Re: [PATCH v4 2/2] ovl: enable fsnotify events on underlying real files

[Jan Kara <jack@suse.cz>]

On Wed 14-06-23 10:49:07, Amir Goldstein wrote:
> Overlayfs creates the real underlying files with fake f_path, whose
> f_inode is on the underlying fs and f_path on overlayfs.
> 
> Those real files were open with FMODE_NONOTIFY, because fsnotify code was
> not prapared to handle fsnotify hooks on files with fake path correctly
> and fanotify would report unexpected event->fd with fake overlayfs path,
> when the underlying fs was being watched.
> 
> Teach fsnotify to handle events on the real files, and do not set real
> files to FMODE_NONOTIFY to allow operations on real file (e.g. open,
> access, modify, close) to generate async and permission events.
> 
> Because fsnotify does not have notifications on address space
> operations, we do not need to worry about ->vm_file not reporting
> events to a watched overlayfs when users are accessing a mapped
> overlayfs file.
> 
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>

Looks good to me. Feel free to add:

Acked-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/overlayfs/file.c      | 4 ++--
>  include/linux/fsnotify.h | 3 ++-
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 8cf099aa97de..1fdfc53f1207 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -34,8 +34,8 @@ static char ovl_whatisit(struct inode *inode, struct inode *realinode)
>  		return 'm';
>  }
>  
> -/* No atime modification nor notify on underlying */
> -#define OVL_OPEN_FLAGS (O_NOATIME | FMODE_NONOTIFY)
> +/* No atime modification on underlying */
> +#define OVL_OPEN_FLAGS (O_NOATIME)
>  
>  static struct file *ovl_open_realfile(const struct file *file,
>  				      const struct path *realpath)
> diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
> index bb8467cd11ae..6f6cbc2dc49b 100644
> --- a/include/linux/fsnotify.h
> +++ b/include/linux/fsnotify.h
> @@ -91,7 +91,8 @@ static inline void fsnotify_dentry(struct dentry *dentry, __u32 mask)
>  
>  static inline int fsnotify_file(struct file *file, __u32 mask)
>  {
> -	const struct path *path = &file->f_path;
> +	/* Overlayfs internal files have fake f_path */
> +	const struct path *path = f_real_path(file);
>  
>  	if (file->f_mode & FMODE_NONOTIFY)
>  		return 0;
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR