1: Introduction
2: ============
3:
4: [![[Xen
5: screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](http://www.netbsd.org/gallery/in-Action/hubertf-xen.png)
6:
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.
16:
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.
24:
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.
29:
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.
36:
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.)
40:
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.
46:
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.
51:
52: NetBSD used to support Xen2; this has been removed.
53:
54: Prerequisites
55: -------------
56:
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.
62:
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/).
67:
68: Versions of Xen and NetBSD
69: ==========================
70:
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.
75:
76: Xen
77: ---
78:
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.
83:
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.
87:
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.
91:
92: xenkernel42 provides Xen 4.2. This is maintained by Xen, but old as
93: of 2014-12.
94:
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.
97:
98: Ideally newer versions of Xen will be added to pkgsrc.
99:
100: Note that NetBSD support is called XEN3. It works with Xen 3 and Xen
101: 4 because the hypercall interface has been stable.
102:
103: Xen command program
104: -------------------
105:
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.
111:
112: NetBSD
113: ------
114:
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.
121:
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.)
126:
127: Architecture
128: ------------
129:
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.
135:
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.
139:
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.)
144:
145: Recommendation
146: --------------
147:
148: Therefore, this HOWTO recommends running xenkernel42 (and xentools42),
149: xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the
150: dom0. Either the i386 or amd64 of NetBSD may be used as domUs.
151:
152: Build problems
153: --------------
154:
155: Ideally, all versions of Xen in pkgsrc would build on all versions of
156: NetBSD on both i386 and amd64. However, that isn't the case. Besides
157: aging code and aging compilers, qemu (included in xentools for HVM
158: support) is difficult to build. The following are known to work or FAIL:
159:
160: xenkernel3 netbsd-5 amd64
161: xentools3 netbsd-5 amd64
162: xentools3=hvm netbsd-5 amd64 ????
163: xenkernel33 netbsd-5 amd64
164: xentools33 netbsd-5 amd64
165: xenkernel41 netbsd-5 amd64
166: xentools41 netbsd-5 amd64
167: xenkernel42 netbsd-5 amd64
168: xentools42 netbsd-5 amd64
169:
170: xenkernel3 netbsd-6 i386 FAIL
171: xentools3 netbsd-6 i386
172: xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
173: xenkernel33 netbsd-6 i386
174: xentools33 netbsd-6 i386
175: xenkernel41 netbsd-6 i386
176: xentools41 netbsd-6 i386
177: xenkernel42 netbsd-6 i386
178: xentools42 netbsd-6 i386 *MIXED
179:
180: (all 3 and 33 seem to FAIL)
181: xenkernel41 netbsd-7 i386
182: xentools41 netbsd-7 i386
183: xenkernel42 netbsd-7 i386
184: xentools42 netbsd-7 i386 ??FAIL
185:
186: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
187: but it does not build for gdt.)
188:
189: NetBSD as a dom0
190: ================
191:
192: NetBSD can be used as a dom0 and works very well. The following
193: sections address installation, updating NetBSD, and updating Xen.
194: Note that it doesn't make sense to talk about installing a dom0 OS
195: without also installing Xen itself. We first address installing
196: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
197: NetBSD install to a dom0 install by just changing the kernel and boot
198: configuration.
199:
200: For experimenting with Xen, a machine with as little as 1G of RAM and
201: 100G of disk can work. For running many domUs in productions, far
202: more will be needed.
203:
204: Styles of dom0 operation
205: ------------------------
206:
207: There are two basic ways to use Xen. The traditional method is for
208: the dom0 to do absolutely nothing other than providing support to some
209: number of domUs. Such a system was probably installed for the sole
210: purpose of hosting domUs, and sits in a server room on a UPS.
211:
212: The other way is to put Xen under a normal-usage computer, so that the
213: dom0 is what the computer would have been without Xen, perhaps a
214: desktop or laptop. Then, one can run domUs at will. Purists will
215: deride this as less secure than the previous approach, and for a
216: computer whose purpose is to run domUs, they are right. But Xen and a
217: dom0 (without domUs) is not meaingfully less secure than the same
218: things running without Xen. One can boot Xen or boot regular NetBSD
219: alternately with little problems, simply refraining from starting the
220: Xen daemons when not running Xen.
