Re: [uml-devel] UML development, anyone?

[Sakari Ailus <sakari.ailus@iki.fi>]

Hi Boaz,

Boaz Harrosh wrote:
> On 08/31/2010 01:17 AM, Sakari Ailus wrote:
>> Hello all,
>>
>> I'm a long-time UML user and lately I've become a bit worried on the
>> state of the UML. This list, as well as the -user one, is very quiet
>> these days. Is there someone still actively developing the UML? I have
>> to say I really like it! Running Linux on Linux reliably and
>> efficiently, just what I need! :-)
>>
>> I'm currently running three UML virtual machines on an server using
>> Athlon XP-M. The host is running 2.6.31 and the guests are 2.6.27.
>>
>> I cannot upgrade neither host nor guests due to these problems:
>>
>> - SKAS 3 patches available up to 2.6.31 only. Merging this to current
>> kernel might not be a problem, just some work, but:
>>
>> - Severe data corruption on guest on recent guest kernel versions. I'm
>> using a few hard disk partitions directly for UML guests. Something
>> after 2.6.27 guest breaks this quite badly. Even for small data sets
>> like 100 MiB, copying a file to a different location on guest and then
>> running md5sum on both often produces a different result.
>>
>> Do I have any options than to switch to Qemu and suffer the performance
>> penalty from emulation (kqemu is obsolete, too) or to switch to newer
>> hardware that supports kvm? Qemu performance is somewhat less than 10 %
>> of the native (or UML) performance.
>>
>> I also found something called lguest but haven't given it a try yet.
>> Looks the most interesting but that doesn't seem to have much list
>> activity either. So it works perfectly for almost everyone or has few
>> users... ;)
>>
>> How are others coping in the current situation? Or is it just me who has
>> these troubles...?
>>
>
> I hear you ...
>
> I'm using UML for years, as my developing platform for new Kernel code.
> You can imagine how it shortens the development cycle. For guests I must
> use the absolute newest Kernel all the time. So ...
>
> - Please send a detailed bug report about that data corruption so someone
>    can reproduce it. I'm not sure what block device you are using but it has
>    a bug. If you have a good version 2.6.27 and a bad version 2.6.28. It should
>    be easy to "git bisect" to the exact patch that broke the system, and should
>    be easy to fix. (Tell me if you need help, it's easy really)

I did write about this back then but it seems no-one else had the same 
problem. It's one thing to find it and the other to fix it. My wild 
guess is that it's not a change to that actual driver that broke it.

> - I probably don't have your problem because in my UMLs /home is an NFS
>    mount to the office /home server. And any other data intensive work
>    is done over iscsi mounts. Look into iscsi Qemu mangament tools , they
>    should work well for UML as well. (Note you'll need to kconfig scsi and
>    iscsi in your guest compile, they are off by default)
>    (The general rule is any UML specific drivers tend to rot faster then
>     any generic driver like iscsi or nfs)

Using NFS root would indeed be another option.

> - SKAS 3: haaa SKAS3, that one is abandoned. It will need a maintainer to
>    get it alive again. How much better is it? do you have some numbers.
>    (I never used it, the all point was to keep the desktop (host) with a
>    distro Kernel, nvidia and all that)

SKAS4 was supposed to replace it and I think I even used it for a while 
but the current SKAS4 patch is even older than SKAS3. SKAS 4, as far as 
I understand, would be a long-term solution since the /dev/mm approach 
of SKAS 3 wasn't accepted by Linus.

<URL:http://user-mode-linux.sourceforge.net/old/skas.html>

You do need that to get decent performance with UML and at some point 
some years ago perhaps, I couldn't get it even working without.

Regards,

-- 
Sakari Ailus
sakari.ailus@iki.fi

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