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: Ideally newer versions of Xen will be added to pkgsrc.
97: Note that NetBSD support is called XEN3. It works with 3.1 through
98: 4.2 because the hypercall interface has been stable.
100: Xen command program
103: Early Xen used a program called "xm" to manipulate the system from the
104: dom0. Starting in 4.1, a replacement program with similar behavior
105: called "xl" is provided. In 4.2 and later, "xl" is preferred. 4.4 is
106: the last version that has "xm".
111: The netbsd-5, netbsd-6, netbsd-7, and -current branches are all
112: reasonable choices, with more or less the same considerations for
113: non-Xen use. Therefore, netbsd-6 is recommended as the stable version
114: of the most recent release for production use. For those wanting to
115: learn Xen or without production stability concerns, netbsd-7 is likely
116: most appropriate.
118: As of NetBSD 6, a NetBSD domU will support multiple vcpus. There is
119: no SMP support for NetBSD as dom0. (The dom0 itself doesn't really
120: need SMP; the lack of support is really a problem when using a dom0 as
121: a normal computer.)
126: Xen itself can run on i386 or amd64 machines. (Practically, almost
127: any computer where one would want to run Xen supports amd64.) If
128: using an i386 NetBSD kernel for the dom0, PAE is required (PAE
129: versions are built by default). While i386 dom0 works fine, amd64 is
130: recommended as more normal.
132: Xen 4.2 is the last version to support i386 as a host. TODO: Clarify
133: if this is about the CPU having to be amd64, or about the dom0 kernel
134: having to be amd64.
136: One can then run i386 domUs and amd64 domUs, in any combination. If
137: running an i386 NetBSD kernel as a domU, the PAE version is required.
138: (Note that emacs (at least) fails if run on i386 with PAE when built
139: without, and vice versa, presumably due to bugs in the undump code.)
144: Therefore, this HOWTO recommends running xenkernel42 (and xentools42),
145: xl, the NetBSD 6 stable branch, and to use an amd64 kernel as the
146: dom0. Either the i386 or amd64 of NetBSD may be used as domUs.
148: Build problems
151: Ideally, all versions of Xen in pkgsrc would build on all versions of
152: NetBSD on both i386 and amd64. However, that isn't the case. Besides
153: aging code and aging compilers, qemu (included in xentools for HVM
154: support) is difficult to build. The following are known to work or FAIL:
156: xenkernel3 netbsd-5 amd64
157: xentools3 netbsd-5 amd64
158: xentools3=hvm netbsd-5 amd64 ????
159: xenkernel33 netbsd-5 amd64
160: xentools33 netbsd-5 amd64
161: xenkernel41 netbsd-5 amd64
162: xentools41 netbsd-5 amd64
163: xenkernel42 netbsd-5 amd64
164: xentools42 netbsd-5 amd64
166: xenkernel3 netbsd-6 i386 FAIL
167: xentools3 netbsd-6 i386
168: xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
169: xenkernel33 netbsd-6 i386
170: xentools33 netbsd-6 i386
171: xenkernel41 netbsd-6 i386
172: xentools41 netbsd-6 i386
173: xenkernel42 netbsd-6 i386
174: xentools42 netbsd-6 i386 *MIXED
176: (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
177: but it does not build for gdt.)
179: NetBSD as a dom0
182: NetBSD can be used as a dom0 and works very well. The following
183: sections address installation, updating NetBSD, and updating Xen.
184: Note that it doesn't make sense to talk about installing a dom0 OS
185: without also installing Xen itself. We first address installing
186: NetBSD, which is not yet a dom0, and then adding Xen, pivoting the
187: NetBSD install to a dom0 install by just changing the kernel and boot
190: For experimenting with Xen, a machine with as little as 1G of RAM and
191: 100G of disk can work. For running many domUs in productions, far
192: more will be needed.
194: Styles of dom0 operation
197: There are two basic ways to use Xen. The traditional method is for
198: the dom0 to do absolutely nothing other than providing support to some
199: number of domUs. Such a system was probably installed for the sole
200: purpose of hosting domUs, and sits in a server room on a UPS.