221:
222: Note that NetBSD as dom0 does not support multiple CPUs. This will
223: limit the performance of the Xen/dom0 workstation approach. In theory
224: the only issue is that the "backend drivers" are not yet MPSAFE:
225: http://mail-index.netbsd.org/netbsd-users/2014/08/29/msg015195.html
226:
227: Installation of NetBSD
228: ----------------------
229:
230: First,
231: [install NetBSD/amd64](/guide/inst/)
232: just as you would if you were not using Xen.
233: However, the partitioning approach is very important.
234:
235: If you want to use RAIDframe for the dom0, there are no special issues
236: for Xen. Typically one provides RAID storage for the dom0, and the
237: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
238: over a RAID1 header to find /boot from a filesystem within a RAID
239: partition; this is no different when booting Xen.
240:
241: There are 4 styles of providing backing storage for the virtual disks
242: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN,
243:
244: With raw partitions, one has a disklabel (or gpt) partition sized for
245: each virtual disk to be used by the domU. (If you are able to predict
246: how domU usage will evolve, please add an explanation to the HOWTO.
247: Seriously, needs tend to change over time.)
248:
249: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
250: for domU disks. This is almost as efficient as raw disk partitions
251: and more flexible. Hence raw disk partitions should typically not
252: be used.
253:
254: One can use files in the dom0 filesystem, typically created by dd'ing
255: /dev/zero to create a specific size. This is somewhat less efficient,
256: but very convenient, as one can cp the files for backup, or move them
257: between dom0 hosts.
258:
259: Finally, in theory one can place the files backing the domU disks in a
260: SAN. (This is an invitation for someone who has done this to add a
261: HOWTO page.)
262:
263: Installation of Xen
264: -------------------
265:
266: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
267: pkgsrc (or another matching pair).
268: See [the pkgsrc
269: documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with pkgsrc.
270:
271: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm. More
272: recent versions have HVM support integrated in the main xentools
273: package. It is entirely reasonable to run only PV guests.
274:
275: Next you need to install the selected Xen kernel itself, which is
276: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
277: For debugging, one may copy xen-debug.gz; this is conceptually similar
278: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
279: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
280: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
281: of a NetBSD build. If using i386, use
282: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz. (If using Xen
283: 3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen. But you
284: should not use Xen 3.1.) Both xen and the NetBSD kernel may be (and
285: typically are) left compressed.
286:
287: In a dom0 kernel, kernfs is mandatory for xend to comunicate with the
288: kernel, so ensure that /kern is in fstab. TODO: Say this is default,
289: or file a PR and give a reference.
290:
291: Because you already installed NetBSD, you have a working boot setup
292: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
293: beginning of your root filesystem, /boot present, and likely
294: /boot.cfg. (If not, fix before continuing!)
295:
296: Add a line to to /boot.cfg to boot Xen. See boot.cfg(5) for an
297: example. The basic line is
298:
299: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
300:
301: which specifies that the dom0 should have 256M, leaving the rest to be
302: allocated for domUs. To use a serial console, use
303:
304: menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
305:
306: which will use the first serial port for Xen (which counts starting
307: from 1), forcing speed/parity, and also for NetBSD (which counts
308: starting at 0). In an attempt to add performance, one can also add
309:
310: dom0_max_vcpus=1 dom0_vcpus_pin
311:
312: to force only one vcpu to be provided (since NetBSD dom0 can't use
313: more) and to pin that vcpu to a physical cpu. TODO: benchmark this.
314:
315: As with non-Xen systems, you should have a line to boot /netbsd (a
316: kernel that works without Xen) and fallback versions of the non-Xen
317: kernel, Xen, and the dom0 kernel.
318:
319: Now, reboot so that you are running a DOM0 kernel under Xen, rather
320: than GENERIC without Xen.
321:
322: Using grub (historic)
323: ---------------------
324:
325: Before NetBSD's native bootloader could support Xen, the use of
326: grub was recommended. If necessary, see the
327: [old grub information](/ports/xen/howto-grub/).
328:
329: The [HowTo on Installing into
330: RAID-1](http://mail-index.NetBSD.org/port-xen/2006/03/01/0010.html)
331: explains how to set up booting a dom0 with Xen using grub with
332: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
333: boot.)
334:
335: Configuring Xen
336: ---------------
337:
338: Xen logs will be in /var/log/xen.
339:
340: Now, you have a system that will boot Xen and the dom0 kernel, but not
341: do anything else special. Make sure that you have rebooted into Xen.
342: There will be no domUs, and none can be started because you still have
343: to configure the dom0 tools. The daemons which should be run vary
344: with Xen version and with whether one is using xm or xl. Note that
345: xend is for supporting "xm", and should only be used if you plan on
346: using "xm". Do NOT enable xend if you plan on using "xl" as it will
347: cause problems.
348:
349: The installation of NetBSD should already have created devices for xen
350: (xencons, xenevt), but if they are not present, create them:
351:
352: cd /dev && sh MAKEDEV xen
353:
354: TODO: Give 3.1 advice (or remove it from pkgsrc).
355:
356: For 3.3 (and thus xm), add to rc.conf (but note that you should have
357: installed 4.1 or 4.2):
358:
359: xend=YES
360: xenbackendd=YES
361:
362: For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
363:
364: xencommons=YES
365: xend=YES
366:
367: (If you are using xentools41 from before 2014-12-26, change
368: rc.d/xendomains to use xm rather than xl.)
369:
370: For 4.2 with xm, add to rc.conf
371:
372: xencommons=YES
373: xend=YES
374:
375: For 4.2 with xl, add to rc.conf:
376:
377: xencommons=YES
378: TODO: explain if there is a xend replacement
379:
380: For 4.5 (and thus with xl), add to rc.conf:
381:
382: xencommons=YES
383: TODO: explain if there is a xend replacement
384:
385: TODO: Recommend for/against xen-watchdog.
386:
387: After you have configured the daemons and either started them (in the
388: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
389: available resources, and running domains. An example with xm follows:
390:
391: # xm dmesg
392: [xen's boot info]
393: # xm info
394: [available memory, etc.]
395: # xm list
396: Name Id Mem(MB) CPU State Time(s) Console
397: Domain-0 0 64 0 r---- 58.1
398:
399: With xl, the commands are the same, and the output may be slightly
400: different. TODO: add example output for xl before the xm example,
401: after confirming on 4.2 and resolving the TODO about rc.conf.
402:
403: anita (for testing NetBSD)
404: --------------------------
405:
406: With the setup so far (assuming 4.2/xl), one should be able to run
407: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
408: root, because anita must create a domU):
409:
410: anita --vmm=xl test file:///usr/obj/i386/
411:
412: Alternatively, one can use --vmm=xm to use xm-based domU creation
413: instead (and must, on Xen <= 4.1). TODO: confirm that anita xl really works.
414:
415: Xen-specific NetBSD issues
416: --------------------------
417:
418: There are (at least) two additional things different about NetBSD as a
419: dom0 kernel compared to hardware.
420:
421: One is that modules are not usable in DOM0 kernels, so one must
422: compile in what's needed. It's not really that modules cannot work,
423: but that modules must be built for XEN3_DOM0 because some of the
424: defines change and the normal module builds don't do this. Basically,
425: enabling Xen changes the kernel ABI, and the module build system
426: doesn't cope with this.
427:
428: The other difference is that XEN3_DOM0 does not have exactly the same
429: options as GENERIC. While it is debatable whether or not this is a
430: bug, users should be aware of this and can simply add missing config
431: items if desired.
432:
433: Updating NetBSD in a dom0
434: -------------------------
435:
436: This is just like updating NetBSD on bare hardware, assuming the new
437: version supports the version of Xen you are running. Generally, one
438: replaces the kernel and reboots, and then overlays userland binaries
439: and adjusts /etc.
