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

[Oren Laadan <orenl@cs.columbia.edu>]

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().

Oren.

>   	mutex_unlock(&inode->i_mutex);
>   	if (!error)
>   		fsnotify_link(dir, inode, new_dentry);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index ee725ff..d932eb7 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1528,6 +1528,7 @@ struct inode_operations {
>   	int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
>   	struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameidata *);
>   	int (*link) (struct dentry *,struct inode *,struct dentry *);
> +	int (*relink) (struct dentry *,struct inode *,struct dentry *);
>   	int (*unlink) (struct inode *,struct dentry *);
>   	int (*symlink) (struct inode *,struct dentry *,const char *);
>   	int (*mkdir) (struct inode *,struct dentry *,int);