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    1: [[!meta title="Xen HowTo"]]
    3: Xen is a Type 1 hypervisor which supports running multiple guest operating
    4: systems on a single physical machine. One uses the Xen kernel to control the
    5: CPU, memory and console, a dom0 operating system which mediates access to
    6: other hardware (e.g., disks, network, USB), and one or more domU operating
    7: systems which operate in an unprivileged virtualized environment. IO requests
    8: from the domU systems are forwarded by the Xen hypervisor to the dom0 to be
    9: fulfilled.
   11: Xen supports different styles of guest:
   13: [[!table data="""
   14: Style of guest	|Supported by NetBSD
   15: PV		|Yes (dom0, domU)
   16: HVM		|Yes (domU)
   17: PVHVM		|No
   18: PVH		|No
   19: """]]
   21: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
   22: hardware directly, but instead makes hypercalls to the hypervisor; PV
   23: guests must be specifically coded for Xen. In HVM mode, no guest
   24: modification is required; however, hardware support is required, such
   25: as VT-x on Intel CPUs and SVM on AMD CPUs.
   27: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   28: The dom0 can start one or more domUs.  (Booting is explained in detail
   29: in the dom0 section.)
   31: This HOWTO presumes a basic familiarity with the Xen system
   32: architecture, with installing NetBSD on i386/amd64 hardware, and with
   33: installing software from pkgsrc.  See also the [Xen
   34: website](
   36: This HOWTO attempts to address both the case of running a NetBSD dom0
   37: on hardware and running domUs under it (NetBSD and other), and also
   38: running NetBSD as a domU in a VPS.
   40: Versions and Support
   41: ====================
   43: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   44: xenkernel and xentools.  We will refer only to the kernel versions,
   45: but note that both packages must be installed together and must have
   46: matching versions.
   48: Versions available in pkgsrc:
   50: [[!table data="""
   51: Xen Version	|Package Name	|Xen CPU Support	|EOL'ed By Upstream
   52: 4.2		|xenkernel42	|32bit, 64bit		|Yes
   53: 4.5		|xenkernel45	|64bit			|Yes
   54: 4.6		|xenkernel46	|64bit			|Partially
   55: 4.8		|xenkernel48	|64bit			|No
   56: 4.11		|xenkernel411	|64bit			|No
   57: """]]
   59: See also the [Xen Security Advisory page](
   61: Multiprocessor (SMP) support in NetBSD differs depending on the domain:
   63: [[!table data="""
   64: Domain		|Supports SMP
   65: dom0		|No
   66: domU		|Yes
   67: """]]
   69: Note: NetBSD support is called XEN3. However, it does support Xen 4,
   70: because the hypercall interface has remained identical.
   72: Architecture
   73: ------------
   75: Xen itself runs on x86_64 hardware.
   77: The dom0 system, plus each domU, can be either i386PAE or amd64.
   78: i386 without PAE is not supported.
   80: The standard approach is to use NetBSD/amd64 for the dom0.
   82: To use an i386PAE dom0, one must build or obtain a 64bit Xen kernel and
   83: install it on the system.
   85: For domUs, i386PAE is considered as
   86: [faster](
   87: than amd64.
   89: NetBSD as a dom0
   90: ================
   92: NetBSD can be used as a dom0 and works very well.  The following
   93: sections address installation, updating NetBSD, and updating Xen.
   95: Note that it doesn't make sense to talk about installing a dom0 OS
   96: without also installing Xen itself.  We first address installing
   97: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
   98: NetBSD install to a dom0 install by just changing the kernel and boot
   99: configuration.
  101: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
  102: 512M it worked reliably.  This does not make sense, but if you see
  103: "not ELF" after Xen boots, try increasing dom0 RAM.
  105: Styles of dom0 operation
  106: ------------------------
  108: There are two basic ways to use Xen.  The traditional method is for
  109: the dom0 to do absolutely nothing other than providing support to some
  110: number of domUs.  Such a system was probably installed for the sole
  111: purpose of hosting domUs, and sits in a server room on a UPS.
  113: The other way is to put Xen under a normal-usage computer, so that the
  114: dom0 is what the computer would have been without Xen, perhaps a
  115: desktop or laptop.  Then, one can run domUs at will.
  117: Installation of NetBSD
  118: ----------------------
  120: [Install NetBSD/amd64](/guide/inst/)
  121: just as you would if you were not using Xen.
  123: Installation of Xen
  124: -------------------
  126: We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as
  127: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
  128: Ensure that your packages are recent.
  130: Once this is done, install the Xen kernel itself:
  132: [[!template id=programlisting text="""
  133: # cp /usr/pkg/xen48-kernel/xen.gz /
  134: """]]
  136: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory, copied from
  137: `releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz` of a NetBSD build.
  139: Add a line to /boot.cfg to boot Xen:
  141: [[!template id=filecontent name="/boot.cfg" text="""
  142: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  143: """]]
  145: which specifies that the dom0 should have 512MB of ram, leaving the rest
  146: to be allocated for domUs.  To use a serial console, use
  148: [[!template id=filecontent name="/boot.cfg" text="""
  149: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  150: """]]
  152: which will use the first serial port for Xen (which counts starting
  153: from 1, unlike NetBSD which counts starting from 0), forcing
  154: speed/parity.  Because the NetBSD command line lacks a
  155: "console=pc" argument, it will use the default "xencons" console device,
  156: which directs the console I/O through Xen to the same console device Xen
  157: itself uses (in this case, the serial port).
  159: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
  160: to force only one vcpu to be provided (since NetBSD dom0 can't use
  161: more) and to pin that vcpu to a physical CPU.
  163: Xen has [many boot
  164: options](,
  165: and other than dom0 memory and max_vcpus, they are generally not
  166: necessary.
  168: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  169: than GENERIC without Xen.
  171: Configuring Xen
  172: ---------------
  174: Now, you have a system that will boot Xen and the dom0 kernel, but not
  175: do anything else special.  Make sure that you have rebooted into Xen.
  176: There will be no domUs, and none can be started because you still have
  177: to configure the dom0 daemons.
  179: Since Xen 4.2, the tool which should be used is `xl`.
  181: For 4.1 and up, you should enable `xencommons`:
  183: [[!template id=filecontent name="/etc/rc.conf" text="""
  184: xencommons=YES
  185: """]]
  187: Not enabling xencommons will result in a hang; it is necessary to hit `^C` on
  188: the console to let the machine finish booting:
  190: TODO: Recommend for/against xen-watchdog.
  192: After you have configured the daemons and either started them (in the
  193: order given) or rebooted, use `xl` to inspect Xen's boot messages,
  194: available resources, and running domains.  For example:
  196: [[!template id=programlisting text="""
  197: # xl dmesg
  198: ... xen's boot info ...
  199: # xl info
  200: ... available memory, etc ...
  201: # xl list
  202: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  203: Domain-0           0       64    0  r----     58.1
  204: """]]
  206: Xen logs will be in /var/log/xen.
  208: ### Issues with xencommons
  210: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
  211: domUs.  It does not currently work to stop and start xenstored.
  212: Certainly all domUs should be shutdown first, following the sort order
  213: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  214: and is not notified when xenstored exits, leading to not recreating
  215: the state when the new xenstored starts.  Until there's a mechanism to
  216: make this work, one should not expect to be able to restart xenstored
  217: (and thus xencommons).  There is currently no reason to expect that
  218: this will get fixed any time soon.
  220: anita (for testing NetBSD)
  221: --------------------------
  223: With the setup so far (assuming 4.8/xl), one should be able to run
  224: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  225: root, because anita must create a domU):
  227: [[!template id=programlisting text="""
  228: anita --vmm=xl test file:///usr/obj/i386/
  229: """]]
  231: Xen-specific NetBSD issues
  232: --------------------------
  234: There are (at least) two additional things different about NetBSD as a
  235: dom0 kernel compared to hardware.
  237: One is that the module ABI is different because some of the #defines
  238: change, so one must build modules for Xen.  As of netbsd-7, the build
  239: system does this automatically.
  241: The other difference is that XEN3_DOM0 does not have exactly the same
  242: options as GENERIC.  While it is debatable whether or not this is a
  243: bug, users should be aware of this and can simply add missing config
  244: items if desired.
  246: Updating NetBSD in a dom0
  247: -------------------------
  249: This is just like updating NetBSD on bare hardware, assuming the new
  250: version supports the version of Xen you are running.  Generally, one
  251: replaces the kernel and reboots, and then overlays userland binaries
  252: and adjusts `/etc`.
  254: Note that one must update both the non-Xen kernel typically used for
  255: rescue purposes and the DOM0 kernel used with Xen.
  257: Converting from grub to /boot
  258: -----------------------------
  260: These instructions were used to convert a system from
  261: grub to /boot.  The system was originally installed in February of
  262: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  263: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  264: 4.1 and grub, much like the message linked earlier in the grub
  265: section.
  267: [[!template id=programlisting text="""
  268: # Install MBR bootblocks on both disks.
  269: fdisk -i /dev/rwd0d
  270: fdisk -i /dev/rwd1d
  271: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  272: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  273: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  274: # Install secondary boot loader
  275: cp -p /usr/mdec/boot /
  276: # Create boot.cfg following earlier guidance:
  277: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  278: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  279: menu=GENERIC:boot
  280: menu=GENERIC single-user:boot -s
  281: menu=GENERIC.ok:boot netbsd.ok
  282: menu=GENERIC.ok single-user:boot netbsd.ok -s
  283: menu=Drop to boot prompt:prompt
  284: default=1
  285: timeout=30
  286: """]]
  288: Upgrading Xen versions
  289: ---------------------
  291: Minor version upgrades are trivial.  Just rebuild/replace the
  292: xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
  293: references it), and reboot.
  295: Unprivileged domains (domU)
  296: ===========================
  298: This section describes general concepts about domUs.  It does not
  299: address specific domU operating systems or how to install them.  The
  300: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
  301: typically named so that the file name, domU name and the domU's host
  302: name match.
  304: The domU is provided with CPU and memory by Xen, configured by the
  305: dom0.  The domU is provided with disk and network by the dom0,
  306: mediated by Xen, and configured in the dom0.
  308: Entropy in domUs can be an issue; physical disks and network are on
  309: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  311: Config files
  312: ------------
  314: There is no good order to present config files and the concepts
  315: surrounding what is being configured.  We first show an example config
  316: file, and then in the various sections give details.
  318: See /usr/pkg/share/examples/xen/xmexample*,
  319: for a large number of well-commented examples, mostly for running
  320: GNU/Linux.
  322: The following is an example minimal domain configuration file. The domU
  323: serves as a network file server.
  325: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  326: name = "domU-id"
  327: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  328: memory = 1024
  329: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  330: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  331:          'file:/n0/xen/foo-wd1,0x1,w' ]
  332: """]]
  334: The domain will have name given in the `name` setting.  The kernel has the
  335: host/domU name in it, so that on the dom0 one can update the various
  336: domUs independently.  The `vif` line causes an interface to be provided,
  337: with a specific mac address (do not reuse MAC addresses!), in bridge
  338: mode.  Two disks are provided, and they are both writable; the bits
  339: are stored in files and Xen attaches them to a vnd(4) device in the
  340: dom0 on domain creation.  The system treats xbd0 as the boot device
  341: without needing explicit configuration.
  343: By default, `xl` looks for domain config files in `/usr/pkg/etc/xen`.  Note
  344: that "xl create" takes the name of a config file, while other commands
  345: take the name of a domain.
  347: Examples of commands:
  349: [[!template id=programlisting text="""
  350: xl create foo
  351: xl console foo
  352: xl create -c foo
  353: xl shutdown foo
  354: xl list
  355: """]]
  357: Typing `^]` will exit the console session.  Shutting down a domain is
  358: equivalent to pushing the power button; a NetBSD domU will receive a
  359: power-press event and do a clean shutdown.  Shutting down the dom0
  360: will trigger controlled shutdowns of all configured domUs.
  362: domU kernels
  363: ------------
  365: On a physical computer, the BIOS reads sector 0, and a chain of boot
  366: loaders finds and loads a kernel.  Normally this comes from the root
  367: file system.  With Xen domUs, the process is totally different.  The
  368: normal path is for the domU kernel to be a file in the dom0's
  369: file system.  At the request of the dom0, Xen loads that kernel into a
  370: new domU instance and starts execution. domU kernels can be anyplace.
  372: Note that loading the domU kernel from the dom0 implies that boot
  373: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
  374: See the VPS section near the end for discussion of alternate ways to
  375: obtain domU kernels.
  377: CPU and memory
  378: --------------
  380: A domain is provided with some number of vcpus, less than the number
  381: of CPUs seen by the hypervisor. For a domU, it is controlled
  382: from the config file by the "vcpus = N" directive.
  384: A domain is provided with memory; this is controlled in the config
  385: file by "memory = N" (in megabytes).  In the straightforward case, the
  386: sum of the the memory allocated to the dom0 and all domUs must be less
  387: than the available memory.
  389: Xen also provides a "balloon" driver, which can be used to let domains
  390: use more memory temporarily.
  392: Virtual disks
  393: -------------
  395: With the file/vnd style, typically one creates a directory,
  396: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
  397: domUs.  Then, for each domU disk, one writes zeros to a file that then
  398: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
  399: for the first virtual disk for the domU called foo.  Writing zeros to
  400: the file serves two purposes.  One is that preallocating the contents
  401: improves performance.  The other is that vnd on sparse files has
  402: failed to work.  TODO: give working/notworking NetBSD versions for
  403: sparse vnd and gnats reference.  Note that the use of file/vnd for Xen
  404: is not really different than creating a file-backed virtual disk for
  405: some other purpose, except that xentools handles the vnconfig
  406: commands.  To create an empty 4G virtual disk, simply do
  408:         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
  410: Do not use qemu-img-xen, because this will create sparse file.  There
  411: have been recent (2015) reports of sparse vnd(4) devices causing
  412: lockups, but there is apparently no PR.
  414: With the lvm style, one creates logical devices.  They are then used
  415: similarly to vnds.  TODO: Add an example with lvm.
  417: In domU config files, the disks are defined as a sequence of 3-tuples.
  418: The first element is "method:/path/to/disk".  Common methods are
  419: "file:" for file-backed vnd. and "phy:" for something that is already
  420: a (TODO: character or block) device.
  422: The second element is an artifact of how virtual disks are passed to
  423: Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  424: are given a device name to associate with the disk, and values like
  425: "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  426: as xbd0, the second as xbd1, and so on.  However, xm/xl demand a
  427: second argument.  The name given is converted to a major/minor by
  428: calling stat(2) on the name in /dev and this is passed to the domU.
  429: In the general case, the dom0 and domU can be different operating
  430: systems, and it is an unwarranted assumption that they have consistent
  431: numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  432: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  433: for the second works fine and avoids this issue.  For a GNU/Linux
  434: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  435: /dev/hda1.
  437: The third element is "w" for writable disks, and "r" for read-only
  438: disks.
  440: Note that NetBSD by default creates only vnd[0123].  If you need more
  441: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  442: dom0.
