)
  334: --------------------------
  335: 
  336: With the setup so far (assuming 4.2/xl), one should be able to run
  337: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  338: root, because anita must create a domU):
  339: 
  340: [[!template id=programlisting text="""
  341: anita --vmm=xl test file:///usr/obj/i386/
  342: """]]
  343: 
  344: Alternatively, one can use --vmm=xm to use xm-based domU creation
  345: instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.
  346:     
  347: Xen-specific NetBSD issues
  348: --------------------------
  349: 
  350: There are (at least) two additional things different about NetBSD as a
  351: dom0 kernel compared to hardware.
  352: 
  353: One is that the module ABI is different because some of the #defines
  354: change, so one must build modules for Xen.  As of netbsd-7, the build
  355: system does this automatically.  TODO: check this.  (Before building
  356: Xen modules was added, it was awkward to use modules to the point
  357: where it was considered that it did not work.)
  358: 
  359: The other difference is that XEN3_DOM0 does not have exactly the same
  360: options as GENERIC.  While it is debatable whether or not this is a
  361: bug, users should be aware of this and can simply add missing config
  362: items if desired.
  363: 
  364: Updating NetBSD in a dom0
  365: -------------------------
  366: 
  367: This is just like updating NetBSD on bare hardware, assuming the new
  368: version supports the version of Xen you are running.  Generally, one
  369: replaces the kernel and reboots, and then overlays userland binaries
  370: and adjusts /etc.
  371: 
  372: Note that one must update both the non-Xen kernel typically used for
  373: rescue purposes and the DOM0 kernel used with Xen.
  374: 
  375: Converting from grub to /boot
  376: -----------------------------
  377: 
  378: These instructions were [TODO: will be] used to convert a system from
  379: grub to /boot.  The system was originally installed in February of
  380: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  381: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  382: 4.1 and grub, much like the message linked earlier in the grub
  383: section.
  384: 
  385:         # Install MBR bootblocks on both disks. 
  386:         fdisk -i /dev/rwd0d
  387:         fdisk -i /dev/rwd1d
  388:         # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  389:         installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  390:         installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  391:         # Install secondary boot loader
  392:         cp -p /usr/mdec/boot /
  393:         # Create boot.cfg following earlier guidance:
  394:         menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  395:         menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  396:         menu=GENERIC:boot
  397:         menu=GENERIC single-user:boot -s
  398:         menu=GENERIC.ok:boot netbsd.ok
  399:         menu=GENERIC.ok single-user:boot netbsd.ok -s
  400:         menu=Drop to boot prompt:prompt
  401:         default=1
  402:         timeout=30
  403: 
  404: TODO: actually do this and fix it if necessary.
  405: 
  406: Upgrading Xen versions
  407: ---------------------
  408: 
  409: Minor version upgrades are trivial.  Just rebuild/replace the
  410: xenkernel version and copy the new xen.gz to / (where /boot.cfg
  411: references it), and reboot.
  412: 
  413: Major version upgrades are conceptually not difficult, but can run
  414: into all the issues found when installing Xen.  Assuming migration
  415: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
  416: install the xenkernel42 and xentools42 packages.  Copy the 4.2 xen.gz
  417: to /.
  418: 
  419: Ensure that the contents of /etc/rc.d/xen* are correct.  Specifically,
  420: they must match the package you just installed and not be left over
  421: from some previous installation.
  422: 
  423: Enable the correct set of daemons; see the configuring section above.
  424: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
  425: 
  426: Ensure that the domU config files are valid for the new version.
  427: Specifically, for 4.x remove autorestart=True, and ensure that disks
  428: are specified with numbers as the second argument, as the examples
  429: above show, and not NetBSD device names.
  430: 
  431: Unprivileged domains (domU)
  432: ===========================
  433: 
  434: This section describes general concepts about domUs.  It does not
  435: address specific domU operating systems or how to install them.  The
  436: config files for domUs are typically in /usr/pkg/etc/xen, and are
  437: typically named so that the file name, domU name and the domU's host
  438: name match.
