File:  [NetBSD Developer Wiki] / wikisrc / ports / xen / howto.mdwn
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Fri Nov 13 20:41:56 2020 UTC (3 months, 2 weeks ago) by gdt
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CVS tags: HEAD
note qemu and HVM

    1: [[!meta title="Xen HowTo"]]
    2: 
    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.
   10: 
   11: Xen supports different styles of guests; see [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM) and [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2)_Domu) for upstream documentation.
   12: 
   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: """]]
   20: 
   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.
   24: 
   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.
   28: 
   29: In PVHVM mode, the guest runs as HVM, but additionally can use PV
   30: drivers for efficiency.
   31: 
   32: In PVHv2H 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.
   35: 
   36: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
   37: The dom0 can start one or more domUs.  (Booting is explained in detail
   38: in the dom0 section.)
   39: 
   40: This HOWTO presumes a basic familiarity with the Xen system
   41: architecture, with installing NetBSD on i386/amd64 hardware, and with
   42: installing software from pkgsrc.  See also the [Xen
   43: website](http://www.xenproject.org/).
   44: 
   45: [[!toc]]
   46: 
   47: # Versions and Support
   48: 
   49: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
   50: xenkernel and xentools.  We will refer only to the kernel versions,
   51: but note that both packages must be installed together and must have
   52: matching versions.
   53: 
   54: Versions available in pkgsrc:
   55: 
   56: [[!table data="""
   57: Xen Version	|Package Name	|Xen CPU Support	|xm?	|EOL'ed By Upstream
   58: 4.11		|xenkernel411	|x86_64			|	|No
   59: 4.13		|xenkernel413	|x86_64			|	|No
   60: """]]
   61: 
   62: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
   63: 
   64: Multiprocessor (SMP) support in NetBSD differs depending on the domain:
   65: 
   66: [[!table data="""
   67: Domain		|Supports SMP
   68: dom0		|No
   69: domU		|Yes
   70: """]]
   71: 
   72: Note: NetBSD support is called XEN3.  However, it does support Xen 4,
   73: because the hypercall interface has remained identical.
   74: 
   75: Older Xen had a python-based management tool called xm, now replaced
   76: by xl.
   77: 
   78: Architecture
   79: ------------
   80: 
   81: Xen 4.5 and later runs on x86_64 hardware (the NetBSD amd64 port).
   82: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
   83: 
   84: The dom0 system should be amd64.  (Instructions for i386PAE dom0 have been removed from the HOWTO.)
   85: 
   86: The domU can be i386PAE or amd64.
   87: i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
   88: 
   89: # Creating a dom0
   90: 
   91: In order to install a NetBSD as a dom0, one must first install a normal
   92: NetBSD system, and then pivot the install to a dom0 install by changing
   93: the kernel and boot configuration.
   94: 
   95: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
   96: 512M it worked reliably.  This does not make sense, but if you see
   97: "not ELF" after Xen boots, try increasing dom0 RAM.
   98: 
   99: Installation of NetBSD
  100: ----------------------
  101: 
  102: [Install NetBSD/amd64](/guide/inst/)
  103: just as you would if you were not using Xen.
  104: 
  105: Installation of Xen
  106: -------------------
  107: 
  108: We will consider that you chose to use Xen 4.8, with NetBSD/amd64 as
  109: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
  110: 
  111: Once this is done, install the Xen kernel itself:
  112: 
  113: [[!template id=programlisting text="""
  114: # cp /usr/pkg/xen48-kernel/xen.gz /
  115: """]]
  116: 
  117: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
  118: can either be compiled manually, or downloaded from the NetBSD FTP, for
  119: example at:
  120: 
  121: [[!template id=programlisting text="""
  122: ftp.netbsd.org/pub/NetBSD/NetBSD-8.0/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
  123: """]]
  124: 
  125: Add a line to /boot.cfg to boot Xen:
  126: 
  127: [[!template id=filecontent name="/boot.cfg" text="""
  128: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  129: """]]
  130: 
  131: This specifies that the dom0 should have 512MB of ram, leaving the rest
  132: to be allocated for domUs.  To use a serial console, use:
  133: 
  134: [[!template id=filecontent name="/boot.cfg" text="""
  135: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
  136: """]]
  137: 
  138: which will use the first serial port for Xen (which counts starting
  139: from 1, unlike NetBSD which counts starting from 0), forcing
  140: speed/parity.  Because the NetBSD command line lacks a
  141: "console=pc" argument, it will use the default "xencons" console device,
  142: which directs the console I/O through Xen to the same console device Xen
  143: itself uses (in this case, the serial port).