202: The other way is to put Xen under a normal-usage computer, so that the
203: dom0 is what the computer would have been without Xen, perhaps a
204: desktop or laptop. Then, one can run domUs at will. Purists will
205: deride this as less secure than the previous approach, and for a
206: computer whose purpose is to run domUs, they are right. But Xen and a
207: dom0 (without domUs) is not meaingfully less secure than the same
208: things running without Xen. One can boot Xen or boot regular NetBSD
209: alternately with little problems, simply refraining from starting the
210: Xen daemons when not running Xen.
212: Note that NetBSD as dom0 does not support multiple CPUs. This will
213: limit the performance of the Xen/dom0 workstation approach. In theory
214: the only issue is that the "backend drivers" are not yet MPSAFE:
217: Installation of NetBSD
221: [install NetBSD/amd64](/guide/inst/)
222: just as you would if you were not using Xen.
223: However, the partitioning approach is very important.
225: If you want to use RAIDframe for the dom0, there are no special issues
226: for Xen. Typically one provides RAID storage for the dom0, and the
227: domU systems are unaware of RAID. The 2nd-stage loader bootxx_* skips
228: over a RAID1 header to find /boot from a filesystem within a RAID
229: partition; this is no different when booting Xen.
231: There are 4 styles of providing backing storage for the virtual disks
232: used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN,
234: With raw partitions, one has a disklabel (or gpt) partition sized for
235: each virtual disk to be used by the domU. (If you are able to predict
236: how domU usage will evolve, please add an explanation to the HOWTO.
237: Seriously, needs tend to change over time.)
239: One can use [lvm(8)](/guide/lvm/) to create logical devices to use
240: for domU disks. This is almost as efficient as raw disk partitions
241: and more flexible. Hence raw disk partitions should typically not
242: be used.
244: One can use files in the dom0 filesystem, typically created by dd'ing
245: /dev/zero to create a specific size. This is somewhat less efficient,
246: but very convenient, as one can cp the files for backup, or move them
247: between dom0 hosts.
249: Finally, in theory one can place the files backing the domU disks in a
250: SAN. (This is an invitation for someone who has done this to add a
251: HOWTO page.)
253: Installation of Xen
256: In the dom0, install sysutils/xenkernel42 and sysutils/xentools42 from
257: pkgsrc (or another matching pair).
258: See [the pkgsrc
259: documentation](http://www.NetBSD.org/docs/pkgsrc/) for help with pkgsrc.
261: For Xen 3.1, support for HVM guests is in sysutils/xentool3-hvm. More
262: recent versions have HVM support integrated in the main xentools
263: package. It is entirely reasonable to run only PV guests.
265: Next you need to install the selected Xen kernel itself, which is
266: installed by pkgsrc as "/usr/pkg/xen*-kernel/xen.gz". Copy it to /.
267: For debugging, one may copy xen-debug.gz; this is conceptually similar
268: to DIAGNOSTIC and DEBUG in NetBSD. xen-debug.gz is basically only
269: useful with a serial console. Then, place a NetBSD XEN3_DOM0 kernel
270: in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
271: of a NetBSD build. Both xen and NetBSD may be left compressed. (If
272: using i386, use releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.)
274: With Xen as the kernel, you must provide a dom0 NetBSD kernel to be
275: used as a module; place this in /. Suitable kernels are provided in
278: i386 XEN3_DOM0
279: i386 XEN3PAE_DOM0
280: amd64 XEN3_DOM0
282: The first one is only for use with Xen 3.1 and i386-mode Xen (and you
283: should not do this). Current Xen always uses PAE on i386, but you
284: should generally use amd64 for the dom0. In a dom0 kernel, kernfs is
285: mandatory for xend to comunicate with the kernel, so ensure that /kern
286: is in fstab. TODO: Say this is default, or file a PR and give a
289: Because you already installed NetBSD, you have a working boot setup
290: with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
291: beginning of your root filesystem, /boot present, and likely
292: /boot.cfg. (If not, fix before continuing!)
294: See boot.cfg(5) for an example. The basic line is
296: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
298: which specifies that the dom0 should have 256M, leaving the rest to be
299: allocated for domUs. In an attempt to add performance, one can also
302: dom0_max_vcpus=1 dom0_vcpus_pin
304: to force only one vcpu to be provided (since NetBSD dom0 can't use
305: more) and to pin that vcpu to a physical cpu. TODO: benchmark this.
307: As with non-Xen systems, you should have a line to boot /netbsd (a
308: kernel that works without Xen) and fallback versions of the non-Xen
309: kernel, Xen, and the dom0 kernel.