  444: Note that NetBSD by default creates only xbd[0123].  If you need more
  445: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  447: Virtual Networking
  448: ------------------
  450: Xen provides virtual Ethernets, each of which connects the dom0 and a
  451: domU.  For each virtual network, there is an interface "xvifN.M" in
  452: the dom0, and in domU index N, a matching interface xennetM (NetBSD
  453: name).  The interfaces behave as if there is an Ethernet with two
  454: adapters connected.  From this primitive, one can construct various
  455: configurations.  We focus on two common and useful cases for which
  456: there are existing scripts: bridging and NAT.
  458: With bridging (in the example above), the domU perceives itself to be
  459: on the same network as the dom0.  For server virtualization, this is
  460: usually best.  Bridging is accomplished by creating a bridge(4) device
  461: and adding the dom0's physical interface and the various xvifN.0
  462: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  463: config file.  The bridge must be set up already in the dom0; an
  464: example /etc/ifconfig.bridge0 is:
  466: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
  467: create
  468: up
  469: !brconfig bridge0 add wm0
  470: """]]
  472: With NAT, the domU perceives itself to be behind a NAT running on the
  473: dom0.  This is often appropriate when running Xen on a workstation.
  474: TODO: NAT appears to be configured by "vif = [ '' ]".
  476: The MAC address specified is the one used for the interface in the new
  477: domain.  The interface in dom0 will use this address XOR'd with
  478: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  480: Sizing domains
  481: --------------
  483: Modern x86 hardware has vast amounts of resources.  However, many
  484: virtual servers can function just fine on far less.  A system with
  485: 512M of RAM and a 4G disk can be a reasonable choice.  Note that it is
  486: far easier to adjust virtual resources than physical ones.  For
  487: memory, it's just a config file edit and a reboot.  For disk, one can
  488: create a new file and vnconfig it (or lvm), and then dump/restore,
  489: just like updating physical disks, but without having to be there and
  490: without those pesky connectors.
  492: Starting domains automatically
  493: ------------------------------
  495: To start domains foo at bar at boot and shut them down cleanly on dom0
  496: shutdown, in rc.conf add:
  498:         xendomains="foo bar"
  500: Note that earlier versions of the xentools41 xendomains rc.d script
  501: used xl, when one should use xm with 4.1.
  503: Creating specific unprivileged domains (domU)
  504: =============================================
  506: Creating domUs is almost entirely independent of operating system.  We
  507: have already presented the basics of config files.  Note that you must
  508: have already completed the dom0 setup so that "xl list" (or "xm list")
  509: works.
  511: Creating an unprivileged NetBSD domain (domU)
  512: ---------------------------------------------
  514: See the earlier config file, and adjust memory.  Decide on how much
  515: storage you will provide, and prepare it (file or lvm).
  517: While the kernel will be obtained from the dom0 file system, the same
  518: file should be present in the domU as /netbsd so that tools like
  519: savecore(8) can work.   (This is helpful but not necessary.)
  521: The kernel must be specifically for Xen and for use as a domU.  The
  522: i386 and amd64 provide the following kernels:
  524:         i386 XEN3PAE_DOMU
  525:         amd64 XEN3_DOMU
  527: This will boot NetBSD, but this is not that useful if the disk is
  528: empty.  One approach is to unpack sets onto the disk outside of xen
  529: (by mounting it, just as you would prepare a physical disk for a
  530: system you can't run the installer on).
  532: A second approach is to run an INSTALL kernel, which has a miniroot
  533: and can load sets from the network.  To do this, copy the INSTALL
  534: kernel to / and change the kernel line in the config file to:
  536:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  538: Then, start the domain as "xl create -c configname".
  540: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  541: line should be used in the config file.
  543:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  545: After booting the domain, the option to install via CDROM may be
  546: selected.  The CDROM device should be changed to `xbd1d`.
  548: Once done installing, "halt -p" the new domain (don't reboot or halt,
  549: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  550: config file), switch the config file back to the XEN3_DOMU kernel,
  551: and start the new domain again. Now it should be able to use "root on
  552: xbd0a" and you should have a, functional NetBSD domU.
