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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: This HOWTO presumes a basic familiarity with the Xen system
   12: architecture, with installing NetBSD on amd64 hardware, and with
   13: installing software from pkgsrc.  See also the [Xen
   14: website](
   16: [[!toc]]
   18: # Overview
   20: The basic concept of Xen is that the hypervisor (xenkernel) runs on
   21: the hardware, and runs a privileged domain ("dom0") that can access
   22: disks/networking/etc.  One then runs additonal unprivileged domains
   23: (each a "domU"), presumably to do something useful.
   25: This HOWTO addresses how to run a NetBSD dom0 (and hence also build
   26: xen itself).  It also addresses how to run domUs in that environment,
   27: and how to deal with having a domU in a Xen environment run by someone
   28: else and/or not running NetBSD.
   30: There are many choices one can make; the HOWTO recommends the standard
   31: approach and limits discussion of alternatives in many cases.
   33: ## Guest Styles
   35: Xen supports different styles of guests.
   37: [[!table data="""
   38: Style of guest	|Supported by NetBSD
   39: PV		|Yes (dom0, domU)
   40: HVM		|Yes (domU)
   41: PVHVM		|current-only (domU)
   42: PVH		|current-only (domU, dom0 not yet)
   43: """]]
   45: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
   46: hardware directly, but instead makes hypercalls to the hypervisor; PV
   47: guests must be specifically coded for Xen.
   48: See [PV](\)).
   50: In HVM mode, no guest modification is required; however, hardware
   51: support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
   52: The dom0 runs qemu to emulate hardware.
   54: In PVHVM mode, the guest runs as HVM, but additionally can use PV
   55: drivers for efficiency.
   56: See [PV on HVM](
   58: There have been two PVH modes: original PVH and PVHv2.  Original PVH
   59: was based on PV mode and is no longer relevant at all.  PVHv2 is
   60: basically lightweight HVM with PV drivers.  A critical feature of it
   61: is that qemu is not needed; the hypervisor can do the emulation that
   62: is required.  Thus, a dom0 can be PVHv2.
   63: The source code uses PVH and config files use pvh; this refers to PVHv2.
   64: See [PVH(v2)](\)_Domu).
   66: At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   67: The dom0 can start one or more domUs.  (Booting is explained in detail
   68: in the dom0 section.)
   70: ## CPU Architecture
   72: Xen runs on x86_64 hardware (the NetBSD amd64 port).
   74: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
   76: The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
   78: The domU can be i386PAE or amd64.
   79: i386PAE at one point was considered as [faster]( than amd64.
   81: ## Xen Versions
   83: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   84: xenkernel and xentools.  We will refer only to the kernel versions,
   85: but note that both packages must be installed together and must have
   86: matching versions.
   88: Versions available in pkgsrc:
   90: [[!table data="""
   91: Xen Version	|Package Name	|Xen CPU Support	|EOL'ed By Upstream
   92: 4.11		|xenkernel411	|x86_64			|No
   93: 4.13		|xenkernel413	|x86_64			|No
   94: """]]
   96: See also the [Xen Security Advisory page](
   98: Older Xen had a python-based management tool called xm, now replaced
   99: by xl.
  101: ## NetBSD versions
  103: Xen has been supported in NetBSD for a long time, at least since 2005.
  104: Initially Xen was PV only.
  106: NetBSD 8 and up support PV and HVM modes.
  108: Support for PVHVM and PVH is available only in NetBSD-current.
  110: NetBSD up to and including NetBSD 9 as a dom0 does not run SMP,
  111: because some drivers are not yet safe for this.  NetBSD-current
  112: supports SMP in dom0.
  114: NetBSD, when run as a domU, can and does typically run SMP.
  116: Note that while Xen 4.13 is current, the kernel support is still
  117: called XEN3, because the hypercall interface has not changed
  118: significantly.
  120: # Creating a NetBSD dom0
  122: In order to install a NetBSD as a dom0, one first installs a normal
  123: NetBSD system, and then pivot the install to a dom0 install by
  124: changing the kernel and boot configuration.
