1: [[!meta title="Xen 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 HOWTO presumes a basic familiarity with the Xen system
12: architecture, with installing NetBSD on amd64 hardware, and with
13: installing software from pkgsrc. See also the [Xen
18: # Overview
20: The basic concept of Xen is that the hypervisor (xenkernel) runs on
21: the hardware, and runs a privileged domain ("dom0") that can access
22: disks/networking/etc. One then runs additonal unprivileged domains
23: (each a "domU"), presumably to do something useful.
25: This HOWTO addresses how to run a NetBSD dom0 (and hence also build
26: xen itself). It also addresses how to run domUs in that environment,
27: and how to deal with having a domU in a Xen environment run by someone
28: else and/or not running NetBSD.
30: ## Guest Styles
32: Xen supports different styles of guests.
34: [[!table data="""
35: Style of guest |Supported by NetBSD
36: PV |Yes (dom0, domU)
37: HVM |Yes (domU)
38: PVHVM |current-only (domU)
39: PVH |current-only (domU, dom0 not yet)
42: In Para-Virtualized (PV) mode, the guest OS does not attempt to access
43: hardware directly, but instead makes hypercalls to the hypervisor; PV
44: guests must be specifically coded for Xen.
45: See [PV](https://wiki.xen.org/wiki/Paravirtualization_(PV\)).
47: In HVM mode, no guest modification is required; however, hardware
48: support is required, such as VT-x on Intel CPUs and SVM on AMD CPUs.
49: The dom0 runs qemu to emulate hardware.
51: In PVHVM mode, the guest runs as HVM, but additionally can use PV
52: drivers for efficiency.
53: See [PV on HVM](https://wiki.xen.org/wiki/PV_on_HVM).
55: There have been two PVH modes: original PVH and PVHv2. Original PVH
56: was based on PV mode and is no longer relevant at all. PVHv2 is
57: basically lightweight HVM with PV drivers. A critical feature of it
58: is that qemu is not needed; the hypervisor can do the emulation that
59: is required. Thus, a dom0 can be PVHv2.
60: The source code uses PVH and config files use pvh; this refers to PVHv2.
61: See [PVH(v2)](https://wiki.xenproject.org/wiki/PVH_(v2\)_Domu).
63: At system boot, the dom0 kernel is loaded as a module with Xen as the kernel.
64: The dom0 can start one or more domUs. (Booting is explained in detail
65: in the dom0 section.)
67: ## CPU Architecture
69: Xen runs on x86_64 hardware (the NetBSD amd64 port).
71: There is a concept of Xen running on ARM, but there are no reports of this working with NetBSD.
73: The dom0 system should be amd64. (Instructions for i386PAE dom0 have been removed from the HOWTO.)
75: The domU can be i386PAE or amd64.
76: i386PAE at one point was considered as [faster](https://lists.xen.org/archives/html/xen-devel/2012-07/msg00085.html) than amd64.
78: ## Xen Versions
80: In NetBSD, Xen is provided in pkgsrc, via matching pairs of packages
81: xenkernel and xentools. We will refer only to the kernel versions,
82: but note that both packages must be installed together and must have
83: matching versions.
85: Versions available in pkgsrc:
87: [[!table data="""
88: Xen Version |Package Name |Xen CPU Support |EOL'ed By Upstream
89: 4.11 |xenkernel411 |x86_64 |No
90: 4.13 |xenkernel413 |x86_64 |No
93: See also the [Xen Security Advisory page](http://xenbits.xen.org/xsa/).
95: Multiprocessor (SMP) support in NetBSD differs depending on the domain:
97: [[!table data="""
98: Domain |Supports SMP
99: dom0 |No
100: domU |Yes
103: Note: NetBSD support is called XEN3. However, it does support Xen 4,
104: because the hypercall interface has remained identical.
106: Older Xen had a python-based management tool called xm, now replaced
107: by xl.
109: ## NetBSD versions
111: Xen has been supported in NetBSD for a long time, at least since 2005.
112: Initially Xen was PV only.
114: NetBSD 8 and up support PV and HVM modes.
116: Support for PVHVM and PVH is available only in NetBSD-current.
