Diff for /wikisrc/ports/xen/howto.mdwn between versions 1.56 and 1.93

version 1.56, 2014/12/27 00:25:48 version 1.93, 2015/03/05 13:27:37
Line 2  Introduction Line 2  Introduction
 ============  ============
   
 [![[Xen  [![[Xen
 screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](../../gallery/in-Action/hubertf-xen.png)  screenshot]](http://www.netbsd.org/gallery/in-Action/hubertf-xens.png)](http://www.netbsd.org/gallery/in-Action/hubertf-xen.png)
   
 Xen is a virtual machine monitor or hypervisor for x86 hardware  Xen is a hypervisor (or virtual machine monitor) for x86 hardware
 (i686-class or higher), which supports running multiple guest  (i686-class or higher), which supports running multiple guest
 operating systems on a single physical machine.  With Xen, one uses  operating systems on a single physical machine.  Xen is a Type 1 or
 the Xen kernel to control the CPU, memory and console, a dom0  bare-metal hypervisor; one uses the Xen kernel to control the CPU,
 operating system which mediates access to other hardware (e.g., disks,  memory and console, a dom0 operating system which mediates access to
 network, USB), and one or more domU operating systems which operate in  other hardware (e.g., disks, network, USB), and one or more domU
 an unprivileged virtualized environment.  IO requests from the domU  operating systems which operate in an unprivileged virtualized
 systems are forwarded by the hypervisor (Xen) to the dom0 to be  environment.  IO requests from the domU systems are forwarded by the
 fulfilled.  hypervisor (Xen) to the dom0 to be fulfilled.
   
 Xen supports two styles of guests.  The original is Para-Virtualized  Xen supports two styles of guests.  The original is Para-Virtualized
 (PV) which means that the guest OS does not attempt to access hardware  (PV) which means that the guest OS does not attempt to access hardware
Line 92  reasonable although trailing-edge choice Line 92  reasonable although trailing-edge choice
 xenkernel42 provides Xen 4.2.  This is maintained by Xen, but old as  xenkernel42 provides Xen 4.2.  This is maintained by Xen, but old as
 of 2014-12.  of 2014-12.
   
   xenkernel45 provides Xen 4.5.  This is new to pkgsrc as of 2015-01 and
   not yet recommended for other than experimental/testing use.
   
 Ideally newer versions of Xen will be added to pkgsrc.  Ideally newer versions of Xen will be added to pkgsrc.
   
 Note that NetBSD support is called XEN3.  It works with 3.1 through  Note that NetBSD support is called XEN3.  It works with Xen 3 and Xen
 4.2 because the hypercall interface has been stable.  4 because the hypercall interface has been stable.
   
 Xen command program  Xen command program
 -------------------  -------------------
   
 Early Xen used a program called "xm" to manipulate the system from the  Early Xen used a program called xm to manipulate the system from the
 dom0.  Starting in 4.1, a replacement program with similar behavior  dom0.  Starting in 4.1, a replacement program with similar behavior
 called "xl" is provided.  In 4.2 and later, "xl" is preferred.  4.4 is  called xl is provided, but it does not work well in 4.1.  In 4.2, both
 the last version that has "xm".  xm and xl work fine.  4.4 is the last version that has xm.  You must
   choose one or the other, because it affects which daemons you run.
   
 NetBSD  NetBSD
 ------  ------
Line 138  running an i386 NetBSD kernel as a domU, Line 142  running an i386 NetBSD kernel as a domU,
 (Note that emacs (at least) fails if run on i386 with PAE when built  (Note that emacs (at least) fails if run on i386 with PAE when built
 without, and vice versa, presumably due to bugs in the undump code.)  without, and vice versa, presumably due to bugs in the undump code.)
   
   Stability
   ---------
   
   Mostly, NetBSD as a dom0 or domU is quite stable.
   However, there are some open PRs indicating problems.
   