  126: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
  127: 512M it worked reliably.  This does not make sense, but if you see
  128: "not ELF" after Xen boots, try increasing dom0 RAM.
  130: ## Installation of NetBSD
  132: [Install NetBSD/amd64](/guide/inst/) just as you would if you were not
  133: using Xen.  Therefore, use the most recent release, or a build from
  134: the most recent stable branch.  Alternatively, use -current, being
  135: mindful of all the usual caveats of lower stability of current, and
  136: likely a bit more so.
  138: ## Installation of Xen
  140: ### Building Xen
  142: Use the most recent version of Xen in pkgsrc, unless the DESCR says that it is not suitable.
  143: Therefore, choose 4.13.
  144: In the dom0, install xenkernel413 and xentools413 from pkgsrc.
  146: Once this is done, copy the Xen kernel from where pkgsrc puts it to
  147: where the boot process will be able to find it:
  149: [[!template id=programlisting text="""
  150: # cp -p /usr/pkg/xen413-kernel/xen.gz /
  151: """]]
  153: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such
  154: kernel can either be taken from a local release run, compiled
  155: manually, or downloaded from the NetBSD FTP, for example at:
  157: [[!template id=programlisting text="""
  159: """]]
  161: ### Configuring booting
  163: Read boot.cfg(8) carefully.  Add lines to /boot.cfg to boot Xen:
  165: [[!template id=filecontent name="/boot.cfg" text="""
  166: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  167: menu=Xen single user:load /netbsd-XEN3_DOM0.gz console=pc -s;multiboot /xen.gz dom0_mem=512M
  168: """]]
  170: \todo Explain why console=pc is given.  Perhaps there is some notion
  171: of a separate console instead of xencons.
  173: \todo Check the single user line.
  175: This specifies that the dom0 should have 512MB of ram, leaving the rest
  176: to be allocated for domUs.
  178: NB: This says add, not replace, so that you will be able to more
  179: easily boot a NetBSD kernel without Xen.  Once Xen boots ok, you may
  180: want to set it as default.  It is highly likely that you will have
  181: trouble at some point, and keeping an up-to-date GENERIC for use in
  182: fixing problems is the standard prudent approach.
  184: ### Console selection
  186: See boot_console(8).  Understand that you should start from a place of
  187: having console setup correct for booting GENERIC before trying to
  188: configure Xen.
  190: By default, the hypervisor (Xen itself) will use \todo as the console
  192: By default, the NetBSD dom0 kernel will use xencons(4) (the man page
  193: does not exist) as console.
  195: To use a serial console for the Xen hypervisor, add settings as follows:
  197: [[!template id=filecontent name="/boot.cfg" text="""
  198: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  199: """]]
  201: which will use the first serial port for Xen (which counts starting
  202: from 1, unlike NetBSD which counts starting from 0), forcing
  203: speed/parity.  Because the NetBSD command line lacks a
  204: "console=pc" argument, it will use the default "xencons" console device,
  205: which directs the console I/O through Xen to the same console device Xen
  206: itself uses (in this case, the serial port).
  208: \todo Explain why boot.cfg shows forcing the dom0 console also,
  209: separately from the hypervisor console.
  211: ### Tuning
  213: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
  214: to force only one vcpu to be provided (since NetBSD dom0 can't use
  215: more) and to pin that vcpu to a physical CPU. Xen has
  216: [many boot options](,
  217: and other than dom0 memory and max_vcpus, they are generally not
  218: necessary.
  219: \todo Revisit this advice with current.
  220: \todo Explain if anyone has ever actually measured that this helps.
  222: ### rc.conf
  224: Ensure that the boot scripts installed in
  225: `/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
  226: have `PKG_RCD_SCRIPTS=yes`, or manually.  (This is not special to Xen,
  227: but a normal part of pkgsrc usage.)