  439: 
  440: The domU is provided with CPU and memory by Xen, configured by the
  441: dom0.  The domU is provided with disk and network by the dom0,
  442: mediated by Xen, and configured in the dom0.
  443: 
  444: Entropy in domUs can be an issue; physical disks and network are on
  445: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  446: 
  447: Config files
  448: ------------
  449: 
  450: There is no good order to present config files and the concepts
  451: surrounding what is being configured.  We first show an example config
  452: file, and then in the various sections give details.
  453: 
  454: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
  455: for a large number of well-commented examples, mostly for running
  456: GNU/Linux.
  457: 
  458: The following is an example minimal domain configuration file
  459: "/usr/pkg/etc/xen/foo".  It is (with only a name change) an actual
  460: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
  461: i386 domU).  The domU serves as a network file server.
  462: 
  463:         # -*- mode: python; -*-
  464: 
  465:         name = "domU-id"
  466:         kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  467:         memory = 1024
  468:         vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  469:         disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  470:                  'file:/n0/xen/foo-wd1,0x1,w' ]
  471: 
  472: The domain will have name given in the name setting.  The kernel has the
  473: host/domU name in it, so that on the dom0 one can update the various
  474: domUs independently.  The vif line causes an interface to be provided,
  475: with a specific mac address (do not reuse MAC addresses!), in bridge
  476: mode.  Two disks are provided, and they are both writable; the bits
  477: are stored in files and Xen attaches them to a vnd(4) device in the
  478: dom0 on domain creation.  The system treats xbd0 as the boot device
  479: without needing explicit configuration.
  480: 
  481: By default xm looks for domain config files in /usr/pkg/etc/xen.  Note
  482: that "xm create" takes the name of a config file, while other commands
  483: take the name of a domain.  To create the domain, connect to the
  484: console, create the domain while attaching the console, shutdown the
  485: domain, and see if it has finished stopping, do (or xl with Xen >=
  486: 4.2):
  487: 
  488:         xm create foo
  489:         xm console foo
  490:         xm create -c foo
  491:         xm shutdown foo
  492:         xm list
  493: 
  494: Typing ^] will exit the console session.  Shutting down a domain is
  495: equivalent to pushing the power button; a NetBSD domU will receive a
  496: power-press event and do a clean shutdown.  Shutting down the dom0
  497: will trigger controlled shutdowns of all configured domUs.
  498: 
  499: domU kernels
  500: ------------
  501: 
  502: On a physical computer, the BIOS reads sector 0, and a chain of boot
  503: loaders finds and loads a kernel.  Normally this comes from the root
  504: file system.  With Xen domUs, the process is totally different.  The
  505: normal path is for the domU kernel to be a file in the dom0's
  506: file system.  At the request of the dom0, Xen loads that kernel into a
  507: new domU instance and starts execution.  While domU kernels can be
  508: anyplace, reasonable places to store domU kernels on the dom0 are in /
  509: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
  510: config files), or in /u0/xen (where the vdisks are).
  511: 
  512: Note that loading the domU kernel from the dom0 implies that boot
  513: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  514: See the VPS section near the end for discussion of alternate ways to
  515: obtain domU kernels.
  516: 
  517: CPU and memory
  518: --------------
  519: 
  520: A domain is provided with some number of vcpus, less than the number
  521: of CPUs seen by the hypervisor.  (For a dom0, this is controlled by
  522: the boot argument "dom0_max_vcpus=1".)  For a domU, it is controlled
  523: from the config file by the "vcpus = N" directive.
  524: 
  525: A domain is provided with memory; this is controlled in the config
  526: file by "memory = N" (in megabytes).  In the straightforward case, the
  527: sum of the the memory allocated to the dom0 and all domUs must be less
  528: than the available memory.
  529: 
  530: Xen also provides a "balloon" driver, which can be used to let domains
  531: use more memory temporarily.  TODO: Explain better, and explain how
  532: well it works with NetBSD.