    - [PR 48125](http://gnats.netbsd.org/48125)
    - [PR 47720](http://gnats.netbsd.org/47720)
   
   Note also that there are issues with sparse vnd(4) instances, but
   these are not about Xen.
   
 Recommendation  Recommendation
 --------------  --------------
   
Line 151  Build problems Line 167  Build problems
 Ideally, all versions of Xen in pkgsrc would build on all versions of  Ideally, all versions of Xen in pkgsrc would build on all versions of
 NetBSD on both i386 and amd64.  However, that isn't the case.  Besides  NetBSD on both i386 and amd64.  However, that isn't the case.  Besides
 aging code and aging compilers, qemu (included in xentools for HVM  aging code and aging compilers, qemu (included in xentools for HVM
 support) is difficult to build.  The following are known to fail:  support) is difficult to build.  The following are known to work or FAIL:
   
         xenkernel3 netbsd-6 i386  
         xentools42 netbsd-6 i386   
   
 The following are known to work:  
   
           xenkernel3 netbsd-5 amd64
           xentools3 netbsd-5 amd64
           xentools3=hvm netbsd-5 amd64 ????
           xenkernel33 netbsd-5 amd64
           xentools33 netbsd-5 amd64
         xenkernel41 netbsd-5 amd64          xenkernel41 netbsd-5 amd64
         xentools41 netbsd-5 amd64          xentools41 netbsd-5 amd64
           xenkernel42 netbsd-5 amd64
           xentools42 netbsd-5 amd64
   
           xenkernel3 netbsd-6 i386 FAIL
           xentools3 netbsd-6 i386
           xentools3-hvm netbsd-6 i386 FAIL (dependencies fail)
           xenkernel33 netbsd-6 i386
           xentools33 netbsd-6 i386
         xenkernel41 netbsd-6 i386          xenkernel41 netbsd-6 i386
         xentools41 netbsd-6 i386          xentools41 netbsd-6 i386
           xenkernel42 netbsd-6 i386
           xentools42 netbsd-6 i386 *MIXED
   
           (all 3 and 33 seem to FAIL)
           xenkernel41 netbsd-7 i386
           xentools41 netbsd-7 i386
           xenkernel42 netbsd-7 i386
           xentools42 netbsd-7 i386 ??FAIL
   
   (*On netbsd-6 i386, there is a xentools42 in the 2014Q3 official builds,
   but it does not build for gdt.)
   
 NetBSD as a dom0  NetBSD as a dom0
 ================  ================
Line 191  dom0 is what the computer would have bee Line 226  dom0 is what the computer would have bee
 desktop or laptop.  Then, one can run domUs at will.  Purists will  desktop or laptop.  Then, one can run domUs at will.  Purists will
 deride this as less secure than the previous approach, and for a  deride this as less secure than the previous approach, and for a
 computer whose purpose is to run domUs, they are right.  But Xen and a  computer whose purpose is to run domUs, they are right.  But Xen and a
 dom0 (without domUs) is not meaingfully less secure than the same  dom0 (without domUs) is not meaningfully less secure than the same
 things running without Xen.  One can boot Xen or boot regular NetBSD  things running without Xen.  One can boot Xen or boot regular NetBSD
 alternately with little problems, simply refraining from starting the  alternately with little problems, simply refraining from starting the
 Xen daemons when not running Xen.  Xen daemons when not running Xen.
Line 216  over a RAID1 header to find /boot from a Line 251  over a RAID1 header to find /boot from a
 partition; this is no different when booting Xen.  partition; this is no different when booting Xen.
   
 There are 4 styles of providing backing storage for the virtual disks  There are 4 styles of providing backing storage for the virtual disks
 used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN,  used by domUs: raw partitions, LVM, file-backed vnd(4), and SAN.
   
