linux-ext4 - Re: [PATCH v1 15/22] tune2fs: add inline

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Message-ID: <20131012083307.GE6462@gmail.com>
Date:	Sat, 12 Oct 2013 16:33:07 +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>
Subject: Re: [PATCH v1 15/22] tune2fs: add inline_data feature in tune2fs

On Sat, Oct 12, 2013 at 01:23:15AM -0700, Darrick J. Wong wrote:
> On Sat, Oct 12, 2013 at 04:16:38PM +0800, Zheng Liu wrote:
> > On Fri, Oct 11, 2013 at 05:39:45PM -0700, Darrick J. Wong wrote:
> > > On Fri, Aug 02, 2013 at 05:49:42PM +0800, Zheng Liu wrote:
> > > > From: Zheng Liu <wenqing.lz@...bao.com>
> > > > 
> > > > Inline_data feature can be set when ext_attr feature is enabled.  Now this
> > > > feature only can be enabled because we may be out of space when disabling
> > > > it.  If this feature is disabled, we need to allocate a block for every
> > > > file and directory, and it might exhaust all space.
> > > > 
> > > > Signed-off-by: Theodore Ts'o <tytso@....edu>
> > > > Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
> > > > ---
> > > >  misc/tune2fs.8.in |    5 +++++
> > > >  misc/tune2fs.c    |   17 ++++++++++++++++-
> > > >  2 files changed, 21 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/misc/tune2fs.8.in b/misc/tune2fs.8.in
> > > > index 55c6dd9..b768fff 100644
> > > > --- a/misc/tune2fs.8.in
> > > > +++ b/misc/tune2fs.8.in
> > > > @@ -531,6 +531,11 @@ Setting the filesystem feature is equivalent to using the
> > > >  .B \-j
> > > >  option.
> > > >  .TP
> > > > +.B inline_data
> > > > +Allow data to be stored in inode.
> > > > +.B Tune2fs
> > > > +only supports setting this filesystem feature.
> > > > +.TP
> > > >  .B large_file
> > > >  Filesystem can contain files that are greater than 2GB.  (Modern kernels
> > > >  set this feature automatically when a file > 2GB is created.)
> > > > diff --git a/misc/tune2fs.c b/misc/tune2fs.c
> > > > index 7d6520e..f22a736 100644
> > > > --- a/misc/tune2fs.c
> > > > +++ b/misc/tune2fs.c
> > > > @@ -137,7 +137,8 @@ static __u32 ok_features[3] = {
> > > >  	EXT2_FEATURE_INCOMPAT_FILETYPE |
> > > >  		EXT3_FEATURE_INCOMPAT_EXTENTS |
> > > >  		EXT4_FEATURE_INCOMPAT_FLEX_BG |
> > > > -		EXT4_FEATURE_INCOMPAT_MMP,
> > > > +		EXT4_FEATURE_INCOMPAT_MMP |
> > > > +		EXT4_FEATURE_INCOMPAT_INLINE_DATA,
> > > >  	/* R/O compat */
> > > >  	EXT2_FEATURE_RO_COMPAT_LARGE_FILE |
> > > >  		EXT4_FEATURE_RO_COMPAT_HUGE_FILE|
> > > > @@ -995,6 +996,20 @@ mmp_error:
> > > >  		disable_uninit_bg(fs,
> > > >  				EXT4_FEATURE_RO_COMPAT_GDT_CSUM);
> > > >  
> > > > +	if (FEATURE_ON(E2P_FEATURE_INCOMPAT,
> > > > +		       EXT4_FEATURE_INCOMPAT_INLINE_DATA)) {
> > > > +		/* Inline_data feature cannot be enabled if ext_attr is
> > > > +		 * disabled.
> > > > +		 */
> > > 
> > > Multiline comment issue.
> > > 
> > > > +		if (!(fs->super->s_feature_compat &
> > > > +		      EXT2_FEATURE_COMPAT_EXT_ATTR)) {
> > > 
> > > EXT2_HAS_COMPAT_FEATURE()?
> > > 
> > > > +			fputs(_("The inline_data feature cannot "
> > > > +				"be set if ext_attr feature is disabled.\n"),
> > > > +				stderr);
> > > > +			return 1;
> > > > +		}
> > > > +	}
> > > > +
> > > 
> > > Maybe I'm missing something, but I don't see anything prohibiting the user from
> > > disabling inline_data?  Or from doing the conversion?
> > 
> > Yes, now in tune2fs we can only enable inline_data feature.  If we want
> > to disable inline_data, that means that we need to allocate a block for
> > every inode with inline data, and we could exhaust all disk space.
> > Another implementation might be just clear inline_data flag from
> > super_block and doesn't allocate a block for these inodes.  The former
> > obviously is not a good choice.  But the latter might be better.  I am
> > really not sure for this.  What do you think?
> 
> I don't think it's a good idea to turn off inline_data once it's been enabled,
> just like we don't let people turn off extents...
> 
> *Oh*, duh, I didn't notice that INLINE_DATA is *NOT* in the clear_ok_features
> list.  Never mind this comment, I'm just making noise.
> 
> (The complaints about the comment issue and not using EXT2_HAS_COMPAT_FEATURE
> remain.)

Got it. :)

                                                - Zheng
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