440:
441: Note that one must update both the non-Xen kernel typically used for
442: rescue purposes and the DOM0 kernel used with Xen.
443:
444: Converting from grub to /boot
445: -----------------------------
446:
447: These instructions were [TODO: will be] used to convert a system from
448: grub to /boot. The system was originally installed in February of
449: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
450: over time. Before these commands, it was running NetBSD 6 i386, Xen
451: 4.1 and grub, much like the message linked earlier in the grub
452: section.
453:
454: # Install mbr bootblocks on both disks.
455: fdisk -i /dev/rwd0d
456: fdisk -i /dev/rwd1d
457: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
458: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
459: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
460: # Install secondary boot loader
461: cp -p /usr/mdec/boot /
462: # Create boog.cfg following earlier guidance:
463: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
464: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
465: menu=GENERIC:boot
466: menu=GENERIC single-user:boot -s
467: menu=GENERIC.ok:boot netbsd.ok
468: menu=GENERIC.ok single-user:boot netbsd.ok -s
469: menu=Drop to boot prompt:prompt
470: default=1
471: timeout=30
472:
473: TODO: actually do this and fix it if necessary.
474:
475: Updating Xen versions
476: ---------------------
477:
478: Updating Xen is conceptually not difficult, but can run into all the
479: issues found when installing Xen. Assuming migration from 4.1 to 4.2,
480: remove the xenkernel41 and xentools41 packages and install the
481: xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz to /.
482:
483: Ensure that the contents of /etc/rc.d/xen* are correct. Enable the
484: correct set of daemons. Ensure that the domU config files are valid
485: for the new version.
486:
487:
488: Running Xen under qemu
489: ----------------------
490:
491: The astute reader will note that this section is somewhat twisted.
492: However, it can be useful to run Xen under qemu either because the
493: version of NetBSD as a dom0 does not run on the hardware in use, or to
494: generate automated test cases involving Xen.
495:
496: In 2015-01, the following combination was reported to mostly work:
497:
498: host OS: NetBSD/amd64 6.1.4
499: qemu: 2.2.0 from pkgsrc
500: Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
501: dom0 kernel: NetBSD/amd64 6.1.5
502: Xen tools: xentools42-4.2.5 from pkgsrc
503:
504: See http://gnats.netbsd.org/47720 for a problem with dom0 shutdown.
505:
506: Unprivileged domains (domU)
507: ===========================
508:
509: This section describes general concepts about domUs. It does not
510: address specific domU operating systems or how to install them. The
511: config files for domUs are typically in /usr/pkg/etc/xen, and are
512: typically named so that the file name, domU name and the domU's host
513: name match.
514:
515: The domU is provided with cpu and memory by Xen, configured by the
516: dom0. The domU is provided with disk and network by the dom0,
517: mediated by Xen, and configured in the dom0.
518:
519: Entropy in domUs can be an issue; physical disks and network are on
520: the dom0. NetBSD's /dev/random system works, but is often challenged.
521:
522: Config files
523: ------------
524:
525: There is no good order to present config files and the concepts
526: surrounding what is being configured. We first show an example config
527: file, and then in the various sections give details.
528:
529: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
530: for a large number of well-commented examples, mostly for running
531: GNU/Linux.
532:
533: The following is an example minimal domain configuration file
534: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
535: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
536: i386 domU). The domU serves as a network file server.
537:
538: # -*- mode: python; -*-
539:
540: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
541: memory = 1024
542: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
543: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
544: 'file:/n0/xen/foo-wd1,0x1,w' ]
545:
546: The domain will have the same name as the file. The kernel has the
547: host/domU name in it, so that on the dom0 one can update the various
548: domUs independently. The vif line causes an interface to be provided,
549: with a specific mac address (do not reuse MAC addresses!), in bridge
550: mode. Two disks are provided, and they are both writable; the bits
551: are stored in files and Xen attaches them to a vnd(4) device in the
552: dom0 on domain creation. The system treates xbd0 as the boot device
553: without needing explicit configuration.