 With raw partitions, one has a disklabel (or gpt) partition sized for  With raw partitions, one has a disklabel (or gpt) partition sized for
 each virtual disk to be used by the domU.  (If you are able to predict  each virtual disk to be used by the domU.  (If you are able to predict
Line 255  For debugging, one may copy xen-debug.gz Line 290  For debugging, one may copy xen-debug.gz
 to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only  to DIAGNOSTIC and DEBUG in NetBSD.  xen-debug.gz is basically only
 useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel  useful with a serial console.  Then, place a NetBSD XEN3_DOM0 kernel
 in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz  in /, copied from releasedir/amd64/binary/kernel/netbsd-XEN3_DOM0.gz
 of a NetBSD build.  Both xen and NetBSD may be left compressed.  (If  of a NetBSD build.  If using i386, use
 using i386, use releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.)  releasedir/i386/binary/kernel/netbsd-XEN3PAE_DOM0.gz.  (If using Xen
   3.1 and i386, you may use XEN3_DOM0 with the non-PAE Xen.  But you
 With Xen as the kernel, you must provide a dom0 NetBSD kernel to be  should not use Xen 3.1.)  Both xen and the NetBSD kernel may be (and
 used as a module; place this in /.  Suitable kernels are provided in  typically are) left compressed.
 releasedir/binary/kernel:  
   In a dom0 kernel, kernfs is mandatory for xend to comunicate with the
         i386 XEN3_DOM0  kernel, so ensure that /kern is in fstab.  TODO: Say this is default,
         i386 XEN3PAE_DOM0  or file a PR and give a reference.
         amd64 XEN3_DOM0  
   
 The first one is only for use with Xen 3.1 and i386-mode Xen (and you  
 should not do this).  Current Xen always uses PAE on i386, but you  
 should generally use amd64 for the dom0.  In a dom0 kernel, kernfs is  
 mandatory for xend to comunicate with the kernel, so ensure that /kern  
 is in fstab.  TODO: Say this is default, or file a PR and give a  
 reference.  
   
 Because you already installed NetBSD, you have a working boot setup  Because you already installed NetBSD, you have a working boot setup
 with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the  with an MBR bootblock, either bootxx_ffsv1 or bootxx_ffsv2 at the
 beginning of your root filesystem, /boot present, and likely  beginning of your root filesystem, /boot present, and likely
 /boot.cfg.  (If not, fix before continuing!)  /boot.cfg.  (If not, fix before continuing!)
   
 See boot.cfg(5) for an example.  The basic line is  Add a line to to /boot.cfg to boot Xen.  See boot.cfg(5) for an
   example.  The basic line is
   
         menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M          menu=Xen:load /netbsd-XEN3_DOM0.gz console=pc;multiboot /xen.gz dom0_mem=256M
   
 which specifies that the dom0 should have 256M, leaving the rest to be  which specifies that the dom0 should have 256M, leaving the rest to be
 allocated for domUs.  In an attempt to add performance, one can also  allocated for domUs.  To use a serial console, use
 add  
           menu=Xen:load /netbsd-XEN3_DOM0.gz console=com0;multiboot /xen.gz dom0_mem=256M console=com1 com1=9600,8n1
   
   which will use the first serial port for Xen (which counts starting
   from 1), forcing speed/parity, and also for NetBSD (which counts
   starting at 0).  In an attempt to add performance, one can also add
   
         dom0_max_vcpus=1 dom0_vcpus_pin          dom0_max_vcpus=1 dom0_vcpus_pin
   
 to force only one vcpu to be provided (since NetBSD dom0 can't use  to force only one vcpu to be provided (since NetBSD dom0 can't use
 more) and to pin that vcpu to a physical cpu.  TODO: benchmark this.  more) and to pin that vcpu to a physical cpu.  TODO: benchmark this.
   
   Xen has [many boot
   options](http://xenbits.xenproject.org/docs/4.5-testing/misc/xen-command-line.html),
   and other tham dom0 memory and max_vcpus, they are generally not
   necessary.
   
