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 (PAE) and
148: 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. Almost no one in the NetBSD/Xen community does
154: this, and the standard, well-tested, approach is to use an amd64 dom0.
156: A [posting on
158: explained that PV system call overhead was higher on amd64, and thus
159: there is some notion that i386 guests are faster. It goes on to
160: caution that the total situation is complex and not entirely
161: understood. On top of that caution, the post is about Linux, not
162: NetBSD. TODO: Include link to benchmarks, if someone posts them.
164: NetBSD as a dom0
167: NetBSD can be used as a dom0 and works very well. The following
168: sections address installation, updating NetBSD, and updating Xen.
169: Note that it doesn't make sense to talk about installing a dom0 OS
170: without also installing Xen itself. We first address installing
171: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
172: NetBSD install to a dom0 install by just changing the kernel and boot
175: For experimenting with Xen, a machine with as little as 1G of RAM and
176: 100G of disk can work. For running many domUs in productions, far
177: more will be needed; e.g. 4-8G and 1T of disk is reasonable for a
178: half-dozen domUs of 512M and 32G each. Basically, the RAM and disk
179: have to be bigger than the sum of the RAM/disk needs of the dom0 and
180: all the domUs.
182: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
183: 512M it worked reliably. This does not make sense, but if you see
184: "not ELF" after Xen boots, try increasing dom0 RAM.
186: Styles of dom0 operation
189: There are two basic ways to use Xen. The traditional method is for
190: the dom0 to do absolutely nothing other than providing support to some
191: number of domUs. Such a system was probably installed for the sole
192: purpose of hosting domUs, and sits in a server room on a UPS.
194: The other way is to put Xen under a normal-usage computer, so that the
195: dom0 is what the computer would have been without Xen, perhaps a
196: desktop or laptop. Then, one can run domUs at will. Purists will
197: deride this as less secure than the previous approach, and for a
198: computer whose purpose is to run domUs, they are right. But Xen and a
199: dom0 (without domUs) is not meaningfully less secure than the same
200: things running without Xen. One can boot Xen or boot regular NetBSD
201: alternately with little problems, simply refraining from starting the
202: Xen daemons when not running Xen.
204: Note that NetBSD as dom0 does not support multiple CPUs. This will
205: limit the performance of the Xen/dom0 workstation approach. In theory
206: the only issue is that the "backend drivers" are not yet MPSAFE:
209: Installation of NetBSD
213: [install NetBSD/amd64](/guide/inst/)
214: just as you would if you were not using Xen.
215: However, the partitioning approach is very important.
217: If you want to use RAIDframe for the dom0, there are no special issues
218: for Xen. Typically one provides RAID storage for the dom0, and the
219: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
220: over a RAID1 header to find /boot from a file system within a RAID
221: partition; this is no different when booting Xen.
223: There are 4 styles of providing backing storage for the virtual disks
224: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
226: With raw partitions, one has a disklabel (or gpt) partition sized for
227: each virtual disk to be used by the domU. (If you are able to predict
228: how domU usage will evolve, please add an explanation to the HOWTO.
229: Seriously, needs tend to change over time.)
231: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
232: for domU disks. This is almost as efficient as raw disk partitions
233: and more flexible. Hence raw disk partitions should typically not
234: be used.
236: One can use files in the dom0 file system, typically created by dd'ing
237: /dev/zero to create a specific size. This is somewhat less efficient,
238: but very convenient, as one can cp the files for backup, or move them
239: between dom0 hosts.
241: Finally, in theory one can place the files backing the domU disks in a
242: SAN. (This is an invitation for someone who has done this to add a
243: HOWTO page.)
245: Installation of Xen
248: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
249: pkgsrc (or another matching pair). See [the pkgsrc
250: documentation](https://www.NetBSD.org/docs/pkgsrc/) for help with
251: pkgsrc. Ensure that your packages are recent; the HOWTO does not
252: contemplate old builds.
254: Next you need to install the selected Xen kernel itself, which is
255: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
256: For debugging, one may copy xen-debug.gz; this is conceptually similar
257: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
258: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
259: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
260: of a NetBSD build. If using i386, use
261: releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz. Both xen and
262: the NetBSD kernel may be (and typically are) left compressed.
264: In a dom0, kernfs is mandatory for xend to communicate with the
265: kernel, so ensure that /kern is in fstab. (A standard NetBSD install
266: should already mount /kern.)
268: Because you already installed NetBSD, you have a working boot setup
269: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
270: beginning of your root file system, have /boot, and likely also
271: /boot.cfg. (If not, fix before continuing!)
273: Add a line to /boot.cfg to boot Xen. See boot.cfg(5) for an
274: example. The basic line is:
276: [[!template id=programlisting text="""
277: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
280: which specifies that the dom0 should have 512M, leaving the rest to be
281: allocated for domUs. To use a serial console, use
283: [[!template id=programlisting text="""
284: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
287: which will use the first serial port for Xen (which counts starting
288: from 1, unlike NetBSD which counts starting from 0), forcing
289: speed/parity. Because the NetBSD command line lacks a
290: "console=pc" argument, it will use the default "xencons" console device,
291: which directs the console I/O through Xen to the same console device Xen
292: itself uses (in this case, the serial port).
294: In an attempt to add performance, one can also add:
296: [[!template id=programlisting text="""
297: dom0_max_vcpus=1 dom0_vcpus_pin
300: to force only one vcpu to be provided (since NetBSD dom0 can't use
301: more) and to pin that vcpu to a physical CPU. TODO: benchmark this.
303: Xen has [many boot
305: and other than dom0 memory and max_vcpus, they are generally not
308: As with non-Xen systems, you should have a line to boot /netbsd (a
309: kernel that works without Xen). Consider a line to boot /netbsd.ok (a
310: fallback version of the non-Xen kernel, updated manually when you are
311: sure /netbsd is ok). Consider also a line to boot fallback versions
312: of Xen and the dom0 kernel, but note that non-Xen NetBSD can be used
313: to resolve Xen booting issues.
315: Now, reboot so that you are running a DOM0 kernel under Xen, rather
316: than GENERIC without Xen.
318: Using grub (historic)
321: Before NetBSD's native bootloader could support Xen, the use of
322: grub was recommended. If necessary, see the
323: [old grub information](/ports/xen/howto-grub).
325: The [HowTo on Installing into
327: explains how to set up booting a dom0 with Xen using grub with
328: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
329: boot. Now, just create a system with RAID-1, and alter /boot.cfg as
330: described above.)
332: Configuring Xen
335: Now, you have a system that will boot Xen and the dom0 kernel, but not
336: do anything else special. Make sure that you have rebooted into Xen.
337: There will be no domUs, and none can be started because you still have
338: to configure the dom0 daemons.
340: The daemons which should be run vary with Xen version and with whether
341: one is using xm or xl. Xen 4.2 and up packages use xl. To use xm with 4.2,
342: edit xendomains to use xm instead.
344: For 4.1 and up, you should enable xencommons. Not enabling xencommons
345: will result in a hang; it is necessary to hit ^C on the console to let
346: the machine finish booting. If you are using xm (default in 4.1, or
347: if you changed xendomains in 4.2), you should also enable xend:
349: [[!template id=programlisting text="""
350: xend=YES # only if using xm, and only installed <= 4.2
354: TODO: Recommend for/against xen-watchdog.
356: After you have configured the daemons and either started them (in the
357: order given) or rebooted, use xm or xl to inspect Xen's boot messages,
358: available resources, and running domains. An example with xl follows:
360: [[!template id=programlisting text="""
361: # xl dmesg
362: ... xen's boot info ...
363: # xl info
364: ... available memory, etc ...
365: # xl list
366: Name Id Mem(MB) CPU State Time(s) Console
367: Domain-0 0 64 0 r---- 58.1
370: Xen logs will be in /var/log/xen.
372: ### Issues with xencommons
374: xencommons starts xenstored, which stores data on behalf of dom0 and
375: domUs. It does not currently work to stop and start xenstored.
376: Certainly all domUs should be shutdown first, following the sort order
377: of the rc.d scripts. However, the dom0 sets up state with xenstored,
378: and is not notified when xenstored exits, leading to not recreating
379: the state when the new xenstored starts. Until there's a mechanism to
380: make this work, one should not expect to be able to restart xenstored
381: (and thus xencommons). There is currently no reason to expect that
382: this will get fixed any time soon.
384: ### No-longer needed advice about devices
386: The installation of NetBSD should already have created devices for xen
387: (xencons, xenevt, xsd_kva), but if they are not present, create them:
389: [[!template id=programlisting text="""
390: cd /dev && sh MAKEDEV xen
393: anita (for testing NetBSD)
396: With the setup so far (assuming 4.2/xl), one should be able to run
397: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
398: root, because anita must create a domU):
400: [[!template id=programlisting text="""
401: anita --vmm=xl test file:///usr/obj/i386/
404: Alternatively, one can use --vmm=xm to use xm-based domU creation
405: instead (and must, on Xen <= 4.1). TODO: confirm that anita xl really works.
407: Xen-specific NetBSD issues
410: There are (at least) two additional things different about NetBSD as a
411: dom0 kernel compared to hardware.
413: One is that the module ABI is different because some of the #defines
414: change, so one must build modules for Xen. As of netbsd-7, the build
415: system does this automatically. TODO: check this. (Before building
416: Xen modules was added, it was awkward to use modules to the point
417: where it was considered that it did not work.)
419: The other difference is that XEN3_DOM0 does not have exactly the same
420: options as GENERIC. While it is debatable whether or not this is a
421: bug, users should be aware of this and can simply add missing config
422: items if desired.
424: Updating NetBSD in a dom0
427: This is just like updating NetBSD on bare hardware, assuming the new
428: version supports the version of Xen you are running. Generally, one
429: replaces the kernel and reboots, and then overlays userland binaries
430: and adjusts /etc.
432: Note that one must update both the non-Xen kernel typically used for
433: rescue purposes and the DOM0 kernel used with Xen.
435: Converting from grub to /boot
438: These instructions were [TODO: will be] used to convert a system from
439: grub to /boot. The system was originally installed in February of
440: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
441: over time. Before these commands, it was running NetBSD 6 i386, Xen
442: 4.1 and grub, much like the message linked earlier in the grub
445: # Install MBR bootblocks on both disks.
446: fdisk -i /dev/rwd0d
447: fdisk -i /dev/rwd1d
448: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
449: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
450: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
451: # Install secondary boot loader
452: cp -p /usr/mdec/boot /
453: # Create boot.cfg following earlier guidance:
454: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
455: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
457: menu=GENERIC single-user:boot -s
458: menu=GENERIC.ok:boot netbsd.ok
459: menu=GENERIC.ok single-user:boot netbsd.ok -s
460: menu=Drop to boot prompt:prompt
464: TODO: actually do this and fix it if necessary.
466: Upgrading Xen versions
469: Minor version upgrades are trivial. Just rebuild/replace the
470: xenkernel version and copy the new xen.gz to / (where /boot.cfg
471: references it), and reboot.
473: Major version upgrades are conceptually not difficult, but can run
474: into all the issues found when installing Xen. Assuming migration
475: from 4.1 to 4.2, remove the xenkernel41 and xentools41 packages and
476: install the xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz
477: to /.
479: Ensure that the contents of /etc/rc.d/xen* are correct. Specifically,
480: they must match the package you just installed and not be left over
481: from some previous installation.
483: Enable the correct set of daemons; see the configuring section above.
484: (Upgrading from 3.x to 4.x without doing this will result in a hang.)
486: Ensure that the domU config files are valid for the new version.
487: Specifically, for 4.x remove autorestart=True, and ensure that disks
488: are specified with numbers as the second argument, as the examples
489: above show, and not NetBSD device names.
491: Unprivileged domains (domU)
494: This section describes general concepts about domUs. It does not
495: address specific domU operating systems or how to install them. The
496: config files for domUs are typically in /usr/pkg/etc/xen, and are
497: typically named so that the file name, domU name and the domU's host
498: name match.
500: The domU is provided with CPU and memory by Xen, configured by the
501: dom0. The domU is provided with disk and network by the dom0,
502: mediated by Xen, and configured in the dom0.
