1: [[!meta title="Xen Status and HowTo"]]
3: Xen is a Type 1 hypervisor which supports running multiple guest operating
4: systems on a single physical machine. One uses the Xen kernel to control the
5: CPU, memory and console, a dom0 operating system which mediates access to
6: other hardware (e.g., disks, network, USB), and one or more domU operating
7: systems which operate in an unprivileged virtualized environment. IO requests
8: from the domU systems are forwarded by the Xen hypervisor to the dom0 to be
11: This document provides status on what Xen things work on NetBSD
12: (upstream documentation might say something works if it works on some
13: particular Linux system).
15: This document is also a HOWTO that presumes a basic familiarity with
16: the Xen system architecture, with installing NetBSD on amd64 hardware,
17: and with installing software from pkgsrc. See also the [Xen
20: If this document says that something works, and you find that it does
21: not, it is best to ask on port-xen and if you are correct to file a
26: # Overview
28: The basic concept of Xen is that the hypervisor (xenkernel) runs on
29: the hardware, and runs a privileged domain ("dom0") that can access
30: disks/networking/etc. One then runs additonal unprivileged domains
31: (each a "domU"), presumably to do something useful.
33: This HOWTO addresses how to run a NetBSD dom0 (and hence also build
34: xen itself). It also addresses how to run domUs in that environment,
35: and how to deal with having a domU in a Xen environment run by someone
36: else and/or not running NetBSD.
38: There are many choices one can make; the HOWTO recommends the standard
39: approach and limits discussion of alternatives in many cases.
41: ## Guest Styles
43: Xen supports different styles of guests.
45: [[!table data="""
46: Style of guest |description |NetBSD dom0? |NetBSD domU?
47: PV |Paravirtualization (hypercalls) |yes |yes
48: HVM |unmodified guest - domU perceives HW |N/A |yes
49: PVHVM |Like HVM but also PV drivers |N/A |current only
50: PVH | |not yet |current only
53: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
54: hardware directly, but instead makes hypercalls to the hypervisor; PV
55: guests must be specifically coded for Xen.
56: See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
58: In HVM mode, no guest modification is required; however, hardware
59: support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
60: The dom0 runs qemu to emulate hardware. It is therefore non-sensical
61: to have an HVM dom0.
63: In PVHVM mode, the guest runs as HVM, but additionally can use PV
64: drivers for efficiency. Therefore it is non-sensical for to have a
65: PVHVM dom0. See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
67: There have been two PVH modes: original PVH and PVHv2. Original PVH
68: was based on PV mode and is no longer relevant at all. Therefore
69: PVHv2 is abreviated PVH. PVHv2 is basically lightweight HVM with PV
70: drivers. A critical feature of it is that qemu is not needed; the
71: hypervisor can do the emulation that is required. Thus, a dom0 can be
72: PVHv2. The source code uses PVH and config files use pvh, but NB that
73: this refers to PVHv2. See
76: At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
77: The dom0 can start one or more domUs. (Booting is explained in detail
78: in the dom0 section.)
80: ## CPU Architecture
82: Xen runs on x86_64 hardware (the NetBSD amd64 port).
84: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
86: The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.)
88: The domU can be i386PAE or amd64.
89: i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
91: ## Xen Versions
93: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
94: xenkernel and xentools. We will refer only to the kernel versions,
95: but note that both packages must be installed together and must have
96: matching versions.
98: Versions available in pkgsrc:
100: [[!table data="""
101: Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream
102: 4.11 |xenkernel411 |x86_64 |No
103: 4.13 |xenkernel413 |x86_64 |No
106: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
108: Older Xen had a python-based management tool called xm, now replaced
109: by xl.
111: ## NetBSD versions
113: Xen has been supported in NetBSD for a long time, at least since 2005.
114: Initially Xen was PV only.
116: NetBSD has supported PV for a very long time, in both dom0 and domU.
117: NetBSD >=8 supports HVM mode as a domU (HVM as a dom0 does not make
120: Support for PVHVM and PVH is available only in NetBSD-current; this is
121: currently somewhat experimental, although PVHVM appears reasonably
124: NetBSD up to and including NetBSD 9 as a dom0 cannot safely run SMP.