  144: 
  145: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
  146: to force only one vcpu to be provided (since NetBSD dom0 can't use
  147: more) and to pin that vcpu to a physical CPU. Xen has
  148: [many boot options](http://xenbits.xenproject.org/docs/4.8-testing/misc/xen-command-line.html),
  149: and other than dom0 memory and max_vcpus, they are generally not
  150: necessary.
  151: 
  152: Copy the boot scripts into `/etc/rc.d`:
  153: 
  154: [[!template id=programlisting text="""
  155: # cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/
  156: """]]
  157: 
  158: Enable `xencommons`:
  159: 
  160: [[!template id=filecontent name="/etc/rc.conf" text="""
  161: xencommons=YES
  162: """]]
  163: 
  164: Now, reboot so that you are running a DOM0 kernel under Xen, rather
  165: than GENERIC without Xen.
  166: 
  167: TODO: Recommend for/against xen-watchdog.
  168: 
  169: Once the reboot is done, use `xl` to inspect Xen's boot messages,
  170: available resources, and running domains.  For example:
  171: 
  172: [[!template id=programlisting text="""
  173: # xl dmesg
  174: ... xen's boot info ...
  175: # xl info
  176: ... available memory, etc ...
  177: # xl list
  178: Name              Id  Mem(MB)  CPU  State  Time(s)  Console
  179: Domain-0           0       64    0  r----     58.1
  180: """]]
  181: 
  182: Xen logs will be in /var/log/xen.
  183: 
  184: ### Issues with xencommons
  185: 
  186: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
  187: domUs.  It does not currently work to stop and start xenstored.
  188: Certainly all domUs should be shutdown first, following the sort order
  189: of the rc.d scripts.  However, the dom0 sets up state with xenstored,
  190: and is not notified when xenstored exits, leading to not recreating
  191: the state when the new xenstored starts.  Until there's a mechanism to
  192: make this work, one should not expect to be able to restart xenstored
  193: (and thus xencommons).  There is currently no reason to expect that
  194: this will get fixed any time soon.
  195: 
  196: anita (for testing NetBSD)
  197: --------------------------
  198: 
  199: With the setup so far (assuming 4.8/xl), 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):
  202: 
  203: [[!template id=programlisting text="""
  204: anita --vmm=xl test file:///usr/obj/i386/
  205: """]]
  206: 
  207: Xen-specific NetBSD issues
  208: --------------------------
  209: 
  210: There are (at least) two additional things different about NetBSD as a
  211: dom0 kernel compared to hardware.
  212: 
  213: One is that the module ABI is different because some of the #defines
  214: change, so one must build modules for Xen.  As of netbsd-7, the build
  215: system does this automatically.
  216: 
  217: The other difference is that XEN3_DOM0 does not have exactly the same
  218: options as GENERIC.  While it is debatable whether or not this is a
  219: bug, users should be aware of this and can simply add missing config
  220: items if desired.
  221: 
  222: Updating NetBSD in a dom0
  223: -------------------------
  224: 
  225: This is just like updating NetBSD on bare hardware, assuming the new
  226: version supports the version of Xen you are running.  Generally, one
  227: replaces the kernel and reboots, and then overlays userland binaries
  228: and adjusts `/etc`.