554:
555: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
556: that "xm create" takes the name of a config file, while other commands
557: take the name of a domain. To create the domain, connect to the
558: console, create the domain while attaching the console, shutdown the
559: domain, and see if it has finished stopping, do (or xl with Xen >=
560: 4.2):
561:
562: xm create foo
563: xm console foo
564: xm create -c foo
565: xm shutdown foo
566: xm list
567:
568: Typing ^] will exit the console session. Shutting down a domain is
569: equivalent to pushing the power button; a NetBSD domU will receive a
570: power-press event and do a clean shutdown. Shutting down the dom0
571: will trigger controlled shutdowns of all configured domUs.
572:
573: domU kernels
574: ------------
575:
576: On a physical computer, the BIOS reads sector 0, and a chain of boot
577: loaders finds and loads a kernel. Normally this comes from the root
578: filesystem. With Xen domUs, the process is totally different. The
579: normal path is for the domU kernel to be a file in the dom0's
580: filesystem. At the request of the dom0, Xen loads that kernel into a
581: new domU instance and starts execution. While domU kernels can be
582: anyplace, reasonable places to store domU kernels on the dom0 are in /
583: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
584: config files), or in /u0/xen (where the vdisks are).
585:
586: Note that loading the domU kernel from the dom0 implies that boot
587: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
588: See the VPS section near the end for discussion of alternate ways to
589: obtain domU kernels.
590:
591: CPU and memory
592: --------------
593:
594: A domain is provided with some number of vcpus, less than the number
595: of cpus seen by the hypervisor. (For a dom0, this is controlled by
596: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
597: from the config file by the "vcpus = N" directive.
598:
599: A domain is provided with memory; this is controlled in the config
600: file by "memory = N" (in megabytes). In the straightforward case, the
601: sum of the the memory allocated to the dom0 and all domUs must be less
602: than the available memory.
603:
604: Xen also provides a "balloon" driver, which can be used to let domains
605: use more memory temporarily. TODO: Explain better, and explain how
606: well it works with NetBSD.
607:
608: Virtual disks
609: -------------
610:
611: With the file/vnd style, typically one creates a directory,
612: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
613: domUs. Then, for each domU disk, one writes zeros to a file that then
614: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
615: for the first virtual disk for the domU called foo. Writing zeros to
616: the file serves two purposes. One is that preallocating the contents
617: improves performance. The other is that vnd on sparse files has
618: failed to work. TODO: give working/notworking NetBSD versions for
619: sparse vnd. Note that the use of file/vnd for Xen is not really
620: different than creating a file-backed virtual disk for some other
621: purpose, except that xentools handles the vnconfig commands. To
622: create an empty 4G virtual disk, simply do
623:
624: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
625:
626: With the lvm style, one creates logical devices. They are then used
627: similarly to vnds. TODO: Add an example with lvm.
628:
629: In domU config files, the disks are defined as a sequence of 3-tuples.
630: The first element is "method:/path/to/disk". Common methods are
631: "file:" for file-backed vnd. and "phy:" for something that is already
632: a (TODO: character or block) device.
633:
634: The second element is an artifact of how virtual disks are passed to
635: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
636: are given a device name to associate with the disk, and values like
637: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
638: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
639: second argument. The name given is converted to a major/minor by
640: calling stat(2) on the name in /dev and this is passed to the domU.
641: In the general case, the dom0 and domU can be different operating
642: systems, and it is an unwarranted assumption that they have consistent
643: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
644: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
645: for the second works fine and avoids this issue. For a GNU/Linux
646: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
647: /dev/hda1.
648:
649: The third element is "w" for writable disks, and "r" for read-only
650: disks.
651:
652: Virtual Networking
653: ------------------
654:
655: Xen provides virtual ethernets, each of which connects the dom0 and a
656: domU. For each virtual network, there is an interface "xvifN.M" in
657: the dom0, and in domU index N, a matching interface xennetM (NetBSD
658: name). The interfaces behave as if there is an Ethernet with two
659: adaptors connected. From this primitive, one can construct various
660: configurations. We focus on two common and useful cases for which
661: there are existing scripts: bridging and NAT.