125: Even if one added "options MULTIPROCESSOR" and configured multiple
126: vcpus, the kernel is likely to crash because of drivers without
127: adequate locking.
129: NetBSD-current supports SMP in dom0, and XEN3_DOM0 includes "options
132: NetBSD (since NetBSD 6), when run as a domU, can run SMP, using
133: multiple CPUs if provided. The XEN3_DOMU kernel is built
134: with "options MULITPROCESSOR".
136: Note that while Xen 4.13 is current, the kernel support is still
137: called XEN3, because the hypercall interface has not changed
140: # Creating a NetBSD dom0
142: In order to install a NetBSD as a dom0, one first installs a normal
143: NetBSD system, and then pivot the install to a dom0 install by
144: changing the kernel and boot configuration.
146: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
147: 512M it worked reliably. This does not make sense, but if you see
148: "not ELF" after Xen boots, try increasing dom0 RAM.
150: ## Installation of NetBSD
152: [Install NetBSD/amd64](/guide/inst/) just as you would if you were not
153: using Xen. Therefore, use the most recent release, or a build from
154: the most recent stable branch. Alternatively, use -current, being
155: mindful of all the usual caveats of lower stability of current, and
156: likely a bit more so.
158: ## Installation of Xen
160: ### Building Xen
162: Use the most recent version of Xen in pkgsrc, unless the DESCR says that it is not suitable.
163: Therefore, choose 4.13.
164: In the dom0, install xenkernel413 and xentools413 from pkgsrc.
166: Once this is done, copy the Xen kernel from where pkgsrc puts it to
167: where the boot process will be able to find it:
169: [[!template id=programlisting text="""
170: # cp -p /usr/pkg/xen413-kernel/xen.gz /
173: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such
174: kernel can either be taken from a local release build.sh run, compiled
175: manually, or downloaded from the NetBSD FTP, for example at:
177: [[!template id=programlisting text="""
181: ### Configuring booting
183: Read boot.cfg(8) carefully. Add lines to /boot.cfg to boot Xen,
184: adjusting for your root filesystem:
186: [[!template id=filecontent name="/boot.cfg" text="""
187: menu=Xen:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc;multiboot /xen.gz dom0_mem=512M
188: menu=Xen single user:load /netbsd-XEN3_DOM0.gz root=wd0a console=pc -s;multiboot /xen.gz dom0_mem=512M
191: This specifies that the dom0 should have 512MB of ram, leaving the rest
192: to be allocated for domUs.
194: NB: This says add, not replace, so that you will be able to more
195: easily boot a NetBSD kernel without Xen. Once Xen boots ok, you may
196: want to set it as default. It is highly likely that you will have
197: trouble at some point, and keeping an up-to-date GENERIC for use in
198: fixing problems is the standard prudent approach.
200: \todo Explain why rndseed is not set with Xen as part of the dom0
203: Note that you are likely to have to set root= because the boot device
204: from /boot is not passed via Xen to the dom0 kernel. With one disk,
205: it will work, but e.g. plugging in USB disk to a machine with root on
206: wd0a causes boot to fail.
208: Beware that userconf statements must be attached to the dom0 load, and
209: may not be at top-level, because then they would try to configure the
210: hypervisor, if there is a way to pass them via multiboot . It appears
211: that adding `userconf=pckbc` to `/boot.cfg` causes Xen to crash very
212: early with a heap overflow.
214: ### Console selection
216: See boot_console(8). Understand that you should start from a place of
217: having console setup correct for booting GENERIC before trying to
218: configure Xen.
220: Generally for GENERIC, one sets the console in bootxx_ffsv1 or
221: equivalent, and this is passed on to /boot (where one typically does
222: not set the console). This configuration of bootxx_ffsv1 should also
223: be in place for Xen systems, to allow seeing messages from /boot and
224: use of a keyboard to select a line from the menu. And, one should
225: have a working boot path to GENERIC for rescue situations.
227: With GENERIC, the boot options are passed on to /netbsd, but there is
228: currently no mechanism to pass these via multiboot to the hypervisor.
229: Thus, in addition to configuring the console in the boot blocks, one
230: must also configure it for Xen.
232: By default, the hypervisor (Xen itself) will use some sort of vga
233: device as the console, much like GENERIC uses by default. The vga
234: console is relinquished at the conclusion of hypervisor boot, before
235: the dom0 is started. Xen when using a vga console does not process
236: console input.
