linux-ext4 - Re: [PATCH 2/6] [RFC] Create the .relink file

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Date:	Wed, 29 Sep 2010 16:07:03 -0700
From:	Matt Helsley <matthltc@...ibm.com>
To:	Oren Laadan <orenl@...columbia.edu>
Cc:	Matt Helsley <matthltc@...ibm.com>,
	containers@...ts.linux-foundation.org, Jan Kara <jack@...e.cz>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-fsdevel@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
	linux-ext4@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Valerie Aurora <vaurora@...hat.com>
Subject: Re: [PATCH 2/6] [RFC] Create the .relink file_operation

On Wed, Sep 29, 2010 at 04:19:31PM -0400, Oren Laadan wrote:
> 
> 
> On 09/23/2010 05:53 PM, Matt Helsley wrote:
> >Not all filesystems will necessarily be able to support relinking an
> >orphan inode back into the filesystem. Some offlist feedback suggested
> >that instead of overloading .link that relinking should be a separate
> >file operation for this reason.
> >
> >Since .relink is a superset of .link make the VFS call .relink where
> >possible and .link otherwise.
> >
> >The next commit will change ext3/4 to enable this operation.
> >
> >Signed-off-by: Matt Helsley<matthltc@...ibm.com>
> >Cc: Theodore Ts'o<tytso@....edu>
> >Cc: Andreas Dilger<adilger.kernel@...ger.ca>
> >Cc: Jan Kara<jack@...e.cz>
> >Cc: linux-fsdevel@...r.kernel.org
> >Cc: linux-ext4@...r.kernel.org
> >Cc: Al Viro<viro@...iv.linux.org.uk>
> >---
> >  fs/namei.c         |    5 ++++-
> >  include/linux/fs.h |    1 +
> >  2 files changed, 5 insertions(+), 1 deletions(-)
> >
> >diff --git a/fs/namei.c b/fs/namei.c
> >index a7dce91..eb279e3 100644
> >--- a/fs/namei.c
> >+++ b/fs/namei.c
> >@@ -2446,7 +2446,10 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
> >  		return error;
> >
> >  	mutex_lock(&inode->i_mutex);
> >-	error = dir->i_op->link(old_dentry, dir, new_dentry);
> >+	if (dir->i_op->relink)
> >+		error = dir->i_op->relink(old_dentry, dir, new_dentry);
> >+	else
> >+		error = dir->i_op->link(old_dentry, dir, new_dentry);
> 
> Can there be a scenario/filesystem in which .relink implementation
> is so much more complex (and expensive) than .link ?
> 
> If the answer is "yes", then this we probably don't want to do
> this, and let vfs_link() call .link, and instead add a new helper
> vfs_relink().

OK, that makes some sense too. I thought the separation would
just be at the file operations layer but we can move it higher too.

I'll adjust the patches to do that and repost them.

Cheers,
	-Matt
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