1: [[!meta title="Xen HowTo"]]
9: Xen is a hypervisor for x86 hardware, which supports running multiple guest
10: operating systems on a single physical machine. Xen is a Type 1 or
11: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
12: memory and console, a dom0 operating system which mediates access to
13: other hardware (e.g., disks, network, USB), and one or more domU
14: operating systems which operate in an unprivileged virtualized
15: environment. IO requests from the domU systems are forwarded by the
16: Xen hypervisor to the dom0 to be fulfilled.
18: Xen supports different styles of guest:
20: [[!table data="""
21: Style of guest |Supported by NetBSD
22: PV |Yes (dom0, domU)
23: HVM |Yes (domU)
24: PVHVM |No
25: PVH |No
28: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
29: hardware directly, but instead makes hypercalls to the hypervisor; PV
30: guests must be specifically coded for Xen. In HVM mode, no guest
31: modification is required; however, hardware support is required, such
32: as VT-x on Intel CPUs and SVM on AMD CPUs.
34: There are further features for IOMMU virtualization, Intel's VT-d and
35: AMD's AMD-Vi. TODO: Explain whether Xen on NetBSD makes use of these
36: features. TODO: Review by someone who really understands this.
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
47: This HOWTO attempts to address both the case of running a NetBSD dom0
48: on hardware and running domUs under it (NetBSD and other), and also
49: running NetBSD as a domU in a VPS.
51: Versions of Xen and NetBSD
54: Most of the installation concepts and instructions are independent
55: of Xen version and NetBSD version. This section gives advice on
56: which version to choose. Versions not in pkgsrc and older unsupported
57: versions of NetBSD are intentionally ignored.
59: The term "amd64" is used to refer to both the NetBSD port and to the
60: hardware architecture on which it runs. Such hardware is generally
61: made by both Intel and AMD, and common on PC computers.
63: Xen versions
66: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
67: xenkernel and xentools. We will refer only to the kernel versions,
68: but note that both packages must be installed together and must have
69: matching versions.
71: Versions available in pkgsrc:
73: [[!table data="""
74: Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream
75: 4.2 |xenkernel42 |32bit, 64bit |Yes
76: 4.5 |xenkernel45 |64bit |Yes
77: 4.6 |xenkernel46 |64bit |Partially
78: 4.8 |xenkernel48 |64bit |No
79: 4.11 |xenkernel411 |64bit |No
82: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
84: Note: Xen 4.2 was the last version to support 32bit CPUs.
86: Xen command program
89: Early Xen used a program called xm to manipulate the system from the
90: dom0. Starting in 4.1, a replacement program with similar behavior
91: called xl is provided, but it does not work well in 4.1. In 4.2, both
92: xm and xl work fine. 4.4 is the last version that has xm.
94: You must make a global choice to use xm or xl, because it affects not
95: only which command you use, but the command used by rc.d scripts
96: (specifically xendomains) and which daemons should be run. The
97: xentools packages provide xl for 4.2 and up.
99: In 4.2, you can choose to use xm by simply changing the ctl_command
100: variable and setting xend=YES in rc.conf.
102: With xl, virtual devices are configured in parallel, which can cause
103: problems if they are written assuming serial operation (e.g., updating
104: firewall rules without explicit locking). There is now locking for
105: the provided scripts, which works for normal casses (e.g, file-backed
106: xbd, where a vnd must be allocated). But, as of 201612, it has not
107: been adequately tested for a complex custom setup with a large number
108: of interfaces.
110: NetBSD versions
113: The netbsd-7, netbsd-8, and -current branches are all reasonable
114: choices, with more or less the same considerations for non-Xen use.
115: NetBSD 8 is recommended as the stable version of the most recent
116: release for production use.
118: For developing Xen, netbsd-current may be appropriate.
120: As of NetBSD 6, a NetBSD domU will support multiple vcpus. There is
121: no SMP support for NetBSD as dom0. (The dom0 itself doesn't really
122: need SMP for dom0 functions; the lack of support is really a problem
123: when using a dom0 as a normal computer.)
125: Note: NetBSD support is called XEN3. However, it does support Xen 4,
126: because the hypercall interface has remained identical.
131: Xen itself can run on i386 (Xen < 4.2) or amd64 hardware (all Xen
132: versions). Practically, almost any computer where one would want to
133: run Xen today supports amd64.