118: # Creating a dom0
120: In order to install a NetBSD as a dom0, one must first install a normal
121: NetBSD system, and then pivot the install to a dom0 install by changing
122: the kernel and boot configuration.
124: In 2018-05, trouble booting a dom0 was reported with 256M of RAM: with
125: 512M it worked reliably. This does not make sense, but if you see
126: "not ELF" after Xen boots, try increasing dom0 RAM.
128: ## Installation of NetBSD
130: [Install NetBSD/amd64](/guide/inst/)
131: just as you would if you were not using Xen.
133: ## Installation of Xen
135: We will consider that you chose to use Xen 4.13, with NetBSD/amd64 as
136: dom0. In the dom0, install xenkernel48 and xentools48 from pkgsrc.
138: Once this is done, install the Xen kernel itself:
140: [[!template id=programlisting text="""
141: # cp /usr/pkg/xen48-kernel/xen.gz /
144: Then, place a NetBSD XEN3_DOM0 kernel in the `/` directory. Such kernel
145: can either be compiled manually, or downloaded from the NetBSD FTP, for
146: example at:
148: [[!template id=programlisting text="""
152: Add a line to /boot.cfg to boot Xen:
154: [[!template id=filecontent name="/boot.cfg" text="""
155: menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
158: This specifies that the dom0 should have 512MB of ram, leaving the rest
159: to be allocated for domUs. To use a serial console, use:
161: [[!template id=filecontent name="/boot.cfg" text="""
162: menu=Xen:load /netbsd-XEN3_DOM0.gz;multiboot /xen.gz dom0_mem=512M console=com1 com1=9600,8n1
165: which will use the first serial port for Xen (which counts starting
166: from 1, unlike NetBSD which counts starting from 0), forcing
167: speed/parity. Because the NetBSD command line lacks a
168: "console=pc" argument, it will use the default "xencons" console device,
169: which directs the console I/O through Xen to the same console device Xen
170: itself uses (in this case, the serial port).
172: In an attempt to add performance, one can also add `dom0_max_vcpus=1 dom0_vcpus_pin`,
173: to force only one vcpu to be provided (since NetBSD dom0 can't use
174: more) and to pin that vcpu to a physical CPU. Xen has
175: [many boot options](http://xenbits.xenproject.org/docs/4.13-testing/misc/xen-command-line.html),
176: and other than dom0 memory and max_vcpus, they are generally not
179: Copy the boot scripts into `/etc/rc.d`:
181: [[!template id=programlisting text="""
182: # cp /usr/pkg/share/examples/rc.d/xen* /etc/rc.d/
185: Enable `xencommons`:
187: [[!template id=filecontent name="/etc/rc.conf" text="""
191: Now, reboot so that you are running a DOM0 kernel under Xen, rather
192: than GENERIC without Xen.
194: TODO: Recommend for/against xen-watchdog.
196: Once the reboot is done, use `xl` to inspect Xen's boot messages,
197: available resources, and running domains. For example:
199: [[!template id=programlisting text="""
200: # xl dmesg
201: ... xen's boot info ...
202: # xl info
203: ... available memory, etc ...
204: # xl list
205: Name Id Mem(MB) CPU State Time(s) Console
206: Domain-0 0 64 0 r---- 58.1
209: Xen logs will be in /var/log/xen.
211: ### Issues with xencommons
213: `xencommons` starts `xenstored`, which stores data on behalf of dom0 and
214: domUs. It does not currently work to stop and start xenstored.
215: Certainly all domUs should be shutdown first, following the sort order
216: of the rc.d scripts. However, the dom0 sets up state with xenstored,
217: and is not notified when xenstored exits, leading to not recreating
218: the state when the new xenstored starts. Until there's a mechanism to
219: make this work, one should not expect to be able to restart xenstored
220: (and thus xencommons). There is currently no reason to expect that
221: this will get fixed any time soon.
223: ## anita (for testing NetBSD)
225: With the setup so far, one should be able to run
226: anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
227: root, because anita must create a domU):
229: [[!template id=programlisting text="""
230: anita --vmm=xl test file:///usr/obj/i386/
233: ## Xen-specific NetBSD issues
235: There are (at least) two additional things different about NetBSD as a
236: dom0 kernel compared to hardware.
