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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 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: PVH		|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: There have been two PVH modes: original PVH and PVHv2.  Original PVH
   33: was based on PV mode and is no longer relevant at all.  PVHv2 is
   34: basically lightweight HVM with PV drivers.  A critical feature of it
   35: is that qemu is not needed; the hypervisor can do the emulation that
   36: is required.  Thus, a dom0 can be PVHv2.
   38: The source code uses PVH and config files use pvh; this refers to PVHv2.
   40: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   41: The dom0 can start one or more domUs.  (Booting is explained in detail
   42: in the dom0 section.)
   44: This HOWTO presumes a basic familiarity with the Xen system
   45: architecture, with installing NetBSD on i386/amd64 hardware, and with
   46: installing software from pkgsrc.  See also the [Xen
   47: website](
   49: [[!toc]]
   51: # Versions and Support
   53: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   54: xenkernel and xentools.  We will refer only to the kernel versions,
   55: but note that both packages must be installed together and must have
   56: matching versions.
   58: Versions available in pkgsrc:
   60: [[!table data="""
   61: Xen Version	|Package Name	|Xen CPU Support	|xm?	|EOL'ed By Upstream
   62: 4.11		|xenkernel411	|x86_64			|	|No
   63: 4.13		|xenkernel413	|x86_64			|	|No
   64: """]]
   66: See also the [Xen Security Advisory page](
   68: Multiprocessor (SMP) support in NetBSD differs depending on the domain:
   70: [[!table data="""
   71: Domain		|Supports SMP
   72: dom0		|No
   73: domU		|Yes
   74: """]]
   76: Note: NetBSD support is called XEN3.  However, it does support Xen 4,
   77: because the hypercall interface has remained identical.
   79: Older Xen had a python-based management tool called xm, now replaced
   80: by xl.
   82: ## Architecture
   84: Xen 4.5 and later runs on x86_64 hardware (the NetBSD amd64 port).
   85: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
   87: The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
   89: The domU can be i386PAE or amd64.
   90: i386PAE at one point was considered as [faster]( than amd64.
   92: # Creating a dom0
   94: In order to install a NetBSD as a dom0, one must first install a normal
   95: NetBSD system, and then pivot the install to a dom0 install by changing
   96: the kernel and boot configuration.
   98: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
   99: 512M it worked reliably.  This does not make sense, but if you see
  100: "not ELF" after Xen boots, try increasing dom0 RAM.
  102: ## Installation of NetBSD
  104: [Install NetBSD/amd64](/guide/inst/)
  105: just as you would if you were not using Xen.
  107: ## Installation of Xen
  109: We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
  110: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
  112: Once this is done, install the Xen kernel itself:
  114: [[!template id=programlisting text="""
  115: # cp /usr/pkg/xen48-kernel/xen.gz /
  116: """]]
  118: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
  119: can either be compiled manually, or downloaded from the NetBSD FTP, for
  120: example at:
  122: [[!template id=programlisting text="""
  124: """]]
  126: Add a line to /boot.cfg to boot Xen:
  128: [[!template id=filecontent name="/boot.cfg" text="""
  129: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  130: """]]
  132: This specifies that the dom0 should have 512MB of ram, leaving the rest
  133: to be allocated for domUs.  To use a serial console, use:
  135: [[!template id=filecontent name="/boot.cfg" text="""
  136: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  137: """]]
  139: which will use the first serial port for Xen (which counts starting
  140: from 1, unlike NetBSD which counts starting from 0), forcing
  141: speed/parity.  Because the NetBSD command line lacks a
  142: "console=pc" argument, it will use the default "xencons" console device,
  143: which directs the console I/O through Xen to the same console device Xen
  144: itself uses (in this case, the serial port).
  146: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
  147: to force only one vcpu to be provided (since NetBSD dom0 can't use
  148: more) and to pin that vcpu to a physical CPU. Xen has
  149: [many boot options](,
  150: and other than dom0 memory and max_vcpus, they are generally not
  151: necessary.