238: The hypervisor can be configured to use a serial port console, e.g.
239: [[!template id=filecontent name="/boot.cfg" text="""
240: menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
242: This example uses the first serial port (Xen counts from 1; this is
243: what NetBSD would call com0), and sets speed and parity. (The dom0 is
244: then configured to use the same serial port in this example.)
246: With the hypervisor configured for a serial console, it can get input,
247: and there is a notion of passing this input to the dom0. \todo
248: Explain why, if Xen has a serial console, the dom0 console is
249: typically also configured to open that same serial port, instead of
250: getting the passthrough input via the xen console.
252: One also configures the console for the dom0. While one might expect
253: console=pc to be default, following behavior of GENERIC, a hasty read
254: of the code suggests there is no default and booting without a
255: selected console might lead to a panic. Also, there is merit in
256: explicit configuration. Therefore the standard approach is to place
257: console=pc as part of the load statement for the dom0 kernel, or
258: alternatively console=com0.
260: The NetBSD dom0 kernel will attach xencons(4) (the man page does not
261: exist), but this is not used as a console. It is used to obtain the
262: messages from the hypervisor's console; run `xl dmesg` to see them.
264: ### Tuning
266: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
267: to force only one vcpu to be provided (since NetBSD dom0 can't use
268: more) and to pin that vcpu to a physical CPU. Xen has
269: [many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
270: and other than dom0 memory and max_vcpus, they are generally not
272: \todo Revisit this advice with current.
273: \todo Explain if anyone has ever actually measured that this helps.
275: ### rc.conf
277: Ensure that the boot scripts installed in
278: `/usr/pkg/share/examples/rc.d` are in `/etc/rc.d`, either because you
279: have `PKG_RCD_SCRIPTS=yes`, or manually. (This is not special to Xen,
280: but a normal part of pkgsrc usage.)
282: Set `xencommons=YES` in rc.conf:
284: [[!template id=filecontent name="/etc/rc.conf" text="""
288: \todo Recommend for/against xen-watchdog.
290: ### Testing
292: Now, reboot so that you are running a DOM0 kernel under Xen, rather
293: than GENERIC without Xen.
295: Once the reboot is done, use `xl` to inspect Xen's boot messages,
296: available resources, and running domains. For example:
298: [[!template id=programlisting text="""
299: # xl dmesg
300: ... xen's boot info ...
301: # xl info
302: ... available memory, etc ...
303: # xl list
304: Name Id Mem(MB) CPU State Time(s) Console
305: Domain-0 0 64 0 r---- 58.1
308: Xen logs will be in /var/log/xen.
310: ### Issues with xencommons
312: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
313: domUs. It does not currently work to stop and start xenstored.
314: Certainly all domUs should be shutdown first, following the sort order
315: of the rc.d scripts. However, the dom0 sets up state with xenstored,
316: and is not notified when xenstored exits, leading to not recreating
317: the state when the new xenstored starts. Until there's a mechanism to
318: make this work, one should not expect to be able to restart xenstored
319: (and thus xencommons). There is currently no reason to expect that
320: this will get fixed any time soon.
321: \todo Confirm if this is still true in 2020.
323: ## Xen-specific NetBSD issues
325: There are (at least) two additional things different about NetBSD as a
326: dom0 kernel compared to hardware.
328: One is that through NetBSD 9 the module ABI is different because some
329: of the #defines change, so there are separate sets of modules in
330: /stand. In NetBSD-current, there is only one set of modules.
332: The other difference is that XEN3_DOM0 does not have exactly the same
333: options as GENERIC. While it is debatable whether or not this is a
334: bug, users should be aware of this and can simply add missing config
335: items if desired.
337: Finally, there have been occasional reports of trouble with X11
338: servers in NetBSD as a dom0.
340: ## Updating Xen in a dom0
342: Basically, update the xenkernel and xentools packages and copy the new
343: Xen kernel into place, and reboot. This procedure should be usable to
344: update to a new Xen release, but the reader is reminded that having a
345: non-Xen boot methods was recommended earlier.
