File:  [NetBSD Developer Wiki] / wikisrc / ports / xen / howto.mdwn
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Sun Nov 15 14:11:07 2020 UTC (5 months, 3 weeks ago) by gdt
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Explain PVHv1

    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 guests; see [PV on HVM]( and [PVH(v2)](\)_Domu) for upstream documentation.
   13: [[!table data="""
   14: Style of guest	|Supported by NetBSD
   15: PV		|Yes (dom0, domU)
   16: HVM		|Yes (domU)
   17: PVHVM		|current-only (domU)
   18: PVHv2		|current-only (domU, dom0 not yet)
   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.
   25: In HVM mode, no guest modification is required; however, hardware
   26: support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
   27: The dom0 runs qemu to emulate hardware.
   29: In PVHVM mode, the guest runs as HVM, but additionally can use PV
   30: drivers for efficiency.
   32: In PVHv2 mode, operation is similar to PVHVM, except that qemu is not
   33: run and thus the PV interfaces for console, disks, networking are the
   34: only way to access these resources.  (There was an original PVH mode
   35: that is no longer in use, and now, sometimes PVHv2 is referred to as
   36: simply PVH.)
   38: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   39: The dom0 can start one or more domUs.  (Booting is explained in detail
   40: in the dom0 section.)
   42: This HOWTO presumes a basic familiarity with the Xen system
   43: architecture, with installing NetBSD on i386/amd64 hardware, and with
   44: installing software from pkgsrc.  See also the [Xen
   45: website](
   47: [[!toc]]
   49: # Versions and Support
   51: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   52: xenkernel and xentools.  We will refer only to the kernel versions,
   53: but note that both packages must be installed together and must have
   54: matching versions.
   56: Versions available in pkgsrc:
   58: [[!table data="""
   59: Xen Version	|Package Name	|Xen CPU Support	|xm?	|EOL'ed By Upstream
   60: 4.11		|xenkernel411	|x86_64			|	|No
   61: 4.13		|xenkernel413	|x86_64			|	|No
   62: """]]
   64: See also the [Xen Security Advisory page](
   66: Multiprocessor (SMP) support in NetBSD differs depending on the domain:
   68: [[!table data="""
   69: Domain		|Supports SMP
   70: dom0		|No
   71: domU		|Yes
   72: """]]
   74: Note: NetBSD support is called XEN3.  However, it does support Xen 4,
   75: because the hypercall interface has remained identical.
   77: Older Xen had a python-based management tool called xm, now replaced
   78: by xl.
   80: Architecture
   81: ------------
   83: Xen 4.5 and later runs on x86_64 hardware (the NetBSD amd64 port).
   84: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
   86: The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
   88: The domU can be i386PAE or amd64.
   89: i386PAE at one point was considered as [faster]( than amd64.
   91: # Creating a dom0
   93: In order to install a NetBSD as a dom0, one must first install a normal
   94: NetBSD system, and then pivot the install to a dom0 install by changing
   95: the kernel and boot configuration.
   97: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
   98: 512M it worked reliably.  This does not make sense, but if you see
   99: "not ELF" after Xen boots, try increasing dom0 RAM.
  101: Installation of NetBSD
  102: ----------------------
  104: [Install NetBSD/amd64](/guide/inst/)
  105: just as you would if you were not using Xen.
  107: Installation of Xen
  108: -------------------
  110: We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
  111: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
  113: Once this is done, install the Xen kernel itself:
  115: [[!template id=programlisting text="""
  116: # cp /usr/pkg/xen48-kernel/xen.gz /
  117: """]]
  119: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
  120: can either be compiled manually, or downloaded from the NetBSD FTP, for
  121: example at:
  123: [[!template id=programlisting text="""
  125: """]]
  127: Add a line to /boot.cfg to boot Xen:
  129: [[!template id=filecontent name="/boot.cfg" text="""
  130: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  131: """]]
  133: This specifies that the dom0 should have 512MB of ram, leaving the rest
  134: to be allocated for domUs.  To use a serial console, use:
  136: [[!template id=filecontent name="/boot.cfg" text="""
  137: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  138: """]]
  140: which will use the first serial port for Xen (which counts starting
  141: from 1, unlike NetBSD which counts starting from 0), forcing
  142: speed/parity.  Because the NetBSD command line lacks a
  143: "console=pc" argument, it will use the default "xencons" console device,
  144: which directs the console I/O through Xen to the same console device Xen
  145: itself uses (in this case, the serial port).