  533: 
  534: Virtual disks
  535: -------------
  536: 
  537: With the file/vnd style, typically one creates a directory,
  538: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  539: domUs.  Then, for each domU disk, one writes zeros to a file that then
  540: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  541: for the first virtual disk for the domU called foo.  Writing zeros to
  542: the file serves two purposes.  One is that preallocating the contents
  543: improves performance.  The other is that vnd on sparse files has
  544: failed to work.  TODO: give working/notworking NetBSD versions for
  545: sparse vnd and gnats reference.  Note that the use of file/vnd for Xen
  546: is not really different than creating a file-backed virtual disk for
  547: some other purpose, except that xentools handles the vnconfig
  548: commands.  To create an empty 4G virtual disk, simply do
  549: 
  550:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  551: 
  552: Do not use qemu-img-xen, because this will create sparse file.  There
  553: have been recent (2015) reports of sparse vnd(4) devices causing
  554: lockups, but there is apparently no PR.
  555: 
  556: With the lvm style, one creates logical devices.  They are then used
  557: similarly to vnds.  TODO: Add an example with lvm.
  558: 
  559: In domU config files, the disks are defined as a sequence of 3-tuples.
  560: The first element is "method:/path/to/disk".  Common methods are
  561: "file:" for file-backed vnd. and "phy:" for something that is already
  562: a (TODO: character or block) device.
  563: 
  564: The second element is an artifact of how virtual disks are passed to
  565: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  566: are given a device name to associate with the disk, and values like
  567: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  568: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  569: second argument.  The name given is converted to a major/minor by
  570: calling stat(2) on the name in /dev and this is passed to the domU.
  571: In the general case, the dom0 and domU can be different operating
  572: systems, and it is an unwarranted assumption that they have consistent
  573: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  574: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  575: for the second works fine and avoids this issue.  For a GNU/Linux
  576: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  577: /dev/hda1.
  578: 
  579: The third element is "w" for writable disks, and "r" for read-only
  580: disks.
  581: 
  582: Note that NetBSD by default creates only vnd[0123].  If you need more
  583: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  584: dom0.
  585: 
  586: Note that NetBSD by default creates only xbd[0123].  If you need more
  587: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  588: 
  589: Virtual Networking
  590: ------------------
  591: 
  592: Xen provides virtual Ethernets, each of which connects the dom0 and a
  593: domU.  For each virtual network, there is an interface "xvifN.M" in
  594: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  595: name).  The interfaces behave as if there is an Ethernet with two
  596: adapters connected.  From this primitive, one can construct various
  597: configurations.  We focus on two common and useful cases for which
  598: there are existing scripts: bridging and NAT.
  599: 
  600: With bridging (in the example above), the domU perceives itself to be
  601: on the same network as the dom0.  For server virtualization, this is
  602: usually best.  Bridging is accomplished by creating a bridge(4) device
  603: and adding the dom0's physical interface and the various xvifN.0
  604: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  605: config file.  The bridge must be set up already in the dom0; an
  606: example /etc/ifconfig.bridge0 is:
  607: 
  608:         create
  609:         up
  610:         !brconfig bridge0 add wm0
  611: 
  612: With NAT, the domU perceives itself to be behind a NAT running on the
  613: dom0.  This is often appropriate when running Xen on a workstation.
  614: TODO: NAT appears to be configured by "vif = [ '' ]".
  615: 
  616: The MAC address specified is the one used for the interface in the new
  617: domain.  The interface in dom0 will use this address XOR'd with
  618: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  619: 
  620: Sizing domains
  621: --------------
  622: 
  623: Modern x86 hardware has vast amounts of resources.  However, many
  624: virtual servers can function just fine on far less.  A system with
  625: 512M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  626: far easier to adjust virtual resources than physical ones.  For
  627: memory, it's just a config file edit and a reboot.  For disk, one can
  628: create a new file and vnconfig it (or lvm), and then dump/restore,
  629: just like updating physical disks, but without having to be there and
  630: without those pesky connectors.
