7: Xen is a hypervisor (or virtual machine monitor) for x86 hardware
8: (i686-class or higher), which supports running multiple guest
9: operating systems on a single physical machine. Xen is a Type 1 or
10: bare-metal hypervisor; one uses the Xen kernel to control the CPU,
11: memory and console, a dom0 operating system which mediates access to
12: other hardware (e.g., disks, network, USB), and one or more domU
13: operating systems which operate in an unprivileged virtualized
14: environment. IO requests from the domU systems are forwarded by the
15: hypervisor (Xen) to the dom0 to be fulfilled.
17: Xen supports two styles of guests. The original is Para-Virtualized
18: (PV) which means that the guest OS does not attempt to access hardware
19: directly, but instead makes hypercalls to the hypervisor. This is
20: analogous to a user-space program making system calls. (The dom0
21: operating system uses PV calls for some functions, such as updating
22: memory mapping page tables, but has direct hardware access for disk
23: and network.) PV guests must be specifically coded for Xen.
25: The more recent style is HVM, which means that the guest does not have
26: code for Xen and need not be aware that it is running under Xen.
27: Attempts to access hardware registers are trapped and emulated. This
28: style is less efficient but can run unmodified guests.
30: Generally any amd64 machine will work with Xen and PV guests. In
31: theory i386 computers without amd64 support can be used for Xen <=
32: 4.2, but we have no recent reports of this working (this is a hint).
33: For HVM guests, the VT or VMX cpu feature (Intel) or SVM/HVM/VT
34: (amd64) is needed; "cpuctl identify 0" will show this. TODO: Clean up
35: and check the above features.
37: At boot, the dom0 kernel is loaded as a module with Xen as the kernel.
38: The dom0 can start one or more domUs. (Booting is explained in detail
39: in the dom0 section.)
41: NetBSD supports Xen in that it can serve as dom0, be used as a domU,
42: and that Xen kernels and tools are available in pkgsrc. This HOWTO
43: attempts to address both the case of running a NetBSD dom0 on hardware
44: and running domUs under it (NetBSD and other), and also running NetBSD
45: as a domU in a VPS.
47: Some versions of Xen support "PCI passthrough", which means that
48: specific PCI devices can be made available to a specific domU instead
49: of the dom0. This can be useful to let a domU run X11, or access some
50: network interface or other peripheral.
52: NetBSD used to support Xen2; this has been removed.
57: Installing NetBSD/Xen is not extremely difficult, but it is more
58: complex than a normal installation of NetBSD.
59: In general, this HOWTO is occasionally overly restrictive about how
60: things must be done, guiding the reader to stay on the established
61: path when there are no known good reasons to stray.
63: This HOWTO presumes a basic familiarity with the Xen system
64: architecture. This HOWTO presumes familiarity with installing NetBSD
65: on i386/amd64 hardware and installing software from pkgsrc.
66: See also the [Xen website](http://www.xenproject.org/).
68: Versions of Xen and NetBSD
71: Most of the installation concepts and instructions are independent
72: of Xen version and NetBSD version. This section gives advice on
73: which version to choose. Versions not in pkgsrc and older unsupported
74: versions of NetBSD are intentionally ignored.
79: In NetBSD, xen is provided in pkgsrc, via matching pairs of packages
80: xenkernel and xentools. We will refer only to the kernel versions,
81: but note that both packages must be installed together and must have
82: matching versions.
84: xenkernel3 and xenkernel33 provide Xen 3.1 and 3.3. These no longer
85: receive security patches and should not be used. Xen 3.1 supports PCI
86: passthrough. Xen 3.1 supports non-PAE on i386.
88: xenkernel41 provides Xen 4.1. This is no longer maintained by Xen,
89: but as of 2014-12 receives backported security patches. It is a
90: reasonable although trailing-edge choice.
92: xenkernel42 provides Xen 4.2. This is maintained by Xen, but old as
93: of 2014-12.
95: xenkernel45 provides Xen 4.5. This is new to pkgsrc as of 2015-01 and
96: not yet recommended for other than experimental/testing use.
98: Ideally newer versions of Xen will be added to pkgsrc.
100: Note that NetBSD support is called XEN3. It works with Xen 3 and Xen
101: 4 because the hypercall interface has been stable.
103: Xen command program
106: Early Xen used a program called xm to manipulate the system from the
107: dom0. Starting in 4.1, a replacement program with similar behavior
108: called xl is provided, but it does not work well in 4.1. In 4.2, both
109: xm and xl work fine. 4.4 is the last version that has xm. You must
110: choose one or the other, because it affects which daemons you run.
115: The netbsd-5, netbsd-6, netbsd-7, and -current branches are all
116: reasonable choices, with more or less the same considerations for
117: non-Xen use. Therefore, netbsd-6 is recommended as the stable version
118: of the most recent release for production use. For those wanting to
119: learn Xen or without production stability concerns, netbsd-7 is likely
120: most appropriate.
122: As of NetBSD 6, a NetBSD domU will support multiple vcpus. There is
123: no SMP support for NetBSD as dom0. (The dom0 itself doesn't really
124: need SMP; the lack of support is really a problem when using a dom0 as
125: a normal computer.)
130: Xen itself can run on i386 or amd64 machines. (Practically, almost
131: any computer where one would want to run Xen supports amd64.) If
132: using an i386 NetBSD kernel for the dom0, PAE is required (PAE
133: versions are built by default). While i386 dom0 works fine, amd64 is
134: recommended as more normal.
136: Xen 4.2 is the last version to support i386 as a host. TODO: Clarify
137: if this is about the CPU having to be amd64, or about the dom0 kernel
138: having to be amd64.
140: One can then run i386 domUs and amd64 domUs, in any combination. If
141: running an i386 NetBSD kernel as a domU, the PAE version is required.
142: (Note that emacs (at least) fails if run on i386 with PAE when built
143: without, and vice versa, presumably due to bugs in the undump code.)
148: Mostly, NetBSD as a dom0 or domU is quite stable.
149: However, there are some open PRs indicating problems.
151: - [PR 48125](http://gnats.netbsd.org/48125)
152: - [PR 47720](http://gnats.netbsd.org/47720)
154: Note also that there are issues with sparse vnd(4) instances, but
155: these are not about Xen.
160: Therefore, this HOWTO recommends running xenkernel42 (and xentools42),
161: xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the
162: dom0. Either the i386 or amd64 of NetBSD may be used as domUs.
164: Build problems
167: Ideally, all versions of Xen in pkgsrc would build on all versions of
168: NetBSD on both i386 and amd64. However, that isn't the case. Besides
169: aging code and aging compilers, qemu (included in xentools for HVM
170: support) is difficult to build. The following are known to work or FAIL:
172: xenkernel3 netbsd-5 amd64
173: xentools3 netbsd-5 amd64
174: xentools3=hvm netbsd-5 amd64 ????
175: xenkernel33 netbsd-5 amd64
176: xentools33 netbsd-5 amd64
177: xenkernel41 netbsd-5 amd64
178: xentools41 netbsd-5 amd64
179: xenkernel42 netbsd-5 amd64
180: xentools42 netbsd-5 amd64
182: xenkernel3 netbsd-6 i386 FAIL
183: xentools3 netbsd-6 i386
184: xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
185: xenkernel33 netbsd-6 i386
186: xentools33 netbsd-6 i386
187: xenkernel41 netbsd-6 i386
188: xentools41 netbsd-6 i386
189: xenkernel42 netbsd-6 i386
190: xentools42 netbsd-6 i386 *MIXED
192: (all 3 and 33 seem to FAIL)
193: xenkernel41 netbsd-7 i386
194: xentools41 netbsd-7 i386
195: xenkernel42 netbsd-7 i386
196: xentools42 netbsd-7 i386 ??FAIL
198: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
199: but it does not build for gdt.)
201: NetBSD as a dom0
204: NetBSD can be used as a dom0 and works very well. The following
205: sections address installation, updating NetBSD, and updating Xen.
206: Note that it doesn't make sense to talk about installing a dom0 OS
207: without also installing Xen itself. We first address installing
208: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
209: NetBSD install to a dom0 install by just changing the kernel and boot
212: For experimenting with Xen, a machine with as little as 1G of RAM and
213: 100G of disk can work. For running many domUs in productions, far
214: more will be needed.
216: Styles of dom0 operation
219: There are two basic ways to use Xen. The traditional method is for
220: the dom0 to do absolutely nothing other than providing support to some
221: number of domUs. Such a system was probably installed for the sole
222: purpose of hosting domUs, and sits in a server room on a UPS.
224: The other way is to put Xen under a normal-usage computer, so that the
225: dom0 is what the computer would have been without Xen, perhaps a
226: desktop or laptop. Then, one can run domUs at will. Purists will
227: deride this as less secure than the previous approach, and for a
228: computer whose purpose is to run domUs, they are right. But Xen and a
229: dom0 (without domUs) is not meaningfully less secure than the same
230: things running without Xen. One can boot Xen or boot regular NetBSD
231: alternately with little problems, simply refraining from starting the
232: Xen daemons when not running Xen.
234: Note that NetBSD as dom0 does not support multiple CPUs. This will
235: limit the performance of the Xen/dom0 workstation approach. In theory
236: the only issue is that the "backend drivers" are not yet MPSAFE:
239: Installation of NetBSD
243: [install NetBSD/amd64](/guide/inst/)
244: just as you would if you were not using Xen.
245: However, the partitioning approach is very important.
247: If you want to use RAIDframe for the dom0, there are no special issues
248: for Xen. Typically one provides RAID storage for the dom0, and the
249: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
250: over a RAID1 header to find /boot from a filesystem within a RAID
251: partition; this is no different when booting Xen.
253: There are 4 styles of providing backing storage for the virtual disks
254: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
256: With raw partitions, one has a disklabel (or gpt) partition sized for
257: each virtual disk to be used by the domU. (If you are able to predict
258: how domU usage will evolve, please add an explanation to the HOWTO.
259: Seriously, needs tend to change over time.)
261: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
262: for domU disks. This is almost as efficient as raw disk partitions
263: and more flexible. Hence raw disk partitions should typically not
264: be used.
266: One can use files in the dom0 filesystem, typically created by dd'ing
267: /dev/zero to create a specific size. This is somewhat less efficient,
268: but very convenient, as one can cp the files for backup, or move them
269: between dom0 hosts.
271: Finally, in theory one can place the files backing the domU disks in a
272: SAN. (This is an invitation for someone who has done this to add a
273: HOWTO page.)
275: Installation of Xen
278: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
279: pkgsrc (or another matching pair).
280: See [the pkgsrc
281: documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with pkgsrc.
283: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm. More
284: recent versions have HVM support integrated in the main xentools
285: package. It is entirely reasonable to run only PV guests.
287: Next you need to install the selected Xen kernel itself, which is
288: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
289: For debugging, one may copy xen-debug.gz; this is conceptually similar
290: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
291: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
292: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
293: of a NetBSD build. If using i386, use
294: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz. (If using Xen
295: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen. But you
296: should not use Xen 3.1.) Both xen and the NetBSD kernel may be (and
297: typically are) left compressed.
299: In a dom0 kernel, kernfs is mandatory for xend to comunicate with the
300: kernel, so ensure that /kern is in fstab. TODO: Say this is default,
301: or file a PR and give a reference.
303: Because you already installed NetBSD, you have a working boot setup
304: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
305: beginning of your root filesystem, /boot present, and likely
306: /boot.cfg. (If not, fix before continuing!)
308: Add a line to to /boot.cfg to boot Xen. See boot.cfg(5) for an
309: example. The basic line is
311: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
313: which specifies that the dom0 should have 256M, leaving the rest to be
314: allocated for domUs. To use a serial console, use
316: menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
318: which will use the first serial port for Xen (which counts starting
319: from 1), forcing speed/parity, and also for NetBSD (which counts
320: starting at 0). In an attempt to add performance, one can also add
322: dom0_max_vcpus=1 dom0_vcpus_pin
324: to force only one vcpu to be provided (since NetBSD dom0 can't use
325: more) and to pin that vcpu to a physical cpu. TODO: benchmark this.
327: Xen has [many boot
329: and other tham dom0 memory and max_vcpus, they are generally not
332: As with non-Xen systems, you should have a line to boot /netbsd (a
333: kernel that works without Xen) and fallback versions of the non-Xen
334: kernel, Xen, and the dom0 kernel.
336: Now, reboot so that you are running a DOM0 kernel under Xen, rather
337: than GENERIC without Xen.
339: Using grub (historic)
342: Before NetBSD's native bootloader could support Xen, the use of
343: grub was recommended. If necessary, see the
344: [old grub information](/ports/xen/howto-grub/).
346: The [HowTo on Installing into
348: explains how to set up booting a dom0 with Xen using grub with
349: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
352: Configuring Xen
355: Xen logs will be in /var/log/xen.
357: Now, you have a system that will boot Xen and the dom0 kernel, but not
358: do anything else special. Make sure that you have rebooted into Xen.
359: There will be no domUs, and none can be started because you still have
360: to configure the dom0 tools. The daemons which should be run vary
361: with Xen version and with whether one is using xm or xl. Note that
362: xend is for supporting "xm", and should only be used if you plan on
363: using "xm". Do NOT enable xend if you plan on using "xl" as it will
364: cause problems. Running xl without xencommons=YES (and starting it)
365: will result in a hang (so don't do that; follow the HOWTO!).