238: One is that the module ABI is different because some of the #defines
239: change, so one must build modules for Xen. As of netbsd-7, the build
240: system does this automatically.
242: The other difference is that XEN3_DOM0 does not have exactly the same
243: options as GENERIC. While it is debatable whether or not this is a
244: bug, users should be aware of this and can simply add missing config
245: items if desired.
247: ## Updating NetBSD in a dom0
249: This is just like updating NetBSD on bare hardware, assuming the new
250: version supports the version of Xen you are running. Generally, one
251: replaces the kernel and reboots, and then overlays userland binaries
252: and adjusts `/etc`.
254: Note that one must update both the non-Xen kernel typically used for
255: rescue purposes and the DOM0 kernel used with Xen.
257: ## Converting from grub to /boot
259: These instructions were used to convert a system from
260: grub to /boot. The system was originally installed in February of
261: 2006 with a RAID1 setup and grub to boot Xen 2, and has been updated
262: over time. Before these commands, it was running NetBSD 6 i386, Xen
263: 4.1 and grub, much like the message linked earlier in the grub
266: [[!template id=programlisting text="""
267: # Install MBR bootblocks on both disks.
268: fdisk -i /dev/rwd0d
269: fdisk -i /dev/rwd1d
270: # Install NetBSD primary boot loader (/ is FFSv1) into RAID1 components.
271: installboot -v /dev/rwd0d /usr/mdec/bootxx_ffsv1
272: installboot -v /dev/rwd1d /usr/mdec/bootxx_ffsv1
273: # Install secondary boot loader
274: cp -p /usr/mdec/boot /
275: # Create boot.cfg following earlier guidance:
276: menu=Xen:load /netbsd-XEN3PAE_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=512M
277: menu=Xen.ok:load /netbsd-XEN3PAE_DOM0.ok.gz console=pc;multiboot /xen.ok.gz dom0_mem=512M
279: menu=GENERIC single-user:boot -s
280: menu=GENERIC.ok:boot netbsd.ok
281: menu=GENERIC.ok single-user:boot netbsd.ok -s
282: menu=Drop to boot prompt:prompt
287: ## Upgrading Xen versions
289: Minor version upgrades are trivial. Just rebuild/replace the
290: xenkernel version and copy the new xen.gz to `/` (where `/boot.cfg`
291: references it), and reboot.
293: #Unprivileged domains (domU)
295: This section describes general concepts about domUs. It does not
296: address specific domU operating systems or how to install them. The
297: config files for domUs are typically in `/usr/pkg/etc/xen`, and are
298: typically named so that the file name, domU name and the domU's host
299: name match.
301: The domU is provided with CPU and memory by Xen, configured by the
302: dom0. The domU is provided with disk and network by the dom0,
303: mediated by Xen, and configured in the dom0.
305: Entropy in domUs can be an issue; physical disks and network are on
306: the dom0. NetBSD's /dev/random system works, but is often challenged.
308: ## Config files
310: See /usr/pkg/share/examples/xen/xlexample*
311: for a small number of well-commented examples, mostly for running
314: The following is an example minimal domain configuration file. The domU
315: serves as a network file server.
317: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
318: name = "domU-id"
319: kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
320: memory = 1024
321: vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
322: disk = [ 'file:/n0/xen/foo-wd0,0x0,w',
323: 'file:/n0/xen/foo-wd1,0x1,w' ]
326: The domain will have name given in the `name` setting. The kernel has the
327: host/domU name in it, so that on the dom0 one can update the various
328: domUs independently. The `vif` line causes an interface to be provided,
329: with a specific mac address (do not reuse MAC addresses!), in bridge
330: mode. Two disks are provided, and they are both writable; the bits
331: are stored in files and Xen attaches them to a vnd(4) device in the
332: dom0 on domain creation. The system treats xbd0 as the boot device
333: without needing explicit configuration.
335: By convention, domain config files are kept in `/usr/pkg/etc/xen`. Note
336: that "xl create" takes the name of a config file, while other commands
337: take the name of a domain.
339: Examples of commands:
341: [[!template id=programlisting text="""
342: xl create /usr/pkg/etc/xen/foo
343: xl console domU-id
344: xl create -c /usr/pkg/etc/xen/foo
345: xl shutdown domU-id
346: xl list
349: Typing `^]` will exit the console session. Shutting down a domain is
350: equivalent to pushing the power button; a NetBSD domU will receive a
351: power-press event and do a clean shutdown. Shutting down the dom0
352: will trigger controlled shutdowns of all configured domUs.
354: ## CPU and memory
356: A domain is provided with some number of vcpus, up to the number
357: of CPUs seen by the hypervisor. For a domU, it is controlled
358: from the config file by the "vcpus = N" directive.
360: A domain is provided with memory; this is controlled in the config
361: file by "memory = N" (in megabytes). In the straightforward case, the
362: sum of the the memory allocated to the dom0 and all domUs must be less
363: than the available memory.
365: Xen also provides a "balloon" driver, which can be used to let domains
366: use more memory temporarily.
368: ## Virtual disks
370: In domU config files, the disks are defined as a sequence of 3-tuples:
372: * The first element is "method:/path/to/disk". Common methods are
373: "file:" for a file-backed vnd, and "phy:" for something that is already
374: a device, such as an LVM logical volume.
376: * The second element is an artifact of how virtual disks are passed to
377: Linux, and a source of confusion with NetBSD Xen usage. Linux domUs
378: are given a device name to associate with the disk, and values like
379: "hda1" or "sda1" are common. In a NetBSD domU, the first disk appears
380: as xbd0, the second as xbd1, and so on. However, xl demands a
381: second argument. The name given is converted to a major/minor by
382: calling stat(2) on the name in /dev and this is passed to the domU.
383: In the general case, the dom0 and domU can be different operating
384: systems, and it is an unwarranted assumption that they have consistent
385: numbering in /dev, or even that the dom0 OS has a /dev. With NetBSD
386: as both dom0 and domU, using values of 0x0 for the first disk and 0x1
387: for the second works fine and avoids this issue. For a GNU/Linux
388: guest, one can create /dev/hda1 in /dev, or to pass 0x301 for
391: * The third element is "w" for writable disks, and "r" for read-only
395: [[!template id=filecontent name="/usr/pkg/etc/xen/foo" text="""
396: disk = [ 'file:/n0/xen/foo-wd0,0x0,w' ]
399: Note that NetBSD by default creates only vnd. If you need more
400: than 4 total virtual disks at a time, run e.g. "./MAKEDEV vnd4" in the
403: Note that NetBSD by default creates only xbd. If you need more
404: virtual disks in a domU, run e.g. "./MAKEDEV xbd4" in the domU.
406: Virtual Networking
409: Xen provides virtual Ethernets, each of which connects the dom0 and a
410: domU. For each virtual network, there is an interface "xvifN.M" in
411: the dom0, and a matching interface xennetM (NetBSD name) in domU index N.
412: The interfaces behave as if there is an Ethernet with two
413: adapters connected. From this primitive, one can construct various
414: configurations. We focus on two common and useful cases for which
415: there are existing scripts: bridging and NAT.
417: With bridging (in the example above), the domU perceives itself to be
418: on the same network as the dom0. For server virtualization, this is
419: usually best. Bridging is accomplished by creating a bridge(4) device
420: and adding the dom0's physical interface and the various xvifN.0
421: interfaces to the bridge. One specifies "bridge=bridge0" in the domU
422: config file. The bridge must be set up already in the dom0; an
423: example /etc/ifconfig.bridge0 is:
425: [[!template id=filecontent name="/etc/ifconfig.bridge0" text="""
428: !brconfig bridge0 add wm0
431: With NAT, the domU perceives itself to be behind a NAT running on the
432: dom0. This is often appropriate when running Xen on a workstation.
433: TODO: NAT appears to be configured by "vif = [ '' ]".
435: The MAC address specified is the one used for the interface in the new
436: domain. The interface in dom0 will use this address XOR'd with
437: 00:00:00:01:00:00. Random MAC addresses are assigned if not given.