311: Using grub (historic)
314: Before NetBSD's native bootloader could support Xen, the use of
315: grub was recommended. If necessary, see the
316: [old grub information](/ports/xen/howto-grub/).
318: The [HowTo on Installing into
320: explains how to set up booting a dom0 with Xen using grub with
321: NetBSD's RAIDframe. (This is obsolete with the use of NetBSD's native
324: Configuring Xen
327: Xen logs will be in /var/log/xen.
329: Now, you have a system that will boot Xen and the dom0 kernel, and
330: just run the dom0 kernel. There will be no domUs, and none can be
331: started because you still have to configure the dom0 tools. The
332: daemons which should be run vary with Xen version and with whether one
333: is using xm or xl. Note that xend is for supporting "xm", and should
334: only be used if you plan on using "xm". Do NOT enable xend if you
335: plan on using "xl" as it will cause problems.
337: The installation of NetBSD should already have created devices for xen
338: (xencons, xenevt), but if they are not present, create them:
340: cd /dev && sh MAKEDEV xen
342: TODO: Give 3.1 advice (or remove it from pkgsrc).
344: For 3.3 (and thus xm), add to rc.conf (but note that you should have
345: installed 4.1 or 4.2):
350: For 4.1 (and thus xm; xl is believed not to work well), add to rc.conf:
355: (If you are using xentools41 from before 2014-12-26, change
356: rc.d/xendomains to use xm rather than xl.)
358: For 4.2 with xm, add to rc.conf
363: For 4.2 with xl (preferred), add to rc.conf:
366: TODO: explain if there is a xend replacement
368: TODO: Recommend for/against xen-watchdog.
370: After you have configured the daemons and either started them (in the
371: order given) or rebooted, run the following (or use xl) to inspect
372: Xen's boot messages, available resources, and running domains:
374: # xm dmesg
375: [xen's boot info]
376: # xm info
377: [available memory, etc.]
378: # xm list
379: Name Id Mem(MB) CPU State Time(s) Console
380: Domain-0 0 64 0 r---- 58.1
382: anita (for testing NetBSD)
385: With the setup so far, one should be able to run anita (see
386: pkgsrc/sysutils/py-anita) to test NetBSD releases, by doing (as root,
387: because anita must create a domU):
389: anita --vmm=xm test file:///usr/obj/i386/
391: Alternatively, one can use --vmm=xl to use xl-based domU creation instead.
392: TODO: check this.
394: Xen-specific NetBSD issues
397: There are (at least) two additional things different about NetBSD as a
398: dom0 kernel compared to hardware.
400: One is that modules are not usable in DOM0 kernels, so one must
401: compile in what's needed. It's not really that modules cannot work,
402: but that modules must be built for XEN3_DOM0 because some of the
403: defines change and the normal module builds don't do this. Basically,
404: enabling Xen changes the kernel ABI, and the module build system
405: doesn't cope with this.
407: The other difference is that XEN3_DOM0 does not have exactly the same
408: options as GENERIC. While it is debatable whether or not this is a
409: bug, users should be aware of this and can simply add missing config
410: items if desired.
412: Updating NetBSD in a dom0
415: This is just like updating NetBSD on bare hardware, assuming the new
416: version supports the version of Xen you are running. Generally, one
417: replaces the kernel and reboots, and then overlays userland binaries
418: and adjusts /etc.
420: Note that one must update both the non-Xen kernel typically used for
421: rescue purposes and the DOM0 kernel used with Xen.
423: Converting from grub to /boot
426: These instructions were [TODO: will be] used to convert a system from
427: grub to /boot. The system was originally installed in February of
428: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
429: over time. Before these commands, it was running NetBSD 6 i386, Xen
430: 4.1 and grub, much like the message linked earlier in the grub
433: # Install mbr bootblocks on both disks.
434: fdisk -i /dev/rwd0d
435: fdisk -i /dev/rwd1d
436: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
437: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
438: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
439: # Install secondary boot loader
440: cp -p /usr/mdec/boot /
441: # Create boog.cfg following earlier guidance:
442: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
443: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=256M
445: menu=GENERIC single-user:boot -s
446: menu=GENERIC.ok:boot netbsd.ok
447: menu=GENERIC.ok single-user:boot netbsd.ok -s
448: menu=Drop to boot prompt:prompt
452: TODO: actually do this and fix it if necessary.