135: Xen, the dom0 system, and each domU system can be either i386 or
136: amd64. When building a xenkernel package, one obtains an i386 Xen
137: kernel on an i386 host, and an amd64 Xen kernel on an amd64 host. If
138: the Xen kernel is i386, then the dom0 kernel and all domU kernels must
139: be i386. With an amd64 Xen kernel, an amd64 dom0 kernel is known to
140: work, and an i386 dom0 kernel should in theory work. An amd64
141: Xen/dom0 is known to support both i386 and amd64 domUs.
143: i386 dom0 and domU kernels must be PAE. PAE kernels are included in
144: the NetBSD default build.
146: Because of the above, the standard approach is to use an amd64 Xen
147: kernel and NetBSD/amd64 for the dom0. For domUs, NetBSD/i386 (with
148: the PAE kernel) and NetBSD/amd64 are in widespread use, and there is
149: little to no Xen-specific reason to prefer one over the other.
151: Note that to use an i386 dom0 with Xen 4.5 or higher, one must build
152: (or obtain from pre-built packages) an amd64 Xen kernel and install
153: that on the system. (One must also use a PAE i386 kernel, but this is
154: also required with an i386 Xen kernel.). Almost no one in the
155: NetBSD/Xen community does this, and the standard, well-tested,
156: approach is to use an amd64 dom0.
158: A [posting on
160: explained that PV system call overhead was higher on amd64, and thus
161: there is some notion that i386 guests are faster. It goes on to
162: caution that the total situation is complex and not entirely
163: understood. On top of that caution, the post is about Linux, not
164: NetBSD. TODO: Include link to benchmarks, if someone posts them.
166: NetBSD as a dom0
169: NetBSD can be used as a dom0 and works very well. The following
170: sections address installation, updating NetBSD, and updating Xen.
171: Note that it doesn't make sense to talk about installing a dom0 OS
172: without also installing Xen itself. We first address installing
173: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
174: NetBSD install to a dom0 install by just changing the kernel and boot
177: For experimenting with Xen, a machine with as little as 1G of RAM and
178: 100G of disk can work. For running many domUs in productions, far
179: more will be needed; e.g. 4-8G and 1T of disk is reasonable for a
180: half-dozen domUs of 512M and 32G each. Basically, the RAM and disk
181: have to be bigger than the sum of the RAM/disk needs of the dom0 and
182: all the domUs.
184: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
185: 512M it worked reliably. This does not make sense, but if you see
186: "not ELF" after Xen boots, try increasing dom0 RAM.
188: Styles of dom0 operation
191: There are two basic ways to use Xen. The traditional method is for
192: the dom0 to do absolutely nothing other than providing support to some
193: number of domUs. Such a system was probably installed for the sole
194: purpose of hosting domUs, and sits in a server room on a UPS.
196: The other way is to put Xen under a normal-usage computer, so that the
197: dom0 is what the computer would have been without Xen, perhaps a
198: desktop or laptop. Then, one can run domUs at will. Purists will
199: deride this as less secure than the previous approach, and for a
200: computer whose purpose is to run domUs, they are right. But Xen and a
201: dom0 (without domUs) is not meaningfully less secure than the same
202: things running without Xen. One can boot Xen or boot regular NetBSD
203: alternately with little problems, simply refraining from starting the
204: Xen daemons when not running Xen.
206: Note that NetBSD as dom0 does not support multiple CPUs. This will
207: limit the performance of the Xen/dom0 workstation approach. In theory
208: the only issue is that the "backend drivers" are not yet MPSAFE:
211: Installation of NetBSD
215: [install NetBSD/amd64](/guide/inst/)
216: just as you would if you were not using Xen.
217: However, the partitioning approach is very important.
219: If you want to use RAIDframe for the dom0, there are no special issues
220: for Xen. Typically one provides RAID storage for the dom0, and the
221: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
222: over a RAID1 header to find /boot from a file system within a RAID
223: partition; this is no different when booting Xen.
225: There are 4 styles of providing backing storage for the virtual disks
226: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
228: With raw partitions, one has a disklabel (or gpt) partition sized for
229: each virtual disk to be used by the domU. (If you are able to predict
230: how domU usage will evolve, please add an explanation to the HOWTO.
231: Seriously, needs tend to change over time.)
233: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
234: for domU disks. This is almost as efficient as raw disk partitions
235: and more flexible. Hence raw disk partitions should typically not
236: be used.
238: One can use files in the dom0 file system, typically created by dd'ing
239: /dev/zero to create a specific size. This is somewhat less efficient,
240: but very convenient, as one can cp the files for backup, or move them
241: between dom0 hosts.