347: ## Updating NetBSD in a dom0
349: This is just like updating NetBSD on bare hardware, assuming the new
350: version supports the version of Xen you are running. Generally, one
351: replaces the kernel and reboots, and then overlays userland binaries
352: and adjusts `/etc`.
354: Note that one should update both the non-Xen kernel typically used for
355: rescue purposes, as well as the DOM0 kernel used with Xen.
357: ## anita (for testing NetBSD)
359: With a NetBSD dom0, even without any domUs, one should be able to run
360: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
361: root, because anita must create a domU):
363: [[!template id=programlisting text="""
364: anita --vmm=xl test file:///usr/obj/i386/
367: # Unprivileged domains (domU)
369: This section describes general concepts about domUs. It does not
370: address specific domU operating systems or how to install them. The
371: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
372: typically named so that the file name, domU name and the domU's host
373: name match.
375: The domU is provided with CPU and memory by Xen, configured by the
376: dom0. The domU is provided with disk and network by the dom0,
377: mediated by Xen, and configured in the dom0.
379: Entropy in domUs can be an issue; physical disks and network are on
380: the dom0. NetBSD's /dev/random system works, but is often challenged.
382: ## Config files
384: See /usr/pkg/share/examples/xen/xlexample* for a very small number of
385: examples for running GNU/Linux.
387: The following is an example minimal domain configuration file. The domU
388: serves as a network file server.
390: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
391: name = "domU-id"
392: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
393: memory = 1024
394: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
395: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
396: 'file:/n0/xen/foo-wd1,0x1,w' ]
399: The domain will have name given in the `name` setting. The kernel has the
400: host/domU name in it, so that on the dom0 one can update the various
401: domUs independently. The `vif` line causes an interface to be provided,
402: with a specific mac address (do not reuse MAC addresses!), in bridge
403: mode. Two disks are provided, and they are both writable; the bits
404: are stored in files and Xen attaches them to a vnd(4) device in the
405: dom0 on domain creation. The system treats xbd0 as the boot device
406: without needing explicit configuration.
408: There is not type line; that implicitly defines a pv domU. Otherwise,
409: one sets type to the lower-case version of the domU type in the table
410: above, e.g. `type = "hvm"`.
412: By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note
413: that "xl create" takes the name of a config file, while other commands
414: take the name of a domain.
416: Examples of commands:
418: [[!template id=programlisting text="""
419: xl create /usr/pkg/etc/xen/foo
420: xl console domU-id
421: xl create -c /usr/pkg/etc/xen/foo
422: xl shutdown domU-id
423: xl list
426: Typing `^]` will exit the console session. Shutting down a domain is
427: equivalent to pushing the power button; a NetBSD domU will receive a
428: power-press event and do a clean shutdown. Shutting down the dom0
429: will trigger controlled shutdowns of all configured domUs.
431: ## CPU and memory
433: A domain is provided with some number of vcpus, up to the number
434: of CPUs seen by the hypervisor. For a domU, it is controlled
435: from the config file by the "vcpus = N" directive.
437: A domain is provided with memory; this is controlled in the config
438: file by "memory = N" (in megabytes). In the straightforward case, the
439: sum of the the memory allocated to the dom0 and all domUs must be less
440: than the available memory.
442: ## Balloon driver
444: Xen provides a `balloon` driver, which can be used to let domains use
445: more memory temporarily.
447: \todo Explain how to set up a aystem to use the balloon scheme in a
448: useful manner.
450: ## Virtual disks
452: In domU config files, the disks are defined as a sequence of 3-tuples:
454: * The first element is "method:/path/to/disk". Common methods are
455: "file:" for a file-backed vnd, and "phy:" for something that is already
456: a device, such as an LVM logical volume.
458: * The second element is an artifact of how virtual disks are passed to
459: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
460: are given a device name to associate with the disk, and values like
461: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
462: as xbd0, the second as xbd1, and so on. However, xl demands a
463: second argument. The name given is converted to a major/minor by
464: calling stat(2) on the name in /dev and this is passed to the domU.
