linux-ext4 - Re: [PATCH v2 09/28] libext2fs: handle inline data in dir iterator function

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Message-ID: <20131204062142.GB26103@gmail.com>
Date:	Wed, 4 Dec 2013 14:21:42 +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 v2 09/28] libext2fs: handle inline data in dir iterator
 function

On Tue, Dec 03, 2013 at 10:07:42PM -0800, Darrick J. Wong wrote:
> On Wed, Dec 04, 2013 at 01:26:19PM +0800, Zheng Liu wrote:
> > On Tue, Dec 03, 2013 at 09:10:25PM -0800, Darrick J. Wong wrote:
> > > On Wed, Dec 04, 2013 at 12:57:36PM +0800, Zheng Liu wrote:
> > > > On Tue, Dec 03, 2013 at 02:13:49PM -0800, Darrick J. Wong wrote:
> > > > > On Tue, Dec 03, 2013 at 08:11:36PM +0800, Zheng Liu wrote:
> > > > > > From: Zheng Liu <wenqing.lz@...bao.com>
> > > > > > 
> > > > > > Inline_data is handled in dir iterator because a lot of commands use
> > > > > > this function to traverse directory entries in debugfs.  We need to
> > > > > > handle inline_data individually because inline_data is saved in two
> > > > > > places.  One is in i_block, and another is in ibody extended attribute.
> > > > > > 
> > > > > > After applied this commit, the following commands in debugfs can
> > > > > > support the inline_data feature:
> > > > > > 	- cd
> > > > > > 	- chroot
> > > > > > 	- link*
> > > > > > 	- ls
> > > > > > 	- ncheck
> > > > > > 	- pwd
> > > > > > 	- unlink
> > > > > > 
> > > > > > * TODO: Inline_data doesn't expand to ibody extended attribute because
> > > > > >   link command doesn't handle DIR_NO_SPACE error until now.  But if we
> > > > > >   have already expanded inline data to ibody ea area, link command can
> > > > > >   occupy this space.
> > > > > 
> > > > > A patch for this TODO is coming, right?
> > > > 
> > > > TBH, I don't have a patch for this because I don't know why ext2fs_link
> > > > doesn't handle DIR_NO_SPACE error.  So I will try to fix it later.
> > > 
> > > Yeah, it's sort of annoying that it doesn't do that.  You might notice that
> > > fuse2fs will detect that error code, call ext2fs_expand_dir(), and try again.
> > > On the other hand, none of the other programs do that...
> > > 
> > > ...it's not difficult to change ext2fs_link() to do that, though.
> > > 
> > > again:
> > > 
> > > /* link_proc magic... */
> > > 
> > > if (!ls.done && !not_again) {
> > > 	ext2fs_expand_dir(fs, dir...);
> > > 	not_again = 1;
> > > 	goto again;
> > > }
> > > 
> > > Hmm.  That /is/ easy to fix.  I might as well fix that.
> > 
> > I don't think we should fix it in ext2fs_link because I am afraid that
> > we could break the client that has handled this problem.  So I am plan
> > to fix it in make_link().  What do you think?
> 
> I think the clients will be fine.  Most likely, if the dir can't be expanded,
> then ext2fs_link will return ext2fs_expand_directory's failure code.
> 
> On the off chance there's a weird bug somewhere such that we successfully
> expand the dir but _link's built-in retry fails again, then the client will see
> the "no dir space" error, expand the dir (again!), and retry the link, which
> will again fail.  Assuming the client doesn't madly retry in a loop, all that
> means is that we bang our heads against the wall a few more times than we need
> to.
> 
> Luckily, most of the _link clients in the e2fsprogs source are too stupid even
> to expand-and-retry.

OK.  So let me fix it. :)

                                                - Zheng
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