439: Starting domains automatically
442: To start domains `domU-netbsd` and `domU-linux` at boot and shut them
443: down cleanly on dom0 shutdown, add the following in rc.conf:
445: [[!template id=filecontent name="/etc/rc.conf" text="""
446: xendomains="domU-netbsd domU-linux"
449: # Creating a domU
451: Creating domUs is almost entirely independent of operating system. We
452: have already presented the basics of config files. Note that you must
453: have already completed the dom0 setup so that "xl list" works.
455: Creating a NetBSD PV domU
458: See the earlier config file, and adjust memory. Decide on how much
459: storage you will provide, and prepare it (file or LVM).
461: While the kernel will be obtained from the dom0 file system, the same
462: file should be present in the domU as /netbsd so that tools like
463: savecore(8) can work. (This is helpful but not necessary.)
465: The kernel must be specifically for Xen and for use as a domU. The
466: i386 and amd64 provide the following kernels:
468: i386 XEN3PAE_DOMU
469: amd64 XEN3_DOMU
471: This will boot NetBSD, but this is not that useful if the disk is
472: empty. One approach is to unpack sets onto the disk outside of xen
473: (by mounting it, just as you would prepare a physical disk for a
474: system you can't run the installer on).
476: A second approach is to run an INSTALL kernel, which has a miniroot
477: and can load sets from the network. To do this, copy the INSTALL
478: kernel to / and change the kernel line in the config file to:
480: kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"
482: Then, start the domain as "xl create -c configfile".
484: Alternatively, if you want to install NetBSD/Xen with a CDROM image, the following
485: line should be used in the config file.
487: disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]
489: After booting the domain, the option to install via CDROM may be
490: selected. The CDROM device should be changed to `xbd1d`.
492: Once done installing, "halt -p" the new domain (don't reboot or halt,
493: it would reload the INSTALL_XEN3_DOMU kernel even if you changed the
494: config file), switch the config file back to the XEN3_DOMU kernel,
495: and start the new domain again. Now it should be able to use "root on
496: xbd0a" and you should have a, functional NetBSD domU.
498: TODO: check if this is still accurate.
499: When the new domain is booting you'll see some warnings about *wscons*
500: and the pseudo-terminals. These can be fixed by editing the files
501: `/etc/ttys` and `/etc/wscons.conf`. You must disable all terminals in
502: `/etc/ttys`, except *console*, like this:
504: console "/usr/libexec/getty Pc" vt100 on secure
505: ttyE0 "/usr/libexec/getty Pc" vt220 off secure
506: ttyE1 "/usr/libexec/getty Pc" vt220 off secure
507: ttyE2 "/usr/libexec/getty Pc" vt220 off secure
508: ttyE3 "/usr/libexec/getty Pc" vt220 off secure
510: Finally, all screens must be commented out from `/etc/wscons.conf`.
512: It is also desirable to add
516: in rc.conf. This way, the domain will be properly shut down if
517: `xl shutdown -R` or `xl shutdown -H` is used on the dom0.
518: \todo Check the translation to xl.
520: It is not strictly necessary to have a kernel (as /netbsd) in the domU
521: file system. However, various programs (e.g. netstat) will use that
522: kernel to look up symbols to read from kernel virtual memory. If
523: /netbsd is not the running kernel, those lookups will fail. (This is
524: not really a Xen-specific issue, but because the domU kernel is
525: obtained from the dom0, it is far more likely to be out of sync or
526: missing with Xen.)
528: Creating a Linux domU
531: Creating unprivileged Linux domains isn't much different from
532: unprivileged NetBSD domains, but there are some details to know.
534: First, the second parameter passed to the disk declaration (the '0x1' in
535: the example below)
537: disk = [ 'phy:/dev/wd0e,0x1,w' ]
539: does matter to Linux. It wants a Linux device number here (e.g. 0x300
540: for hda). Linux builds device numbers as: (major \<\< 8 + minor).