504: Entropy in domUs can be an issue; physical disks and network are on
505: the dom0. NetBSD's /dev/random system works, but is often challenged.
507: Config files
510: There is no good order to present config files and the concepts
511: surrounding what is being configured. We first show an example config
512: file, and then in the various sections give details.
514: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
515: for a large number of well-commented examples, mostly for running
518: The following is an example minimal domain configuration file
519: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
520: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
521: i386 domU). The domU serves as a network file server.
523: # -*- mode: python; -*-
525: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
526: memory = 1024
527: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
528: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
529: 'file:/n0/xen/foo-wd1,0x1,w' ]
531: The domain will have the same name as the file. The kernel has the
532: host/domU name in it, so that on the dom0 one can update the various
533: domUs independently. The vif line causes an interface to be provided,
534: with a specific mac address (do not reuse MAC addresses!), in bridge
535: mode. Two disks are provided, and they are both writable; the bits
536: are stored in files and Xen attaches them to a vnd(4) device in the
537: dom0 on domain creation. The system treats xbd0 as the boot device
538: without needing explicit configuration.
540: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
541: that "xm create" takes the name of a config file, while other commands
542: take the name of a domain. To create the domain, connect to the
543: console, create the domain while attaching the console, shutdown the
544: domain, and see if it has finished stopping, do (or xl with Xen >=
547: xm create foo
548: xm console foo
549: xm create -c foo
550: xm shutdown foo
551: xm list
553: Typing ^] will exit the console session. Shutting down a domain is
554: equivalent to pushing the power button; a NetBSD domU will receive a
555: power-press event and do a clean shutdown. Shutting down the dom0
556: will trigger controlled shutdowns of all configured domUs.
558: domU kernels
561: On a physical computer, the BIOS reads sector 0, and a chain of boot
562: loaders finds and loads a kernel. Normally this comes from the root
563: file system. With Xen domUs, the process is totally different. The
564: normal path is for the domU kernel to be a file in the dom0's
565: file system. At the request of the dom0, Xen loads that kernel into a
566: new domU instance and starts execution. While domU kernels can be
567: anyplace, reasonable places to store domU kernels on the dom0 are in /
568: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
569: config files), or in /u0/xen (where the vdisks are).
571: Note that loading the domU kernel from the dom0 implies that boot
572: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
573: See the VPS section near the end for discussion of alternate ways to
574: obtain domU kernels.
576: CPU and memory
579: A domain is provided with some number of vcpus, less than the number
580: of CPUs seen by the hypervisor. (For a dom0, this is controlled by
581: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
582: from the config file by the "vcpus = N" directive.
584: A domain is provided with memory; this is controlled in the config
585: file by "memory = N" (in megabytes). In the straightforward case, the
586: sum of the the memory allocated to the dom0 and all domUs must be less
587: than the available memory.
589: Xen also provides a "balloon" driver, which can be used to let domains
590: use more memory temporarily. TODO: Explain better, and explain how
591: well it works with NetBSD.
593: Virtual disks
596: With the file/vnd style, typically one creates a directory,
597: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
598: domUs. Then, for each domU disk, one writes zeros to a file that then
599: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
600: for the first virtual disk for the domU called foo. Writing zeros to
601: the file serves two purposes. One is that preallocating the contents
602: improves performance. The other is that vnd on sparse files has
603: failed to work. TODO: give working/notworking NetBSD versions for
604: sparse vnd and gnats reference. Note that the use of file/vnd for Xen
605: is not really different than creating a file-backed virtual disk for
606: some other purpose, except that xentools handles the vnconfig
607: commands. To create an empty 4G virtual disk, simply do
609: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
611: Do not use qemu-img-xen, because this will create sparse file. There
612: have been recent (2015) reports of sparse vnd(4) devices causing
613: lockups, but there is apparently no PR.
615: With the lvm style, one creates logical devices. They are then used
616: similarly to vnds. TODO: Add an example with lvm.
618: In domU config files, the disks are defined as a sequence of 3-tuples.
619: The first element is "method:/path/to/disk". Common methods are
620: "file:" for file-backed vnd. and "phy:" for something that is already
621: a (TODO: character or block) device.