  229: 
  230: Note that one must update both the non-Xen kernel typically used for
  231: rescue purposes and the DOM0 kernel used with Xen.
  232: 
  233: Converting from grub to /boot
  234: -----------------------------
  235: 
  236: These instructions were used to convert a system from
  237: grub to /boot.  The system was originally installed in February of
  238: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
  239: over time.  Before these commands, it was running NetBSD 6 i386, Xen
  240: 4.1 and grub, much like the message linked earlier in the grub
  241: section.
  242: 
  243: [[!template id=programlisting text="""
  244: # Install MBR bootblocks on both disks.
  245: fdisk -i /dev/rwd0d
  246: fdisk -i /dev/rwd1d
  247: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
  248: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
  249: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
  250: # Install secondary boot loader
  251: cp -p /usr/mdec/boot /
  252: # Create boot.cfg following earlier guidance:
  253: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
  254: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
  255: menu=GENERIC:boot
  256: menu=GENERIC single-user:boot -s
  257: menu=GENERIC.ok:boot netbsd.ok
  258: menu=GENERIC.ok single-user:boot netbsd.ok -s
  259: menu=Drop to boot prompt:prompt
  260: default=1
  261: timeout=30
  262: """]]
  263: 
  264: Upgrading Xen versions
  265: ---------------------
  266: 
  267: Minor version upgrades are trivial.  Just rebuild/replace the
  268: xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
  269: references it), and reboot.
  270: 
  271: #Unprivileged domains (domU)
  272: 
  273: This section describes general concepts about domUs.  It does not
  274: address specific domU operating systems or how to install them.  The
  275: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
  276: typically named so that the file name, domU name and the domU's host
  277: name match.
  278: 
  279: The domU is provided with CPU and memory by Xen, configured by the
  280: dom0.  The domU is provided with disk and network by the dom0,
  281: mediated by Xen, and configured in the dom0.
  282: 
  283: Entropy in domUs can be an issue; physical disks and network are on
  284: the dom0.  NetBSD's /dev/random system works, but is often challenged.
  285: 
  286: Config files
  287: ------------
  288: 
  289: See /usr/pkg/share/examples/xen/xlexample*
  290: for a small number of well-commented examples, mostly for running
  291: GNU/Linux.
  292: 
  293: The following is an example minimal domain configuration file. The domU
  294: serves as a network file server.
  295: 
  296: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  297: name = "domU-id"
  298: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
  299: memory = 1024
  300: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
  301: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
  302:          'file:/n0/xen/foo-wd1,0x1,w' ]
  303: """]]
  304: 
  305: The domain will have name given in the `name` setting.  The kernel has the
  306: host/domU name in it, so that on the dom0 one can update the various
  307: domUs independently.  The `vif` line causes an interface to be provided,
  308: with a specific mac address (do not reuse MAC addresses!), in bridge
  309: mode.  Two disks are provided, and they are both writable; the bits
  310: are stored in files and Xen attaches them to a vnd(4) device in the
  311: dom0 on domain creation.  The system treats xbd0 as the boot device
  312: without needing explicit configuration.
  313: 
  314: By convention, domain config files are kept in `/usr/pkg/etc/xen`.  Note
  315: that "xl create" takes the name of a config file, while other commands
  316: take the name of a domain.
  317: 
  318: Examples of commands:
  319: 
  320: [[!template id=programlisting text="""
  321: xl create /usr/pkg/etc/xen/foo
  322: xl console domU-id
  323: xl create -c /usr/pkg/etc/xen/foo
  324: xl shutdown domU-id
  325: xl list
  326: """]]
  327: 
  328: Typing `^]` will exit the console session.  Shutting down a domain is
  329: equivalent to pushing the power button; a NetBSD domU will receive a
  330: power-press event and do a clean shutdown.  Shutting down the dom0
  331: will trigger controlled shutdowns of all configured domUs.
