linux-kernel - Re: [PATCH 04/12] fsnotify: support overlayfs

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Date:   Fri, 16 Sep 2016 18:38:07 +0200
From:   Jan Kara <jack@...e.cz>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org,
        Aihua Zhang <zhangaihua1@...wei.com>,
        linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.cz>, Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH 04/12] fsnotify: support overlayfs

On Fri 16-09-16 14:19:23, Miklos Szeredi wrote:
> From: Aihua Zhang <zhangaihua1@...wei.com>
> 
> When an event occurs direct it to the overlay inode instead of the real
> underlying inode.
> 
> This will work even if the file was first on the lower layer and then
> copied up, while the watch is there.  This is because the watch is on the
> overlay inode, which stays the same through the copy-up.
> 
> For filesystems other than overlayfs this is a no-op, except for the
> performance impact of an extra pointer dereferece.
> 
> Verified to work correctly with the inotify/fanotify tests in LTP.
> 
> Signed-off-by: Aihua Zhang <zhangaihua1@...wei.com>
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Eric Paris <eparis@...hat.com>
> ---
>  include/linux/fsnotify.h | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
> index eed9e853a06f..b8bcc058e031 100644
> --- a/include/linux/fsnotify.h
> +++ b/include/linux/fsnotify.h
> @@ -29,7 +29,11 @@ static inline int fsnotify_parent(struct path *path, struct dentry *dentry, __u3
>  static inline int fsnotify_perm(struct file *file, int mask)
>  {
>  	struct path *path = &file->f_path;
> -	struct inode *inode = file_inode(file);
> +	/*
> +	 * Do not use file_inode() here or anywhere in this file to get the
> +	 * inode.  That would break *notity on overlayfs.
> +	 */
> +	struct inode *inode = path->dentry->d_inode;

So shouldn't we rather have d_backing_inode(path->dentry) here and
everywhere else?

									Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR