uclibc-dom0/xen 2.0.5 trivia

uclibc-dom0/xen 2.0.5 trivia

[Yvette]

Uclibc seems to come up occasionally in the lists, and since I use one
of my uclibc-based build images as a domU,  I thought I'd see for
myself if "no reason Xen _shouldn't work with a uclibc-based dom0"
meant that it _would_ work. (It's quite likely this has already been
addressed and I just missed it.) Admittedly I haven't stress-tested
the result, but the uclibc-based system seems to boot and bring up my
domains as well as the glibc-based one I normally use.

This was Xen 2.0.5, uclibc-snapshot circa July 2004, gcc 3.3.4 and
otherwise relatively standard components. I had to use a few normal
uclibc-type workarounds to get Xen to build (my image has the library
cache disabled, so any Xen check/build scripts that use "ldconfig -p |
grep something.so" fail; xentrace uses some things from argp, so one
would have  to get by without it or use the stand-alone),  but not
many.

Clearly this begs the question of if anybody would need or want such a
system. (I didn't, but now I have one...)

-Yvette


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Re: uclibc-dom0/xen 2.0.5 trivia

[Jacob Gorm Hansen]

Yvette wrote:

> Clearly this begs the question of if anybody would need or want such a
> system. (I didn't, but now I have one...)

Yes please, though for me I would want to use this with vm-tools rather 
than the Python toolset. I've done a busybox dom0 myself, but that was 
in the old world where very few user-space tools were needed, and they 
were simple enough that you could easily roll your own. How large are 
your changes to the standard xen tree?

Jacob


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Re: uclibc-dom0/xen 2.0.5 trivia

[Anthony Liguori]

Jacob Gorm Hansen wrote:

> Yvette wrote:
>
>> Clearly this begs the question of if anybody would need or want such a
>> system. (I didn't, but now I have one...)
>
>
> Yes please, though for me I would want to use this with vm-tools 
> rather than the Python toolset. I've done a busybox dom0 myself, but 
> that was in the old world where very few user-space tools were needed, 
> and they were simple enough that you could easily roll your own. How 
> large are your changes to the standard xen tree?

libxc builds quite fine against uClibc as does vm-tools.  I use it 
busybox imagine (with uClibc) quite frequently for testing and development.

It's quite trivial to setup.  Once the wiki goes live I'd be happy to 
post a howto there.

Regards,
Anthony Liguori

> Jacob
>
>
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Re: uclibc-dom0/xen 2.0.5 trivia

[Yvette]

On Sun, 20 Mar 2005 23:35:21 -0600, Anthony Liguori <aliguori@us.ibm.com> wrote:
> 
> libxc builds quite fine against uClibc as does vm-tools.  I use it
> busybox imagine (with uClibc) quite frequently for testing and development.
> 
> It's quite trivial to setup.  Once the wiki goes live I'd be happy to
> post a howto there.
> 
> Regards,
> Anthony Liguori
> 

Yes, other than what I originally mentioned, there really weren't any
issues/modifications. Now I just need to wait for the howto to see
what I missed...

-Yvette


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Re: uclibc-dom0/xen 2.0.5 trivia

[Jacob Gorm Hansen]

Anthony Liguori wrote:

 > libxc builds quite fine against uClibc as does vm-tools.  I use it
 > busybox imagine (with uClibc) quite frequently for testing and 
development.

Did you try how small you could make dom0 by any chance?

Jacob


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Re: uclibc-dom0/xen 2.0.5 trivia

[Anthony Liguori]

Jacob Gorm Hansen wrote:

> Anthony Liguori wrote:
>
> > libxc builds quite fine against uClibc as does vm-tools.  I use it
> > busybox imagine (with uClibc) quite frequently for testing and 
> development.
>
> Did you try how small you could make dom0 by any chance?

root@codemonkey.ws rh# df
/xen/rockhopper.img       3963      1666      2093  45% /xen/rh

So a bit over 1.5MB.  I must admit, while the prospect of a super-small 
dom0 is quite appealing, using a ramdisk just hasn't proved to be all 
that useful.

The thing that always comes back to bite me too is that I cannot get X 
to start in a domU.  If I could get that to work it might be practical.

Obviously, the key to getting things to build so small is to use busybox 
and uClibc but another important tip is to be very careful about what 
goes in /dev.  /dev can eat a ton of space in certain file systems.

Regards,
Anthony Liguori

> Jacob
>
>
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Re: uclibc-dom0/xen 2.0.5 trivia

[Jacob Gorm Hansen]

Anthony Liguori wrote:

> root@codemonkey.ws rh# df
> /xen/rockhopper.img       3963      1666      2093  45% /xen/rh
> 
> So a bit over 1.5MB.  I must admit, while the prospect of a super-small 
> dom0 is quite appealing, using a ramdisk just hasn't proved to be all 
> that useful.
> 
> The thing that always comes back to bite me too is that I cannot get X 
> to start in a domU.  If I could get that to work it might be practical.

I guess this is more interesting when running a bunch of headless nodes. 
  How little memory can your dom0 survive on?

Jacob


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Re: uclibc-dom0/xen 2.0.5 trivia

[Anthony Liguori]

Jacob Gorm Hansen wrote:

> Anthony Liguori wrote:
>
>> The thing that always comes back to bite me too is that I cannot get 
>> X to start in a domU.  If I could get that to work it might be 
>> practical.
>
>
> I guess this is more interesting when running a bunch of headless 
> nodes.  How little memory can your dom0 survive on?

Hard to say.  It could be tuned a lot more than it is (especially wrt to 
the kernel config).  With a standard Xen kernel I can balloon down to 
12MB and things seem ok.

Ballooning down to 8MB leads to the OOM killer kicking in.

I reckon 16MB is probably a reasonable foot print to shoot for in the 
future.  My goal is to, at some point, build an LVM-aware ramdisk that's 
under 4MB with a full Xen management toolset on it.

Regards,
Anthony Liguori

> Jacob
>
>
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