367: The installation of NetBSD should already have created devices for xen
368: (xencons, xenevt), but if they are not present, create them:
370: cd /dev && sh MAKEDEV xen
372: TODO: Give 3.1 advice (or remove it from pkgsrc).
374: For 3.3 (and thus xm), add to rc.conf (but note that you should have
375: installed 4.1 or 4.2):
380: For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
385: (If you are using xentools41 from before 2014-12-26, change
386: rc.d/xendomains to use xm rather than xl.)
388: For 4.2 with xm, add to rc.conf
393: For 4.2 with xl, add to rc.conf:
396: TODO: explain if there is a xend replacement
398: For 4.5 (and thus with xl), add to rc.conf:
401: TODO: explain if there is a xend replacement
403: TODO: Recommend for/against xen-watchdog.
405: After you have configured the daemons and either started them (in the
406: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
407: available resources, and running domains. An example with xm follows:
409: # xm dmesg
410: [xen's boot info]
411: # xm info
412: [available memory, etc.]
413: # xm list
414: Name Id Mem(MB) CPU State Time(s) Console
415: Domain-0 0 64 0 r---- 58.1
417: With xl, the commands are the same, and the output may be slightly
418: different. TODO: add example output for xl before the xm example,
419: after confirming on 4.2 and resolving the TODO about rc.conf.
421: ### Issues with xencommons
423: xencommons starts xenstored, which stores data on behalf of dom0 and
424: domUs. It does not currently work to stop and start xenstored.
425: Certainly all domUs should be shutdown first, following the sort order
426: of the rc.d scripts. However, the dom0 sets up state with xenstored,
427: and is not notified when xenstored exits, leading to not recreating
428: the state when the new xenstored starts. Until there's a mechanism to
429: make this work, one should not expect to be able to restart xenstored
430: (and thus xencommons). There is currently no reason to expect that
431: this will get fixed any time soon.
433: anita (for testing NetBSD)
436: With the setup so far (assuming 4.2/xl), one should be able to run
437: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
438: root, because anita must create a domU):
440: anita --vmm=xl test file:///usr/obj/i386/
442: Alternatively, one can use --vmm=xm to use xm-based domU creation
443: instead (and must, on Xen <= 4.1). TODO: confirm that anita xl really works.
445: Xen-specific NetBSD issues
448: There are (at least) two additional things different about NetBSD as a
449: dom0 kernel compared to hardware.
451: One is that modules are not usable in DOM0 kernels, so one must
452: compile in what's needed. It's not really that modules cannot work,
453: but that modules must be built for XEN3_DOM0 because some of the
454: defines change and the normal module builds don't do this. Basically,
455: enabling Xen changes the kernel ABI, and the module build system
456: doesn't cope with this.
458: The other difference is that XEN3_DOM0 does not have exactly the same
459: options as GENERIC. While it is debatable whether or not this is a
460: bug, users should be aware of this and can simply add missing config
461: items if desired.
463: Updating NetBSD in a dom0
466: This is just like updating NetBSD on bare hardware, assuming the new
467: version supports the version of Xen you are running. Generally, one
468: replaces the kernel and reboots, and then overlays userland binaries
469: and adjusts /etc.
471: Note that one must update both the non-Xen kernel typically used for
472: rescue purposes and the DOM0 kernel used with Xen.
474: Converting from grub to /boot
477: These instructions were [TODO: will be] used to convert a system from
478: grub to /boot. The system was originally installed in February of
479: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
480: over time. Before these commands, it was running NetBSD 6 i386, Xen
481: 4.1 and grub, much like the message linked earlier in the grub
484: # Install mbr bootblocks on both disks.
485: fdisk -i /dev/rwd0d
486: fdisk -i /dev/rwd1d
487: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
488: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
489: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
490: # Install secondary boot loader
491: cp -p /usr/mdec/boot /
492: # Create boog.cfg following earlier guidance:
493: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
494: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
496: menu=GENERIC single-user:boot -s
497: menu=GENERIC.ok:boot netbsd.ok
498: menu=GENERIC.ok single-user:boot netbsd.ok -s
499: menu=Drop to boot prompt:prompt
503: TODO: actually do this and fix it if necessary.
505: Updating Xen versions
508: Updating Xen is conceptually not difficult, but can run into all the
509: issues found when installing Xen. Assuming migration from 4.1 to 4.2,
510: remove the xenkernel41 and xentools41 packages and install the
511: xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz to /.