  147: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
  148: to force only one vcpu to be provided (since NetBSD dom0 can't use
  149: more) and to pin that vcpu to a physical CPU. Xen has
  150: [many boot options](,
  151: and other than dom0 memory and max_vcpus, they are generally not
  152: necessary.
  154: Copy the boot scripts into `/etc/rc.d`:
  156: [[!template id=programlisting text="""
  157: # cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/
  158: """]]
  160: Enable `xencommons`:
  162: [[!template id=filecontent name="/etc/rc.conf" text="""
  163: xencommons=YES
  164: """]]
  166: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  167: than GENERIC without Xen.
  169: TODO: Recommend for/against xen-watchdog.
  171: Once the reboot is done, use `xl` to inspect Xen's boot messages,
  172: available resources, and running domains.  For example:
  174: [[!template id=programlisting text="""
  175: # xl dmesg
  176: ... xen's boot info ...
  177: # xl info
  178: ... available memory, etc ...
  179: # xl list
  180: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  181: Domain-0           0       64    0  r----     58.1
  182: """]]
  184: Xen logs will be in /var/log/xen.
  186: ### Issues with xencommons
  188: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
  189: domUs.  It does not currently work to stop and start xenstored.
  190: Certainly all domUs should be shutdown first, following the sort order
  191: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  192: and is not notified when xenstored exits, leading to not recreating
  193: the state when the new xenstored starts.  Until there's a mechanism to
  194: make this work, one should not expect to be able to restart xenstored
  195: (and thus xencommons).  There is currently no reason to expect that
  196: this will get fixed any time soon.
  198: anita (for testing NetBSD)
  199: --------------------------
  201: With the setup so far, one should be able to run
  202: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  203: root, because anita must create a domU):
  205: [[!template id=programlisting text="""
  206: anita --vmm=xl test file:///usr/obj/i386/
  207: """]]
  209: Xen-specific NetBSD issues
  210: --------------------------
  212: There are (at least) two additional things different about NetBSD as a
  213: dom0 kernel compared to hardware.
  215: One is that the module ABI is different because some of the #defines
  216: change, so one must build modules for Xen.  As of netbsd-7, the build
  217: system does this automatically.
  219: The other difference is that XEN3_DOM0 does not have exactly the same
  220: options as GENERIC.  While it is debatable whether or not this is a
  221: bug, users should be aware of this and can simply add missing config
  222: items if desired.
  224: Updating NetBSD in a dom0
  225: -------------------------
  227: This is just like updating NetBSD on bare hardware, assuming the new
  228: version supports the version of Xen you are running.  Generally, one
  229: replaces the kernel and reboots, and then overlays userland binaries
  230: and adjusts `/etc`.
  232: Note that one must update both the non-Xen kernel typically used for
  233: rescue purposes and the DOM0 kernel used with Xen.
  235: Converting from grub to /boot
  236: -----------------------------
  238: These instructions were used to convert a system from
  239: grub to /boot.  The system was originally installed in February of
  240: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  241: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  242: 4.1 and grub, much like the message linked earlier in the grub
  243: section.
  245: [[!template id=programlisting text="""
  246: # Install MBR bootblocks on both disks.