541: So, hda1 which has major 3 and minor 1 on a Linux system will have
542: device number 0x301. Alternatively, devices names can be used (hda,
543: hdb, ...) as xentools has a table to map these names to devices
544: numbers. To export a partition to a Linux guest we can use:
546: disk = [ 'phy:/dev/wd0e,0x300,w' ]
547: root = "/dev/hda1 ro"
549: and it will appear as /dev/hda on the Linux system, and be used as root
552: To install the Linux system on the partition to be exported to the
553: guest domain, the following method can be used: install
554: sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition
555: that will be the root partition of your Linux domain, and mount it.
556: Then copy the files from a working Linux system, make adjustments in
557: `/etc` (fstab, network config). It should also be possible to extract
558: binary packages such as .rpm or .deb directly to the mounted partition
559: using the appropriate tool, possibly running under NetBSD's Linux
560: emulation. Once the file system has been populated, umount it. If
561: desirable, the file system can be converted to ext3 using tune2fs -j.
562: It should now be possible to boot the Linux guest domain, using one of
563: the vmlinuz-\*-xenU kernels available in the Xen binary distribution.
565: To get the Linux console right, you need to add:
567: extra = "xencons=tty1"
569: to your configuration since not all Linux distributions auto-attach a
570: tty to the xen console.
572: ## Creating a NetBSD HVM domU
574: Use type='hmv', probably. Use a GENERIC kernel within the disk image.
576: ## Creating a NetBSD PVH domU
578: Use type='pvh'.
580: \todo Explain where the kernel comes from.
583: Creating a Solaris domU
586: See possibly outdated
587: [Solaris domU instructions](/ports/xen/howto-solaris/).
590: PCI passthrough: Using PCI devices in guest domains
593: NB: PCI passthrough only works on some Xen versions and as of 2020 it
594: is not clear that it works on any version in pkgsrc. Reports
595: confirming or denying this notion should be sent to port-xen@.
597: The dom0 can give other domains access to selected PCI
598: devices. This can allow, for example, a non-privileged domain to have
599: access to a physical network interface or disk controller. However,
600: keep in mind that giving a domain access to a PCI device most likely
601: will give the domain read/write access to the whole physical memory,
602: as PCs don't have an IOMMU to restrict memory access to DMA-capable
603: device. Also, it's not possible to export ISA devices to non-dom0
604: domains, which means that the primary VGA adapter can't be exported.
605: A guest domain trying to access the VGA registers will panic.
607: If the dom0 is NetBSD, it has to be running Xen 3.1, as support has
608: not been ported to later versions at this time.
610: For a PCI device to be exported to a domU, is has to be attached to
611: the "pciback" driver in dom0. Devices passed to the dom0 via the
612: pciback.hide boot parameter will attach to "pciback" instead of the
613: usual driver. The list of devices is specified as "(bus:dev.func)",
614: where bus and dev are 2-digit hexadecimal numbers, and func a
615: single-digit number:
619: pciback devices should show up in the dom0's boot messages, and the
620: devices should be listed in the `/kern/xen/pci` directory.
622: PCI devices to be exported to a domU are listed in the "pci" array of
623: the domU's config file, with the format "0000:bus:dev.func".
625: pci = [ '0000:00:06.0', '0000:00:0a.0' ]
627: In the domU an "xpci" device will show up, to which one or more pci
628: buses will attach. Then the PCI drivers will attach to PCI buses as
629: usual. Note that the default NetBSD DOMU kernels do not have "xpci"
630: or any PCI drivers built in by default; you have to build your own
631: kernel to use PCI devices in a domU. Here's a kernel config example;
632: note that only the "xpci" lines are unusual.
634: include "arch/i386/conf/XEN3_DOMU"
636: # Add support for PCI buses to the XEN3_DOMU kernel
637: xpci* at xenbus ?
638: pci* at xpci ?
640: # PCI USB controllers
641: uhci* at pci? dev ? function ? # Universal Host Controller (Intel)
643: # USB bus support
644: usb* at uhci?
646: # USB Hubs
647: uhub* at usb?
648: uhub* at uhub? port ? configuration ? interface ?
650: # USB Mass Storage
651: umass* at uhub? port ? configuration ? interface ?
652: wd* at umass?
653: # SCSI controllers
654: ahc* at pci? dev ? function ? # Adaptec 94x, aic78x0 SCSI
656: # SCSI bus support (for both ahc and umass)
657: scsibus* at scsi?