662:
663: With bridging (in the example above), the domU perceives itself to be
664: on the same network as the dom0. For server virtualization, this is
665: usually best. Bridging is accomplished by creating a bridge(4) device
666: and adding the dom0's physical interface and the various xvifN.0
667: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
668: config file. The bridge must be set up already in the dom0; an
669: example /etc/ifconfig.bridge0 is:
670:
671: create
672: up
673: !brconfig bridge0 add wm0
674:
675: With NAT, the domU perceives itself to be behind a NAT running on the
676: dom0. This is often appropriate when running Xen on a workstation.
677: TODO: NAT appears to be configured by "vif = [ '' ]".
678:
679: The MAC address specified is the one used for the interface in the new
680: domain. The interface in dom0 will use this address XOR'd with
681: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
682:
683: Sizing domains
684: --------------
685:
686: Modern x86 hardware has vast amounts of resources. However, many
687: virtual servers can function just fine on far less. A system with
688: 256M of RAM and a 4G disk can be a reasonable choice. Note that it is
689: far easier to adjust virtual resources than physical ones. For
690: memory, it's just a config file edit and a reboot. For disk, one can
691: create a new file and vnconfig it (or lvm), and then dump/restore,
692: just like updating physical disks, but without having to be there and
693: without those pesky connectors.
694:
695: Starting domains automatically
696: ------------------------------
697:
698: To start domains foo at bar at boot and shut them down cleanly on dom0
699: shutdown, in rc.conf add:
700:
701: xendomains="foo bar"
702:
703: Note that earlier versions of the xentools41 xendomains rc.d scripth
704: usd xl, when one should use xm with 4.1.
705:
706: Creating specific unprivileged domains (domU)
707: =============================================
708:
709: Creating domUs is almost entirely independent of operating system. We
710: have already presented the basics of config files. Note that you must
711: have already completed the dom0 setup so that "xl list" (or "xm list")
712: works.
713:
714: Creating an unprivileged NetBSD domain (domU)
715: ---------------------------------------------
716:
717: See the earlier config file, and adjust memory. Decide on how much
718: storage you will provide, and prepare it (file or lvm).
719:
720: While the kernel will be obtained from the dom0 filesystem, the same
721: file should be present in the domU as /netbsd so that tools like
722: savecore(8) can work. (This is helpful but not necessary.)
723:
724: The kernel must be specifically for Xen and for use as a domU. The
725: i386 and amd64 provide the following kernels:
726:
727: i386 XEN3_DOMU
728: i386 XEN3PAE_DOMU
729: amd64 XEN3_DOMU
730:
731: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
732: use the PAE version of the i386 kernel.
733:
734: This will boot NetBSD, but this is not that useful if the disk is
735: empty. One approach is to unpack sets onto the disk outside of xen
736: (by mounting it, just as you would prepare a physical disk for a
737: system you can't run the installer on).
738:
739: A second approach is to run an INSTALL kernel, which has a miniroot
740: and can load sets from the network. To do this, copy the INSTALL
741: kernel to / and change the kernel line in the config file to:
742:
743: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
744:
745: Then, start the domain as "xl create -c configname".
746:
747: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
748: line should be used in the config file.
749:
750: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
751:
752: After booting the domain, the option to install via CDROM may be
753: selected. The CDROM device should be changed to `xbd1d`.
754:
755: Once done installing, "halt -p" the new domain (don't reboot or halt,
756: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
757: config file), switch the config file back to the XEN3_DOMU kernel,
758: and start the new domain again. Now it should be able to use "root on
759: xbd0a" and you should have a, functional NetBSD domU.
760:
761: TODO: check if this is still accurate.
762: When the new domain is booting you'll see some warnings about *wscons*
763: and the pseudo-terminals. These can be fixed by editing the files
764: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
765: `/etc/ttys`, except *console*, like this:
766:
767: console "/usr/libexec/getty Pc" vt100 on secure
768: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
769: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
770: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
771: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
772:
773: Finally, all screens must be commented out from `/etc/wscons.conf`.