465: In the general case, the dom0 and domU can be different operating
466: systems, and it is an unwarranted assumption that they have consistent
467: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
468: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
469: for the second works fine and avoids this issue. For a GNU/Linux
470: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
473: * The third element is "w" for writable disks, and "r" for read-only
477: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
478: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
481: Note that NetBSD by default creates only vnd. If you need more
482: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
485: ## Virtual Networking
487: Xen provides virtual Ethernets, each of which connects the dom0 and a
488: domU. For each virtual network, there is an interface "xvifN.M" in
489: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
490: The interfaces behave as if there is an Ethernet with two
491: adapters connected. From this primitive, one can construct various
492: configurations. We focus on two common and useful cases for which
493: there are existing scripts: bridging and NAT.
495: With bridging (in the example above), the domU perceives itself to be
496: on the same network as the dom0. For server virtualization, this is
497: usually best. Bridging is accomplished by creating a bridge(4) device
498: and adding the dom0's physical interface and the various xvifN.0
499: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
500: config file. The bridge must be set up already in the dom0; an
501: example /etc/ifconfig.bridge0 is:
503: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
506: !brconfig bridge0 add wm0
509: With NAT, the domU perceives itself to be behind a NAT running on the
510: dom0. This is often appropriate when running Xen on a workstation.
511: TODO: NAT appears to be configured by "vif = [ '' ]".
513: The MAC address specified is the one used for the interface in the new
514: domain. The interface in dom0 will use this address XOR'd with
515: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
517: ## Starting domains automatically
519: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
520: down cleanly on dom0 shutdown, add the following in rc.conf:
522: [[!template id=filecontent name="/etc/rc.conf" text="""
523: xendomains="domU-netbsd domU-linux"
526: # domU setup for specific systems
528: Creating domUs is almost entirely independent of operating system. We
529: have already presented the basics of config files in the previous system.
531: Of course, this section presumes that you have a working dom0.
533: ## Creating a NetBSD PV domU
535: See the earlier config file, and adjust memory. Decide on how much
536: storage you will provide, and prepare it (file or LVM).
538: While the kernel will be obtained from the dom0 file system, the same
539: file should be present in the domU as /netbsd so that tools like
540: savecore(8) can work. (This is helpful but not necessary.)
542: The kernel must be specifically built for Xen, to use PV interfacesas
543: a domU. NetBSD release builds provide the following kernels:
545: i386 XEN3PAE_DOMU
546: amd64 XEN3_DOMU
548: This will boot NetBSD, but this is not that useful if the disk is
549: empty. One approach is to unpack sets onto the disk outside of Xen
550: (by mounting it, just as you would prepare a physical disk for a
551: system you can't run the installer on).
553: A second approach is to run an INSTALL kernel, which has a miniroot
554: and can load sets from the network. To do this, copy the INSTALL
555: kernel to / and change the kernel line in the config file to:
557: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
559: Then, start the domain as "xl create -c configfile".
561: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
562: line should be used in the config file.
564: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
566: After booting the domain, the option to install via CDROM may be
567: selected. The CDROM device should be changed to `xbd1d`.
569: Once done installing, "halt -p" the new domain (don't reboot or halt:
570: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
571: config file), switch the config file back to the XEN3_DOMU kernel,
572: and start the new domain again. Now it should be able to use "root on
573: xbd0a" and you should have a functional NetBSD domU.
575: TODO: check if this is still accurate.
576: When the new domain is booting you'll see some warnings about *wscons*
577: and the pseudo-terminals. These can be fixed by editing the files
578: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
579: `/etc/ttys`, except *console*, like this:
581: console "/usr/libexec/getty Pc" vt100 on secure
582: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
583: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
584: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
585: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
587: Finally, all screens must be commented out from `/etc/wscons.conf`.
589: One should also run `powerd` in a domU, but this should not need
590: configuring. With powerd, the domain will run a controlled shutdown
591: if `xl shutdown -R` or `xl shutdown -H` is used on the dom0, via
592: receiving a synthetic `power button pressed` signal. In 9 and
593: current, `powerd` is run by default under Xen kernels (or if ACPI is
594: present), and it can be added to rc.conf if not.
596: It is not strictly necessary to have a kernel (as /netbsd) in the domU
597: file system. However, various programs (e.g. netstat) will use that
598: kernel to look up symbols to read from kernel virtual memory. If
599: /netbsd is not the running kernel, those lookups will fail. (This is
600: not really a Xen-specific issue, but because the domU kernel is
601: obtained from the dom0, it is far more likely to be out of sync or
602: missing with Xen.)