  554: TODO: check if this is still accurate.
  555: When the new domain is booting you'll see some warnings about *wscons*
  556: and the pseudo-terminals. These can be fixed by editing the files
  557: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  558: `/etc/ttys`, except *console*, like this:
  560:     console "/usr/libexec/getty Pc"         vt100   on secure
  561:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  562:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  563:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  564:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  566: Finally, all screens must be commented out from `/etc/wscons.conf`.
  568: It is also desirable to add
  570:         powerd=YES
  572: in rc.conf. This way, the domain will be properly shut down if
  573: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  575: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  576: file system.  However, various programs (e.g. netstat) will use that
  577: kernel to look up symbols to read from kernel virtual memory.  If
  578: /netbsd is not the running kernel, those lookups will fail.  (This is
  579: not really a Xen-specific issue, but because the domU kernel is
  580: obtained from the dom0, it is far more likely to be out of sync or
  581: missing with Xen.)
  583: Creating an unprivileged Linux domain (domU)
  584: --------------------------------------------
  586: Creating unprivileged Linux domains isn't much different from
  587: unprivileged NetBSD domains, but there are some details to know.
  589: First, the second parameter passed to the disk declaration (the '0x1' in
  590: the example below)
  592:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  594: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  595: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  596: So, hda1 which has major 3 and minor 1 on a Linux system will have
  597: device number 0x301.  Alternatively, devices names can be used (hda,
  598: hdb, ...)  as xentools has a table to map these names to devices
  599: numbers.  To export a partition to a Linux guest we can use:
  601:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  602:         root = "/dev/hda1 ro"
  604: and it will appear as /dev/hda on the Linux system, and be used as root
  605: partition.
  607: To install the Linux system on the partition to be exported to the
  608: guest domain, the following method can be used: install
  609: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  610: that will be the root partition of your Linux domain, and mount it.
  611: Then copy the files from a working Linux system, make adjustments in
  612: `/etc` (fstab, network config).  It should also be possible to extract
  613: binary packages such as .rpm or .deb directly to the mounted partition
  614: using the appropriate tool, possibly running under NetBSD's Linux
  615: emulation.  Once the file system has been populated, umount it.  If
  616: desirable, the file system can be converted to ext3 using tune2fs -j.
  617: It should now be possible to boot the Linux guest domain, using one of
  618: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  620: To get the Linux console right, you need to add:
  622:     extra = "xencons=tty1"
  624: to your configuration since not all Linux distributions auto-attach a
  625: tty to the xen console.
  627: Creating an unprivileged Solaris domain (domU)
  628: ----------------------------------------------
  630: See possibly outdated
  631: [Solaris domU instructions](/ports/xen/howto-solaris/).
  634: PCI passthrough: Using PCI devices in guest domains
  635: ---------------------------------------------------
  637: The dom0 can give other domains access to selected PCI
  638: devices. This can allow, for example, a non-privileged domain to have
  639: access to a physical network interface or disk controller.  However,
  640: keep in mind that giving a domain access to a PCI device most likely
  641: will give the domain read/write access to the whole physical memory,
  642: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  643: device.  Also, it's not possible to export ISA devices to non-dom0
  644: domains, which means that the primary VGA adapter can't be exported.
  645: A guest domain trying to access the VGA registers will panic.
  647: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  648: not been ported to later versions at this time.
  650: For a PCI device to be exported to a domU, is has to be attached to
  651: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  652: pciback.hide boot parameter will attach to "pciback" instead of the
  653: usual driver.  The list of devices is specified as "(bus:dev.func)",
  654: where bus and dev are 2-digit hexadecimal numbers, and func a
  655: single-digit number:
  657:         pciback.hide=(00:0a.0)(00:06.0)
  659: pciback devices should show up in the dom0's boot messages, and the
  660: devices should be listed in the `/kern/xen/pci` directory.