  247: fdisk -i /dev/rwd0d
  248: fdisk -i /dev/rwd1d
  249: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  250: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  251: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  252: # Install secondary boot loader
  253: cp -p /usr/mdec/boot /
  254: # Create boot.cfg following earlier guidance:
  255: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  256: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  257: menu=GENERIC:boot
  258: menu=GENERIC single-user:boot -s
  259: menu=GENERIC.ok:boot netbsd.ok
  260: menu=GENERIC.ok single-user:boot netbsd.ok -s
  261: menu=Drop to boot prompt:prompt
  262: default=1
  263: timeout=30
  264: """]]
  266: Upgrading Xen versions
  267: ---------------------
  269: Minor version upgrades are trivial.  Just rebuild/replace the
  270: xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
  271: references it), and reboot.
  273: #Unprivileged domains (domU)
  275: This section describes general concepts about domUs.  It does not
  276: address specific domU operating systems or how to install them.  The
  277: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
  278: typically named so that the file name, domU name and the domU's host
  279: name match.
  281: The domU is provided with CPU and memory by Xen, configured by the
  282: dom0.  The domU is provided with disk and network by the dom0,
  283: mediated by Xen, and configured in the dom0.
  285: Entropy in domUs can be an issue; physical disks and network are on
  286: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  288: Config files
  289: ------------
  291: See /usr/pkg/share/examples/xen/xlexample*
  292: for a small number of well-commented examples, mostly for running
  293: GNU/Linux.
  295: The following is an example minimal domain configuration file. The domU
  296: serves as a network file server.
  298: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  299: name = "domU-id"
  300: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  301: memory = 1024
  302: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  303: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  304:          'file:/n0/xen/foo-wd1,0x1,w' ]
  305: """]]
  307: The domain will have name given in the `name` setting.  The kernel has the
  308: host/domU name in it, so that on the dom0 one can update the various
  309: domUs independently.  The `vif` line causes an interface to be provided,
  310: with a specific mac address (do not reuse MAC addresses!), in bridge
  311: mode.  Two disks are provided, and they are both writable; the bits
  312: are stored in files and Xen attaches them to a vnd(4) device in the
  313: dom0 on domain creation.  The system treats xbd0 as the boot device
  314: without needing explicit configuration.
  316: By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
  317: that "xl create" takes the name of a config file, while other commands
  318: take the name of a domain.
  320: Examples of commands:
  322: [[!template id=programlisting text="""
  323: xl create /usr/pkg/etc/xen/foo
  324: xl console domU-id
  325: xl create -c /usr/pkg/etc/xen/foo
  326: xl shutdown domU-id
  327: xl list
  328: """]]
  330: Typing `^]` will exit the console session.  Shutting down a domain is
  331: equivalent to pushing the power button; a NetBSD domU will receive a
  332: power-press event and do a clean shutdown.  Shutting down the dom0
  333: will trigger controlled shutdowns of all configured domUs.
  335: CPU and memory
  336: --------------
  338: A domain is provided with some number of vcpus, up to the number
  339: of CPUs seen by the hypervisor. For a domU, it is controlled
  340: from the config file by the "vcpus = N" directive.
  342: A domain is provided with memory; this is controlled in the config
  343: file by "memory = N" (in megabytes).  In the straightforward case, the
  344: sum of the the memory allocated to the dom0 and all domUs must be less
  345: than the available memory.
  347: Xen also provides a "balloon" driver, which can be used to let domains
  348: use more memory temporarily.
  350: Virtual disks
  351: -------------
  353: In domU config files, the disks are defined as a sequence of 3-tuples:
  355:  * The first element is "method:/path/to/disk". Common methods are
  356:    "file:" for a file-backed vnd, and "phy:" for something that is already
  357:    a device, such as an LVM logical volume.
  359:  * The second element is an artifact of how virtual disks are passed to
  360:    Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  361:    are given a device name to associate with the disk, and values like
  362:    "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  363:    as xbd0, the second as xbd1, and so on.  However, xl demands a
  364:    second argument.  The name given is converted to a major/minor by
  365:    calling stat(2) on the name in /dev and this is passed to the domU.