  153: Copy the boot scripts into `/etc/rc.d`:
  155: [[!template id=programlisting text="""
  156: # cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/
  157: """]]
  159: Enable `xencommons`:
  161: [[!template id=filecontent name="/etc/rc.conf" text="""
  162: xencommons=YES
  163: """]]
  165: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  166: than GENERIC without Xen.
  168: TODO: Recommend for/against xen-watchdog.
  170: Once the reboot is done, use `xl` to inspect Xen's boot messages,
  171: available resources, and running domains.  For example:
  173: [[!template id=programlisting text="""
  174: # xl dmesg
  175: ... xen's boot info ...
  176: # xl info
  177: ... available memory, etc ...
  178: # xl list
  179: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  180: Domain-0           0       64    0  r----     58.1
  181: """]]
  183: Xen logs will be in /var/log/xen.
  185: ### Issues with xencommons
  187: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
  188: domUs.  It does not currently work to stop and start xenstored.
  189: Certainly all domUs should be shutdown first, following the sort order
  190: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  191: and is not notified when xenstored exits, leading to not recreating
  192: the state when the new xenstored starts.  Until there's a mechanism to
  193: make this work, one should not expect to be able to restart xenstored
  194: (and thus xencommons).  There is currently no reason to expect that
  195: this will get fixed any time soon.
  197: ## anita (for testing NetBSD)
  199: With the setup so far, one should be able to run
  200: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
  201: root, because anita must create a domU):
  203: [[!template id=programlisting text="""
  204: anita --vmm=xl test file:///usr/obj/i386/
  205: """]]
  207: ## Xen-specific NetBSD issues
  209: There are (at least) two additional things different about NetBSD as a
  210: dom0 kernel compared to hardware.
  212: One is that the module ABI is different because some of the #defines
  213: change, so one must build modules for Xen.  As of netbsd-7, the build
  214: system does this automatically.
  216: The other difference is that XEN3_DOM0 does not have exactly the same
  217: options as GENERIC.  While it is debatable whether or not this is a
  218: bug, users should be aware of this and can simply add missing config
  219: items if desired.
  221: ## Updating NetBSD in a dom0
  223: This is just like updating NetBSD on bare hardware, assuming the new
  224: version supports the version of Xen you are running.  Generally, one
  225: replaces the kernel and reboots, and then overlays userland binaries
  226: and adjusts `/etc`.
  228: Note that one must update both the non-Xen kernel typically used for
  229: rescue purposes and the DOM0 kernel used with Xen.
  231: ## Converting from grub to /boot
  233: These instructions were used to convert a system from
  234: grub to /boot.  The system was originally installed in February of
  235: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  236: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  237: 4.1 and grub, much like the message linked earlier in the grub
  238: section.
  240: [[!template id=programlisting text="""
  241: # Install MBR bootblocks on both disks.
  242: fdisk -i /dev/rwd0d
  243: fdisk -i /dev/rwd1d
  244: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  245: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  246: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  247: # Install secondary boot loader
  248: cp -p /usr/mdec/boot /
  249: # Create boot.cfg following earlier guidance:
  250: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  251: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  252: menu=GENERIC:boot
  253: menu=GENERIC single-user:boot -s
  254: menu=GENERIC.ok:boot netbsd.ok
  255: menu=GENERIC.ok single-user:boot netbsd.ok -s
  256: menu=Drop to boot prompt:prompt
  257: default=1
  258: timeout=30
  259: """]]
  261: ## Upgrading Xen versions
  263: Minor version upgrades are trivial.  Just rebuild/replace the
  264: xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
  265: references it), and reboot.
  267: #Unprivileged domains (domU)
  269: This section describes general concepts about domUs.  It does not
  270: address specific domU operating systems or how to install them.  The
  271: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
  272: typically named so that the file name, domU name and the domU's host
  273: name match.
  275: The domU is provided with CPU and memory by Xen, configured by the
  276: dom0.  The domU is provided with disk and network by the dom0,
  277: mediated by Xen, and configured in the dom0.