  332: 
  333: CPU and memory
  334: --------------
  335: 
  336: A domain is provided with some number of vcpus, up to the number
  337: of CPUs seen by the hypervisor. For a domU, it is controlled
  338: from the config file by the "vcpus = N" directive.
  339: 
  340: A domain is provided with memory; this is controlled in the config
  341: file by "memory = N" (in megabytes).  In the straightforward case, the
  342: sum of the the memory allocated to the dom0 and all domUs must be less
  343: than the available memory.
  344: 
  345: Xen also provides a "balloon" driver, which can be used to let domains
  346: use more memory temporarily.
  347: 
  348: Virtual disks
  349: -------------
  350: 
  351: In domU config files, the disks are defined as a sequence of 3-tuples:
  352: 
  353:  * The first element is "method:/path/to/disk". Common methods are
  354:    "file:" for a file-backed vnd, and "phy:" for something that is already
  355:    a device, such as an LVM logical volume.
  356: 
  357:  * The second element is an artifact of how virtual disks are passed to
  358:    Linux, and a source of confusion with NetBSD Xen usage.  Linux domUs
  359:    are given a device name to associate with the disk, and values like
  360:    "hda1" or "sda1" are common.  In a NetBSD domU, the first disk appears
  361:    as xbd0, the second as xbd1, and so on.  However, xl demands a
  362:    second argument.  The name given is converted to a major/minor by
  363:    calling stat(2) on the name in /dev and this is passed to the domU.
  364:    In the general case, the dom0 and domU can be different operating
  365:    systems, and it is an unwarranted assumption that they have consistent
  366:    numbering in /dev, or even that the dom0 OS has a /dev.  With NetBSD
  367:    as both dom0 and domU, using values of 0x0 for the first disk and 0x1
  368:    for the second works fine and avoids this issue.  For a GNU/Linux
  369:    guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
  370:    /dev/hda1.
  371: 
  372:  * The third element is "w" for writable disks, and "r" for read-only
  373:    disks.
  374: 
  375: Example:
  376: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
  377: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
  378: """]]
  379: 
  380: Note that NetBSD by default creates only vnd[0123].  If you need more
  381: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
  382: dom0.
  383: 
  384: Note that NetBSD by default creates only xbd[0123].  If you need more
  385: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
  386: 
  387: Virtual Networking
  388: ------------------
  389: 
  390: Xen provides virtual Ethernets, each of which connects the dom0 and a
  391: domU.  For each virtual network, there is an interface "xvifN.M" in
  392: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
  393: The interfaces behave as if there is an Ethernet with two
  394: adapters connected.  From this primitive, one can construct various
  395: configurations.  We focus on two common and useful cases for which
  396: there are existing scripts: bridging and NAT.
  397: 
  398: With bridging (in the example above), the domU perceives itself to be
  399: on the same network as the dom0.  For server virtualization, this is
  400: usually best.  Bridging is accomplished by creating a bridge(4) device
  401: and adding the dom0's physical interface and the various xvifN.0
  402: interfaces to the bridge.  One specifies "bridge=bridge0" in the domU
  403: config file.  The bridge must be set up already in the dom0; an
  404: example /etc/ifconfig.bridge0 is:
  405: 
  406: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
  407: create
  408: up
  409: !brconfig bridge0 add wm0
  410: """]]
  411: 
  412: With NAT, the domU perceives itself to be behind a NAT running on the
  413: dom0.  This is often appropriate when running Xen on a workstation.
  414: TODO: NAT appears to be configured by "vif = [ '' ]".
  415: 
  416: The MAC address specified is the one used for the interface in the new
  417: domain.  The interface in dom0 will use this address XOR'd with
  418: 00:00:00:01:00:00.  Random MAC addresses are assigned if not given.