243: Finally, in theory one can place the files backing the domU disks in a
244: SAN. (This is an invitation for someone who has done this to add a
245: HOWTO page.)
247: Installation of Xen
250: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
251: pkgsrc (or another matching pair). See [the pkgsrc
252: documentation](https://www.NetBSD.org/docs/pkgsrc/) for help with
253: pkgsrc. Ensure that your packages are recent; the HOWTO does not
254: contemplate old builds.
256: Next you need to install the selected Xen kernel itself, which is
257: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
258: For debugging, one may copy xen-debug.gz; this is conceptually similar
259: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
260: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
261: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
262: of a NetBSD build. If using i386, use
263: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz. (If using Xen
264: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen. But you
265: should not use Xen 3.1.) Both xen and the NetBSD kernel may be (and
266: typically are) left compressed.
268: In a dom0, kernfs is mandatory for xend to communicate with the
269: kernel, so ensure that /kern is in fstab. (A standard NetBSD install
270: should already mount /kern.)
272: Because you already installed NetBSD, you have a working boot setup
273: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
274: beginning of your root file system, have /boot, and likely also
275: /boot.cfg. (If not, fix before continuing!)
277: Add a line to /boot.cfg to boot Xen. See boot.cfg(5) for an
278: example. The basic line is:
280: [[!template id=programlisting text="""
281: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
284: which specifies that the dom0 should have 512M, leaving the rest to be
285: allocated for domUs. To use a serial console, use
287: [[!template id=programlisting text="""
288: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
291: which will use the first serial port for Xen (which counts starting
292: from 1, unlike NetBSD which counts starting from 0), forcing
293: speed/parity. Because the NetBSD command line lacks a
294: "console=pc" argument, it will use the default "xencons" console device,
295: which directs the console I/O through Xen to the same console device Xen
296: itself uses (in this case, the serial port).
298: In an attempt to add performance, one can also add:
300: [[!template id=programlisting text="""
301: dom0_max_vcpus=1 dom0_vcpus_pin
304: to force only one vcpu to be provided (since NetBSD dom0 can't use
305: more) and to pin that vcpu to a physical CPU. TODO: benchmark this.
307: Xen has [many boot
309: and other than dom0 memory and max_vcpus, they are generally not
312: As with non-Xen systems, you should have a line to boot /netbsd (a
313: kernel that works without Xen). Consider a line to boot /netbsd.ok (a
314: fallback version of the non-Xen kernel, updated manually when you are
315: sure /netbsd is ok). Consider also a line to boot fallback versions
316: of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used
317: to resolve Xen booting issues.
319: Probably you want a default=N line to choose Xen in the absence of
322: Now, reboot so that you are running a DOM0 kernel under Xen, rather
323: than GENERIC without Xen.
325: Using grub (historic)
328: Before NetBSD's native bootloader could support Xen, the use of
329: grub was recommended. If necessary, see the
330: [old grub information](/ports/xen/howto-grub).
332: The [HowTo on Installing into
334: explains how to set up booting a dom0 with Xen using grub with
335: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
336: boot. Now, just create a system with RAID-1, and alter /boot.cfg as
337: described above.)
339: Configuring Xen
342: Xen logs will be in /var/log/xen.
344: Now, you have a system that will boot Xen and the dom0 kernel, but not
345: do anything else special. Make sure that you have rebooted into Xen.
346: There will be no domUs, and none can be started because you still have
347: to configure the dom0 daemons.
349: The daemons which should be run vary with Xen version and with whether
350: one is using xm or xl. Xen 4.2 and up packages use xl. To use xm with 4.2,
351: edit xendomains to use xm instead.
353: For 4.1 and up, you should enable xencommons. Not enabling xencommons
354: will result in a hang; it is necessary to hit ^C on the console to let
355: the machine finish booting. If you are using xm (default in 4.1, or
356: if you changed xendomains in 4.2), you should also enable xend:
358: [[!template id=programlisting text="""
359: xend=YES # only if using xm, and only installed <= 4.2
363: TODO: Recommend for/against xen-watchdog.
365: After you have configured the daemons and either started them (in the
366: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
367: available resources, and running domains. An example with xl follows:
369: # xl dmesg
370: [xen's boot info]
371: # xl info
372: [available memory, etc.]
373: # xl list
374: Name Id Mem(MB) CPU State Time(s) Console
375: Domain-0 0 64 0 r---- 58.1
377: ### Issues with xencommons
379: xencommons starts xenstored, which stores data on behalf of dom0 and
380: domUs. It does not currently work to stop and start xenstored.
