Re: [Xen-devel] [PATCH] libfsimage: add ext4 support for CentOS 5.x

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Thu, Sep 06, 2012 at 08:23:05AM +0100, Ian Campbell wrote:
> On Wed, 2012-09-05 at 21:55 +0100, Pasi Kärkkäinen wrote:
> > On Wed, Sep 05, 2012 at 07:04:49PM +0100, Ian Campbell wrote:
> > > On Wed, 2012-09-05 at 13:03 +0100, Roger Pau Monne wrote:
> > > > CentOS 5.x forked e2fs ext4 support into a different package called
> > > > e4fs, and so headers and library names changed from ext2fs to ext4fs.
> > > > Check if ext4fs/ext2fs.h and -lext4fs work, and use that instead of
> > > > ext2fs to build libfsimage. This patch assumes that if the ext4fs
> > > > library is present it should always be used instead of ext2fs.
> > > > 
> > > > This patch includes a rework of the ext2fs check, a new ext4fs check
> > > > and a minor modification in libfsimage to use the correct library.
> > > > 
> > > > Signed-off-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> > > 
> > > Thanks.
> > > 
> > > Any patch which is intended for 4.2 at this stage needs to come with
> > > some rationale as to why it is acceptable at this late stage.
> > > 
> > 
> > rhel5/centos5 has a lot of Xen users, so it'd be nice if those people
> > could build Xen 4.2 from sources and still have pygrub ext4 support.
> 
> I'm sorry but two days (now one day) before the final RC we need more
> justification than "it would be nice".
> 

I understand that. 

> Who are these people? How many of them are there? Why are they doing
> this? If you are building from source what reason is there to be using
> RHEL5?
> 
> We certainly don't seem to be getting bugs reports (either on -devel@ or
> -users@) about this problem.
> 

Ok, so it'd be mostly *CentOS5* users, who don't have the support contracts 
anyway.
I'm not able to give you any numbers. I hit this issue myself,
so I thought it'd be nice to get it fixed in upstream Xen aswell. 


> > (the stock redhat el5 Xen 3.1.2 rpms have similar tweaks and 
> > they do provide pygrub ext4 support out-of-the-box on el5).
> > 
> > Also XenServer/XCP has hacks to get pygrub ext4 support enabled in similar 
> > way,
> > so it'd make sense to fix/workaround this properly in Xen upstream.
> 
> This seems right and proper to me and isn't an argument for us taking
> and carry this hack in our tree.
> 
> IMHO the presence of libe4fs in RHEL5 is a distro specific packaging
> hack and it is appropriate that the fallout be dealt with via RHEL5
> specific packaging hacks.
> 

The patch that Roger submitted is dealing with this in a nice way though.. 
Or was there something wrong with the patch? 


> > > Therefore unless someone can argue convincingly for it this is 4.3
> > > material.
> > > 
> > 
> > I'm not expecting that was convincing enough :) so if not 4.2.0 then 4.3 
> > and 4.2.1 ? 
> 
> Perhaps. I'm not entirely convinced of the need at all though. If RHEL5
> was the current release then maybe, but RHEL6 is nearly two years old at
> this point.
> 

RHEL5 has "Production Phase" support until 2017. It's still getting 
improvements and new features in 5.x point releases, and still keeping 
the ABI stable and compatible with earlier 5.x versions; 
that's why the e4fs stuff exists in the first place - to not break the ABI.

Next year it'll transform into "security maintenance and minor fixes"-mode.


-- Pasi


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