513: Ensure that the contents of /etc/rc.d/xen* are correct. Enable the
514: correct set of daemons. Ensure that the domU config files are valid
515: for the new version.
518: Running Xen under qemu
521: The astute reader will note that this section is somewhat twisted.
522: However, it can be useful to run Xen under qemu either because the
523: version of NetBSD as a dom0 does not run on the hardware in use, or to
524: generate automated test cases involving Xen.
526: In 2015-01, the following combination was reported to mostly work:
528: host OS: NetBSD/amd64 6.1.4
529: qemu: 2.2.0 from pkgsrc
530: Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
531: dom0 kernel: NetBSD/amd64 6.1.5
532: Xen tools: xentools42-4.2.5 from pkgsrc
534: See [PR 47720](http://gnats.netbsd.org/47720) for a problem with dom0
537: Unprivileged domains (domU)
540: This section describes general concepts about domUs. It does not
541: address specific domU operating systems or how to install them. The
542: config files for domUs are typically in /usr/pkg/etc/xen, and are
543: typically named so that the file name, domU name and the domU's host
544: name match.
546: The domU is provided with cpu and memory by Xen, configured by the
547: dom0. The domU is provided with disk and network by the dom0,
548: mediated by Xen, and configured in the dom0.
550: Entropy in domUs can be an issue; physical disks and network are on
551: the dom0. NetBSD's /dev/random system works, but is often challenged.
553: Config files
556: There is no good order to present config files and the concepts
557: surrounding what is being configured. We first show an example config
558: file, and then in the various sections give details.
560: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
561: for a large number of well-commented examples, mostly for running
564: The following is an example minimal domain configuration file
565: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
566: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
567: i386 domU). The domU serves as a network file server.
569: # -*- mode: python; -*-
571: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
572: memory = 1024
573: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
574: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
575: 'file:/n0/xen/foo-wd1,0x1,w' ]
577: The domain will have the same name as the file. The kernel has the
578: host/domU name in it, so that on the dom0 one can update the various
579: domUs independently. The vif line causes an interface to be provided,
580: with a specific mac address (do not reuse MAC addresses!), in bridge
581: mode. Two disks are provided, and they are both writable; the bits
582: are stored in files and Xen attaches them to a vnd(4) device in the
583: dom0 on domain creation. The system treates xbd0 as the boot device
584: without needing explicit configuration.
586: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
587: that "xm create" takes the name of a config file, while other commands
588: take the name of a domain. To create the domain, connect to the
589: console, create the domain while attaching the console, shutdown the
590: domain, and see if it has finished stopping, do (or xl with Xen >=
593: xm create foo
594: xm console foo
595: xm create -c foo
596: xm shutdown foo
597: xm list
599: Typing ^] will exit the console session. Shutting down a domain is
600: equivalent to pushing the power button; a NetBSD domU will receive a
601: power-press event and do a clean shutdown. Shutting down the dom0
602: will trigger controlled shutdowns of all configured domUs.
604: domU kernels
607: On a physical computer, the BIOS reads sector 0, and a chain of boot
608: loaders finds and loads a kernel. Normally this comes from the root
609: filesystem. With Xen domUs, the process is totally different. The
610: normal path is for the domU kernel to be a file in the dom0's
611: filesystem. At the request of the dom0, Xen loads that kernel into a
612: new domU instance and starts execution. While domU kernels can be
613: anyplace, reasonable places to store domU kernels on the dom0 are in /
614: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
615: config files), or in /u0/xen (where the vdisks are).
617: Note that loading the domU kernel from the dom0 implies that boot
618: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
619: See the VPS section near the end for discussion of alternate ways to
620: obtain domU kernels.
622: CPU and memory
625: A domain is provided with some number of vcpus, less than the number
626: of cpus seen by the hypervisor. (For a dom0, this is controlled by
627: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
628: from the config file by the "vcpus = N" directive.
630: A domain is provided with memory; this is controlled in the config
631: file by "memory = N" (in megabytes). In the straightforward case, the
632: sum of the the memory allocated to the dom0 and all domUs must be less
633: than the available memory.
635: Xen also provides a "balloon" driver, which can be used to let domains
636: use more memory temporarily. TODO: Explain better, and explain how
637: well it works with NetBSD.