454: Updating Xen versions
457: Updating Xen is conceptually not difficult, but can run into all the
458: issues found when installing Xen. Assuming migration from 4.1 to 4.2,
459: remove the xenkernel41 and xentools41 packages and install the
460: xenkernel42 and xentools42 packages. Copy the 4.2 xen.gz to /.
462: Ensure that the contents of /etc/rc.d/xen* are correct. Enable the
463: correct set of daemons. Ensure that the domU config files are valid
464: for the new version.
467: Unprivileged domains (domU)
470: This section describes general concepts about domUs. It does not
471: address specific domU operating systems or how to install them. The
472: config files for domUs are typically in /usr/pkg/etc/xen, and are
473: typically named so that the file name, domU name and the domU's host
474: name match.
476: The domU is provided with cpu and memory by Xen, configured by the
477: dom0. The domU is provided with disk and network by the dom0,
478: mediated by Xen, and configured in the dom0.
480: Entropy in domUs can be an issue; physical disks and network are on
481: the dom0. NetBSD's /dev/random system works, but is often challenged.
483: Config files
486: There is no good order to present config files and the concepts
487: surrounding what is being configured. We first show an example config
488: file, and then in the various sections give details.
490: See (at least in xentools41) /usr/pkg/share/examples/xen/xmexample*,
491: for a large number of well-commented examples, mostly for running
494: The following is an example minimal domain configuration file
495: "/usr/pkg/etc/xen/foo". It is (with only a name change) an actual
496: known working config file on Xen 4.1 (NetBSD 5 amd64 dom0 and NetBSD 5
497: i386 domU). The domU serves as a network file server.
499: # -*- mode: python; -*-
501: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
502: memory = 1024
503: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
504: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
505: 'file:/n0/xen/foo-wd1,0x1,w' ]
507: The domain will have the same name as the file. The kernel has the
508: host/domU name in it, so that on the dom0 one can update the various
509: domUs independently. The vif line causes an interface to be provided,
510: with a specific mac address (do not reuse MAC addresses!), in bridge
511: mode. Two disks are provided, and they are both writable; the bits
512: are stored in files and Xen attaches them to a vnd(4) device in the
513: dom0 on domain creation. The system treates xbd0 as the boot device
514: without needing explicit configuration.
516: By default xm looks for domain config files in /usr/pkg/etc/xen. Note
517: that "xm create" takes the name of a config file, while other commands
518: take the name of a domain. To create the domain, connect to the
519: console, create the domain while attaching the console, shutdown the
520: domain, and see if it has finished stopping, do (or xl with Xen >=
523: xm create foo
524: xm console foo
525: xm create -c foo
526: xm shutdown foo
527: xm list
529: Typing ^] will exit the console session. Shutting down a domain is
530: equivalent to pushing the power button; a NetBSD domU will receive a
531: power-press event and do a clean shutdown. Shutting down the dom0
532: will trigger controlled shutdowns of all configured domUs.
534: domU kernels
537: On a physical computer, the BIOS reads sector 0, and a chain of boot
538: loaders finds and loads a kernel. Normally this comes from the root
539: filesystem. With Xen domUs, the process is totally different. The
540: normal path is for the domU kernel to be a file in the dom0's
541: filesystem. At the request of the dom0, Xen loads that kernel into a
542: new domU instance and starts execution. While domU kernels can be
543: anyplace, reasonable places to store domU kernels on the dom0 are in /
544: (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
545: config files), or in /u0/xen (where the vdisks are).
547: Note that loading the domU kernel from the dom0 implies that boot
548: blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
549: See the VPS section near the end for discussion of alternate ways to
550: obtain domU kernels.
552: CPU and memory
555: A domain is provided with some number of vcpus, less than the number
556: of cpus seen by the hypervisor. (For a dom0, this is controlled by
557: the boot argument "dom0_max_vcpus=1".) For a domU, it is controlled
558: from the config file by the "vcpus = N" directive.
560: A domain is provided with memory; this is controlled in the config
561: file by "memory = N" (in megabytes). In the straightforward case, the
562: sum of the the memory allocated to the dom0 and all domUs must be less
563: than the available memory.