 As with non-Xen systems, you should have a line to boot /netbsd (a  As with non-Xen systems, you should have a line to boot /netbsd (a
 kernel that works without Xen) and fallback versions of the non-Xen  kernel that works without Xen) and fallback versions of the non-Xen
 kernel, Xen, and the dom0 kernel.  kernel, Xen, and the dom0 kernel.
   
   Now, reboot so that you are running a DOM0 kernel under Xen, rather
   than GENERIC without Xen.
   
 Using grub (historic)  Using grub (historic)
 ---------------------  ---------------------
   
Line 313  Configuring Xen Line 354  Configuring Xen
   
 Xen logs will be in /var/log/xen.  Xen logs will be in /var/log/xen.
   
 Now, you have a system that will boot Xen and the dom0 kernel, and  Now, you have a system that will boot Xen and the dom0 kernel, but not
 just run the dom0 kernel.  There will be no domUs, and none can be  do anything else special.  Make sure that you have rebooted into Xen.
 started because you still have to configure the dom0 tools.  The  There will be no domUs, and none can be started because you still have
 daemons which should be run vary with Xen version and with whether one  to configure the dom0 tools.  The daemons which should be run vary
 is using xm or xl.  Note that xend is for supporting "xm", and should  with Xen version and with whether one is using xm or xl.  Note that
 only be used if you plan on using "xm".  Do NOT enable xend if you  xend is for supporting "xm", and should only be used if you plan on
 plan on using "xl" as it will cause problems.  using "xm".  Do NOT enable xend if you plan on using "xl" as it will
   cause problems.  Running xl without xencommons=YES (and starting it)
   will result in a hang (so don't do that; follow the HOWTO!).
   
 The installation of NetBSD should already have created devices for xen  The installation of NetBSD should already have created devices for xen
 (xencons, xenevt), but if they are not present, create them:  (xencons, xenevt), but if they are not present, create them:
Line 347  For 4.2 with xm, add to rc.conf Line 390  For 4.2 with xm, add to rc.conf
         xencommons=YES          xencommons=YES
         xend=YES          xend=YES
   
 For 4.2 with xl (preferred), add to rc.conf:  For 4.2 with xl, add to rc.conf:
   
           xencommons=YES
           TODO: explain if there is a xend replacement
   
   For 4.5 (and thus with xl), add to rc.conf:
   
         xencommons=YES          xencommons=YES
         TODO: explain if there is a xend replacement          TODO: explain if there is a xend replacement
Line 355  For 4.2 with xl (preferred), add to rc.c Line 403  For 4.2 with xl (preferred), add to rc.c
 TODO: Recommend for/against xen-watchdog.  TODO: Recommend for/against xen-watchdog.
   
 After you have configured the daemons and either started them (in the  After you have configured the daemons and either started them (in the
 order given) or rebooted, run the following (or use xl) to inspect  order given) or rebooted, use xm or xl to inspect Xen's boot messages,
 Xen's boot messages, available resources, and running domains:  available resources, and running domains.  An example with xm follows:
   
         # xm dmesg          # xm dmesg
         [xen's boot info]          [xen's boot info]
Line 366  Xen's boot messages, available resources Line 414  Xen's boot messages, available resources
         Name              Id  Mem(MB)  CPU  State  Time(s)  Console          Name              Id  Mem(MB)  CPU  State  Time(s)  Console
         Domain-0           0       64    0  r----     58.1          Domain-0           0       64    0  r----     58.1
   
   With xl, the commands are the same, and the output may be slightly
   different.  TODO: add example output for xl before the xm example,
   after confirming on 4.2 and resolving the TODO about rc.conf.
   
