Xen devel - Jul 2005 - How is a file-backed FreeBSD filesystem mounted for a FreeBSD XenU?

> Now, since the system isn''t in production yet I''d like to
show a FreeBSD
> XenU instance running so that I can show the rest of the staff to convince
> them of the benefits of running Xen servers, even if they insist on
> continuing to run FreeBSD for all servers.
Cool :-)
> I''ve examined the XenDemo CD and the FreeBSD filesystem and XenU
there, but
> for the life of me I cannot figure out how the FreeBSD filesystem (on the
> CD as /freebsd.fs) is handed to the FreeBSD XenU kernel to be mounted.
> I''ve been able to mount the /root.fs filesystem under FC4
("mount -o loop
> root.fs /debian.root"), but that doesn''t work for the
/freebsd.fs file,
> even using the "-t ufs -o ufstype=44bsd" options.  I also
don''t know how to
> mount it on our FreeBSD systems.
Just a guess: if the FreeBSD rootfs is sliced (BSD partitions) then
won''t
Linux have trouble mounting it?
> 1) How is /freebsd.fs hooked to the FreeBSD XenU on the XenDemo CD?  If I
> know how this is done I can do a quick demo of a FreeBSD XenU on our Linux
> FC4 system.
The same way you''d hook a disk file to a Linux domU: add a 
''file:/blah/blah/foo,target_dev,w'' to the disks line in the
config file.  I''m
not sure what syntax is supported for specifying the target dev for FreeBSD.  
the FreeBSD config file on the demo CD should be useful as a template.

Doing this causes the file to be attached as to a block loop in dom0 - this 
block device is then exported to BSD, which can use it like any other block 
device.

I''d suggest that to start with you copy the filesystem image from the
demo CD,
tweak the config file from the CD and then try and start a domain using that.

Does that answer your question?

Cheers,
Mark
> 2) An alternative method would be to use an NFS mounted root filesystem
> served from one of our FreeBSD servers.  The easiest and quickest
> filesystem to use would be the /freebsd.fs or Kip Macy''s mdroot
file system
> from http://www.fsmware.com/xenofreebsd/5.3/.  How do you mount a file-back
> filesystem under FreeBSD?
>
> Thank you much,
>
> David Schmidt
> NOC Analyst - Northwest Open Access Network
> dschmidt@noanet.net  1-866-662-6380
>
> There are 10 types of people in this world.  Those that understand binary
> and those that do not.
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
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I work in a shop that is predominately FreeBSD.  However, Xen offers a number of
benefits over running FreeBSD jails for virtual hosts.

We recently came upon a requirement for a Linux server to run some commercial
software and I managed to get enough time with it before the commercial software
arrived to install Fedora Core 4 and Xen.  So now I have a Xen0 running FC4, a
XenU running FC3 (because the vendor wouldn''t verify the product could
run under FC4 <sigh>).  The commercial software is installed on the XenU
instance and appears to be running fine.  The system is not in production use
while the software is being configured.

Now, since the system isn''t in production yet I''d like to show
a FreeBSD XenU instance running so that I can show the rest of the staff to
convince them of the benefits of running Xen servers, even if they insist on
continuing to run FreeBSD for all servers.

I''ve examined the XenDemo CD and the FreeBSD filesystem and XenU there,
but for the life of me I cannot figure out how the FreeBSD filesystem (on the CD
as /freebsd.fs) is handed to the FreeBSD XenU kernel to be mounted.

I''ve been able to mount the /root.fs filesystem under FC4 ("mount
-o loop root.fs /debian.root"), but that doesn''t work for the
/freebsd.fs file, even using the "-t ufs -o ufstype=44bsd" options.  I
also don''t know how to mount it on our FreeBSD systems.

So, I have the following questions:

1) How is /freebsd.fs hooked to the FreeBSD XenU on the XenDemo CD?  If I know
how this is done I can do a quick demo of a FreeBSD XenU on our Linux FC4
system.

2) An alternative method would be to use an NFS mounted root filesystem served
from one of our FreeBSD servers.  The easiest and quickest filesystem to use
would be the /freebsd.fs or Kip Macy''s mdroot file system from
http://www.fsmware.com/xenofreebsd/5.3/.  How do you mount a file-back
filesystem under FreeBSD?

Thank you much,

David Schmidt
NOC Analyst - Northwest Open Access Network
dschmidt@noanet.net  1-866-662-6380

There are 10 types of people in this world.  Those that understand binary and
those that do not.



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> > I''ve been able to mount the /root.fs filesystem under FC4
("mount -o
> > loop root.fs /debian.root"), but that doesn''t work for
the
> > /freebsd.fs file, even using the "-t ufs -o ufstype=44bsd"
options.
> > I also don''t know how to mount it on our FreeBSD systems.
> 
> Just a guess: if the FreeBSD rootfs is sliced (BSD partitions) then
> won''t  Linux have trouble mounting it?
The FreeBSD rootfs is indeed sliced. Note in /sbin/start_freebsd.sh that
it maps the filesystem to hda rather than to hda1 as you usually would.
> > 1) How is /freebsd.fs hooked to the FreeBSD XenU on the XenDemo CD? 
> > If I know how this is done I can do a quick demo of a FreeBSD XenU
> > on our Linux FC4 system.
> 
> The same way you''d hook a disk file to a Linux domU: add a 
> ''file:/blah/blah/foo,target_dev,w'' to the disks line in
the config
> file.  I''m  not sure what syntax is supported for specifying the
> target dev for FreeBSD.   the FreeBSD config file on the demo CD
> should be useful as a template.
The demo CD uses some exciting DM snapshotting to produce a CoW
filesystem so it''s probably not that useful as a config template.
I''m
not a FreeBSD user myself, but if you want to give it a file on a proper
filesystem as file-backed storage, file:/freebsd.fs,hda,w should just
work AFAIK.
> I''d suggest that to start with you copy the filesystem image from
the
> demo CD,
I''d agree with this suggestion, but the filesystem on the demo CD
doesn''t appear to boot under Xen unstable at the moment. This could be
just me, though, I''ll have to check it more fully.

HTH,
Daniel

-- 
"The  rules  of  programming  are  transitory;  only  Tao  is  eternal.
 Therefore you  must contemplate Tao before you receive  enlightenment."
"How will I know when I have received enlightenment?"  asked the
novice.
"Your program will then run correctly," replied the master.


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