565: Xen also provides a "balloon" driver, which can be used to let domains
566: use more memory temporarily. TODO: Explain better, and explain how
567: well it works with NetBSD.
569: Virtual disks
572: With the file/vnd style, typically one creates a directory,
573: e.g. /u0/xen, on a disk large enough to hold virtual disks for all
574: domUs. Then, for each domU disk, one writes zeros to a file that then
575: serves to hold the virtual disk's bits; a suggested name is foo-xbd0
576: for the first virtual disk for the domU called foo. Writing zeros to
577: the file serves two purposes. One is that preallocating the contents
578: improves performance. The other is that vnd on sparse files has
579: failed to work. TODO: give working/notworking NetBSD versions for
580: sparse vnd. Note that the use of file/vnd for Xen is not really
581: different than creating a file-backed virtual disk for some other
582: purpose, except that xentools handles the vnconfig commands. To
583: create an empty 4G virtual disk, simply do
585: dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
587: With the lvm style, one creates logical devices. They are then used
588: similarly to vnds. TODO: Add an example with lvm.
590: In domU config files, the disks are defined as a sequence of 3-tuples.
591: The first element is "method:/path/to/disk". Common methods are
592: "file:" for file-backed vnd. and "phy:" for something that is already
593: a (TODO: character or block) device.
595: The second element is an artifact of how virtual disks are passed to
596: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
597: are given a device name to associate with the disk, and values like
598: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
599: as xbd0, the second as xbd1, and so on. However, xm/xl demand a
600: second argument. The name given is converted to a major/minor by
601: calling stat(2) on the name in /dev and this is passed to the domU.
602: In the general case, the dom0 and domU can be different operating
603: systems, and it is an unwarranted assumption that they have consistent
604: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
605: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
606: for the second works fine and avoids this issue. For a GNU/Linux
607: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
610: The third element is "w" for writable disks, and "r" for read-only
613: Virtual Networking
616: Xen provides virtual ethernets, each of which connects the dom0 and a
617: domU. For each virtual network, there is an interface "xvifN.M" in
618: the dom0, and in domU index N, a matching interface xennetM (NetBSD
619: name). The interfaces behave as if there is an Ethernet with two
620: adaptors connected. From this primitive, one can construct various
621: configurations. We focus on two common and useful cases for which
622: there are existing scripts: bridging and NAT.
624: With bridging (in the example above), the domU perceives itself to be
625: on the same network as the dom0. For server virtualization, this is
626: usually best. Bridging is accomplished by creating a bridge(4) device
627: and adding the dom0's physical interface and the various xvifN.0
628: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
629: config file. The bridge must be set up already in the dom0; an
630: example /etc/ifconfig.bridge0 is:
634: !brconfig bridge0 add wm0
636: With NAT, the domU perceives itself to be behind a NAT running on the
637: dom0. This is often appropriate when running Xen on a workstation.
638: TODO: NAT appears to be configured by "vif = [ '' ]".
640: The MAC address specified is the one used for the interface in the new
641: domain. The interface in dom0 will use this address XOR'd with
642: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
644: Sizing domains
647: Modern x86 hardware has vast amounts of resources. However, many
648: virtual servers can function just fine on far less. A system with
649: 256M of RAM and a 4G disk can be a reasonable choice. Note that it is
650: far easier to adjust virtual resources than physical ones. For
651: memory, it's just a config file edit and a reboot. For disk, one can
652: create a new file and vnconfig it (or lvm), and then dump/restore,
653: just like updating physical disks, but without having to be there and
654: without those pesky connectors.
656: Starting domains automatically
659: To start domains foo at bar at boot and shut them down cleanly on dom0
660: shutdown, in rc.conf add:
662: xendomains="foo bar"
664: TODO: Explain why 4.1 rc.d/xendomains has xl, when one should use xm
665: on 4.1. Or fix the xentools41 package to have xm
667: Creating specific unprivileged domains (domU)
670: Creating domUs is almost entirely independent of operating system. We
671: have already presented the basics of config files. Note that you must
672: have already completed the dom0 setup so that "xl list" (or "xm list")
675: Creating an unprivileged NetBSD domain (domU)
678: See the earlier config file, and adjust memory. Decide on how much
679: storage you will provide, and prepare it (file or lvm).
681: While the kernel will be obtained from the dom0 filesystem, the same
682: file should be present in the domU as /netbsd so that tools like
683: savecore(8) can work. (This is helpful but not necessary.)