774:
775: It is also desirable to add
776:
777: powerd=YES
778:
779: in rc.conf. This way, the domain will be properly shut down if
780: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
781:
782: Your domain should be now ready to work, enjoy.
783:
784: Creating an unprivileged Linux domain (domU)
785: --------------------------------------------
786:
787: Creating unprivileged Linux domains isn't much different from
788: unprivileged NetBSD domains, but there are some details to know.
789:
790: First, the second parameter passed to the disk declaration (the '0x1' in
791: the example below)
792:
793: disk = [ 'phy:/dev/wd0e,0x1,w' ]
794:
795: does matter to Linux. It wants a Linux device number here (e.g. 0x300
796: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
797: So, hda1 which has major 3 and minor 1 on a Linux system will have
798: device number 0x301. Alternatively, devices names can be used (hda,
799: hdb, ...) as xentools has a table to map these names to devices
800: numbers. To export a partition to a Linux guest we can use:
801:
802: disk = [ 'phy:/dev/wd0e,0x300,w' ]
803: root = "/dev/hda1 ro"
804:
805: and it will appear as /dev/hda on the Linux system, and be used as root
806: partition.
807:
808: To install the Linux system on the partition to be exported to the
809: guest domain, the following method can be used: install
810: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
811: that will be the root partition of your Linux domain, and mount it.
812: Then copy the files from a working Linux system, make adjustments in
813: `/etc` (fstab, network config). It should also be possible to extract
814: binary packages such as .rpm or .deb directly to the mounted partition
815: using the appropriate tool, possibly running under NetBSD's Linux
816: emulation. Once the filesystem has been populated, umount it. If
817: desirable, the filesystem can be converted to ext3 using tune2fs -j.
818: It should now be possible to boot the Linux guest domain, using one of
819: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
820:
821: To get the linux console right, you need to add:
822:
823: extra = "xencons=tty1"
824:
825: to your configuration since not all linux distributions auto-attach a
826: tty to the xen console.
827:
828: Creating an unprivileged Solaris domain (domU)
829: ----------------------------------------------
830:
831: See possibly outdated
832: [Solaris domU instructions](/ports/xen/howto-solaris/).
833:
834:
835: PCI passthrough: Using PCI devices in guest domains
836: ---------------------------------------------------
837:
838: The dom0 can give other domains access to selected PCI
839: devices. This can allow, for example, a non-privileged domain to have
840: access to a physical network interface or disk controller. However,
841: keep in mind that giving a domain access to a PCI device most likely
842: will give the domain read/write access to the whole physical memory,
843: as PCs don't have an IOMMU to restrict memory access to DMA-capable
844: device. Also, it's not possible to export ISA devices to non-dom0
845: domains, which means that the primary VGA adapter can't be exported.
846: A guest domain trying to access the VGA registers will panic.
847:
848: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
849: not been ported to later versions at this time.
850:
851: For a PCI device to be exported to a domU, is has to be attached to
852: the "pciback" driver in dom0. Devices passed to the dom0 via the
853: pciback.hide boot parameter will attach to "pciback" instead of the
854: usual driver. The list of devices is specified as "(bus:dev.func)",
855: where bus and dev are 2-digit hexadecimal numbers, and func a
856: single-digit number:
857:
858: pciback.hide=(00:0a.0)(00:06.0)
859:
860: pciback devices should show up in the dom0's boot messages, and the
861: devices should be listed in the `/kern/xen/pci` directory.
862:
863: PCI devices to be exported to a domU are listed in the "pci" array of
864: the domU's config file, with the format "0000:bus:dev.func".
865:
866: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
867:
868: In the domU an "xpci" device will show up, to which one or more pci
869: busses will attach. Then the PCI drivers will attach to PCI busses as
870: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
871: or any PCI drivers built in by default; you have to build your own
872: kernel to use PCI devices in a domU. Here's a kernel config example;
873: note that only the "xpci" lines are unusual.
874:
875: include "arch/i386/conf/XEN3_DOMU"
876:
877: # Add support for PCI busses to the XEN3_DOMU kernel
878: xpci* at xenbus ?
879: pci* at xpci ?