  366:    In the general case, the dom0 and domU can be different operating
  367:    systems, and it is an unwarranted assumption that they have consistent
  368:    numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  369:    as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  370:    for the second works fine and avoids this issue.  For a GNU/Linux
  371:    guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  372:    /dev/hda1.
  374:  * The third element is "w" for writable disks, and "r" for read-only
  375:    disks.
  377: Example:
  378: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  379: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
  380: """]]
  382: Note that NetBSD by default creates only vnd[0123].  If you need more
  383: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  384: dom0.
  386: Note that NetBSD by default creates only xbd[0123].  If you need more
  387: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  389: Virtual Networking
  390: ------------------
  392: Xen provides virtual Ethernets, each of which connects the dom0 and a
  393: domU.  For each virtual network, there is an interface "xvifN.M" in
  394: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
  395: The interfaces behave as if there is an Ethernet with two
  396: adapters connected.  From this primitive, one can construct various
  397: configurations.  We focus on two common and useful cases for which
  398: there are existing scripts: bridging and NAT.
  400: With bridging (in the example above), the domU perceives itself to be
  401: on the same network as the dom0.  For server virtualization, this is
  402: usually best.  Bridging is accomplished by creating a bridge(4) device
  403: and adding the dom0's physical interface and the various xvifN.0
  404: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  405: config file.  The bridge must be set up already in the dom0; an
  406: example /etc/ifconfig.bridge0 is:
  408: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
  409: create
  410: up
  411: !brconfig bridge0 add wm0
  412: """]]
  414: With NAT, the domU perceives itself to be behind a NAT running on the
  415: dom0.  This is often appropriate when running Xen on a workstation.
  416: TODO: NAT appears to be configured by "vif = [ '' ]".
  418: The MAC address specified is the one used for the interface in the new
  419: domain.  The interface in dom0 will use this address XOR'd with
  420: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  422: Starting domains automatically
  423: ------------------------------
  425: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
  426: down cleanly on dom0 shutdown, add the following in rc.conf:
  428: [[!template id=filecontent name="/etc/rc.conf" text="""
  429: xendomains="domU-netbsd domU-linux"
  430: """]]
  432: #Creating a domU
  434: Creating domUs is almost entirely independent of operating system.  We
  435: have already presented the basics of config files.  Note that you must
  436: have already completed the dom0 setup so that "xl list" works.
  438: Creating a NetBSD domU
  439: ----------------------
  441: See the earlier config file, and adjust memory.  Decide on how much
  442: storage you will provide, and prepare it (file or LVM).
  444: While the kernel will be obtained from the dom0 file system, the same
  445: file should be present in the domU as /netbsd so that tools like
  446: savecore(8) can work.   (This is helpful but not necessary.)
  448: The kernel must be specifically for Xen and for use as a domU.  The
  449: i386 and amd64 provide the following kernels:
  451:         i386 XEN3PAE_DOMU
  452:         amd64 XEN3_DOMU
  454: This will boot NetBSD, but this is not that useful if the disk is
  455: empty.  One approach is to unpack sets onto the disk outside of xen
  456: (by mounting it, just as you would prepare a physical disk for a
  457: system you can't run the installer on).
  459: A second approach is to run an INSTALL kernel, which has a miniroot
  460: and can load sets from the network.  To do this, copy the INSTALL
  461: kernel to / and change the kernel line in the config file to:
  463:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  465: Then, start the domain as "xl create -c configfile".
  467: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  468: line should be used in the config file.
  470:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  472: After booting the domain, the option to install via CDROM may be
  473: selected.  The CDROM device should be changed to `xbd1d`.
  475: Once done installing, "halt -p" the new domain (don't reboot or halt,
  476: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  477: config file), switch the config file back to the XEN3_DOMU kernel,
  478: and start the new domain again. Now it should be able to use "root on
  479: xbd0a" and you should have a, functional NetBSD domU.