  631: 
  632: Starting domains automatically
  633: ------------------------------
  634: 
  635: To start domains foo at bar at boot and shut them down cleanly on dom0
  636: shutdown, in rc.conf add:
  637: 
  638:         xendomains="foo bar"
  639: 
  640: Note that earlier versions of the xentools41 xendomains rc.d script
  641: used xl, when one should use xm with 4.1.
  642: 
  643: Creating specific unprivileged domains (domU)
  644: =============================================
  645: 
  646: Creating domUs is almost entirely independent of operating system.  We
  647: have already presented the basics of config files.  Note that you must
  648: have already completed the dom0 setup so that "xl list" (or "xm list")
  649: works.
  650: 
  651: Creating an unprivileged NetBSD domain (domU)
  652: ---------------------------------------------
  653: 
  654: See the earlier config file, and adjust memory.  Decide on how much
  655: storage you will provide, and prepare it (file or lvm).
  656: 
  657: While the kernel will be obtained from the dom0 file system, the same
  658: file should be present in the domU as /netbsd so that tools like
  659: savecore(8) can work.   (This is helpful but not necessary.)
  660: 
  661: The kernel must be specifically for Xen and for use as a domU.  The
  662: i386 and amd64 provide the following kernels:
  663: 
  664:         i386 XEN3PAE_DOMU
  665:         amd64 XEN3_DOMU
  666: 
  667: This will boot NetBSD, but this is not that useful if the disk is
  668: empty.  One approach is to unpack sets onto the disk outside of xen
  669: (by mounting it, just as you would prepare a physical disk for a
  670: system you can't run the installer on).
  671: 
  672: A second approach is to run an INSTALL kernel, which has a miniroot
  673: and can load sets from the network.  To do this, copy the INSTALL
  674: kernel to / and change the kernel line in the config file to:
  675: 
  676:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  677: 
  678: Then, start the domain as "xl create -c configname".
  679: 
  680: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  681: line should be used in the config file.
  682: 
  683:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  684: 
  685: After booting the domain, the option to install via CDROM may be
  686: selected.  The CDROM device should be changed to `xbd1d`.
  687: 
  688: Once done installing, "halt -p" the new domain (don't reboot or halt,
  689: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  690: config file), switch the config file back to the XEN3_DOMU kernel,
  691: and start the new domain again. Now it should be able to use "root on
  692: xbd0a" and you should have a, functional NetBSD domU.
  693: 
  694: TODO: check if this is still accurate.
  695: When the new domain is booting you'll see some warnings about *wscons*
  696: and the pseudo-terminals. These can be fixed by editing the files
  697: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  698: `/etc/ttys`, except *console*, like this:
  699: 
  700:     console "/usr/libexec/getty Pc"         vt100   on secure
  701:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  702:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  703:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  704:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  705: 
  706: Finally, all screens must be commented out from `/etc/wscons.conf`.
  707: 
  708: It is also desirable to add
  709: 
  710:         powerd=YES
  711: 
  712: in rc.conf. This way, the domain will be properly shut down if
  713: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  714: 
  715: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  716: file system.  However, various programs (e.g. netstat) will use that
  717: kernel to look up symbols to read from kernel virtual memory.  If
  718: /netbsd is not the running kernel, those lookups will fail.  (This is
  719: not really a Xen-specific issue, but because the domU kernel is
  720: obtained from the dom0, it is far more likely to be out of sync or
  721: missing with Xen.)
  722: 
  723: Creating an unprivileged Linux domain (domU)
  724: --------------------------------------------
  725: 
  726: Creating unprivileged Linux domains isn't much different from
  727: unprivileged NetBSD domains, but there are some details to know.