   ### Issues with xencommons
   
   xencommons starts xenstored, which stores data on behalf of dom0 and
   domUs.  It does not currently work to stop and start xenstored.
   Certainly all domUs should be shutdown first, following the sort order
   of the rc.d scripts.  However, the dom0 sets up state with xenstored,
   and is not notified when xenstored exits, leading to not recreating
   the state when the new xenstored starts.  Until there's a mechanism to
   make this work, one should not expect to be able to restart xenstored
   (and thus xencommons).  There is currently no reason to expect that
   this will get fixed any time soon.
   
 anita (for testing NetBSD)  anita (for testing NetBSD)
 --------------------------  --------------------------
   
 With the setup so far, one should be able to run anita (see  With the setup so far (assuming 4.2/xl), one should be able to run
 pkgsrc/sysutils/py-anita) to test NetBSD releases, by doing (as root,  anita (see pkgsrc/misc/py-anita) to test NetBSD releases, by doing (as
 because anita must create a domU):  root, because anita must create a domU):
   
         anita --vmm=xm test file:///usr/obj/i386/          anita --vmm=xl test file:///usr/obj/i386/
   
 Alternatively, one can use --vmm=xl to use xl-based domU creation instead.  Alternatively, one can use --vmm=xm to use xm-based domU creation
 TODO: check this.  instead (and must, on Xen <= 4.1).   TODO: confirm that anita xl really works.
       
 Xen-specific NetBSD issues  Xen-specific NetBSD issues
 --------------------------  --------------------------
   
Line 451  correct set of daemons.  Ensure that the Line 515  correct set of daemons.  Ensure that the
 for the new version.  for the new version.
   
   
   Running Xen under qemu
   ----------------------
   
   The astute reader will note that this section is somewhat twisted.
   However, it can be useful to run Xen under qemu either because the
   version of NetBSD as a dom0 does not run on the hardware in use, or to
   generate automated test cases involving Xen.
   
   In 2015-01, the following combination was reported to mostly work:
   
           host OS: NetBSD/amd64 6.1.4
           qemu: 2.2.0 from pkgsrc
           Xen kernel: xenkernel42-4.2.5nb1 from pkgsrc
           dom0 kernel: NetBSD/amd64 6.1.5
           Xen tools: xentools42-4.2.5 from pkgsrc
   
   See [PR 47720](http://gnats.netbsd.org/47720) for a problem with dom0
   shutdown.
   
 Unprivileged domains (domU)  Unprivileged domains (domU)
 ===========================  ===========================
   
 This section describes general concepts about domUs.  It does not  This section describes general concepts about domUs.  It does not
 address specific domU operating systems or how to install them.  The  address specific domU operating systems or how to install them.  The
 config files for domUs are typically in /usr/pkg/etc/xen, and are  config files for domUs are typically in /usr/pkg/etc/xen, and are
 typically named so that the file anme, domU name and the domU's host  typically named so that the file name, domU name and the domU's host
 name match.  name match.
   
 The domU is provided with cpu and memory by Xen, configured by the  The domU is provided with cpu and memory by Xen, configured by the
Line 511  domain, and see if it has finished stopp Line 594  domain, and see if it has finished stopp
         xm console foo          xm console foo
         xm create -c foo          xm create -c foo
         xm shutdown foo          xm shutdown foo
         xm list          xm list
   
 Typing ^] will exit the console session.  Shutting down a domain is  Typing ^] will exit the console session.  Shutting down a domain is
 equivalent to pushing the power button; a NetBSD domU will receive a  equivalent to pushing the power button; a NetBSD domU will receive a
Line 531  anyplace, reasonable places to store dom Line 614  anyplace, reasonable places to store dom
 (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the  (so they are near the dom0 kernel), in /usr/pkg/etc/xen (near the
 config files), or in /u0/xen (where the vdisks are).  config files), or in /u0/xen (where the vdisks are).
   
   Note that loading the domU kernel from the dom0 implies that boot
   blocks, /boot, /boot.cfg, and so on are all ignored in the domU.
 See the VPS section near the end for discussion of alternate ways to  See the VPS section near the end for discussion of alternate ways to
 obtain domU kernels.  obtain domU kernels.
   