685: The kernel must be specifically for Xen and for use as a domU. The
686: i386 and amd64 provide the following kernels:
688: i386 XEN3_DOMU
689: i386 XEN3PAE_DOMU
690: amd64 XEN3_DOMU
692: Unless using Xen 3.1 (and you shouldn't) with i386-mode Xen, you must
693: use the PAE version of the i386 kernel.
695: This will boot NetBSD, but this is not that useful if the disk is
696: empty. One approach is to unpack sets onto the disk outside of xen
697: (by mounting it, just as you would prepare a physical disk for a
698: system you can't run the installer on).
700: A second approach is to run an INSTALL kernel, which has a miniroot
701: and can load sets from the network. To do this, copy the INSTALL
702: kernel to / and change the kernel line in the config file to:
704: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
706: Then, start the domain as "xl create -c configname".
708: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
709: line should be used in the config file.
711: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
713: After booting the domain, the option to install via CDROM may be
714: selected. The CDROM device should be changed to `xbd1d`.
716: Once done installing, "halt -p" the new domain (don't reboot or halt,
717: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
718: config file), switch the config file back to the XEN3_DOMU kernel,
719: and start the new domain again. Now it should be able to use "root on
720: xbd0a" and you should have a, functional NetBSD domU.
722: TODO: check if this is still accurate.
723: When the new domain is booting you'll see some warnings about *wscons*
724: and the pseudo-terminals. These can be fixed by editing the files
725: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
726: `/etc/ttys`, except *console*, like this:
728: console "/usr/libexec/getty Pc" vt100 on secure
729: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
730: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
731: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
732: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
734: Finally, all screens must be commented out from `/etc/wscons.conf`.
736: It is also desirable to add
740: in rc.conf. This way, the domain will be properly shut down if
741: `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
743: Your domain should be now ready to work, enjoy.
745: Creating an unprivileged Linux domain (domU)
748: Creating unprivileged Linux domains isn't much different from
749: unprivileged NetBSD domains, but there are some details to know.
751: First, the second parameter passed to the disk declaration (the '0x1' in
752: the example below)
754: disk = [ 'phy:/dev/wd0e,0x1,w' ]
756: does matter to Linux. It wants a Linux device number here (e.g. 0x300
757: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
758: So, hda1 which has major 3 and minor 1 on a Linux system will have
759: device number 0x301. Alternatively, devices names can be used (hda,
760: hdb, ...) as xentools has a table to map these names to devices
761: numbers. To export a partition to a Linux guest we can use:
763: disk = [ 'phy:/dev/wd0e,0x300,w' ]
764: root = "/dev/hda1 ro"
766: and it will appear as /dev/hda on the Linux system, and be used as root
769: To install the Linux system on the partition to be exported to the
770: guest domain, the following method can be used: install
771: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
772: that will be the root partition of your Linux domain, and mount it.
773: Then copy the files from a working Linux system, make adjustments in
774: `/etc` (fstab, network config). It should also be possible to extract
775: binary packages such as .rpm or .deb directly to the mounted partition
776: using the appropriate tool, possibly running under NetBSD's Linux
777: emulation. Once the filesystem has been populated, umount it. If
778: desirable, the filesystem can be converted to ext3 using tune2fs -j.
779: It should now be possible to boot the Linux guest domain, using one of
780: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
782: To get the linux console right, you need to add:
784: extra = "xencons=tty1"
786: to your configuration since not all linux distributions auto-attach a
787: tty to the xen console.
789: Creating an unprivileged Solaris domain (domU)
792: See possibly outdated
793: [Solaris domU instructions](/ports/xen/howto-solaris/).
796: PCI passthrough: Using PCI devices in guest domains
799: The dom0 can give other domains access to selected PCI
800: devices. This can allow, for example, a non-privileged domain to have
801: access to a physical network interface or disk controller. However,
802: keep in mind that giving a domain access to a PCI device most likely
803: will give the domain read/write access to the whole physical memory,
804: as PCs don't have an IOMMU to restrict memory access to DMA-capable
805: device. Also, it's not possible to export ISA devices to non-dom0
806: domains, which means that the primary VGA adapter can't be exported.
807: A guest domain trying to access the VGA registers will panic.