381: Certainly all domUs should be shutdown first, following the sort order
382: of the rc.d scripts. However, the dom0 sets up state with xenstored,
383: and is not notified when xenstored exits, leading to not recreating
384: the state when the new xenstored starts. Until there's a mechanism to
385: make this work, one should not expect to be able to restart xenstored
386: (and thus xencommons). There is currently no reason to expect that
387: this will get fixed any time soon.
389: ### No-longer needed advice about devices
391: The installation of NetBSD should already have created devices for xen
392: (xencons, xenevt, xsd_kva), but if they are not present, create them:
394: cd /dev && sh MAKEDEV xen
396: anita (for testing NetBSD)
399: With the setup so far (assuming 4.2/xl), one should be able to run
400: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
401: root, because anita must create a domU):
403: anita --vmm=xl test file:///usr/obj/i386/
405: Alternatively, one can use --vmm=xm to use xm-based domU creation
406: instead (and must, on Xen <= 4.1). TODO: confirm that anita xl really works.
408: Xen-specific NetBSD issues
411: There are (at least) two additional things different about NetBSD as a
412: dom0 kernel compared to hardware.
414: One is that the module ABI is different because some of the #defines
415: change, so one must build modules for Xen. As of netbsd-7, the build
416: system does this automatically. TODO: check this. (Before building
417: Xen modules was added, it was awkward to use modules to the point
418: where it was considered that it did not work.)
420: The other difference is that XEN3_DOM0 does not have exactly the same
421: options as GENERIC. While it is debatable whether or not this is a
422: bug, users should be aware of this and can simply add missing config
423: items if desired.
425: Updating NetBSD in a dom0
428: This is just like updating NetBSD on bare hardware, assuming the new
429: version supports the version of Xen you are running. Generally, one
430: replaces the kernel and reboots, and then overlays userland binaries
431: and adjusts /etc.
433: Note that one must update both the non-Xen kernel typically used for
434: rescue purposes and the DOM0 kernel used with Xen.
436: Converting from grub to /boot
439: These instructions were [TODO: will be] used to convert a system from
440: grub to /boot. The system was originally installed in February of
441: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
442: over time. Before these commands, it was running NetBSD 6 i386, Xen
443: 4.1 and grub, much like the message linked earlier in the grub
446: # Install MBR bootblocks on both disks.
447: fdisk -i /dev/rwd0d
448: fdisk -i /dev/rwd1d
449: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
450: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
451: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
452: # Install secondary boot loader
453: cp -p /usr/mdec/boot /
454: # Create boot.cfg following earlier guidance:
455: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
456: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
458: menu=GENERIC single-user:boot -s
459: menu=GENERIC.ok:boot netbsd.ok
460: menu=GENERIC.ok single-user:boot netbsd.ok -s
461: menu=Drop to boot prompt:prompt
465: TODO: actually do this and fix it if necessary.
467: Upgrading Xen versions
470: Minor version upgrades are trivial. Just rebuild/replace the
471: xenkernel version and copy the new xen.gz to / (where /boot.cfg
472: references it), and reboot.
474: Major version upgrades are conceptually not difficult, but can run
475: into all the issues found when installing Xen. Assuming migration
476: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
477: install the xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz
478: to /.
480: Ensure that the contents of /etc/rc.d/xen* are correct. Specifically,
481: they must match the package you just installed and not be left over
482: from some previous installation.
484: Enable the correct set of daemons; see the configuring section above.
485: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
487: Ensure that the domU config files are valid for the new version.
488: Specifically, for 4.x remove autorestart=True, and ensure that disks
489: are specified with numbers as the second argument, as the examples
490: above show, and not NetBSD device names.
492: Hardware known to work
495: Arguably, this section is misplaced, and there should be a page of
496: hardware that runs NetBSD/amd64 well, with the mostly-well-founded
497: assumption that NetBSD/xen runs fine on any modern hardware that
498: NetBSD/amd64 runs well on. Until then, we give motherboard/CPU (and
499: sometimes RAM) pairs/triples to aid those choosing a motherboard.
500: Note that Xen systems usually do not run X, so a listing here does not
501: imply that X works at all.
503: Supermicro X9SRL-F, Xeon E5-1650 v2, 96 GiB ECC
504: Supermicro ??, Atom C2758 (8 core), 32 GiB ECC
505: ASUS M5A78L-M/USB3 AM3+ microATX, AMD Piledriver X8 4000MHz, 16 GiB ECC
507: Older hardware:
509: Intel D915GEV, Pentium4 CPU 3.40GHz, 4GB 533MHz Synchronous DDR2
510: INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU E6850 @ 3.00GHz"
511: INTEL DG33FB, "Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz"
513: Running Xen under qemu
516: The astute reader will note that this section is somewhat twisted.