Line 569  create an empty 4G virtual disk, simply  Line 654  create an empty 4G virtual disk, simply 
   
         dd if=/dev/zero of=foo-xbd0 bs=1m count=4096          dd if=/dev/zero of=foo-xbd0 bs=1m count=4096
   
   Do not use qemu-img-xen, because this will create sparse file.  There
   have been recent (2015) reports of sparse vnd(4) devices causing
   lockups, but there is apparently no PR.
   
 With the lvm style, one creates logical devices.  They are then used  With the lvm style, one creates logical devices.  They are then used
 similarly to vnds.  TODO: Add an example with lvm.  similarly to vnds.  TODO: Add an example with lvm.
   
Line 646  shutdown, in rc.conf add: Line 735  shutdown, in rc.conf add:
   
         xendomains="foo bar"          xendomains="foo bar"
   
 TODO: Explain why 4.1 rc.d/xendomains has xl, when one should use xm  Note that earlier versions of the xentools41 xendomains rc.d scripth
 on 4.1.  Or fix the xentools41 package to have xm  usd xl, when one should use xm with 4.1.
   
 Creating specific unprivileged domains (domU)  Creating specific unprivileged domains (domU)
 =============================================  =============================================
Line 725  It is also desirable to add Line 814  It is also desirable to add
 in rc.conf. This way, the domain will be properly shut down if  in rc.conf. This way, the domain will be properly shut down if
 `xm shutdown -R` or `xm shutdown -H` is used on the dom0.  `xm shutdown -R` or `xm shutdown -H` is used on the dom0.
   
   It is not strictly necessary to have a kernel (as /netbsd) in the domU
   filesystem.  However, various programs (e.g. netstat) will use that
   kernel to look up symbols to read from kernel virtual memory.  If
   /netbsd is not the running kernel, those lookups will fail.  (This is
   not really a Xen-specific issue, but because the domU kernel is
   obtained from the dom0, it is far more likely to be out of sync or
   missing with Xen.)
   
 Your domain should be now ready to work, enjoy.  Your domain should be now ready to work, enjoy.
   
 Creating an unprivileged Linux domain (domU)  Creating an unprivileged Linux domain (domU)
Line 854  NetBSD as a domU in a VPS Line 951  NetBSD as a domU in a VPS
 The bulk of the HOWTO is about using NetBSD as a dom0 on your own  The bulk of the HOWTO is about using NetBSD as a dom0 on your own
 hardware.  This section explains how to deal with Xen in a domU as a  hardware.  This section explains how to deal with Xen in a domU as a
 virtual private server where you do not control or have access to the  virtual private server where you do not control or have access to the
 dom0.  dom0.  This is not intended to be an exhaustive list of VPS providers;
   only a few are mentioned that specifically support NetBSD.
   
 VPS operators provide varying degrees of access and mechanisms for  VPS operators provide varying degrees of access and mechanisms for
 configuration.  The big issue is usually how one controls which kernel  configuration.  The big issue is usually how one controls which kernel
 is booted, because the kernel is nominally in the dom0 filesystem (to  is booted, because the kernel is nominally in the dom0 filesystem (to
 which VPS users do not normally have acesss).  which VPS users do not normally have acesss).  A second issue is how
   to install NetBSD.
 A VPS user may want to compile a kernel for security updates, to run  A VPS user may want to compile a kernel for security updates, to run
 npf, run IPsec, or any other reason why someone would want to change  npf, run IPsec, or any other reason why someone would want to change
 their kernel.  their kernel.
   
 One approach is to have an adminstrative interface to upload a kernel,  One approach is to have an adminstrative interface to upload a kernel,
 or to select from a prepopulated list.  or to select from a prepopulated list.  Other approaches are pygrub
   (deprecated) and pvgrub, which are ways to have a bootloader obtain a
   kernel from the domU filesystem.  This is closer to a regular physical
   computer, where someone who controls a machine can replace the kernel.
   