809: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
810: not been ported to later versions at this time.
812: For a PCI device to be exported to a domU, is has to be attached to
813: the "pciback" driver in dom0. Devices passed to the dom0 via the
814: pciback.hide boot parameter will attach to "pciback" instead of the
815: usual driver. The list of devices is specified as "(bus:dev.func)",
816: where bus and dev are 2-digit hexadecimal numbers, and func a
817: single-digit number:
821: pciback devices should show up in the dom0's boot messages, and the
822: devices should be listed in the `/kern/xen/pci` directory.
824: PCI devices to be exported to a domU are listed in the "pci" array of
825: the domU's config file, with the format "0000:bus:dev.func".
827: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
829: In the domU an "xpci" device will show up, to which one or more pci
830: busses will attach. Then the PCI drivers will attach to PCI busses as
831: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
832: or any PCI drivers built in by default; you have to build your own
833: kernel to use PCI devices in a domU. Here's a kernel config example;
834: note that only the "xpci" lines are unusual.
836: include "arch/i386/conf/XEN3_DOMU"
838: # Add support for PCI busses to the XEN3_DOMU kernel
839: xpci* at xenbus ?
840: pci* at xpci ?
842: # PCI USB controllers
843: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
845: # USB bus support
846: usb* at uhci?
848: # USB Hubs
849: uhub* at usb?
850: uhub* at uhub? port ? configuration ? interface ?
852: # USB Mass Storage
853: umass* at uhub? port ? configuration ? interface ?
854: wd* at umass?
855: # SCSI controllers
856: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
858: # SCSI bus support (for both ahc and umass)
859: scsibus* at scsi?
861: # SCSI devices
862: sd* at scsibus? target ? lun ? # SCSI disk drives
863: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
866: NetBSD as a domU in a VPS
869: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
870: hardware. This section explains how to deal with Xen in a domU as a
871: virtual private server where you do not control or have access to the
874: VPS operators provide varying degrees of access and mechanisms for
875: configuration. The big issue is usually how one controls which kernel
876: is booted, because the kernel is nominally in the dom0 filesystem (to
877: which VPS users do not normally have acesss).
879: A VPS user may want to compile a kernel for security updates, to run
880: npf, run IPsec, or any other reason why someone would want to change
881: their kernel.
883: One approach is to have an adminstrative interface to upload a kernel,
884: or to select from a prepopulated list. Other approaches are pygrub
885: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
886: kernel from the domU filesystem. This is closer to a regular physical
887: computer, where someone who controls a machine can replace the kernel.
892: pygrub runs in the dom0 and looks into the domU filesystem. This
893: implies that the domU must have a kernel in a filesystem in a format
894: known to pygrub. As of 2014, pygrub seems to be of mostly historical
900: pvgrub is a version of grub that uses PV operations instead of BIOS
901: calls. It is booted from the dom0 as the domU kernel, and then reads
902: /grub/menu.lst and loads a kernel from the domU filesystem.
904: [prgmr.com](http://prgmr.com/) uses this approach to let users choose
905: their own operating system and kernel. See then [prgmr.com NetBSD
908: Because [grub's FFS code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
909: appears not to support all aspects of modern FFS,
910: typically one has an ext2 or FAT partition for the kernel, so that
911: grub can understand it, which leads to /netbsd not being the actual
912: kernel. One must remember to update the special boot partiion.
917: TODO: add link to NetBSD amazon howto.
919: Using npf
922: In standard kernels, npf is a module, and thus cannot be loadeed in a
923: DOMU kernel.
925: TODO: explain how to compile npf into a custom kernel, answering (but
926: note that the problem was caused by not booting the right kernel):
929: TODO items for improving NetBSD/xen
932: * Package Xen 4.4.
933: * Get PCI passthrough working on Xen 4.2 (or 4.4).
934: * Get pvgrub into pkgsrc, either via xentools or separately.
935: * grub
936: * Add support to pkgsrc grub2 for UFS2 and arbitrary
937: fragsize/blocksize (UFS2 support may be present; the point is to
938: make it so that with any UFS1/UFS2 filesystem setup that works
939: with NetBSD grub will also work).
940: * Push patches upstream.
941: * Get UFS2 patches into pvgrub.
942: * Add support for PV ops to a version of /boot, and make it usable as
943: a kernel in Xen, similar to pvgrub.
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