  481: TODO: check if this is still accurate.
  482: When the new domain is booting you'll see some warnings about *wscons*
  483: and the pseudo-terminals. These can be fixed by editing the files
  484: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  485: `/etc/ttys`, except *console*, like this:
  487:     console "/usr/libexec/getty Pc"         vt100   on secure
  488:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  489:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  490:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  491:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  493: Finally, all screens must be commented out from `/etc/wscons.conf`.
  495: It is also desirable to add
  497:         powerd=YES
  499: in rc.conf. This way, the domain will be properly shut down if
  500: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  502: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  503: file system.  However, various programs (e.g. netstat) will use that
  504: kernel to look up symbols to read from kernel virtual memory.  If
  505: /netbsd is not the running kernel, those lookups will fail.  (This is
  506: not really a Xen-specific issue, but because the domU kernel is
  507: obtained from the dom0, it is far more likely to be out of sync or
  508: missing with Xen.)
  510: Creating a Linux domU
  511: ---------------------
  513: Creating unprivileged Linux domains isn't much different from
  514: unprivileged NetBSD domains, but there are some details to know.
  516: First, the second parameter passed to the disk declaration (the '0x1' in
  517: the example below)
  519:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  521: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  522: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  523: So, hda1 which has major 3 and minor 1 on a Linux system will have
  524: device number 0x301.  Alternatively, devices names can be used (hda,
  525: hdb, ...)  as xentools has a table to map these names to devices
  526: numbers.  To export a partition to a Linux guest we can use:
  528:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  529:         root = "/dev/hda1 ro"
  531: and it will appear as /dev/hda on the Linux system, and be used as root
  532: partition.
  534: To install the Linux system on the partition to be exported to the
  535: guest domain, the following method can be used: install
  536: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  537: that will be the root partition of your Linux domain, and mount it.
  538: Then copy the files from a working Linux system, make adjustments in
  539: `/etc` (fstab, network config).  It should also be possible to extract
  540: binary packages such as .rpm or .deb directly to the mounted partition
  541: using the appropriate tool, possibly running under NetBSD's Linux
  542: emulation.  Once the file system has been populated, umount it.  If
  543: desirable, the file system can be converted to ext3 using tune2fs -j.
  544: It should now be possible to boot the Linux guest domain, using one of
  545: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  547: To get the Linux console right, you need to add:
  549:     extra = "xencons=tty1"
  551: to your configuration since not all Linux distributions auto-attach a
  552: tty to the xen console.
  554: Creating a Solaris domU
  555: -----------------------
  557: See possibly outdated
  558: [Solaris domU instructions](/ports/xen/howto-solaris/).
  561: PCI passthrough: Using PCI devices in guest domains
  562: ---------------------------------------------------
  564: The dom0 can give other domains access to selected PCI
  565: devices. This can allow, for example, a non-privileged domain to have
  566: access to a physical network interface or disk controller.  However,
  567: keep in mind that giving a domain access to a PCI device most likely
  568: will give the domain read/write access to the whole physical memory,
  569: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  570: device.  Also, it's not possible to export ISA devices to non-dom0
  571: domains, which means that the primary VGA adapter can't be exported.
  572: A guest domain trying to access the VGA registers will panic.
  574: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  575: not been ported to later versions at this time.
  577: For a PCI device to be exported to a domU, is has to be attached to
  578: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  579: pciback.hide boot parameter will attach to "pciback" instead of the
  580: usual driver.  The list of devices is specified as "(bus:dev.func)",
  581: where bus and dev are 2-digit hexadecimal numbers, and func a
  582: single-digit number:
  584:         pciback.hide=(00:0a.0)(00:06.0)
  586: pciback devices should show up in the dom0's boot messages, and the
  587: devices should be listed in the `/kern/xen/pci` directory.
  589: PCI devices to be exported to a domU are listed in the "pci" array of
  590: the domU's config file, with the format "0000:bus:dev.func".