880:
881: # PCI USB controllers
882: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
883:
884: # USB bus support
885: usb* at uhci?
886:
887: # USB Hubs
888: uhub* at usb?
889: uhub* at uhub? port ? configuration ? interface ?
890:
891: # USB Mass Storage
892: umass* at uhub? port ? configuration ? interface ?
893: wd* at umass?
894: # SCSI controllers
895: ahc* at pci? dev ? function ? # Adaptec [23]94x, aic78x0 SCSI
896:
897: # SCSI bus support (for both ahc and umass)
898: scsibus* at scsi?
899:
900: # SCSI devices
901: sd* at scsibus? target ? lun ? # SCSI disk drives
902: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
903:
904:
905: NetBSD as a domU in a VPS
906: =========================
907:
908: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
909: hardware. This section explains how to deal with Xen in a domU as a
910: virtual private server where you do not control or have access to the
911: dom0. This is not intended to be an exhaustive list of VPS providers;
912: only a few are mentioned that specifically support NetBSD.
913:
914: VPS operators provide varying degrees of access and mechanisms for
915: configuration. The big issue is usually how one controls which kernel
916: is booted, because the kernel is nominally in the dom0 filesystem (to
917: which VPS users do not normally have acesss). A second issue is how
918: to install NetBSD.
919: A VPS user may want to compile a kernel for security updates, to run
920: npf, run IPsec, or any other reason why someone would want to change
921: their kernel.
922:
923: One approach is to have an adminstrative interface to upload a kernel,
924: or to select from a prepopulated list. Other approaches are pygrub
925: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
926: kernel from the domU filesystem. This is closer to a regular physical
927: computer, where someone who controls a machine can replace the kernel.
928:
929: A second issue is multiple CPUs. With NetBSD 6, domUs support
930: multiple vcpus, and it is typical for VPS providers to enable multiple
931: CPUs for NetBSD domUs.
932:
933: pygrub
934: -------
935:
936: pygrub runs in the dom0 and looks into the domU filesystem. This
937: implies that the domU must have a kernel in a filesystem in a format
938: known to pygrub. As of 2014, pygrub seems to be of mostly historical
939: interest.
940:
941: pvgrub
942: ------
943:
944: pvgrub is a version of grub that uses PV operations instead of BIOS
945: calls. It is booted from the dom0 as the domU kernel, and then reads
946: /grub/menu.lst and loads a kernel from the domU filesystem.
947:
948: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
949: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
950: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
951: page](http://www.panix.com/v-colo/grub.html), which describes only
952: Linux but should be updated to cover NetBSD :-).
953:
954: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
955: their own kernel. See then [prgmr.com NetBSD
956: HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
957: (which is in need of updating).
958:
959: It appears that [grub's FFS
960: code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
961: does not support all aspects of modern FFS, but there are also reports
962: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
963: partition for the kernel with the intent that grub can understand it,
964: which leads to /netbsd not being the actual kernel. One must remember
965: to update the special boot partiion.
966:
967: Amazon
968: ------
969:
970: TODO: add link to NetBSD amazon howto.
971:
972: Using npf
973: ---------
974:
975: In standard kernels, npf is a module, and thus cannot be loaded in a
976: DOMU kernel.
977:
978: TODO: explain how to compile npf into a custom kernel, answering (but
979: note that the problem was caused by not booting the right kernel):
980: http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html
981:
982: TODO items for improving NetBSD/xen
983: ===================================
984:
985: * Package Xen 4.4.
986: * Get PCI passthrough working on Xen 4.2 (or 4.4).
987: * Get pvgrub into pkgsrc, either via xentools or separately.
988: * grub
989: * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
990: fragsize/blocksize (UFS2 support may be present; the point is to
991: make it so that with any UFS1/UFS2 filesystem setup that works
992: with NetBSD grub will also work).
993: See [pkg/40258](http://gnats.netbsd.org/40258).
994: * Push patches upstream.
995: * Get UFS2 patches into pvgrub.
996: * Add support for PV ops to a version of /boot, and make it usable as
997: a kernel in Xen, similar to pvgrub.
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