  662: PCI devices to be exported to a domU are listed in the "pci" array of
  663: the domU's config file, with the format "0000:bus:dev.func".
  665:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  667: In the domU an "xpci" device will show up, to which one or more pci
  668: buses will attach.  Then the PCI drivers will attach to PCI buses as
  669: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  670: or any PCI drivers built in by default; you have to build your own
  671: kernel to use PCI devices in a domU.  Here's a kernel config example;
  672: note that only the "xpci" lines are unusual.
  674:         include         "arch/i386/conf/XEN3_DOMU"
  676:         # Add support for PCI buses to the XEN3_DOMU kernel
  677:         xpci* at xenbus ?
  678:         pci* at xpci ?
  680:         # PCI USB controllers
  681:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  683:         # USB bus support
  684:         usb*    at uhci?
  686:         # USB Hubs
  687:         uhub*   at usb?
  688:         uhub*   at uhub? port ? configuration ? interface ?
  690:         # USB Mass Storage
  691:         umass*  at uhub? port ? configuration ? interface ?
  692:         wd*     at umass?
  693:         # SCSI controllers
  694:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  696:         # SCSI bus support (for both ahc and umass)
  697:         scsibus* at scsi?
  699:         # SCSI devices
  700:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  701:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  704: NetBSD as a domU in a VPS
  705: =========================
  707: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  708: hardware.  This section explains how to deal with Xen in a domU as a
  709: virtual private server where you do not control or have access to the
  710: dom0.  This is not intended to be an exhaustive list of VPS providers;
  711: only a few are mentioned that specifically support NetBSD.
  713: VPS operators provide varying degrees of access and mechanisms for
  714: configuration.  The big issue is usually how one controls which kernel
  715: is booted, because the kernel is nominally in the dom0 file system (to
  716: which VPS users do not normally have access).  A second issue is how
  717: to install NetBSD.
  718: A VPS user may want to compile a kernel for security updates, to run
  719: npf, run IPsec, or any other reason why someone would want to change
  720: their kernel.
  722: One approach is to have an administrative interface to upload a kernel,
  723: or to select from a prepopulated list.  Other approaches are pygrub
  724: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  725: kernel from the domU file system.  This is closer to a regular physical
  726: computer, where someone who controls a machine can replace the kernel.
  728: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  729: multiple vcpus, and it is typical for VPS providers to enable multiple
  730: CPUs for NetBSD domUs.
  732: pygrub
  733: -------
  735: pygrub runs in the dom0 and looks into the domU file system.  This
  736: implies that the domU must have a kernel in a file system in a format
  737: known to pygrub.  As of 2014, pygrub seems to be of mostly historical
  738: interest.
  740: pvgrub
  741: ------
  743: pvgrub is a version of grub that uses PV operations instead of BIOS
  744: calls.  It is booted from the dom0 as the domU kernel, and then reads
  745: /grub/menu.lst and loads a kernel from the domU file system.
  747: [Panix]( lets users use pvgrub.  Panix reports
  748: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  749: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  750: page](, which describes only
  751: Linux but should be updated to cover NetBSD :-).
  753: []( also lets users with pvgrub to boot
  754: their own kernel.  See then [ NetBSD
  755: HOWTO](
  756: (which is in need of updating).
  758: It appears that [grub's FFS
  759: code](
  760: does not support all aspects of modern FFS, but there are also reports
  761: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  762: partition for the kernel with the intent that grub can understand it,
  763: which leads to /netbsd not being the actual kernel.  One must remember
  764: to update the special boot partition.
  766: Amazon
  767: ------
  769: See the [Amazon EC2 page](/amazon_ec2/).
  771: Random pointers
  772: ===============
  774: This section contains links from elsewhere not yet integrated into the
  775: HOWTO, and other guides.
  777: *
  778: *
  779: *

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