517: However, it can be useful to run Xen under qemu either because the
518: version of NetBSD as a dom0 does not run on the hardware in use, or to
519: generate automated test cases involving Xen.
521: In 2015-01, the following combination was reported to mostly work:
523: host OS: NetBSD/amd64 6.1.4
524: qemu: 2.2.0 from pkgsrc
525: Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
526: dom0 kernel: NetBSD/amd64 6.1.5
527: Xen tools: xentools42-4.2.5 from pkgsrc
529: See [PR 47720](https://gnats.netbsd.org/47720) for a problem with dom0
532: Unprivileged domains (domU)
535: This section describes general concepts about domUs. It does not
536: address specific domU operating systems or how to install them. The
537: config files for domUs are typically in /usr/pkg/etc/xen, and are
538: typically named so that the file name, domU name and the domU's host
539: name match.
541: The domU is provided with CPU and memory by Xen, configured by the
542: dom0. The domU is provided with disk and network by the dom0,
543: mediated by Xen, and configured in the dom0.
545: Entropy in domUs can be an issue; physical disks and network are on
546: the dom0. NetBSD's /dev/random system works, but is often challenged.
548: Config files
551: There is no good order to present config files and the concepts
552: surrounding what is being configured. We first show an example config
553: file, and then in the various sections give details.
555: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
556: for a large number of well-commented examples, mostly for running
559: The following is an example minimal domain configuration file
560: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
561: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
562: i386 domU). The domU serves as a network file server.
564: # -*- mode: python; -*-
566: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
567: memory = 1024
568: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
569: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
570: 'file:/n0/xen/foo-wd1,0x1,w' ]
572: The domain will have the same name as the file. The kernel has the
573: host/domU name in it, so that on the dom0 one can update the various
574: domUs independently. The vif line causes an interface to be provided,
575: with a specific mac address (do not reuse MAC addresses!), in bridge
576: mode. Two disks are provided, and they are both writable; the bits
577: are stored in files and Xen attaches them to a vnd(4) device in the
578: dom0 on domain creation. The system treats xbd0 as the boot device
579: without needing explicit configuration.
581: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
582: that "xm create" takes the name of a config file, while other commands
583: take the name of a domain. To create the domain, connect to the
584: console, create the domain while attaching the console, shutdown the
585: domain, and see if it has finished stopping, do (or xl with Xen >=
588: xm create foo
589: xm console foo
590: xm create -c foo
591: xm shutdown foo
592: xm list
594: Typing ^] will exit the console session. Shutting down a domain is
595: equivalent to pushing the power button; a NetBSD domU will receive a
596: power-press event and do a clean shutdown. Shutting down the dom0
597: will trigger controlled shutdowns of all configured domUs.
599: domU kernels
602: On a physical computer, the BIOS reads sector 0, and a chain of boot
603: loaders finds and loads a kernel. Normally this comes from the root
604: file system. With Xen domUs, the process is totally different. The
605: normal path is for the domU kernel to be a file in the dom0's
606: file system. At the request of the dom0, Xen loads that kernel into a
607: new domU instance and starts execution. While domU kernels can be
608: anyplace, reasonable places to store domU kernels on the dom0 are in /
609: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
610: config files), or in /u0/xen (where the vdisks are).
612: Note that loading the domU kernel from the dom0 implies that boot
613: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
614: See the VPS section near the end for discussion of alternate ways to
615: obtain domU kernels.
617: CPU and memory
620: A domain is provided with some number of vcpus, less than the number
621: of CPUs seen by the hypervisor. (For a dom0, this is controlled by
622: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
623: from the config file by the "vcpus = N" directive.
625: A domain is provided with memory; this is controlled in the config
626: file by "memory = N" (in megabytes). In the straightforward case, the
627: sum of the the memory allocated to the dom0 and all domUs must be less
628: than the available memory.
630: Xen also provides a "balloon" driver, which can be used to let domains
631: use more memory temporarily. TODO: Explain better, and explain how
632: well it works with NetBSD.