  279: Entropy in domUs can be an issue; physical disks and network are on
  280: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  282: ## Config files
  284: See /usr/pkg/share/examples/xen/xlexample*
  285: for a small number of well-commented examples, mostly for running
  286: GNU/Linux.
  288: The following is an example minimal domain configuration file. The domU
  289: serves as a network file server.
  291: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  292: name = "domU-id"
  293: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  294: memory = 1024
  295: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  296: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  297:          'file:/n0/xen/foo-wd1,0x1,w' ]
  298: """]]
  300: The domain will have name given in the `name` setting.  The kernel has the
  301: host/domU name in it, so that on the dom0 one can update the various
  302: domUs independently.  The `vif` line causes an interface to be provided,
  303: with a specific mac address (do not reuse MAC addresses!), in bridge
  304: mode.  Two disks are provided, and they are both writable; the bits
  305: are stored in files and Xen attaches them to a vnd(4) device in the
  306: dom0 on domain creation.  The system treats xbd0 as the boot device
  307: without needing explicit configuration.
  309: By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
  310: that "xl create" takes the name of a config file, while other commands
  311: take the name of a domain.
  313: Examples of commands:
  315: [[!template id=programlisting text="""
  316: xl create /usr/pkg/etc/xen/foo
  317: xl console domU-id
  318: xl create -c /usr/pkg/etc/xen/foo
  319: xl shutdown domU-id
  320: xl list
  321: """]]
  323: Typing `^]` will exit the console session.  Shutting down a domain is
  324: equivalent to pushing the power button; a NetBSD domU will receive a
  325: power-press event and do a clean shutdown.  Shutting down the dom0
  326: will trigger controlled shutdowns of all configured domUs.
  328: ## CPU and memory
  330: A domain is provided with some number of vcpus, up to the number
  331: of CPUs seen by the hypervisor. For a domU, it is controlled
  332: from the config file by the "vcpus = N" directive.
  334: A domain is provided with memory; this is controlled in the config
  335: file by "memory = N" (in megabytes).  In the straightforward case, the
  336: sum of the the memory allocated to the dom0 and all domUs must be less
  337: than the available memory.
  339: Xen also provides a "balloon" driver, which can be used to let domains
  340: use more memory temporarily.
  342: ## Virtual disks
  344: In domU config files, the disks are defined as a sequence of 3-tuples:
  346:  * The first element is "method:/path/to/disk". Common methods are
  347:    "file:" for a file-backed vnd, and "phy:" for something that is already
  348:    a device, such as an LVM logical volume.
  350:  * The second element is an artifact of how virtual disks are passed to
  351:    Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  352:    are given a device name to associate with the disk, and values like
  353:    "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  354:    as xbd0, the second as xbd1, and so on.  However, xl demands a
  355:    second argument.  The name given is converted to a major/minor by
  356:    calling stat(2) on the name in /dev and this is passed to the domU.
  357:    In the general case, the dom0 and domU can be different operating
  358:    systems, and it is an unwarranted assumption that they have consistent
  359:    numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  360:    as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  361:    for the second works fine and avoids this issue.  For a GNU/Linux
  362:    guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  363:    /dev/hda1.
  365:  * The third element is "w" for writable disks, and "r" for read-only
  366:    disks.
  368: Example:
  369: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  370: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
  371: """]]
  373: Note that NetBSD by default creates only vnd[0123].  If you need more
  374: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  375: dom0.
  377: Note that NetBSD by default creates only xbd[0123].  If you need more
  378: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  380: Virtual Networking
  381: ------------------
  383: Xen provides virtual Ethernets, each of which connects the dom0 and a
  384: domU.  For each virtual network, there is an interface "xvifN.M" in
  385: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
  386: The interfaces behave as if there is an Ethernet with two
  387: adapters connected.  From this primitive, one can construct various
  388: configurations.  We focus on two common and useful cases for which
  389: there are existing scripts: bridging and NAT.