623: The second element is an artifact of how virtual disks are passed to
624: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
625: are given a device name to associate with the disk, and values like
626: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
627: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
628: second argument. The name given is converted to a major/minor by
629: calling stat(2) on the name in /dev and this is passed to the domU.
630: In the general case, the dom0 and domU can be different operating
631: systems, and it is an unwarranted assumption that they have consistent
632: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
633: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
634: for the second works fine and avoids this issue. For a GNU/Linux
635: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
638: The third element is "w" for writable disks, and "r" for read-only
641: Note that NetBSD by default creates only vnd. If you need more
642: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
645: Note that NetBSD by default creates only xbd. If you need more
646: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
648: Virtual Networking
651: Xen provides virtual Ethernets, each of which connects the dom0 and a
652: domU. For each virtual network, there is an interface "xvifN.M" in
653: the dom0, and in domU index N, a matching interface xennetM (NetBSD
654: name). The interfaces behave as if there is an Ethernet with two
655: adapters connected. From this primitive, one can construct various
656: configurations. We focus on two common and useful cases for which
657: there are existing scripts: bridging and NAT.
659: With bridging (in the example above), the domU perceives itself to be
660: on the same network as the dom0. For server virtualization, this is
661: usually best. Bridging is accomplished by creating a bridge(4) device
662: and adding the dom0's physical interface and the various xvifN.0
663: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
664: config file. The bridge must be set up already in the dom0; an
665: example /etc/ifconfig.bridge0 is:
669: !brconfig bridge0 add wm0
671: With NAT, the domU perceives itself to be behind a NAT running on the
672: dom0. This is often appropriate when running Xen on a workstation.
673: TODO: NAT appears to be configured by "vif = [ '' ]".
675: The MAC address specified is the one used for the interface in the new
676: domain. The interface in dom0 will use this address XOR'd with
677: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
679: Sizing domains
682: Modern x86 hardware has vast amounts of resources. However, many
683: virtual servers can function just fine on far less. A system with
684: 512M of RAM and a 4G disk can be a reasonable choice. Note that it is
685: far easier to adjust virtual resources than physical ones. For
686: memory, it's just a config file edit and a reboot. For disk, one can
687: create a new file and vnconfig it (or lvm), and then dump/restore,
688: just like updating physical disks, but without having to be there and
689: without those pesky connectors.
691: Starting domains automatically
694: To start domains foo at bar at boot and shut them down cleanly on dom0
695: shutdown, in rc.conf add:
697: xendomains="foo bar"
699: Note that earlier versions of the xentools41 xendomains rc.d script
700: used xl, when one should use xm with 4.1.
702: Creating specific unprivileged domains (domU)
705: Creating domUs is almost entirely independent of operating system. We
706: have already presented the basics of config files. Note that you must
707: have already completed the dom0 setup so that "xl list" (or "xm list")
710: Creating an unprivileged NetBSD domain (domU)
713: See the earlier config file, and adjust memory. Decide on how much
714: storage you will provide, and prepare it (file or lvm).
716: While the kernel will be obtained from the dom0 file system, the same
717: file should be present in the domU as /netbsd so that tools like
718: savecore(8) can work. (This is helpful but not necessary.)
720: The kernel must be specifically for Xen and for use as a domU. The
721: i386 and amd64 provide the following kernels:
723: i386 XEN3PAE_DOMU
724: amd64 XEN3_DOMU
726: This will boot NetBSD, but this is not that useful if the disk is
727: empty. One approach is to unpack sets onto the disk outside of xen
728: (by mounting it, just as you would prepare a physical disk for a
729: system you can't run the installer on).
731: A second approach is to run an INSTALL kernel, which has a miniroot
732: and can load sets from the network. To do this, copy the INSTALL
733: kernel to / and change the kernel line in the config file to:
735: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
737: Then, start the domain as "xl create -c configname".
739: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
740: line should be used in the config file.
742: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
744: After booting the domain, the option to install via CDROM may be
745: selected. The CDROM device should be changed to `xbd1d`.
747: Once done installing, "halt -p" the new domain (don't reboot or halt,
748: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
749: config file), switch the config file back to the XEN3_DOMU kernel,
750: and start the new domain again. Now it should be able to use "root on
751: xbd0a" and you should have a, functional NetBSD domU.