604: Note that NetBSD by default creates only xbd. If you need more
605: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
607: ## Creating a Linux PV domU
609: Creating unprivileged Linux domains isn't much different from
610: unprivileged NetBSD domains, but there are some details to know.
612: First, the second parameter passed to the disk declaration (the '0x1' in
613: the example below)
615: disk = [ 'phy:/dev/wd0e,0x1,w' ]
617: does matter to Linux. It wants a Linux device number here (e.g. 0x300
618: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
619: So, hda1 which has major 3 and minor 1 on a Linux system will have
620: device number 0x301. Alternatively, devices names can be used (hda,
621: hdb, ...) as xentools has a table to map these names to devices
622: numbers. To export a partition to a Linux guest we can use:
624: disk = [ 'phy:/dev/wd0e,0x300,w' ]
625: root = "/dev/hda1 ro"
627: and it will appear as /dev/hda on the Linux system, and be used as root
630: To install the Linux system on the partition to be exported to the
631: guest domain, the following method can be used: install
632: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
633: that will be the root partition of your Linux domain, and mount it.
634: Then copy the files from a working Linux system, make adjustments in
635: `/etc` (fstab, network config). It should also be possible to extract
636: binary packages such as .rpm or .deb directly to the mounted partition
637: using the appropriate tool, possibly running under NetBSD's Linux
638: emulation. Once the file system has been populated, umount it. If
639: desirable, the file system can be converted to ext3 using tune2fs -j.
640: It should now be possible to boot the Linux guest domain, using one of
641: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
643: To get the Linux console right, you need to add:
645: extra = "xencons=tty1"
647: to your configuration since not all Linux distributions auto-attach a
648: tty to the xen console.
650: ## Creating a NetBSD HVM domU
652: Use type='hvm', probably. Use a GENERIC kernel within the disk image.
654: ## Creating a NetBSD PVH domU
656: This only works with a current kernel in the domU.
658: Use type='pvh'. Probably, use a GENERIC kernel within the disk image,
659: which in current has PV support.
661: \todo Verify.
663: \todo Verify if one can have current PVH domU on a 9 dom0.
665: ## Creating a Solaris domU
667: See possibly outdated
668: [Solaris domU instructions](/ports/xen/howto-solaris/).
670: ## PCI passthrough: Using PCI devices in guest domains
672: NB: PCI passthrough only works on some Xen versions and as of 2020 it
673: is not clear that it works on any version in pkgsrc. \todo Reports
674: confirming or denying this notion should be sent to port-xen@.
676: The dom0 can give other domains access to selected PCI
677: devices. This can allow, for example, a non-privileged domain to have
678: access to a physical network interface or disk controller. However,
679: keep in mind that giving a domain access to a PCI device most likely
680: will give the domain read/write access to the whole physical memory,
681: as PCs don't have an IOMMU to restrict memory access to DMA-capable
682: device. Also, it's not possible to export ISA devices to non-dom0
683: domains, which means that the primary VGA adapter can't be exported.
684: A guest domain trying to access the VGA registers will panic.
686: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
687: not been ported to later versions at this time.
689: For a PCI device to be exported to a domU, is has to be attached to
690: the "pciback" driver in dom0. Devices passed to the dom0 via the
691: pciback.hide boot parameter will attach to "pciback" instead of the
692: usual driver. The list of devices is specified as "(bus:dev.func)",
693: where bus and dev are 2-digit hexadecimal numbers, and func a
694: single-digit number:
698: pciback devices should show up in the dom0's boot messages, and the
699: devices should be listed in the `/kern/xen/pci` directory.
701: PCI devices to be exported to a domU are listed in the "pci" array of
702: the domU's config file, with the format "0000:bus:dev.func".
704: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
706: In the domU an "xpci" device will show up, to which one or more pci
707: buses will attach. Then the PCI drivers will attach to PCI buses as
708: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
709: or any PCI drivers built in by default; you have to build your own
710: kernel to use PCI devices in a domU. Here's a kernel config example;
711: note that only the "xpci" lines are unusual.
713: include "arch/i386/conf/XEN3_DOMU"
715: # Add support for PCI buses to the XEN3_DOMU kernel
716: xpci* at xenbus ?
717: pci* at xpci ?