  391: With bridging (in the example above), the domU perceives itself to be
  392: on the same network as the dom0.  For server virtualization, this is
  393: usually best.  Bridging is accomplished by creating a bridge(4) device
  394: and adding the dom0's physical interface and the various xvifN.0
  395: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  396: config file.  The bridge must be set up already in the dom0; an
  397: example /etc/ifconfig.bridge0 is:
  399: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
  400: create
  401: up
  402: !brconfig bridge0 add wm0
  403: """]]
  405: With NAT, the domU perceives itself to be behind a NAT running on the
  406: dom0.  This is often appropriate when running Xen on a workstation.
  407: TODO: NAT appears to be configured by "vif = [ '' ]".
  409: The MAC address specified is the one used for the interface in the new
  410: domain.  The interface in dom0 will use this address XOR'd with
  411: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  413: Starting domains automatically
  414: ------------------------------
  416: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
  417: down cleanly on dom0 shutdown, add the following in rc.conf:
  419: [[!template id=filecontent name="/etc/rc.conf" text="""
  420: xendomains="domU-netbsd domU-linux"
  421: """]]
  423: # Creating a domU
  425: Creating domUs is almost entirely independent of operating system.  We
  426: have already presented the basics of config files.  Note that you must
  427: have already completed the dom0 setup so that "xl list" works.
  429: Creating a NetBSD PV domU
  430: --------------------------
  432: See the earlier config file, and adjust memory.  Decide on how much
  433: storage you will provide, and prepare it (file or LVM).
  435: While the kernel will be obtained from the dom0 file system, the same
  436: file should be present in the domU as /netbsd so that tools like
  437: savecore(8) can work.   (This is helpful but not necessary.)
  439: The kernel must be specifically for Xen and for use as a domU.  The
  440: i386 and amd64 provide the following kernels:
  442:         i386 XEN3PAE_DOMU
  443:         amd64 XEN3_DOMU
  445: This will boot NetBSD, but this is not that useful if the disk is
  446: empty.  One approach is to unpack sets onto the disk outside of xen
  447: (by mounting it, just as you would prepare a physical disk for a
  448: system you can't run the installer on).
  450: A second approach is to run an INSTALL kernel, which has a miniroot
  451: and can load sets from the network.  To do this, copy the INSTALL
  452: kernel to / and change the kernel line in the config file to:
  454:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  456: Then, start the domain as "xl create -c configfile".
  458: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  459: line should be used in the config file.
  461:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  463: After booting the domain, the option to install via CDROM may be
  464: selected.  The CDROM device should be changed to `xbd1d`.
  466: Once done installing, "halt -p" the new domain (don't reboot or halt,
  467: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  468: config file), switch the config file back to the XEN3_DOMU kernel,
  469: and start the new domain again. Now it should be able to use "root on
  470: xbd0a" and you should have a, functional NetBSD domU.
  472: TODO: check if this is still accurate.
  473: When the new domain is booting you'll see some warnings about *wscons*
  474: and the pseudo-terminals. These can be fixed by editing the files
  475: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  476: `/etc/ttys`, except *console*, like this:
  478:     console "/usr/libexec/getty Pc"         vt100   on secure
  479:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  480:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  481:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  482:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  484: Finally, all screens must be commented out from `/etc/wscons.conf`.
  486: It is also desirable to add
  488:         powerd=YES
  490: in rc.conf. This way, the domain will be properly shut down if
  491: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  493: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  494: file system.  However, various programs (e.g. netstat) will use that
  495: kernel to look up symbols to read from kernel virtual memory.  If
  496: /netbsd is not the running kernel, those lookups will fail.  (This is
  497: not really a Xen-specific issue, but because the domU kernel is
  498: obtained from the dom0, it is far more likely to be out of sync or
  499: missing with Xen.)
  501: Creating a Linux domU
  502: ---------------------
  504: Creating unprivileged Linux domains isn't much different from
  505: unprivileged NetBSD domains, but there are some details to know.