  592:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  594: In the domU an "xpci" device will show up, to which one or more pci
  595: buses will attach.  Then the PCI drivers will attach to PCI buses as
  596: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  597: or any PCI drivers built in by default; you have to build your own
  598: kernel to use PCI devices in a domU.  Here's a kernel config example;
  599: note that only the "xpci" lines are unusual.
  601:         include         "arch/i386/conf/XEN3_DOMU"
  603:         # Add support for PCI buses to the XEN3_DOMU kernel
  604:         xpci* at xenbus ?
  605:         pci* at xpci ?
  607:         # PCI USB controllers
  608:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  610:         # USB bus support
  611:         usb*    at uhci?
  613:         # USB Hubs
  614:         uhub*   at usb?
  615:         uhub*   at uhub? port ? configuration ? interface ?
  617:         # USB Mass Storage
  618:         umass*  at uhub? port ? configuration ? interface ?
  619:         wd*     at umass?
  620:         # SCSI controllers
  621:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  623:         # SCSI bus support (for both ahc and umass)
  624:         scsibus* at scsi?
  626:         # SCSI devices
  627:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  628:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  631: # Specific Issues
  633: ## domU
  635: [NetBSD 5 is known to panic.](
  636: (However, NetBSD 5 systems should be updated to a supported version.)
  638: # NetBSD as a domU in a VPS
  640: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  641: hardware.  This section explains how to deal with Xen in a domU as a
  642: virtual private server where you do not control or have access to the
  643: dom0.  This is not intended to be an exhaustive list of VPS providers;
  644: only a few are mentioned that specifically support NetBSD.
  646: VPS operators provide varying degrees of access and mechanisms for
  647: configuration.  The big issue is usually how one controls which kernel
  648: is booted, because the kernel is nominally in the dom0 file system (to
  649: which VPS users do not normally have access).  A second issue is how
  650: to install NetBSD.
  651: A VPS user may want to compile a kernel for security updates, to run
  652: npf, run IPsec, or any other reason why someone would want to change
  653: their kernel.
  655: One approach is to have an administrative interface to upload a kernel,
  656: or to select from a prepopulated list.  Other approaches are pygrub
  657: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  658: kernel from the domU file system.  This is closer to a regular physical
  659: computer, where someone who controls a machine can replace the kernel.
  661: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  662: multiple vcpus, and it is typical for VPS providers to enable multiple
  663: CPUs for NetBSD domUs.
  665: pvgrub
  666: ------
  668: pvgrub is a version of grub that uses PV operations instead of BIOS
  669: calls.  It is booted from the dom0 as the domU kernel, and then reads
  670: /grub/menu.lst and loads a kernel from the domU file system.
  672: [Panix]( lets users use pvgrub.  Panix reports
  673: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  674: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  675: page](, which describes only
  676: Linux but should be updated to cover NetBSD :-).
  678: []( also lets users with pvgrub to boot
  679: their own kernel.  See then [ NetBSD
  680: HOWTO](
  681: (which is in need of updating).
  683: It appears that [grub's FFS
  684: code](
  685: does not support all aspects of modern FFS, but there are also reports
  686: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  687: partition for the kernel with the intent that grub can understand it,
  688: which leads to /netbsd not being the actual kernel.  One must remember
  689: to update the special boot partition.
  691: pygrub
  692: -------
  694: pygrub runs in the dom0 and looks into the domU file system.  This
  695: implies that the domU must have a kernel in a file system in a format
  696: known to pygrub.
  698: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
  699: and is inherently less secure than pvgrub due to running inside dom0. For both these
  700: reasons, pygrub should not be used, and is only still present so that
  701: historical DomU images using it still work.
  703: As of 2014, pygrub seems to be of mostly historical
  704: interest. New DomUs should use pvgrub.
  706: Amazon
  707: ------
  709: See the [Amazon EC2 page](/amazon_ec2/).

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