-xen config...

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-xen config...

James Harper
I've just noticed that with the 3.0.0 -xen config, ext2 appears to be
compiled into the kernel, but ext3 is only present as a module.

If I use a domU without a ramdisk (as I have been doing), it's not going
to have the ext3 module loaded at boot time and therefore won't mount
the root filesystem as ext3. This may be part of the reason I've been
getting filesystem corruption...

Is there any reason that ext2 is set as 'y' while ext3 is set as 'm'? It
seems to me that they (and the other 'common' filesystems) should be the
same...

Going against the grain of making everything modules, maybe most of the
'common' filesystems should be compiled into the -xen kernel? On the one
hand, an initramfs is a bit of an overkill if all it's doing is loading
in a filesystem module... but on the other hand, we do it for just about
every  other kernel in the linux world!

Comments?

James

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RE: -xen config...

Ian Pratt
> Is there any reason that ext2 is set as 'y' while ext3 is set
> as 'm'? It seems to me that they (and the other 'common'
> filesystems) should be the same...

I agree this is pretty odd. The -xen config was based on one for a
distro kernel, so I think it's standard practice.

Can anyone put forward a good reason not to compile ext3 in?

Ian

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RE: -xen config...

James Harper
In reply to this post by James Harper
> > Is there any reason that ext2 is set as 'y' while ext3 is set
> > as 'm'? It seems to me that they (and the other 'common'
> > filesystems) should be the same...
>
> I agree this is pretty odd. The -xen config was based on one for a
> distro kernel, so I think it's standard practice.
>
> Can anyone put forward a good reason not to compile ext3 in?

Or to exclude ext2 and make everything modular? If you include ext3 then
you probably should be asking do we include xfs, reiser, jfs, etc.

For the tiny amount of administration that an initial ramdisk incurs, it
does buy you a fair bit of flexibility, including the ability to
function as a recovery boot environment if things go sour.

James

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Re: -xen config...

Anthony Liguori
In reply to this post by Ian Pratt
Ian Pratt wrote:

>>Is there any reason that ext2 is set as 'y' while ext3 is set
>>as 'm'? It seems to me that they (and the other 'common'
>>filesystems) should be the same...
>>    
>>
>
>I agree this is pretty odd. The -xen config was based on one for a
>distro kernel, so I think it's standard practice.
>
>Can anyone put forward a good reason not to compile ext3 in?
>  
>
I don't know that it matters, but for what it's worth, this shouldn't
create problems.

ext3 is (almost) backwards compatible with ext2.  ext2 is suffient to
mount the root device such that modules can be loaded (and then the root
filesystem is actually mounted).

If you watch an Ubuntu boot-up, you'll notice that modules are loaded
before the root file system is mounted as ext2.

This is not likely to be the reason you're seeing filesystem corruption
as if there are any problems with the ext3 filesystem, the ext2 driver
will refuse to mount it (complaining that it contains "unsupported
features").

Can you ellaborate on the filesystem corruption problems you have been
seeing?  xm destroy (as opposed to xm shutdown) is an easy way to
corrupt yourself.

Regards,

Anthony

>Ian
>
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>  
>


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RE: -xen config...

Ian Pratt
In reply to this post by James Harper
> >Can anyone put forward a good reason not to compile ext3 in?
> >  
> I don't know that it matters, but for what it's worth, this
> shouldn't create problems.
>
> ext3 is (almost) backwards compatible with ext2.  ext2 is
> suffient to mount the root device such that modules can be
> loaded (and then the root filesystem is actually mounted).

I've seen problems in the past (on native) when the filesystem has not
been shut down cleanly and ext2 didn't want to mount it, and I needed to
create an initrd with ext3 to boot.

Ian

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RE: -xen config...

James Harper
In reply to this post by James Harper
> I don't know that it matters, but for what it's worth, this shouldn't
> create problems.
>
> ext3 is (almost) backwards compatible with ext2.  ext2 is suffient to
> mount the root device such that modules can be loaded (and then the
root
> filesystem is actually mounted).
>
> If you watch an Ubuntu boot-up, you'll notice that modules are loaded
> before the root file system is mounted as ext2.
>
> This is not likely to be the reason you're seeing filesystem
corruption
> as if there are any problems with the ext3 filesystem, the ext2 driver
> will refuse to mount it (complaining that it contains "unsupported
> features").
>
> Can you ellaborate on the filesystem corruption problems you have been
> seeing?  xm destroy (as opposed to xm shutdown) is an easy way to
> corrupt yourself.
>

Just input/output type errors. I'm completely willing to put it down to
abrupt crashes under xen, and am not really concerned about the
corruption itself, it was more just a comment on what triggered me to
notice the module situation.

Per your comments above... are you saying that if the filesystem is
mounted with ext2, you can then remount it with ext3? This would be
contrary to my understanding of how it works.

What happens under Debian (and probably almost all distributions which
use a ramdisk), is that the initramfs is extracted to a ramdisk, enough
modules are loaded to mount the root filesystem, which is then mounted
and control passed to it.

I'm trying out xfs now :)

James


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Re: -xen config...

Gerd Hoffmann
In reply to this post by Ian Pratt
Ian Pratt wrote:
>> Is there any reason that ext2 is set as 'y' while ext3 is set
>> as 'm'? It seems to me that they (and the other 'common'
>> filesystems) should be the same...
>
> I agree this is pretty odd. The -xen config was based on one for a
> distro kernel, so I think it's standard practice.

Bootstrapping issue:  suse did it that way because the initrd loading
driver and filesystem modules used to be ext2-formated ramdisk.  These
days initramfs is used instead, probably suse comes with ext2 being
modular soon ;)

cheers,

   Gerd


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