linux-kernel - Re: fs: Remove ext3 filesystem driver In-Reply-To: <20150715124709.GA11446@...ck.suse.cz>

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Message-ID: <20150722174010.GJ17243@quack.suse.cz>
Date:	Wed, 22 Jul 2015 19:40:10 +0200
From:	Jan Kara <jack@...e.cz>
To:	Dimitri John Ledkov <dimitri.j.ledkov@...ux.intel.com>
Cc:	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: fs: Remove ext3 filesystem driver In-Reply-To:
 <20150715124709.GA11446@...ck.suse.cz>

  Hello,

On Wed 22-07-15 15:49:51, Dimitri John Ledkov wrote:
> So I did a trimmed export of the patch from repository pointed out, and I have a comment about the config change below. I'm pretty sure i probably got the headers wrong, so sorry if i break threading with this email.
> 
> On 18/06/15 15:52, Jan Kara wrote:
> > The functionality of ext3 is fully supported by ext4 driver. Major
> > distributions (SUSE, RedHat) already use ext4 driver to handle ext3
> > filesystems for quite some time. There is some ugliness in mm resulting
> > from jbd cleaning buffers in a dirty page without cleaning page dirty
> > bit and also support for buffer bouncing in the block layer when stable
> > pages are required is there only because of jbd. So let's remove the
> > ext3 driver.
> > 
> > Signed-off-by: Jan Kara <jack@...e.cz>
> > 
> > diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
> > index bf8bc8a..8be84ad 100644
> > --- a/fs/ext4/Kconfig
> > +++ b/fs/ext4/Kconfig
> > @@ -28,14 +28,14 @@ config EXT4_FS
> >  
> >  	  If unsure, say N.
> >  
> > -config EXT4_USE_FOR_EXT23
> > +config EXT4_USE_FOR_EXT2
> >  	bool "Use ext4 for ext2/ext3 file systems"
> >  	depends on EXT4_FS
> > -	depends on EXT3_FS=n || EXT2_FS=n
> > +	depends on EXT2_FS=n
> >  	default y
> >  	help
> > -	  Allow the ext4 file system driver code to be used for ext2 or
> > -	  ext3 file system mounts.  This allows users to reduce their
> > +	  Allow the ext4 file system driver code to be used for ext2
> > +	  file system mounts.  This allows users to reduce their
> >  	  compiled kernel size by using one file system driver for
> >  	  ext2, ext3, and ext4 file systems.
> 
> I would prefer not to change the config option name or text, and only
> change the depends. Cause ext4 driver in fact can be used for ext2/3, and
> can be used for ext2 or ext3 system mounts. The fact that there isn't an
> ext3 module anymore, doesn't change ext4 driver.

But the fact is that even if this config option will be disabled, ext4 will
still be used for handling ext3 filesystems. That's the reason why I
changed the config name and description. And in the last patch of the
series you can see I've somewhat updated ext4 description to make it
clearer it's used for ext3 as well.
 
> I presume this option will remain even when both ext2 and ext3 drivers
> get dropped, such that one can toggle off ext2/3 portions of ext4 driver.
> Or am I wrong?

I don't plan this option to remain if we ever drop ext2 codebase as well.
We don't have anything like "ext2" or "ext3" portion of the ext4 driver
(well, we do but it's like 30 lines of code) because from the fs driver
point of view it's all the same filesystem just with particular on
filesystem features being disabled or enabled...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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