  229: Set `xencommons=YES` in rc.conf:
  231: [[!template id=filecontent name="/etc/rc.conf" text="""
  232: xencommons=YES
  233: """]]
  235: \todo Recommend for/against xen-watchdog.
  237: ### Testing
  239: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  240: than GENERIC without Xen.
  242: Once the reboot is done, use `xl` to inspect Xen's boot messages,
  243: available resources, and running domains.  For example:
  245: [[!template id=programlisting text="""
  246: # xl dmesg
  247: ... xen's boot info ...
  248: # xl info
  249: ... available memory, etc ...
  250: # xl list
  251: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  252: Domain-0           0       64    0  r----     58.1
  253: """]]
  255: Xen logs will be in /var/log/xen.
  257: ### Issues with xencommons
  259: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
  260: domUs.  It does not currently work to stop and start xenstored.
  261: Certainly all domUs should be shutdown first, following the sort order
  262: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  263: and is not notified when xenstored exits, leading to not recreating
  264: the state when the new xenstored starts.  Until there's a mechanism to
  265: make this work, one should not expect to be able to restart xenstored
  266: (and thus xencommons).  There is currently no reason to expect that
  267: this will get fixed any time soon.
  268: \todo Confirm if this is still true in 2020.
  270: ## Xen-specific NetBSD issues
  272: There are (at least) two additional things different about NetBSD as a
  273: dom0 kernel compared to hardware.
  275: One is that through NetBSD 9 the module ABI is different because some
  276: of the #defines change, so there are separate sets of modules in
  277: /stand.  In NetBSD-current, there is only one set of modules.
  279: The other difference is that XEN3_DOM0 does not have exactly the same
  280: options as GENERIC.  While it is debatable whether or not this is a
  281: bug, users should be aware of this and can simply add missing config
  282: items if desired.
  284: Finally, there have been occasional reports of trouble with X11
  285: servers in NetBSD as a dom0.
  287: ## Updating Xen in a dom0
  289: Basically, update the xenkernel and xentools packages and copy the new
  290: Xen kernel into place, and reboot.  This procedure should be usable to
  291: update to a new Xen release, but the reader is reminded that having a
  292: non-Xen boot methods was recommended earlier.
  294: ## Updating NetBSD in a dom0
  296: This is just like updating NetBSD on bare hardware, assuming the new
  297: version supports the version of Xen you are running.  Generally, one
  298: replaces the kernel and reboots, and then overlays userland binaries
  299: and adjusts `/etc`.
  301: Note that one should update both the non-Xen kernel typically used for
  302: rescue purposes, as well as the DOM0 kernel used with Xen.
  304: ## anita (for testing NetBSD)
  306: With a NetBSD dom0, even without any domUs, one should be able to run
  307: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  308: root, because anita must create a domU):
  310: [[!template id=programlisting text="""
  311: anita --vmm=xl test file:///usr/obj/i386/
  312: """]]
  314: # Unprivileged domains (domU)
  316: This section describes general concepts about domUs.  It does not
  317: address specific domU operating systems or how to install them.  The
  318: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
  319: typically named so that the file name, domU name and the domU's host
  320: name match.
  322: The domU is provided with CPU and memory by Xen, configured by the
  323: dom0.  The domU is provided with disk and network by the dom0,
  324: mediated by Xen, and configured in the dom0.
  326: Entropy in domUs can be an issue; physical disks and network are on
  327: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  329: ## Config files
  331: See /usr/pkg/share/examples/xen/xlexample*
  332: for a small number of well-commented examples, mostly for running
  333: GNU/Linux.
  335: The following is an example minimal domain configuration file. The domU
  336: serves as a network file server.
  338: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  339: name = "domU-id"
  340: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  341: memory = 1024
  342: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  343: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  344:          'file:/n0/xen/foo-wd1,0x1,w' ]
  345: """]]
  347: The domain will have name given in the `name` setting.  The kernel has the
  348: host/domU name in it, so that on the dom0 one can update the various
  349: domUs independently.  The `vif` line causes an interface to be provided,
  350: with a specific mac address (do not reuse MAC addresses!), in bridge
  351: mode.  Two disks are provided, and they are both writable; the bits
  352: are stored in files and Xen attaches them to a vnd(4) device in the
  353: dom0 on domain creation.  The system treats xbd0 as the boot device
  354: without needing explicit configuration.