753: TODO: check if this is still accurate.
754: When the new domain is booting you'll see some warnings about *wscons*
755: and the pseudo-terminals. These can be fixed by editing the files
756: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
757: `/etc/ttys`, except *console*, like this:
759: console "/usr/libexec/getty Pc" vt100 on secure
760: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
761: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
762: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
763: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
765: Finally, all screens must be commented out from `/etc/wscons.conf`.
767: It is also desirable to add
771: in rc.conf. This way, the domain will be properly shut down if
772: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
774: It is not strictly necessary to have a kernel (as /netbsd) in the domU
775: file system. However, various programs (e.g. netstat) will use that
776: kernel to look up symbols to read from kernel virtual memory. If
777: /netbsd is not the running kernel, those lookups will fail. (This is
778: not really a Xen-specific issue, but because the domU kernel is
779: obtained from the dom0, it is far more likely to be out of sync or
780: missing with Xen.)
782: Creating an unprivileged Linux domain (domU)
785: Creating unprivileged Linux domains isn't much different from
786: unprivileged NetBSD domains, but there are some details to know.
788: First, the second parameter passed to the disk declaration (the '0x1' in
789: the example below)
791: disk = [ 'phy:/dev/wd0e,0x1,w' ]
793: does matter to Linux. It wants a Linux device number here (e.g. 0x300
794: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
795: So, hda1 which has major 3 and minor 1 on a Linux system will have
796: device number 0x301. Alternatively, devices names can be used (hda,
797: hdb, ...) as xentools has a table to map these names to devices
798: numbers. To export a partition to a Linux guest we can use:
800: disk = [ 'phy:/dev/wd0e,0x300,w' ]
801: root = "/dev/hda1 ro"
803: and it will appear as /dev/hda on the Linux system, and be used as root
806: To install the Linux system on the partition to be exported to the
807: guest domain, the following method can be used: install
808: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
809: that will be the root partition of your Linux domain, and mount it.
810: Then copy the files from a working Linux system, make adjustments in
811: `/etc` (fstab, network config). It should also be possible to extract
812: binary packages such as .rpm or .deb directly to the mounted partition
813: using the appropriate tool, possibly running under NetBSD's Linux
814: emulation. Once the file system has been populated, umount it. If
815: desirable, the file system can be converted to ext3 using tune2fs -j.
816: It should now be possible to boot the Linux guest domain, using one of
817: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
819: To get the Linux console right, you need to add:
821: extra = "xencons=tty1"
823: to your configuration since not all Linux distributions auto-attach a
824: tty to the xen console.
826: Creating an unprivileged Solaris domain (domU)
829: See possibly outdated
830: [Solaris domU instructions](/ports/xen/howto-solaris/).
833: PCI passthrough: Using PCI devices in guest domains
836: The dom0 can give other domains access to selected PCI
837: devices. This can allow, for example, a non-privileged domain to have
838: access to a physical network interface or disk controller. However,
839: keep in mind that giving a domain access to a PCI device most likely
840: will give the domain read/write access to the whole physical memory,
841: as PCs don't have an IOMMU to restrict memory access to DMA-capable
842: device. Also, it's not possible to export ISA devices to non-dom0
843: domains, which means that the primary VGA adapter can't be exported.
844: A guest domain trying to access the VGA registers will panic.
846: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
847: not been ported to later versions at this time.
849: For a PCI device to be exported to a domU, is has to be attached to
850: the "pciback" driver in dom0. Devices passed to the dom0 via the
851: pciback.hide boot parameter will attach to "pciback" instead of the
852: usual driver. The list of devices is specified as "(bus:dev.func)",
853: where bus and dev are 2-digit hexadecimal numbers, and func a
854: single-digit number:
858: pciback devices should show up in the dom0's boot messages, and the
859: devices should be listed in the `/kern/xen/pci` directory.
861: PCI devices to be exported to a domU are listed in the "pci" array of
862: the domU's config file, with the format "0000:bus:dev.func".