  728: 
  729: First, the second parameter passed to the disk declaration (the '0x1' in
  730: the example below)
  731: 
  732:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  733: 
  734: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  735: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  736: So, hda1 which has major 3 and minor 1 on a Linux system will have
  737: device number 0x301.  Alternatively, devices names can be used (hda,
  738: hdb, ...)  as xentools has a table to map these names to devices
  739: numbers.  To export a partition to a Linux guest we can use:
  740: 
  741:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  742:         root = "/dev/hda1 ro"
  743: 
  744: and it will appear as /dev/hda on the Linux system, and be used as root
  745: partition.
  746: 
  747: To install the Linux system on the partition to be exported to the
  748: guest domain, the following method can be used: install
  749: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  750: that will be the root partition of your Linux domain, and mount it.
  751: Then copy the files from a working Linux system, make adjustments in
  752: `/etc` (fstab, network config).  It should also be possible to extract
  753: binary packages such as .rpm or .deb directly to the mounted partition
  754: using the appropriate tool, possibly running under NetBSD's Linux
  755: emulation.  Once the file system has been populated, umount it.  If
  756: desirable, the file system can be converted to ext3 using tune2fs -j.
  757: It should now be possible to boot the Linux guest domain, using one of
  758: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  759: 
  760: To get the Linux console right, you need to add:
  761: 
  762:     extra = "xencons=tty1"
  763: 
  764: to your configuration since not all Linux distributions auto-attach a
  765: tty to the xen console.
  766: 
  767: Creating an unprivileged Solaris domain (domU)
  768: ----------------------------------------------
  769: 
  770: See possibly outdated
  771: [Solaris domU instructions](/ports/xen/howto-solaris/).
  772: 
  773: 
  774: PCI passthrough: Using PCI devices in guest domains
  775: ---------------------------------------------------
  776: 
  777: The dom0 can give other domains access to selected PCI
  778: devices. This can allow, for example, a non-privileged domain to have
  779: access to a physical network interface or disk controller.  However,
  780: keep in mind that giving a domain access to a PCI device most likely
  781: will give the domain read/write access to the whole physical memory,
  782: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  783: device.  Also, it's not possible to export ISA devices to non-dom0
  784: domains, which means that the primary VGA adapter can't be exported.
  785: A guest domain trying to access the VGA registers will panic.
  786: 
  787: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  788: not been ported to later versions at this time.
  789: 
  790: For a PCI device to be exported to a domU, is has to be attached to
  791: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  792: pciback.hide boot parameter will attach to "pciback" instead of the
  793: usual driver.  The list of devices is specified as "(bus:dev.func)",
  794: where bus and dev are 2-digit hexadecimal numbers, and func a
  795: single-digit number:
  796: 
  797:         pciback.hide=(00:0a.0)(00:06.0)
  798: 
  799: pciback devices should show up in the dom0's boot messages, and the
  800: devices should be listed in the `/kern/xen/pci` directory.
  801: 
  802: PCI devices to be exported to a domU are listed in the "pci" array of
  803: the domU's config file, with the format "0000:bus:dev.func".
  804: 
  805:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  806: 
  807: In the domU an "xpci" device will show up, to which one or more pci
  808: buses will attach.  Then the PCI drivers will attach to PCI buses as
  809: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  810: or any PCI drivers built in by default; you have to build your own
  811: kernel to use PCI devices in a domU.  Here's a kernel config example;
  812: note that only the "xpci" lines are unusual.
  813: 
  814:         include         "arch/i386/conf/XEN3_DOMU"
  815: 
  816:         # Add support for PCI buses to the XEN3_DOMU kernel
  817:         xpci* at xenbus ?
  818:         pci* at xpci ?
  819: 
  820:         # PCI USB controllers
  821:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  822: 
  823:         # USB bus support
  824:         usb*    at uhci?
  825: 
  826:         # USB Hubs
  827:         uhub*   at usb?
  828:         uhub*   at uhub? port ? configuration ? interface ?
  829: 
  830:         # USB Mass Storage
  831:         umass*  at uhub? port ? configuration ? interface ?
  832:         wd*     at umass?
