linux-ext4 - Re: [PATCH v2 19/28] mke2fs: add inline

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Message-ID: <20131204055051.GA25689@gmail.com>
Date:	Wed, 4 Dec 2013 13:50:52 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	Zheng Liu <wenqing.lz@...bao.com>, Tao Ma <tm@....ma>
Subject: Re: [PATCH v2 19/28] mke2fs: add inline_data support in mke2fs

[Cc Tao to get some comments]

On Tue, Dec 03, 2013 at 09:26:08PM -0800, Darrick J. Wong wrote:
> On Wed, Dec 04, 2013 at 01:21:50PM +0800, Zheng Liu wrote:
> > On Tue, Dec 03, 2013 at 08:08:19PM -0800, Darrick J. Wong wrote:
> > > On Wed, Dec 04, 2013 at 11:27:57AM +0800, Zheng Liu wrote:
> > > > On Tue, Dec 03, 2013 at 02:30:26PM -0800, Darrick J. Wong wrote:
> > > > [...]
> > > > > > +		 * notify users that inline data will never be useful.
> > > > > > +		 */
> > > > > > +		if ((fs_param.s_feature_incompat &
> > > > > > +		     EXT4_FEATURE_INCOMPAT_INLINE_DATA) &&
> > > > > > +		    inode_size == EXT2_GOOD_OLD_INODE_SIZE) {
> > > > > 
> > > > > Perhaps I'm missing something here, but why is it impossible to use i_blocks
> > > > > for inline data even if there's no space for EAs?
> > > > 
> > > > If I understand correctly, on kernel side, we determine an inode has
> > > > inline data according to whether we have 'system.data' xattr entry on
> > > > inode extended attribute space.  If an inode doesn't have enough space
> > > > to store an entry with 'system.data', we just think this inode doesn't
> > > > has inline data.  So that is why I add this sanity check.
> > > 
> > > Ok.  I was curious.  Small inode => no inline data seems like an unfortunate
> > > restriction to me, but oh well, it's your feature.  I don't plan to go back to
> > > 128 byte inodes ever. :)
> > > 
> > > Also, we could store four more bytes if we created a new e_name_index value (5?
> > > 9?) to represent "system.data".  Any thoughts about that?
> > 
> > Sorry, I don't get your point.  Do you want to create a new e_name_index?
> > Any reason lets you want to do this?
> 
> Yep, that's exactly what I propose to do, so we can cram four more bytes into
> the inline data.

Agree.  I believe it is fine.  But I am wondering if it will break the
file system that inline data has been enabled.

                                                - Zheng
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