634: Virtual disks
637: With the file/vnd style, typically one creates a directory,
638: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
639: domUs. Then, for each domU disk, one writes zeros to a file that then
640: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
641: for the first virtual disk for the domU called foo. Writing zeros to
642: the file serves two purposes. One is that preallocating the contents
643: improves performance. The other is that vnd on sparse files has
644: failed to work. TODO: give working/notworking NetBSD versions for
645: sparse vnd and gnats reference. Note that the use of file/vnd for Xen
646: is not really different than creating a file-backed virtual disk for
647: some other purpose, except that xentools handles the vnconfig
648: commands. To create an empty 4G virtual disk, simply do
650: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
652: Do not use qemu-img-xen, because this will create sparse file. There
653: have been recent (2015) reports of sparse vnd(4) devices causing
654: lockups, but there is apparently no PR.
656: With the lvm style, one creates logical devices. They are then used
657: similarly to vnds. TODO: Add an example with lvm.
659: In domU config files, the disks are defined as a sequence of 3-tuples.
660: The first element is "method:/path/to/disk". Common methods are
661: "file:" for file-backed vnd. and "phy:" for something that is already
662: a (TODO: character or block) device.
664: The second element is an artifact of how virtual disks are passed to
665: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
666: are given a device name to associate with the disk, and values like
667: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
668: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
669: second argument. The name given is converted to a major/minor by
670: calling stat(2) on the name in /dev and this is passed to the domU.
671: In the general case, the dom0 and domU can be different operating
672: systems, and it is an unwarranted assumption that they have consistent
673: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
674: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
675: for the second works fine and avoids this issue. For a GNU/Linux
676: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
679: The third element is "w" for writable disks, and "r" for read-only
682: Note that NetBSD by default creates only vnd. If you need more
683: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
686: Note that NetBSD by default creates only xbd. If you need more
687: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
689: Virtual Networking
692: Xen provides virtual Ethernets, each of which connects the dom0 and a
693: domU. For each virtual network, there is an interface "xvifN.M" in
694: the dom0, and in domU index N, a matching interface xennetM (NetBSD
695: name). The interfaces behave as if there is an Ethernet with two
696: adapters connected. From this primitive, one can construct various
697: configurations. We focus on two common and useful cases for which
698: there are existing scripts: bridging and NAT.
700: With bridging (in the example above), the domU perceives itself to be
701: on the same network as the dom0. For server virtualization, this is
702: usually best. Bridging is accomplished by creating a bridge(4) device
703: and adding the dom0's physical interface and the various xvifN.0
704: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
705: config file. The bridge must be set up already in the dom0; an
706: example /etc/ifconfig.bridge0 is:
710: !brconfig bridge0 add wm0
712: With NAT, the domU perceives itself to be behind a NAT running on the
713: dom0. This is often appropriate when running Xen on a workstation.
714: TODO: NAT appears to be configured by "vif = [ '' ]".
716: The MAC address specified is the one used for the interface in the new
717: domain. The interface in dom0 will use this address XOR'd with
718: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
720: Sizing domains
723: Modern x86 hardware has vast amounts of resources. However, many
724: virtual servers can function just fine on far less. A system with
725: 512M of RAM and a 4G disk can be a reasonable choice. Note that it is
726: far easier to adjust virtual resources than physical ones. For
727: memory, it's just a config file edit and a reboot. For disk, one can
728: create a new file and vnconfig it (or lvm), and then dump/restore,
729: just like updating physical disks, but without having to be there and
730: without those pesky connectors.
732: Starting domains automatically
735: To start domains foo at bar at boot and shut them down cleanly on dom0
736: shutdown, in rc.conf add:
738: xendomains="foo bar"
740: Note that earlier versions of the xentools41 xendomains rc.d script
741: used xl, when one should use xm with 4.1.
743: Creating specific unprivileged domains (domU)
746: Creating domUs is almost entirely independent of operating system. We
747: have already presented the basics of config files. Note that you must
748: have already completed the dom0 setup so that "xl list" (or "xm list")
751: Creating an unprivileged NetBSD domain (domU)
754: See the earlier config file, and adjust memory. Decide on how much
755: storage you will provide, and prepare it (file or lvm).
757: While the kernel will be obtained from the dom0 file system, the same
758: file should be present in the domU as /netbsd so that tools like
759: savecore(8) can work. (This is helpful but not necessary.)
761: The kernel must be specifically for Xen and for use as a domU. The
762: i386 and amd64 provide the following kernels:
764: i386 XEN3_DOMU
765: i386 XEN3PAE_DOMU
766: amd64 XEN3_DOMU
768: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
769: use the PAE version of the i386 kernel.