659: # SCSI devices
660: sd* at scsibus? target ? lun ? # SCSI disk drives
661: cd* at scsibus? target ? lun ? # SCSI CD-ROM drives
664: # Specific Issues
666: ## domU
668: [NetBSD 5 is known to panic.](http://mail-index.netbsd.org/port-xen/2018/04/17/msg009181.html)
669: (However, NetBSD 5 systems should be updated to a supported version.)
671: # NetBSD as a domU in a VPS
673: The bulk of the HOWTO is about using NetBSD as a dom0 on your own
674: hardware. This section explains how to deal with Xen in a domU as a
675: virtual private server where you do not control or have access to the
676: dom0. This is not intended to be an exhaustive list of VPS providers;
677: only a few are mentioned that specifically support NetBSD.
679: VPS operators provide varying degrees of access and mechanisms for
680: configuration. The big issue is usually how one controls which kernel
681: is booted, because the kernel is nominally in the dom0 file system (to
682: which VPS users do not normally have access). A second issue is how
683: to install NetBSD.
684: A VPS user may want to compile a kernel for security updates, to run
685: npf, run IPsec, or any other reason why someone would want to change
686: their kernel.
688: One approach is to have an administrative interface to upload a kernel,
689: or to select from a prepopulated list. Other approaches are pygrub
690: (deprecated) and pvgrub, which are ways to have a bootloader obtain a
691: kernel from the domU file system. This is closer to a regular physical
692: computer, where someone who controls a machine can replace the kernel.
694: A second issue is multiple CPUs. With NetBSD 6, domUs support
695: multiple vcpus, and it is typical for VPS providers to enable multiple
696: CPUs for NetBSD domUs.
698: ## Complexities due to Xen changes
700: Xen has many security advisories and people running Xen systems make
701: different choices.
703: ### stub domains
705: Some (Linux only?) dom0 systems use something called "stub domains" to
706: isolate qemu from the dom0 system, as a security and reliabilty
707: mechanism when running HVM domUs. Somehow, NetBSD's GENERIC kernel
708: ends up using PIO for disks rather than DMA. Of course, all of this
709: is emulated, but emulated PIO is unusably slow. This problem is not
710: currently understood.
712: ### Grant tables
714: There are multiple versions of using grant tables, and some security
715: advisories have suggested disabling some versions. Some versions of
716: NetBSD apparently only use specific versions and this can lead to
717: "NetBSD current doesn't run on hosting provider X" situations.
719: \todo Explain better.
721: ## Boot methods
723: ### pvgrub
725: pvgrub is a version of grub that uses PV operations instead of BIOS
726: calls. It is booted from the dom0 as the domU kernel, and then reads
727: /grub/menu.lst and loads a kernel from the domU file system.
729: [Panix](http://www.panix.com/) lets users use pvgrub. Panix reports
730: that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
731: (and hence with defaults from "newfs -O 2"). See [Panix's pvgrub
732: page](http://www.panix.com/v-colo/grub.html), which describes only
733: Linux but should be updated to cover NetBSD :-).
735: [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
736: their own kernel. See then [prgmr.com NetBSD
738: (which is in need of updating).
740: It appears that [grub's FFS
742: does not support all aspects of modern FFS, but there are also reports
743: that FFSv2 works fine. At prgmr, typically one has an ext2 or FAT
744: partition for the kernel with the intent that grub can understand it,
745: which leads to /netbsd not being the actual kernel. One must remember
746: to update the special boot partition.
748: ### pygrub
750: pygrub runs in the dom0 and looks into the domU file system. This
751: implies that the domU must have a kernel in a file system in a format
752: known to pygrub.
754: pygrub doesn't seem to work to load Linux images under NetBSD dom0,
755: and is inherently less secure than pvgrub due to running inside dom0. For both these
756: reasons, pygrub should not be used, and is only still present so that
757: historical DomU images using it still work.
759: As of 2014, pygrub seems to be of mostly historical
760: interest. New DomUs should use pvgrub.
762: ## Specific Providers
764: ### Amazon
766: See the [Amazon EC2 page](/amazon_ec2/).
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