   A second issue is multiple CPUs.  With NetBSD 6, domUs support
   multiple vcpus, and it is typical for VPS providers to enable multiple
   CPUs for NetBSD domUs.
   
   pygrub
   -------
   
   pygrub runs in the dom0 and looks into the domU filesystem.  This
   implies that the domU must have a kernel in a filesystem in a format
   known to pygrub.  As of 2014, pygrub seems to be of mostly historical
   interest.
   
 Otehr approaches are pvgrub and py-grub, which are ways to start a  pvgrub
 bootloader from the dom0 instead of the actual domU kernel, and for  ------
 that loader to then load a kernel from the domU filesystem.  This is  
 closer to a regular physical computer, where someone who controls a  
 machine can replace the kernel.  
   
 prmgr and pvgrub  pvgrub is a version of grub that uses PV operations instead of BIOS
 ----------------  calls.  It is booted from the dom0 as the domU kernel, and then reads
   /grub/menu.lst and loads a kernel from the domU filesystem.
   
   [Panix](http://www.panix.com/) lets users use pvgrub.  Panix reports
   that pvgrub works with FFsv2 with 16K/2K and 32K/4K block/frag sizes
   (and hence with defaults from "newfs -O 2").  See [Panix's pvgrub
   page](http://www.panix.com/v-colo/grub.html), which describes only
   Linux but should be updated to cover NetBSD :-).
   
   [prgmr.com](http://prgmr.com/) also lets users with pvgrub to boot
   their own kernel.  See then [prgmr.com NetBSD
   HOWTO](http://wiki.prgmr.com/mediawiki/index.php/NetBSD_as_a_DomU)
   (which is in need of updating).
   
   It appears that [grub's FFS
   code](http://xenbits.xensource.com/hg/xen-unstable.hg/file/bca284f67702/tools/libfsimage/ufs/fsys_ufs.c)
   does not support all aspects of modern FFS, but there are also reports
   that FFSv2 works fine.  At prgmr, typically one has an ext2 or FAT
   partition for the kernel with the intent that grub can understand it,
   which leads to /netbsd not being the actual kernel.  One must remember
   to update the special boot partiion.
   
 TODO: Perhaps reference panix, prmgr, amazon as interesting examples.  Amazon
 Explain what prmgr does.  ------
   
   TODO: add link to NetBSD amazon howto.
   
 Using npf  Using npf
 ---------  ---------
   
 In standard kernels, npf is a module, and thus cannot be loadeed in a  In standard kernels, npf is a module, and thus cannot be loaded in a
 DOMU kernel.  DOMU kernel.
   
 TODO: explain how to compile npf into a custom kernel, answering:  TODO: explain how to compile npf into a custom kernel, answering (but
   note that the problem was caused by not booting the right kernel):
 http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html  http://mail-index.netbsd.org/netbsd-users/2014/12/26/msg015576.html
   
   TODO items for improving NetBSD/xen
   ===================================
   
   * Make the NetBSD dom0 kernel work with SMP.
   * Test the Xen 4.5 packages adequately to be able to recommend them as
     the standard approach.
   * Get PCI passthrough working on Xen 4.5
   * Get pvgrub into pkgsrc, either via xentools or separately.
   * grub
     * Check/add support to pkgsrc grub2 for UFS2 and arbitrary
       fragsize/blocksize (UFS2 support may be present; the point is to
       make it so that with any UFS1/UFS2 filesystem setup that works
       with NetBSD grub will also work).
       See [pkg/40258](http://gnats.netbsd.org/40258).
     * Push patches upstream.
     * Get UFS2 patches into pvgrub.
   * Add support for PV ops to a version of /boot, and make it usable as
     a kernel in Xen, similar to pvgrub.
   * Solve somehow the issue with modules for GENERIC not being loadable
     in a Xen dom0 or domU kernel.
   
   Random pointers
   ===============
   
   TODO: This section contains links from elsewhere not yet integrated
   into the HOWTO.
   
   * http://www.lumbercartel.ca/library/xen/
   * http://pbraun.nethence.com/doc/sysutils/xen_netbsd_dom0.html

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  Added in v.1.93


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