  419: 
  420: Starting domains automatically
  421: ------------------------------
  422: 
  423: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
  424: down cleanly on dom0 shutdown, add the following in rc.conf:
  425: 
  426: [[!template id=filecontent name="/etc/rc.conf" text="""
  427: xendomains="domU-netbsd domU-linux"
  428: """]]
  429: 
  430: #Creating a domU
  431: 
  432: Creating domUs is almost entirely independent of operating system.  We
  433: have already presented the basics of config files.  Note that you must
  434: have already completed the dom0 setup so that "xl list" works.
  435: 
  436: Creating a NetBSD domU
  437: ----------------------
  438: 
  439: See the earlier config file, and adjust memory.  Decide on how much
  440: storage you will provide, and prepare it (file or LVM).
  441: 
  442: While the kernel will be obtained from the dom0 file system, the same
  443: file should be present in the domU as /netbsd so that tools like
  444: savecore(8) can work.   (This is helpful but not necessary.)
  445: 
  446: The kernel must be specifically for Xen and for use as a domU.  The
  447: i386 and amd64 provide the following kernels:
  448: 
  449:         i386 XEN3PAE_DOMU
  450:         amd64 XEN3_DOMU
  451: 
  452: This will boot NetBSD, but this is not that useful if the disk is
  453: empty.  One approach is to unpack sets onto the disk outside of xen
  454: (by mounting it, just as you would prepare a physical disk for a
  455: system you can't run the installer on).
  456: 
  457: A second approach is to run an INSTALL kernel, which has a miniroot
  458: and can load sets from the network.  To do this, copy the INSTALL
  459: kernel to / and change the kernel line in the config file to:
  460: 
  461:         kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
  462: 
  463: Then, start the domain as "xl create -c configfile".
  464: 
  465: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
  466: line should be used in the config file.
  467: 
  468:     disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
  469: 
  470: After booting the domain, the option to install via CDROM may be
  471: selected.  The CDROM device should be changed to `xbd1d`.
  472: 
  473: Once done installing, "halt -p" the new domain (don't reboot or halt,
  474: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
  475: config file), switch the config file back to the XEN3_DOMU kernel,
  476: and start the new domain again. Now it should be able to use "root on
  477: xbd0a" and you should have a, functional NetBSD domU.
  478: 
  479: TODO: check if this is still accurate.
  480: When the new domain is booting you'll see some warnings about *wscons*
  481: and the pseudo-terminals. These can be fixed by editing the files
  482: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
  483: `/etc/ttys`, except *console*, like this:
  484: 
  485:     console "/usr/libexec/getty Pc"         vt100   on secure
  486:     ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
  487:     ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
  488:     ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
  489:     ttyE3   "/usr/libexec/getty Pc"         vt220   off secure
  490: 
  491: Finally, all screens must be commented out from `/etc/wscons.conf`.
  492: 
  493: It is also desirable to add
  494: 
  495:         powerd=YES
  496: 
  497: in rc.conf. This way, the domain will be properly shut down if
  498: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
  499: 
  500: It is not strictly necessary to have a kernel (as /netbsd) in the domU
  501: file system.  However, various programs (e.g. netstat) will use that
  502: kernel to look up symbols to read from kernel virtual memory.  If
  503: /netbsd is not the running kernel, those lookups will fail.  (This is
  504: not really a Xen-specific issue, but because the domU kernel is
  505: obtained from the dom0, it is far more likely to be out of sync or
  506: missing with Xen.)
  507: 
  508: Creating a Linux domU
  509: ---------------------
  510: 
  511: Creating unprivileged Linux domains isn't much different from
  512: unprivileged NetBSD domains, but there are some details to know.
  513: 
  514: First, the second parameter passed to the disk declaration (the '0x1' in
  515: the example below)
  516: 
  517:     disk = [ 'phy:/dev/wd0e,0x1,w' ]
  518: 
  519: does matter to Linux. It wants a Linux device number here (e.g. 0x300
  520: for hda).  Linux builds device numbers as: (major \<\< 8 + minor).