  507: First, the second parameter passed to the disk declaration (the '0x1' in
  508: the example below)
  510:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  512: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  513: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  514: So, hda1 which has major 3 and minor 1 on a Linux system will have
  515: device number 0x301.  Alternatively, devices names can be used (hda,
  516: hdb, ...)  as xentools has a table to map these names to devices
  517: numbers.  To export a partition to a Linux guest we can use:
  519:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  520:         root = "/dev/hda1 ro"
  522: and it will appear as /dev/hda on the Linux system, and be used as root
  523: partition.
  525: To install the Linux system on the partition to be exported to the
  526: guest domain, the following method can be used: install
  527: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  528: that will be the root partition of your Linux domain, and mount it.
  529: Then copy the files from a working Linux system, make adjustments in
  530: `/etc` (fstab, network config).  It should also be possible to extract
  531: binary packages such as .rpm or .deb directly to the mounted partition
  532: using the appropriate tool, possibly running under NetBSD's Linux
  533: emulation.  Once the file system has been populated, umount it.  If
  534: desirable, the file system can be converted to ext3 using tune2fs -j.
  535: It should now be possible to boot the Linux guest domain, using one of
  536: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  538: To get the Linux console right, you need to add:
  540:     extra = "xencons=tty1"
  542: to your configuration since not all Linux distributions auto-attach a
  543: tty to the xen console.
  545: ## Creating a NetBSD HVM domU
  547: Use type='hmv', probably.  Use a GENERIC kernel within the disk image.
  549: ## Creating a NetBSD PVH domU
  551: Use type='pvh'.
  553: \todo Explain where the kernel comes from.
  556: Creating a Solaris domU
  557: -----------------------
  559: See possibly outdated
  560: [Solaris domU instructions](/ports/xen/howto-solaris/).
  563: PCI passthrough: Using PCI devices in guest domains
  564: ---------------------------------------------------
  566: NB: PCI passthrough only works on some Xen versions and as of 2020 it
  567: is not clear that it works on any version in pkgsrc.  Reports
  568: confirming or denying this notion should be sent to port-xen@.
  570: The dom0 can give other domains access to selected PCI
  571: devices. This can allow, for example, a non-privileged domain to have
  572: access to a physical network interface or disk controller.  However,
  573: keep in mind that giving a domain access to a PCI device most likely
  574: will give the domain read/write access to the whole physical memory,
  575: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  576: device.  Also, it's not possible to export ISA devices to non-dom0
  577: domains, which means that the primary VGA adapter can't be exported.
  578: A guest domain trying to access the VGA registers will panic.
  580: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  581: not been ported to later versions at this time.
  583: For a PCI device to be exported to a domU, is has to be attached to
  584: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  585: pciback.hide boot parameter will attach to "pciback" instead of the
  586: usual driver.  The list of devices is specified as "(bus:dev.func)",
  587: where bus and dev are 2-digit hexadecimal numbers, and func a
  588: single-digit number:
  590:         pciback.hide=(00:0a.0)(00:06.0)
  592: pciback devices should show up in the dom0's boot messages, and the
  593: devices should be listed in the `/kern/xen/pci` directory.
  595: PCI devices to be exported to a domU are listed in the "pci" array of
  596: the domU's config file, with the format "0000:bus:dev.func".
  598:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  600: In the domU an "xpci" device will show up, to which one or more pci
  601: buses will attach.  Then the PCI drivers will attach to PCI buses as
  602: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  603: or any PCI drivers built in by default; you have to build your own
  604: kernel to use PCI devices in a domU.  Here's a kernel config example;
  605: note that only the "xpci" lines are unusual.
  607:         include         "arch/i386/conf/XEN3_DOMU"
  609:         # Add support for PCI buses to the XEN3_DOMU kernel
  610:         xpci* at xenbus ?
  611:         pci* at xpci ?
  613:         # PCI USB controllers
  614:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  616:         # USB bus support
  617:         usb*    at uhci?
  619:         # USB Hubs
  620:         uhub*   at usb?