771: This will boot NetBSD, but this is not that useful if the disk is
772: empty. One approach is to unpack sets onto the disk outside of xen
773: (by mounting it, just as you would prepare a physical disk for a
774: system you can't run the installer on).
776: A second approach is to run an INSTALL kernel, which has a miniroot
777: and can load sets from the network. To do this, copy the INSTALL
778: kernel to / and change the kernel line in the config file to:
780: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
782: Then, start the domain as "xl create -c configname".
784: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
785: line should be used in the config file.
787: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
789: After booting the domain, the option to install via CDROM may be
790: selected. The CDROM device should be changed to `xbd1d`.
792: Once done installing, "halt -p" the new domain (don't reboot or halt,
793: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
794: config file), switch the config file back to the XEN3_DOMU kernel,
795: and start the new domain again. Now it should be able to use "root on
796: xbd0a" and you should have a, functional NetBSD domU.
798: TODO: check if this is still accurate.
799: When the new domain is booting you'll see some warnings about *wscons*
800: and the pseudo-terminals. These can be fixed by editing the files
801: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
802: `/etc/ttys`, except *console*, like this:
804: console "/usr/libexec/getty Pc" vt100 on secure
805: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
806: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
807: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
808: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
810: Finally, all screens must be commented out from `/etc/wscons.conf`.
812: It is also desirable to add
816: in rc.conf. This way, the domain will be properly shut down if
817: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
819: It is not strictly necessary to have a kernel (as /netbsd) in the domU
820: file system. However, various programs (e.g. netstat) will use that
821: kernel to look up symbols to read from kernel virtual memory. If
822: /netbsd is not the running kernel, those lookups will fail. (This is
823: not really a Xen-specific issue, but because the domU kernel is
824: obtained from the dom0, it is far more likely to be out of sync or
825: missing with Xen.)
827: Creating an unprivileged Linux domain (domU)
830: Creating unprivileged Linux domains isn't much different from
831: unprivileged NetBSD domains, but there are some details to know.
833: First, the second parameter passed to the disk declaration (the '0x1' in
834: the example below)
836: disk = [ 'phy:/dev/wd0e,0x1,w' ]
838: does matter to Linux. It wants a Linux device number here (e.g. 0x300
839: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
840: So, hda1 which has major 3 and minor 1 on a Linux system will have
841: device number 0x301. Alternatively, devices names can be used (hda,
842: hdb, ...) as xentools has a table to map these names to devices
843: numbers. To export a partition to a Linux guest we can use:
845: disk = [ 'phy:/dev/wd0e,0x300,w' ]
846: root = "/dev/hda1 ro"
848: and it will appear as /dev/hda on the Linux system, and be used as root
851: To install the Linux system on the partition to be exported to the
852: guest domain, the following method can be used: install
853: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
854: that will be the root partition of your Linux domain, and mount it.
855: Then copy the files from a working Linux system, make adjustments in
856: `/etc` (fstab, network config). It should also be possible to extract
857: binary packages such as .rpm or .deb directly to the mounted partition
858: using the appropriate tool, possibly running under NetBSD's Linux
859: emulation. Once the file system has been populated, umount it. If
860: desirable, the file system can be converted to ext3 using tune2fs -j.
861: It should now be possible to boot the Linux guest domain, using one of
862: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
864: To get the Linux console right, you need to add:
866: extra = "xencons=tty1"
868: to your configuration since not all Linux distributions auto-attach a
869: tty to the xen console.
871: Creating an unprivileged Solaris domain (domU)
874: See possibly outdated
875: [Solaris domU instructions](/ports/xen/howto-solaris/).
878: PCI passthrough: Using PCI devices in guest domains
881: The dom0 can give other domains access to selected PCI
882: devices. This can allow, for example, a non-privileged domain to have
883: access to a physical network interface or disk controller. However,
884: keep in mind that giving a domain access to a PCI device most likely
885: will give the domain read/write access to the whole physical memory,
886: as PCs don't have an IOMMU to restrict memory access to DMA-capable
887: device. Also, it's not possible to export ISA devices to non-dom0
888: domains, which means that the primary VGA adapter can't be exported.
889: A guest domain trying to access the VGA registers will panic.
891: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
892: not been ported to later versions at this time.
894: For a PCI device to be exported to a domU, is has to be attached to
895: the "pciback" driver in dom0. Devices passed to the dom0 via the
896: pciback.hide boot parameter will attach to "pciback" instead of the
897: usual driver. The list of devices is specified as "(bus:dev.func)",
898: where bus and dev are 2-digit hexadecimal numbers, and func a
899: single-digit number:
903: pciback devices should show up in the dom0's boot messages, and the
904: devices should be listed in the `/kern/xen/pci` directory.