719: # PCI USB controllers
720: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
722: # USB bus support
723: usb* at uhci?
725: # USB Hubs
726: uhub* at usb?
727: uhub* at uhub? port ? configuration ? interface ?
729: # USB Mass Storage
730: umass* at uhub? port ? configuration ? interface ?
731: wd* at umass?
732: # SCSI controllers
733: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
735: # SCSI bus support (for both ahc and umass)
736: scsibus* at scsi?
738: # SCSI devices
739: sd* at scsibus? target ? lun ? # SCSI disk drives
740: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
743: # Miscellaneous Information
745: ## Nesting under Linux KVM
747: It is possible to run a Xen and a NetBSD dom0 under Linux KVM. One
748: can enable virtio in the dom0 for greater speed.
750: ## Other nesting
752: In theory, any full emulation should be able to run Xen and a NetBSD
753: dom0. The HOWTO does not currently have information about Xen XVM
754: mode, nvmm, qemu, Virtualbox, etc.
756: ## NetBSD 5 as domU
758: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
759: (However, NetBSD 5 systems should be updated to a supported version.)
761: # NetBSD as a domU in a VPS
763: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
764: hardware. This section explains how to deal with Xen in a domU as a
765: virtual private server where you do not control or have access to the
766: dom0. This is not intended to be an exhaustive list of VPS providers;
767: only a few are mentioned that specifically support NetBSD.
769: VPS operators provide varying degrees of access and mechanisms for
770: configuration. The big issue is usually how one controls which kernel
771: is booted, because the kernel is nominally in the dom0 file system (to
772: which VPS users do not normally have access). A second issue is how
773: to install NetBSD.
774: A VPS user may want to compile a kernel for security updates, to run
775: npf, run IPsec, or any other reason why someone would want to change
776: their kernel.
778: One approach is to have an administrative interface to upload a kernel,
779: or to select from a prepopulated list. Other approaches are pygrub
780: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
781: kernel from the domU file system. This is closer to a regular physical
782: computer, where someone who controls a machine can replace the kernel.
784: A second issue is multiple CPUs. With NetBSD 6, domUs support
785: multiple vcpus, and it is typical for VPS providers to enable multiple
786: CPUs for NetBSD domUs.
788: ## Complexities due to Xen changes
790: Xen has many security advisories and people running Xen systems make
791: different choices.
793: ### stub domains
795: Some (Linux only?) dom0 systems use something called "stub domains" to
796: isolate qemu from the dom0 system, as a security and reliabilty
797: mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel
798: ends up using PIO for disks rather than DMA. Of course, all of this
799: is emulated, but emulated PIO is unusably slow. This problem is not
800: currently understood.
802: ### Grant tables
804: There are multiple versions of using grant tables, and some security
805: advisories have suggested disabling some versions. Some versions of
806: NetBSD apparently only use specific versions and this can lead to
807: "NetBSD current doesn't run on hosting provider X" situations.
809: \todo Explain better.
811: ## Boot methods
813: ### pvgrub
815: pvgrub is a version of grub that uses PV operations instead of BIOS
816: calls. It is booted from the dom0 as the domU kernel, and then reads
817: /grub/menu.lst and loads a kernel from the domU file system.
819: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
820: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
821: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
822: page](http://www.panix.com/v-colo/grub.html), which describes only
823: Linux but should be updated to cover NetBSD :-).
825: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
826: their own kernel. See then [prgmr.com NetBSD
828: (which is in need of updating).
830: It appears that [grub's FFS
832: does not support all aspects of modern FFS, but there are also reports
833: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
834: partition for the kernel with the intent that grub can understand it,
835: which leads to /netbsd not being the actual kernel. One must remember
836: to update the special boot partition.
838: ### pygrub
840: pygrub runs in the dom0 and looks into the domU file system. This
841: implies that the domU must have a kernel in a file system in a format
842: known to pygrub.
844: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
845: and is inherently less secure than pvgrub due to running inside dom0. For both these
846: reasons, pygrub should not be used, and is only still present so that
847: historical DomU images using it still work.
849: As of 2014, pygrub seems to be of mostly historical
850: interest. New DomUs should use pvgrub.
852: ## Specific Providers
854: ### Amazon
856: See the [Amazon EC2 page](/amazon_ec2/).
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