  621:         uhub*   at uhub? port ? configuration ? interface ?
  623:         # USB Mass Storage
  624:         umass*  at uhub? port ? configuration ? interface ?
  625:         wd*     at umass?
  626:         # SCSI controllers
  627:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  629:         # SCSI bus support (for both ahc and umass)
  630:         scsibus* at scsi?
  632:         # SCSI devices
  633:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  634:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  637: # Specific Issues
  639: ## domU
  641: [NetBSD 5 is known to panic.](
  642: (However, NetBSD 5 systems should be updated to a supported version.)
  644: # NetBSD as a domU in a VPS
  646: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  647: hardware.  This section explains how to deal with Xen in a domU as a
  648: virtual private server where you do not control or have access to the
  649: dom0.  This is not intended to be an exhaustive list of VPS providers;
  650: only a few are mentioned that specifically support NetBSD.
  652: VPS operators provide varying degrees of access and mechanisms for
  653: configuration.  The big issue is usually how one controls which kernel
  654: is booted, because the kernel is nominally in the dom0 file system (to
  655: which VPS users do not normally have access).  A second issue is how
  656: to install NetBSD.
  657: A VPS user may want to compile a kernel for security updates, to run
  658: npf, run IPsec, or any other reason why someone would want to change
  659: their kernel.
  661: One approach is to have an administrative interface to upload a kernel,
  662: or to select from a prepopulated list.  Other approaches are pygrub
  663: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  664: kernel from the domU file system.  This is closer to a regular physical
  665: computer, where someone who controls a machine can replace the kernel.
  667: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  668: multiple vcpus, and it is typical for VPS providers to enable multiple
  669: CPUs for NetBSD domUs.
  671: ## Complexities due to Xen changes
  673: Xen has many security advisories and people running Xen systems make
  674: different choices.
  676: ### stub domains
  678: Some (Linux only?) dom0 systems use something called "stub domains" to
  679: isolate qemu from the dom0 system, as a security and reliabilty
  680: mechanism when running HVM domUs.  Somehow, NetBSD's GENERIC kernel
  681: ends up using PIO for disks rather than DMA.  Of course, all of this
  682: is emulated, but emulated PIO is unusably slow.  This problem is not
  683: currently understood.
  685: ### Grant tables
  687: There are multiple versions of using grant tables, and some security
  688: advisories have suggested disabling some versions.  Some versions of
  689: NetBSD apparently only use specific versions and this can lead to
  690: "NetBSD current doesn't run on hosting provider X" situations.
  692: \todo Explain better.
  694: ## Boot methods
  696: ### pvgrub
  698: pvgrub is a version of grub that uses PV operations instead of BIOS
  699: calls.  It is booted from the dom0 as the domU kernel, and then reads
  700: /grub/menu.lst and loads a kernel from the domU file system.
  702: [Panix]( lets users use pvgrub.  Panix reports
  703: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  704: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  705: page](, which describes only
  706: Linux but should be updated to cover NetBSD :-).
  708: []( also lets users with pvgrub to boot
  709: their own kernel.  See then [ NetBSD
  710: HOWTO](
  711: (which is in need of updating).
  713: It appears that [grub's FFS
  714: code](
  715: does not support all aspects of modern FFS, but there are also reports
  716: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  717: partition for the kernel with the intent that grub can understand it,
  718: which leads to /netbsd not being the actual kernel.  One must remember
  719: to update the special boot partition.
  721: ### pygrub
  723: pygrub runs in the dom0 and looks into the domU file system.  This
  724: implies that the domU must have a kernel in a file system in a format
  725: known to pygrub.
  727: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
  728: and is inherently less secure than pvgrub due to running inside dom0. For both these
  729: reasons, pygrub should not be used, and is only still present so that
  730: historical DomU images using it still work.
  732: As of 2014, pygrub seems to be of mostly historical
  733: interest. New DomUs should use pvgrub.
  735: ## Specific Providers
  737: ### Amazon
  739: See the [Amazon EC2 page](/amazon_ec2/).

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