  356: There is not type line; that implicitly defines a pv domU.
  358: By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
  359: that "xl create" takes the name of a config file, while other commands
  360: take the name of a domain.
  362: Examples of commands:
  364: [[!template id=programlisting text="""
  365: xl create /usr/pkg/etc/xen/foo
  366: xl console domU-id
  367: xl create -c /usr/pkg/etc/xen/foo
  368: xl shutdown domU-id
  369: xl list
  370: """]]
  372: Typing `^]` will exit the console session.  Shutting down a domain is
  373: equivalent to pushing the power button; a NetBSD domU will receive a
  374: power-press event and do a clean shutdown.  Shutting down the dom0
  375: will trigger controlled shutdowns of all configured domUs.
  377: ## CPU and memory
  379: A domain is provided with some number of vcpus, up to the number
  380: of CPUs seen by the hypervisor. For a domU, it is controlled
  381: from the config file by the "vcpus = N" directive.
  383: A domain is provided with memory; this is controlled in the config
  384: file by "memory = N" (in megabytes).  In the straightforward case, the
  385: sum of the the memory allocated to the dom0 and all domUs must be less
  386: than the available memory.
  388: Xen also provides a "balloon" driver, which can be used to let domains
  389: use more memory temporarily.
  391: ## Virtual disks
  393: In domU config files, the disks are defined as a sequence of 3-tuples:
  395:  * The first element is "method:/path/to/disk". Common methods are
  396:    "file:" for a file-backed vnd, and "phy:" for something that is already
  397:    a device, such as an LVM logical volume.
  399:  * The second element is an artifact of how virtual disks are passed to
  400:    Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  401:    are given a device name to associate with the disk, and values like
  402:    "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  403:    as xbd0, the second as xbd1, and so on.  However, xl demands a
  404:    second argument.  The name given is converted to a major/minor by
  405:    calling stat(2) on the name in /dev and this is passed to the domU.
  406:    In the general case, the dom0 and domU can be different operating
  407:    systems, and it is an unwarranted assumption that they have consistent
  408:    numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  409:    as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  410:    for the second works fine and avoids this issue.  For a GNU/Linux
  411:    guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  412:    /dev/hda1.
  414:  * The third element is "w" for writable disks, and "r" for read-only
  415:    disks.
  417: Example:
  418: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  419: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
  420: """]]
  422: Note that NetBSD by default creates only vnd[0123].  If you need more
  423: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  424: dom0.
  426: ## Virtual Networking
  428: Xen provides virtual Ethernets, each of which connects the dom0 and a
  429: domU.  For each virtual network, there is an interface "xvifN.M" in
  430: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
  431: The interfaces behave as if there is an Ethernet with two
  432: adapters connected.  From this primitive, one can construct various
  433: configurations.  We focus on two common and useful cases for which
  434: there are existing scripts: bridging and NAT.
  436: With bridging (in the example above), the domU perceives itself to be
  437: on the same network as the dom0.  For server virtualization, this is
  438: usually best.  Bridging is accomplished by creating a bridge(4) device
  439: and adding the dom0's physical interface and the various xvifN.0
  440: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  441: config file.  The bridge must be set up already in the dom0; an
  442: example /etc/ifconfig.bridge0 is:
  444: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
  445: create
  446: up
  447: !brconfig bridge0 add wm0
  448: """]]
  450: With NAT, the domU perceives itself to be behind a NAT running on the
  451: dom0.  This is often appropriate when running Xen on a workstation.
  452: TODO: NAT appears to be configured by "vif = [ '' ]".