864: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
866: In the domU an "xpci" device will show up, to which one or more pci
867: buses will attach. Then the PCI drivers will attach to PCI buses as
868: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
869: or any PCI drivers built in by default; you have to build your own
870: kernel to use PCI devices in a domU. Here's a kernel config example;
871: note that only the "xpci" lines are unusual.
873: include "arch/i386/conf/XEN3_DOMU"
875: # Add support for PCI buses to the XEN3_DOMU kernel
876: xpci* at xenbus ?
877: pci* at xpci ?
879: # PCI USB controllers
880: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
882: # USB bus support
883: usb* at uhci?
885: # USB Hubs
886: uhub* at usb?
887: uhub* at uhub? port ? configuration ? interface ?
889: # USB Mass Storage
890: umass* at uhub? port ? configuration ? interface ?
891: wd* at umass?
892: # SCSI controllers
893: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
895: # SCSI bus support (for both ahc and umass)
896: scsibus* at scsi?
898: # SCSI devices
899: sd* at scsibus? target ? lun ? # SCSI disk drives
900: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
903: NetBSD as a domU in a VPS
906: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
907: hardware. This section explains how to deal with Xen in a domU as a
908: virtual private server where you do not control or have access to the
909: dom0. This is not intended to be an exhaustive list of VPS providers;
910: only a few are mentioned that specifically support NetBSD.
912: VPS operators provide varying degrees of access and mechanisms for
913: configuration. The big issue is usually how one controls which kernel
914: is booted, because the kernel is nominally in the dom0 file system (to
915: which VPS users do not normally have access). A second issue is how
916: to install NetBSD.
917: A VPS user may want to compile a kernel for security updates, to run
918: npf, run IPsec, or any other reason why someone would want to change
919: their kernel.
921: One approach is to have an administrative interface to upload a kernel,
922: or to select from a prepopulated list. Other approaches are pygrub
923: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
924: kernel from the domU file system. This is closer to a regular physical
925: computer, where someone who controls a machine can replace the kernel.
927: A second issue is multiple CPUs. With NetBSD 6, domUs support
928: multiple vcpus, and it is typical for VPS providers to enable multiple
929: CPUs for NetBSD domUs.
934: pygrub runs in the dom0 and looks into the domU file system. This
935: implies that the domU must have a kernel in a file system in a format
936: known to pygrub. As of 2014, pygrub seems to be of mostly historical
942: pvgrub is a version of grub that uses PV operations instead of BIOS
943: calls. It is booted from the dom0 as the domU kernel, and then reads
944: /grub/menu.lst and loads a kernel from the domU file system.
946: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
947: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
948: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
949: page](http://www.panix.com/v-colo/grub.html), which describes only
950: Linux but should be updated to cover NetBSD :-).
952: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
953: their own kernel. See then [prgmr.com NetBSD
955: (which is in need of updating).
957: It appears that [grub's FFS
959: does not support all aspects of modern FFS, but there are also reports
960: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
961: partition for the kernel with the intent that grub can understand it,
962: which leads to /netbsd not being the actual kernel. One must remember
963: to update the special boot partition.
968: See the [Amazon EC2 page](/amazon_ec2/).
970: TODO items for improving NetBSD/xen
973: * Make the NetBSD dom0 kernel work with SMP.
974: * Test the Xen 4.5 packages adequately to be able to recommend them as
975: the standard approach.
976: * Get PCI passthrough working on Xen 4.5
977: * Get pvgrub into pkgsrc, either via xentools or separately.
978: * grub
979: * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
980: fragsize/blocksize (UFS2 support may be present; the point is to
981: make it so that with any UFS1/UFS2 file system setup that works
982: with NetBSD grub will also work).
983: See [pkg/40258](https://gnats.netbsd.org/40258).
984: * Push patches upstream.
985: * Get UFS2 patches into pvgrub.
986: * Add support for PV ops to a version of /boot, and make it usable as
987: a kernel in Xen, similar to pvgrub.
989: Random pointers
992: This section contains links from elsewhere not yet integrated into the
993: HOWTO, and other guides.
995: * http://www.lumbercartel.ca/library/xen/
996: * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html
997: * https://gmplib.org/~tege/xen.html
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