639: Virtual disks
642: With the file/vnd style, typically one creates a directory,
643: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
644: domUs. Then, for each domU disk, one writes zeros to a file that then
645: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
646: for the first virtual disk for the domU called foo. Writing zeros to
647: the file serves two purposes. One is that preallocating the contents
648: improves performance. The other is that vnd on sparse files has
649: failed to work. TODO: give working/notworking NetBSD versions for
650: sparse vnd. Note that the use of file/vnd for Xen is not really
651: different than creating a file-backed virtual disk for some other
652: purpose, except that xentools handles the vnconfig commands. To
653: create an empty 4G virtual disk, simply do
655: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
657: Do not use qemu-img-xen, because this will create sparse file. There
658: have been recent (2015) reports of sparse vnd(4) devices causing
659: lockups, but there is apparently no PR.
661: With the lvm style, one creates logical devices. They are then used
662: similarly to vnds. TODO: Add an example with lvm.
664: In domU config files, the disks are defined as a sequence of 3-tuples.
665: The first element is "method:/path/to/disk". Common methods are
666: "file:" for file-backed vnd. and "phy:" for something that is already
667: a (TODO: character or block) device.
669: The second element is an artifact of how virtual disks are passed to
670: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
671: are given a device name to associate with the disk, and values like
672: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
673: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
674: second argument. The name given is converted to a major/minor by
675: calling stat(2) on the name in /dev and this is passed to the domU.
676: In the general case, the dom0 and domU can be different operating
677: systems, and it is an unwarranted assumption that they have consistent
678: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
679: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
680: for the second works fine and avoids this issue. For a GNU/Linux
681: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
684: The third element is "w" for writable disks, and "r" for read-only
687: Virtual Networking
690: Xen provides virtual ethernets, each of which connects the dom0 and a
691: domU. For each virtual network, there is an interface "xvifN.M" in
692: the dom0, and in domU index N, a matching interface xennetM (NetBSD
693: name). The interfaces behave as if there is an Ethernet with two
694: adaptors connected. From this primitive, one can construct various
695: configurations. We focus on two common and useful cases for which
696: there are existing scripts: bridging and NAT.
698: With bridging (in the example above), the domU perceives itself to be
699: on the same network as the dom0. For server virtualization, this is
700: usually best. Bridging is accomplished by creating a bridge(4) device
701: and adding the dom0's physical interface and the various xvifN.0
702: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
703: config file. The bridge must be set up already in the dom0; an
704: example /etc/ifconfig.bridge0 is:
708: !brconfig bridge0 add wm0
710: With NAT, the domU perceives itself to be behind a NAT running on the
711: dom0. This is often appropriate when running Xen on a workstation.
712: TODO: NAT appears to be configured by "vif = [ '' ]".
714: The MAC address specified is the one used for the interface in the new
715: domain. The interface in dom0 will use this address XOR'd with
716: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
718: Sizing domains
721: Modern x86 hardware has vast amounts of resources. However, many
722: virtual servers can function just fine on far less. A system with
723: 256M of RAM and a 4G disk can be a reasonable choice. Note that it is
724: far easier to adjust virtual resources than physical ones. For
725: memory, it's just a config file edit and a reboot. For disk, one can
726: create a new file and vnconfig it (or lvm), and then dump/restore,
727: just like updating physical disks, but without having to be there and
728: without those pesky connectors.
730: Starting domains automatically
733: To start domains foo at bar at boot and shut them down cleanly on dom0
734: shutdown, in rc.conf add:
736: xendomains="foo bar"
738: Note that earlier versions of the xentools41 xendomains rc.d scripth
739: usd xl, when one should use xm with 4.1.
741: Creating specific unprivileged domains (domU)
744: Creating domUs is almost entirely independent of operating system. We
745: have already presented the basics of config files. Note that you must
746: have already completed the dom0 setup so that "xl list" (or "xm list")
749: Creating an unprivileged NetBSD domain (domU)
752: See the earlier config file, and adjust memory. Decide on how much
753: storage you will provide, and prepare it (file or lvm).
755: While the kernel will be obtained from the dom0 filesystem, the same
756: file should be present in the domU as /netbsd so that tools like
757: savecore(8) can work. (This is helpful but not necessary.)
759: The kernel must be specifically for Xen and for use as a domU. The
760: i386 and amd64 provide the following kernels:
762: i386 XEN3_DOMU
763: i386 XEN3PAE_DOMU
764: amd64 XEN3_DOMU
766: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
767: use the PAE version of the i386 kernel.
769: This will boot NetBSD, but this is not that useful if the disk is
770: empty. One approach is to unpack sets onto the disk outside of xen
771: (by mounting it, just as you would prepare a physical disk for a
772: system you can't run the installer on).
774: A second approach is to run an INSTALL kernel, which has a miniroot
775: and can load sets from the network. To do this, copy the INSTALL
776: kernel to / and change the kernel line in the config file to:
778: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
780: Then, start the domain as "xl create -c configname".