  454: The MAC address specified is the one used for the interface in the new
  455: domain.  The interface in dom0 will use this address XOR'd with
  456: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  458: ## Starting domains automatically
  460: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
  461: down cleanly on dom0 shutdown, add the following in rc.conf:
  463: [[!template id=filecontent name="/etc/rc.conf" text="""
  464: xendomains="domU-netbsd domU-linux"
  465: """]]
  467: # domU setup for specific systems
  469: Creating domUs is almost entirely independent of operating system.  We
  470: have already presented the basics of config files in the previous system.
  472: Of course, this section presumes that you have a working dom0.
  474: ## Creating a NetBSD PV domU
  476: See the earlier config file, and adjust memory.  Decide on how much
  477: storage you will provide, and prepare it (file or LVM).
  479: While the kernel will be obtained from the dom0 file system, the same
  480: file should be present in the domU as /netbsd so that tools like
  481: savecore(8) can work.   (This is helpful but not necessary.)
  483: The kernel must be specifically built for Xen, to use PV interfacesas
  484: a domU.  NetBSD release builds provide the following kernels:
  486:         i386 XEN3PAE_DOMU
  487:         amd64 XEN3_DOMU
  489: This will boot NetBSD, but this is not that useful if the disk is
  490: empty.  One approach is to unpack sets onto the disk outside of Xen
  491: (by mounting it, just as you would prepare a physical disk for a
  492: system you can't run the installer on).
  494: A second approach is to run an INSTALL kernel, which has a miniroot
  495: and can load sets from the network.  To do this, copy the INSTALL
  496: kernel to / and change the kernel line in the config file to:
  498:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  500: Then, start the domain as "xl create -c configfile".
  502: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  503: line should be used in the config file.
  505:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  507: After booting the domain, the option to install via CDROM may be
  508: selected.  The CDROM device should be changed to `xbd1d`.
  510: Once done installing, "halt -p" the new domain (don't reboot or halt:
  511: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  512: config file), switch the config file back to the XEN3_DOMU kernel,
  513: and start the new domain again. Now it should be able to use "root on
  514: xbd0a" and you should have a functional NetBSD domU.
  516: TODO: check if this is still accurate.
  517: When the new domain is booting you'll see some warnings about *wscons*
  518: and the pseudo-terminals. These can be fixed by editing the files
  519: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  520: `/etc/ttys`, except *console*, like this:
  522:     console "/usr/libexec/getty Pc"         vt100   on secure
  523:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  524:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  525:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  526:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  528: Finally, all screens must be commented out from `/etc/wscons.conf`.
  530: One should also run `powerd` in a domU, but this should not need
  531: configuring.  With powerd, the domain will run a controlled shutdown
  532: if `xl shutdown -R` or `xl shutdown -H` is used on the dom0, via
  533: receiving a synthetic `power button pressed` signal.  In 9 and
  534: current, `powerd` is run by default under Xen kernels (or if ACPI is
  535: present), and it can be added to rc.conf if not.
  537: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  538: file system.  However, various programs (e.g. netstat) will use that
  539: kernel to look up symbols to read from kernel virtual memory.  If
  540: /netbsd is not the running kernel, those lookups will fail.  (This is
  541: not really a Xen-specific issue, but because the domU kernel is
  542: obtained from the dom0, it is far more likely to be out of sync or
  543: missing with Xen.)
  545: Note that NetBSD by default creates only xbd[0123].  If you need more
  546: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  548: ## Creating a Linux domU
  550: Creating unprivileged Linux domains isn't much different from
  551: unprivileged NetBSD domains, but there are some details to know.
  553: First, the second parameter passed to the disk declaration (the '0x1' in
  554: the example below)
  556:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  558: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  559: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  560: So, hda1 which has major 3 and minor 1 on a Linux system will have
  561: device number 0x301.  Alternatively, devices names can be used (hda,
  562: hdb, ...)  as xentools has a table to map these names to devices
  563: numbers.  To export a partition to a Linux guest we can use:
  565:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  566:         root = "/dev/hda1 ro"
  568: and it will appear as /dev/hda on the Linux system, and be used as root
  569: partition.