  833:         # SCSI controllers
  834:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  835: 
  836:         # SCSI bus support (for both ahc and umass)
  837:         scsibus* at scsi?
  838: 
  839:         # SCSI devices
  840:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  841:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  842: 
  843: 
  844: NetBSD as a domU in a VPS
  845: =========================
  846: 
  847: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  848: hardware.  This section explains how to deal with Xen in a domU as a
  849: virtual private server where you do not control or have access to the
  850: dom0.  This is not intended to be an exhaustive list of VPS providers;
  851: only a few are mentioned that specifically support NetBSD.
  852: 
  853: VPS operators provide varying degrees of access and mechanisms for
  854: configuration.  The big issue is usually how one controls which kernel
  855: is booted, because the kernel is nominally in the dom0 file system (to
  856: which VPS users do not normally have access).  A second issue is how
  857: to install NetBSD.
  858: A VPS user may want to compile a kernel for security updates, to run
  859: npf, run IPsec, or any other reason why someone would want to change
  860: their kernel.
  861: 
  862: One approach is to have an administrative interface to upload a kernel,
  863: or to select from a prepopulated list.  Other approaches are pygrub
  864: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  865: kernel from the domU file system.  This is closer to a regular physical
  866: computer, where someone who controls a machine can replace the kernel.
  867: 
  868: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  869: multiple vcpus, and it is typical for VPS providers to enable multiple
  870: CPUs for NetBSD domUs.
  871: 
  872: pygrub
  873: -------
  874: 
  875: pygrub runs in the dom0 and looks into the domU file system.  This
  876: implies that the domU must have a kernel in a file system in a format
  877: known to pygrub.  As of 2014, pygrub seems to be of mostly historical
  878: interest.
  879: 
  880: pvgrub
  881: ------
  882: 
  883: pvgrub is a version of grub that uses PV operations instead of BIOS
  884: calls.  It is booted from the dom0 as the domU kernel, and then reads
  885: /grub/menu.lst and loads a kernel from the domU file system.
  886: 
  887: [Panix](http://www.panix.com/) lets users use pvgrub.  Panix reports
  888: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  889: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  890: page](http://www.panix.com/v-colo/grub.html), which describes only
  891: Linux but should be updated to cover NetBSD :-).
  892: 
  893: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
  894: their own kernel.  See then [prgmr.com NetBSD
  895: HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
  896: (which is in need of updating).
  897: 
  898: It appears that [grub's FFS
  899: code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
  900: does not support all aspects of modern FFS, but there are also reports
  901: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  902: partition for the kernel with the intent that grub can understand it,
  903: which leads to /netbsd not being the actual kernel.  One must remember
  904: to update the special boot partition.
  905: 
  906: Amazon
  907: ------
  908: 
  909: See the [Amazon EC2 page](/amazon_ec2/).
  910: 
  911: TODO items for improving NetBSD/xen
  912: ===================================
  913: 
  914: * Make the NetBSD dom0 kernel work with SMP.
  915: * Test the Xen 4.5 packages adequately to be able to recommend them as
  916:   the standard approach.
  917: * Get PCI passthrough working on Xen 4.5
  918: * Get pvgrub into pkgsrc, either via xentools or separately.
  919: * grub
  920:   * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
  921:     fragsize/blocksize (UFS2 support may be present; the point is to
  922:     make it so that with any UFS1/UFS2 file system setup that works
  923:     with NetBSD grub will also work).
  924:     See [pkg/40258](https://gnats.netbsd.org/40258).
  925:   * Push patches upstream.
  926:   * Get UFS2 patches into pvgrub.
  927: * Add support for PV ops to a version of /boot, and make it usable as
  928:   a kernel in Xen, similar to pvgrub.
  929: 
  930: Random pointers
  931: ===============
  932: 
  933: This section contains links from elsewhere not yet integrated into the
  934: HOWTO, and other guides.
  935: 
  936: * http://www.lumbercartel.ca/library/xen/
  937: * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html
  938: * https://gmplib.org/~tege/xen.html

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