Re: [linux-lvm] LVM2 modifies the buffer_head struct?

[Jens Axboe]

On Thu, Jul 04 2002, Andrew Morton wrote:
> Jens Axboe wrote:
> > 
> > ...
> > > We just want ext3/jbd to make sure that it only calls bh2jh on
> > > an unlocked buffer... is that easy?
> > 
> > That's the question indeed, someone with a good grasp of jbd should make
> > that call. If that is the only 'violator' (depending on your point of
> > view), then yes lets just fix that up and say that the above is pb
> > private is valid.
> 
> We really don't want to do this, please.  Changing things so
> that we can only run bh2jh() and, particularly, journal_add_journal_head()
> on a locked buffer would involve fairly unpleasant surgery against
> parts of ext3 which are already prone to exploding.  Like
> do_get_write_access().
> 
> If it was needed for 2.5 then hmm, maybe.  But as this is only a
> 2.4 problem then I really don't think we should risk breaking
> or slowing down the filesystem for this.
> 
> Look, it's easy: delete buffer_head.b_inode (which is only used as 
> a boolean), move its function to a b_state bit.  Add a new
> buffer_head.ext3_hack and we can use that for pointing at the journal_head.

Thank you, this is what I was looking for (if you look further up, I was
advocating this very thing). Slimming down buffer_head and just add the
ext3 hack is perfectly acceptable to me.

Which just means that device mapper needs to do the stacking properly,
EOD.

-- 
Jens Axboe