782: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
783: line should be used in the config file.
785: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
787: After booting the domain, the option to install via CDROM may be
788: selected. The CDROM device should be changed to `xbd1d`.
790: Once done installing, "halt -p" the new domain (don't reboot or halt,
791: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
792: config file), switch the config file back to the XEN3_DOMU kernel,
793: and start the new domain again. Now it should be able to use "root on
794: xbd0a" and you should have a, functional NetBSD domU.
796: TODO: check if this is still accurate.
797: When the new domain is booting you'll see some warnings about *wscons*
798: and the pseudo-terminals. These can be fixed by editing the files
799: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
800: `/etc/ttys`, except *console*, like this:
802: console "/usr/libexec/getty Pc" vt100 on secure
803: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
804: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
805: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
806: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
808: Finally, all screens must be commented out from `/etc/wscons.conf`.
810: It is also desirable to add
814: in rc.conf. This way, the domain will be properly shut down if
815: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
817: It is not strictly necessary to have a kernel (as /netbsd) in the domU
818: filesystem. However, various programs (e.g. netstat) will use that
819: kernel to look up symbols to read from kernel virtual memory. If
820: /netbsd is not the running kernel, those lookups will fail. (This is
821: not really a Xen-specific issue, but because the domU kernel is
822: obtained from the dom0, it is far more likely to be out of sync or
823: missing with Xen.)
825: Creating an unprivileged Linux domain (domU)
828: Creating unprivileged Linux domains isn't much different from
829: unprivileged NetBSD domains, but there are some details to know.
831: First, the second parameter passed to the disk declaration (the '0x1' in
832: the example below)
834: disk = [ 'phy:/dev/wd0e,0x1,w' ]
836: does matter to Linux. It wants a Linux device number here (e.g. 0x300
837: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
838: So, hda1 which has major 3 and minor 1 on a Linux system will have
839: device number 0x301. Alternatively, devices names can be used (hda,
840: hdb, ...) as xentools has a table to map these names to devices
841: numbers. To export a partition to a Linux guest we can use:
843: disk = [ 'phy:/dev/wd0e,0x300,w' ]
844: root = "/dev/hda1 ro"
846: and it will appear as /dev/hda on the Linux system, and be used as root
849: To install the Linux system on the partition to be exported to the
850: guest domain, the following method can be used: install
851: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
852: that will be the root partition of your Linux domain, and mount it.
853: Then copy the files from a working Linux system, make adjustments in
854: `/etc` (fstab, network config). It should also be possible to extract
855: binary packages such as .rpm or .deb directly to the mounted partition
856: using the appropriate tool, possibly running under NetBSD's Linux
857: emulation. Once the filesystem has been populated, umount it. If
858: desirable, the filesystem can be converted to ext3 using tune2fs -j.
859: It should now be possible to boot the Linux guest domain, using one of
860: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
862: To get the linux console right, you need to add:
864: extra = "xencons=tty1"
866: to your configuration since not all linux distributions auto-attach a
867: tty to the xen console.
869: Creating an unprivileged Solaris domain (domU)
872: See possibly outdated
873: [Solaris domU instructions](/ports/xen/howto-solaris/).
876: PCI passthrough: Using PCI devices in guest domains
879: The dom0 can give other domains access to selected PCI
880: devices. This can allow, for example, a non-privileged domain to have
881: access to a physical network interface or disk controller. However,
882: keep in mind that giving a domain access to a PCI device most likely
883: will give the domain read/write access to the whole physical memory,
884: as PCs don't have an IOMMU to restrict memory access to DMA-capable
885: device. Also, it's not possible to export ISA devices to non-dom0
886: domains, which means that the primary VGA adapter can't be exported.
887: A guest domain trying to access the VGA registers will panic.
889: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
890: not been ported to later versions at this time.
892: For a PCI device to be exported to a domU, is has to be attached to
893: the "pciback" driver in dom0. Devices passed to the dom0 via the
894: pciback.hide boot parameter will attach to "pciback" instead of the
895: usual driver. The list of devices is specified as "(bus:dev.func)",
896: where bus and dev are 2-digit hexadecimal numbers, and func a
897: single-digit number:
901: pciback devices should show up in the dom0's boot messages, and the
902: devices should be listed in the `/kern/xen/pci` directory.
904: PCI devices to be exported to a domU are listed in the "pci" array of
905: the domU's config file, with the format "0000:bus:dev.func".
