Re: [PATCH 2/6] [RFC] Create the .relink file_operation

[Matt Helsley <matthltc@us.ibm.com>]

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@us.ibm.com>
> >Cc: Theodore Ts'o<tytso@mit.edu>
> >Cc: Andreas Dilger<adilger.kernel@dilger.ca>
> >Cc: Jan Kara<jack@suse.cz>
> >Cc: linux-fsdevel@vger.kernel.org
> >Cc: linux-ext4@vger.kernel.org
> >Cc: Al Viro<viro@zeniv.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