906: PCI devices to be exported to a domU are listed in the "pci" array of
907: the domU's config file, with the format "0000:bus:dev.func".
909: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
911: In the domU an "xpci" device will show up, to which one or more pci
912: buses will attach. Then the PCI drivers will attach to PCI buses as
913: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
914: or any PCI drivers built in by default; you have to build your own
915: kernel to use PCI devices in a domU. Here's a kernel config example;
916: note that only the "xpci" lines are unusual.
918: include "arch/i386/conf/XEN3_DOMU"
920: # Add support for PCI buses to the XEN3_DOMU kernel
921: xpci* at xenbus ?
922: pci* at xpci ?
924: # PCI USB controllers
925: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
927: # USB bus support
928: usb* at uhci?
930: # USB Hubs
931: uhub* at usb?
932: uhub* at uhub? port ? configuration ? interface ?
934: # USB Mass Storage
935: umass* at uhub? port ? configuration ? interface ?
936: wd* at umass?
937: # SCSI controllers
938: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
940: # SCSI bus support (for both ahc and umass)
941: scsibus* at scsi?
943: # SCSI devices
944: sd* at scsibus? target ? lun ? # SCSI disk drives
945: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
948: NetBSD as a domU in a VPS
951: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
952: hardware. This section explains how to deal with Xen in a domU as a
953: virtual private server where you do not control or have access to the
954: dom0. This is not intended to be an exhaustive list of VPS providers;
955: only a few are mentioned that specifically support NetBSD.
957: VPS operators provide varying degrees of access and mechanisms for
958: configuration. The big issue is usually how one controls which kernel
959: is booted, because the kernel is nominally in the dom0 file system (to
960: which VPS users do not normally have access). A second issue is how
961: to install NetBSD.
962: A VPS user may want to compile a kernel for security updates, to run
963: npf, run IPsec, or any other reason why someone would want to change
964: their kernel.
966: One approach is to have an administrative interface to upload a kernel,
967: or to select from a prepopulated list. Other approaches are pygrub
968: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
969: kernel from the domU file system. This is closer to a regular physical
970: computer, where someone who controls a machine can replace the kernel.
972: A second issue is multiple CPUs. With NetBSD 6, domUs support
973: multiple vcpus, and it is typical for VPS providers to enable multiple
974: CPUs for NetBSD domUs.
979: pygrub runs in the dom0 and looks into the domU file system. This
980: implies that the domU must have a kernel in a file system in a format
981: known to pygrub. As of 2014, pygrub seems to be of mostly historical
987: pvgrub is a version of grub that uses PV operations instead of BIOS
988: calls. It is booted from the dom0 as the domU kernel, and then reads
989: /grub/menu.lst and loads a kernel from the domU file system.
991: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
992: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
993: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
994: page](http://www.panix.com/v-colo/grub.html), which describes only
995: Linux but should be updated to cover NetBSD :-).
997: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
998: their own kernel. See then [prgmr.com NetBSD
1000: (which is in need of updating).
1002: It appears that [grub's FFS
1004: does not support all aspects of modern FFS, but there are also reports
1005: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
1006: partition for the kernel with the intent that grub can understand it,
1007: which leads to /netbsd not being the actual kernel. One must remember
1008: to update the special boot partition.
1013: See the [Amazon EC2 page](/amazon_ec2/).
1015: TODO items for improving NetBSD/xen
1018: * Make the NetBSD dom0 kernel work with SMP.
1019: * Test the Xen 4.5 packages adequately to be able to recommend them as
1020: the standard approach.
1021: * Get PCI passthrough working on Xen 4.5
1022: * Get pvgrub into pkgsrc, either via xentools or separately.
1023: * grub
1024: * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
1025: fragsize/blocksize (UFS2 support may be present; the point is to
1026: make it so that with any UFS1/UFS2 file system setup that works
1027: with NetBSD grub will also work).
1028: See [pkg/40258](https://gnats.netbsd.org/40258).
1029: * Push patches upstream.
1030: * Get UFS2 patches into pvgrub.
1031: * Add support for PV ops to a version of /boot, and make it usable as
1032: a kernel in Xen, similar to pvgrub.
1034: Random pointers
1037: This section contains links from elsewhere not yet integrated into the
1038: HOWTO, and other guides.
1040: * http://www.lumbercartel.ca/library/xen/
1041: * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html
1042: * https://gmplib.org/~tege/xen.html
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