  521: So, hda1 which has major 3 and minor 1 on a Linux system will have
  522: device number 0x301.  Alternatively, devices names can be used (hda,
  523: hdb, ...)  as xentools has a table to map these names to devices
  524: numbers.  To export a partition to a Linux guest we can use:
  525: 
  526:         disk = [ 'phy:/dev/wd0e,0x300,w' ]
  527:         root = "/dev/hda1 ro"
  528: 
  529: and it will appear as /dev/hda on the Linux system, and be used as root
  530: partition.
  531: 
  532: To install the Linux system on the partition to be exported to the
  533: guest domain, the following method can be used: install
  534: sysutils/e2fsprogs from pkgsrc.  Use mke2fs to format the partition
  535: that will be the root partition of your Linux domain, and mount it.
  536: Then copy the files from a working Linux system, make adjustments in
  537: `/etc` (fstab, network config).  It should also be possible to extract
  538: binary packages such as .rpm or .deb directly to the mounted partition
  539: using the appropriate tool, possibly running under NetBSD's Linux
  540: emulation.  Once the file system has been populated, umount it.  If
  541: desirable, the file system can be converted to ext3 using tune2fs -j.
  542: It should now be possible to boot the Linux guest domain, using one of
  543: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
  544: 
  545: To get the Linux console right, you need to add:
  546: 
  547:     extra = "xencons=tty1"
  548: 
  549: to your configuration since not all Linux distributions auto-attach a
  550: tty to the xen console.
  551: 
  552: Creating a Solaris domU
  553: -----------------------
  554: 
  555: See possibly outdated
  556: [Solaris domU instructions](/ports/xen/howto-solaris/).
  557: 
  558: 
  559: PCI passthrough: Using PCI devices in guest domains
  560: ---------------------------------------------------
  561: 
  562: The dom0 can give other domains access to selected PCI
  563: devices. This can allow, for example, a non-privileged domain to have
  564: access to a physical network interface or disk controller.  However,
  565: keep in mind that giving a domain access to a PCI device most likely
  566: will give the domain read/write access to the whole physical memory,
  567: as PCs don't have an IOMMU to restrict memory access to DMA-capable
  568: device.  Also, it's not possible to export ISA devices to non-dom0
  569: domains, which means that the primary VGA adapter can't be exported.
  570: A guest domain trying to access the VGA registers will panic.
  571: 
  572: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
  573: not been ported to later versions at this time.
  574: 
  575: For a PCI device to be exported to a domU, is has to be attached to
  576: the "pciback" driver in dom0.  Devices passed to the dom0 via the
  577: pciback.hide boot parameter will attach to "pciback" instead of the
  578: usual driver.  The list of devices is specified as "(bus:dev.func)",
  579: where bus and dev are 2-digit hexadecimal numbers, and func a
  580: single-digit number:
  581: 
  582:         pciback.hide=(00:0a.0)(00:06.0)
  583: 
  584: pciback devices should show up in the dom0's boot messages, and the
  585: devices should be listed in the `/kern/xen/pci` directory.
  586: 
  587: PCI devices to be exported to a domU are listed in the "pci" array of
  588: the domU's config file, with the format "0000:bus:dev.func".
  589: 
  590:         pci = [ '0000:00:06.0', '0000:00:0a.0' ]
  591: 
  592: In the domU an "xpci" device will show up, to which one or more pci
  593: buses will attach.  Then the PCI drivers will attach to PCI buses as
  594: usual.  Note that the default NetBSD DOMU kernels do not have "xpci"
  595: or any PCI drivers built in by default; you have to build your own
  596: kernel to use PCI devices in a domU.  Here's a kernel config example;
  597: note that only the "xpci" lines are unusual.
  598: 
  599:         include         "arch/i386/conf/XEN3_DOMU"
  600: 
  601:         # Add support for PCI buses to the XEN3_DOMU kernel
  602:         xpci* at xenbus ?
  603:         pci* at xpci ?
  604: 
  605:         # PCI USB controllers
  606:         uhci*   at pci? dev ? function ?        # Universal Host Controller (Intel)
  607: 
  608:         # USB bus support
  609:         usb*    at uhci?