907: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
909: In the domU an "xpci" device will show up, to which one or more pci
910: busses will attach. Then the PCI drivers will attach to PCI busses as
911: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
912: or any PCI drivers built in by default; you have to build your own
913: kernel to use PCI devices in a domU. Here's a kernel config example;
914: note that only the "xpci" lines are unusual.
916: include "arch/i386/conf/XEN3_DOMU"
918: # Add support for PCI busses to the XEN3_DOMU kernel
919: xpci* at xenbus ?
920: pci* at xpci ?
922: # PCI USB controllers
923: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
925: # USB bus support
926: usb* at uhci?
928: # USB Hubs
929: uhub* at usb?
930: uhub* at uhub? port ? configuration ? interface ?
932: # USB Mass Storage
933: umass* at uhub? port ? configuration ? interface ?
934: wd* at umass?
935: # SCSI controllers
936: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
938: # SCSI bus support (for both ahc and umass)
939: scsibus* at scsi?
941: # SCSI devices
942: sd* at scsibus? target ? lun ? # SCSI disk drives
943: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
946: NetBSD as a domU in a VPS
949: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
950: hardware. This section explains how to deal with Xen in a domU as a
951: virtual private server where you do not control or have access to the
952: dom0. This is not intended to be an exhaustive list of VPS providers;
953: only a few are mentioned that specifically support NetBSD.
955: VPS operators provide varying degrees of access and mechanisms for
956: configuration. The big issue is usually how one controls which kernel
957: is booted, because the kernel is nominally in the dom0 filesystem (to
958: which VPS users do not normally have acesss). A second issue is how
959: to install NetBSD.
960: A VPS user may want to compile a kernel for security updates, to run
961: npf, run IPsec, or any other reason why someone would want to change
962: their kernel.
964: One approach is to have an adminstrative interface to upload a kernel,
965: or to select from a prepopulated list. Other approaches are pygrub
966: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
967: kernel from the domU filesystem. This is closer to a regular physical
968: computer, where someone who controls a machine can replace the kernel.
970: A second issue is multiple CPUs. With NetBSD 6, domUs support
971: multiple vcpus, and it is typical for VPS providers to enable multiple
972: CPUs for NetBSD domUs.
977: pygrub runs in the dom0 and looks into the domU filesystem. This
978: implies that the domU must have a kernel in a filesystem in a format
979: known to pygrub. As of 2014, pygrub seems to be of mostly historical
985: pvgrub is a version of grub that uses PV operations instead of BIOS
986: calls. It is booted from the dom0 as the domU kernel, and then reads
987: /grub/menu.lst and loads a kernel from the domU filesystem.
989: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
990: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
991: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
992: page](http://www.panix.com/v-colo/grub.html), which describes only
993: Linux but should be updated to cover NetBSD :-).
995: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
996: their own kernel. See then [prgmr.com NetBSD
998: (which is in need of updating).
1000: It appears that [grub's FFS
1002: does not support all aspects of modern FFS, but there are also reports
1003: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
1004: partition for the kernel with the intent that grub can understand it,
1005: which leads to /netbsd not being the actual kernel. One must remember
1006: to update the special boot partiion.
1011: See the [Amazon EC2 page](../amazon_ec2/).
1013: Using npf
1016: In standard kernels, npf is a module, and thus cannot be loaded in a
1017: DOMU kernel.
1019: TODO: Explain how to compile npf into a custom kernel, answering (but
1020: note that the problem was caused by not booting the right kernel)
1021: [this email to
1024: TODO items for improving NetBSD/xen
1027: * Make the NetBSD dom0 kernel work with SMP.
1028: * Test the Xen 4.5 packages adequately to be able to recommend them as
1029: the standard approach.
1030: * Get PCI passthrough working on Xen 4.5
1031: * Get pvgrub into pkgsrc, either via xentools or separately.
1032: * grub
1033: * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
1034: fragsize/blocksize (UFS2 support may be present; the point is to
1035: make it so that with any UFS1/UFS2 filesystem setup that works
1036: with NetBSD grub will also work).
1037: See [pkg/40258](http://gnats.netbsd.org/40258).
1038: * Push patches upstream.
1039: * Get UFS2 patches into pvgrub.
1040: * Add support for PV ops to a version of /boot, and make it usable as
1041: a kernel in Xen, similar to pvgrub.
1042: * Solve somehow the issue with modules for GENERIC not being loadable
1043: in a Xen dom0 or domU kernel.
1045: Random pointers
1048: TODO: This section contains links from elsewhere not yet integrated
1049: into the HOWTO.
1051: * http://www.lumbercartel.ca/library/xen/
1052: * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html
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