linux-kernel - Re: [PATCH 16/28] ovl: Do not expose metacopy only dentry from d

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Date:   Wed, 30 May 2018 17:05:56 -0400
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/28] ovl: Do not expose metacopy only dentry from
 d_real()

On Tue, May 29, 2018 at 04:46:00PM +0200, Miklos Szeredi wrote:
> From: Vivek Goyal <vgoyal@...hat.com>
> 
> Metacopy dentry/inode is internal to overlay and is never exposed outside
> of it.  Exception is metacopy upper file used for fsync().  Modify d_real()
> to look for dentries/inode which have data, but also allow matching upper
> inode without data for the fsync case.
> 

Hi Miklos,

I am not able to see how in fsync() path d_real() gets called. If we
decide to do fsync() on upper metacopy, then opening upper will not
go through d_real(). And we never issue fsync() on lower.

So I am scratching my head while trying to understand the d_real() and
fsync() connection.

Thanks
Vivek

> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> Reviewed-by: Amir Goldstein <amir73il@...il.com>
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> ---
>  fs/overlayfs/super.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index e0326a686f45..6687d547ec6b 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -101,10 +101,13 @@ static struct dentry *ovl_d_real(struct dentry *dentry,
>  	}
>  
>  	real = ovl_dentry_upper(dentry);
> -	if (real && (!inode || inode == d_inode(real)))
> +	if (real && (inode == d_inode(real)))
>  		return real;
>  
> -	real = ovl_dentry_lower(dentry);
> +	if (real && !inode && ovl_has_upperdata(d_inode(dentry)))
> +		return real;
> +
> +	real = ovl_dentry_lowerdata(dentry);
>  	if (!real)
>  		goto bug;
>  
> -- 
> 2.14.3
> 
> --
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