  610: 
  611:         # USB Hubs
  612:         uhub*   at usb?
  613:         uhub*   at uhub? port ? configuration ? interface ?
  614: 
  615:         # USB Mass Storage
  616:         umass*  at uhub? port ? configuration ? interface ?
  617:         wd*     at umass?
  618:         # SCSI controllers
  619:         ahc*    at pci? dev ? function ?        # Adaptec [23]94x, aic78x0 SCSI
  620: 
  621:         # SCSI bus support (for both ahc and umass)
  622:         scsibus* at scsi?
  623: 
  624:         # SCSI devices
  625:         sd*     at scsibus? target ? lun ?      # SCSI disk drives
  626:         cd*     at scsibus? target ? lun ?      # SCSI CD-ROM drives
  627: 
  628: 
  629: # Specific Issues
  630: 
  631: ## domU
  632: 
  633: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
  634: (However, NetBSD 5 systems should be updated to a supported version.)
  635: 
  636: # NetBSD as a domU in a VPS
  637: 
  638: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
  639: hardware.  This section explains how to deal with Xen in a domU as a
  640: virtual private server where you do not control or have access to the
  641: dom0.  This is not intended to be an exhaustive list of VPS providers;
  642: only a few are mentioned that specifically support NetBSD.
  643: 
  644: VPS operators provide varying degrees of access and mechanisms for
  645: configuration.  The big issue is usually how one controls which kernel
  646: is booted, because the kernel is nominally in the dom0 file system (to
  647: which VPS users do not normally have access).  A second issue is how
  648: to install NetBSD.
  649: A VPS user may want to compile a kernel for security updates, to run
  650: npf, run IPsec, or any other reason why someone would want to change
  651: their kernel.
  652: 
  653: One approach is to have an administrative interface to upload a kernel,
  654: or to select from a prepopulated list.  Other approaches are pygrub
  655: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
  656: kernel from the domU file system.  This is closer to a regular physical
  657: computer, where someone who controls a machine can replace the kernel.
  658: 
  659: A second issue is multiple CPUs.  With NetBSD 6, domUs support
  660: multiple vcpus, and it is typical for VPS providers to enable multiple
  661: CPUs for NetBSD domUs.
  662: 
  663: pvgrub
  664: ------
  665: 
  666: pvgrub is a version of grub that uses PV operations instead of BIOS
  667: calls.  It is booted from the dom0 as the domU kernel, and then reads
  668: /grub/menu.lst and loads a kernel from the domU file system.
  669: 
  670: [Panix](http://www.panix.com/) lets users use pvgrub.  Panix reports
  671: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
  672: (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
  673: page](http://www.panix.com/v-colo/grub.html), which describes only
  674: Linux but should be updated to cover NetBSD :-).
  675: 
  676: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
  677: their own kernel.  See then [prgmr.com NetBSD
  678: HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
  679: (which is in need of updating).
  680: 
  681: It appears that [grub's FFS
  682: code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
  683: does not support all aspects of modern FFS, but there are also reports
  684: that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
  685: partition for the kernel with the intent that grub can understand it,
  686: which leads to /netbsd not being the actual kernel.  One must remember
  687: to update the special boot partition.
  688: 
  689: pygrub
  690: -------
  691: 
  692: pygrub runs in the dom0 and looks into the domU file system.  This
  693: implies that the domU must have a kernel in a file system in a format
  694: known to pygrub.
  695: 
  696: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
  697: and is inherently less secure than pvgrub due to running inside dom0. For both these
  698: reasons, pygrub should not be used, and is only still present so that
  699: historical DomU images using it still work.
  700: 
  701: As of 2014, pygrub seems to be of mostly historical
  702: interest. New DomUs should use pvgrub.
  703: 
  704: Amazon
  705: ------
  706: 
  707: See the [Amazon EC2 page](/amazon_ec2/).

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