  571: To install the Linux system on the partition to be exported to the
  572: guest domain, the following method can be used: install
  573: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  574: that will be the root partition of your Linux domain, and mount it.
  575: Then copy the files from a working Linux system, make adjustments in
  576: `/etc` (fstab, network config).  It should also be possible to extract
  577: binary packages such as .rpm or .deb directly to the mounted partition
  578: using the appropriate tool, possibly running under NetBSD's Linux
  579: emulation.  Once the file system has been populated, umount it.  If
  580: desirable, the file system can be converted to ext3 using tune2fs -j.
  581: It should now be possible to boot the Linux guest domain, using one of
  582: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  584: To get the Linux console right, you need to add:
  586:     extra = "xencons=tty1"
  588: to your configuration since not all Linux distributions auto-attach a
  589: tty to the xen console.
  591: ## Creating a NetBSD HVM domU
  593: Use type='hmv', probably.  Use a GENERIC kernel within the disk image.
  595: ## Creating a NetBSD PVH domU
  597: Use type='pvh'.
  599: \todo Explain where the kernel comes from.
  601: ## Creating a Solaris domU
  603: See possibly outdated
  604: [Solaris domU instructions](/ports/xen/howto-solaris/).
  606: ## PCI passthrough: Using PCI devices in guest domains
  608: NB: PCI passthrough only works on some Xen versions and as of 2020 it
  609: is not clear that it works on any version in pkgsrc.  Reports
  610: confirming or denying this notion should be sent to port-xen@.
  612: The dom0 can give other domains access to selected PCI
  613: devices. This can allow, for example, a non-privileged domain to have
  614: access to a physical network interface or disk controller.  However,
  615: keep in mind that giving a domain access to a PCI device most likely
  616: will give the domain read/write access to the whole physical memory,
  617: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  618: device.  Also, it's not possible to export ISA devices to non-dom0
  619: domains, which means that the primary VGA adapter can't be exported.
  620: A guest domain trying to access the VGA registers will panic.
  622: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  623: not been ported to later versions at this time.
  625: For a PCI device to be exported to a domU, is has to be attached to
  626: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  627: pciback.hide boot parameter will attach to "pciback" instead of the
  628: usual driver.  The list of devices is specified as "(bus:dev.func)",
  629: where bus and dev are 2-digit hexadecimal numbers, and func a
  630: single-digit number:
  632:         pciback.hide=(00:0a.0)(00:06.0)
  634: pciback devices should show up in the dom0's boot messages, and the
  635: devices should be listed in the `/kern/xen/pci` directory.
  637: PCI devices to be exported to a domU are listed in the "pci" array of
  638: the domU's config file, with the format "0000:bus:dev.func".
  640:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  642: In the domU an "xpci" device will show up, to which one or more pci
  643: buses will attach.  Then the PCI drivers will attach to PCI buses as
  644: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  645: or any PCI drivers built in by default; you have to build your own
  646: kernel to use PCI devices in a domU.  Here's a kernel config example;
  647: note that only the "xpci" lines are unusual.
  649:         include         "arch/i386/conf/XEN3_DOMU"
  651:         # Add support for PCI buses to the XEN3_DOMU kernel
  652:         xpci* at xenbus ?
  653:         pci* at xpci ?
  655:         # PCI USB controllers
  656:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  658:         # USB bus support
  659:         usb*    at uhci?
  661:         # USB Hubs
  662:         uhub*   at usb?
  663:         uhub*   at uhub? port ? configuration ? interface ?
  665:         # USB Mass Storage
  666:         umass*  at uhub? port ? configuration ? interface ?
  667:         wd*     at umass?
  668:         # SCSI controllers
  669:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  671:         # SCSI bus support (for both ahc and umass)
  672:         scsibus* at scsi?
  674:         # SCSI devices
  675:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  676:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  679: # Miscellaneous Information
  681: ## Nesting under Linux KVM
  683: It is possible to run a Xen and a NetBSD dom0 under Linux KVM.  One
  684: can enable virtio in the dom0 for greater speed.
  686: ## Other nesting
  688: In theory, any full emulation should be able to run Xen and a NetBSD
  689: dom0.  The HOWTO does not currently have information about Xen XVM
  690: mode, nvmm, qemu, Virtualbox, etc.
  692: ## NetBSD 5 as domU
  694: [NetBSD 5 is known to panic.](
  695: (However, NetBSD 5 systems should be updated to a supported version.)
  697: # NetBSD as a domU in a VPS
  699: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  700: hardware.  This section explains how to deal with Xen in a domU as a
  701: virtual private server where you do not control or have access to the
  702: dom0.  This is not intended to be an exhaustive list of VPS providers;
  703: only a few are mentioned that specifically support NetBSD.
  705: VPS operators provide varying degrees of access and mechanisms for
  706: configuration.  The big issue is usually how one controls which kernel
  707: is booted, because the kernel is nominally in the dom0 file system (to
  708: which VPS users do not normally have access).  A second issue is how
  709: to install NetBSD.
  710: A VPS user may want to compile a kernel for security updates, to run
  711: npf, run IPsec, or any other reason why someone would want to change
  712: their kernel.
  714: One approach is to have an administrative interface to upload a kernel,
  715: or to select from a prepopulated list.  Other approaches are pygrub
  716: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  717: kernel from the domU file system.  This is closer to a regular physical
  718: computer, where someone who controls a machine can replace the kernel.
  720: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  721: multiple vcpus, and it is typical for VPS providers to enable multiple
  722: CPUs for NetBSD domUs.
  724: ## Complexities due to Xen changes
  726: Xen has many security advisories and people running Xen systems make
  727: different choices.
  729: ### stub domains
  731: Some (Linux only?) dom0 systems use something called "stub domains" to
  732: isolate qemu from the dom0 system, as a security and reliabilty
  733: mechanism when running HVM domUs.  Somehow, NetBSD's GENERIC kernel
  734: ends up using PIO for disks rather than DMA.  Of course, all of this
  735: is emulated, but emulated PIO is unusably slow.  This problem is not
  736: currently understood.
  738: ### Grant tables
  740: There are multiple versions of using grant tables, and some security
  741: advisories have suggested disabling some versions.  Some versions of
  742: NetBSD apparently only use specific versions and this can lead to
  743: "NetBSD current doesn't run on hosting provider X" situations.
  745: \todo Explain better.
  747: ## Boot methods
  749: ### pvgrub
  751: pvgrub is a version of grub that uses PV operations instead of BIOS
  752: calls.  It is booted from the dom0 as the domU kernel, and then reads
  753: /grub/menu.lst and loads a kernel from the domU file system.
  755: [Panix]( lets users use pvgrub.  Panix reports
  756: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  757: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  758: page](, which describes only
  759: Linux but should be updated to cover NetBSD :-).
  761: []( also lets users with pvgrub to boot
  762: their own kernel.  See then [ NetBSD
  763: HOWTO](
  764: (which is in need of updating).
  766: It appears that [grub's FFS
  767: code](
  768: does not support all aspects of modern FFS, but there are also reports
  769: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  770: partition for the kernel with the intent that grub can understand it,
  771: which leads to /netbsd not being the actual kernel.  One must remember
  772: to update the special boot partition.
  774: ### pygrub
  776: pygrub runs in the dom0 and looks into the domU file system.  This
  777: implies that the domU must have a kernel in a file system in a format
  778: known to pygrub.
  780: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
  781: and is inherently less secure than pvgrub due to running inside dom0. For both these
  782: reasons, pygrub should not be used, and is only still present so that
  783: historical DomU images using it still work.
  785: As of 2014, pygrub seems to be of mostly historical
  786: interest. New DomUs should use pvgrub.
  788: ## Specific Providers
  790: ### Amazon
  792: See the [Amazon EC2 page](/amazon_ec2/).

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