Re: [PATCH 23/39] ovl: add O_DIRECT support

[Al Viro <viro@xxxxxxxxxxxxxxxxxx>]

On Tue, May 29, 2018 at 04:43:23PM +0200, Miklos Szeredi wrote:
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
>  fs/overlayfs/file.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 3f610a5b38e4..e5e7ccaaf9ec 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -110,6 +110,9 @@ static int ovl_open(struct inode *inode, struct file *file)
>  	if (IS_ERR(realfile))
>  		return PTR_ERR(realfile);
>  
> +	/* For O_DIRECT dentry_open() checks f_mapping->a_ops->direct_IO */
> +	file->f_mapping = realfile->f_mapping;

Umm...  What happens if upper layer doesn't allow O_DIRECT, while the lower one does?