linux-kernel - Re: [PATCH 01/10] ovl: small optimisation for ovl

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Message-Id: <E1Osf0g-0005it-BZ@pomaz-ex.szeredi.hu>
Date:	Mon, 06 Sep 2010 18:57:34 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	NeilBrown <neilb@...e.de>
CC:	miklos@...redi.hu, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/10] ovl: small optimisation for ovl_lookup

On Mon, 06 Sep 2010, NeilBrown wrote:
> If we find a non-directory in the upper layer, there is no point
> performing a lookup in the lower layer as whatever is found will just
> be ignored anyway.
> 
> Signed-off-by: NeilBrown <neilb@...e.de>
> ---
>  fs/overlayfs/overlayfs.c |   17 ++++++++---------
>  1 files changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/overlayfs/overlayfs.c b/fs/overlayfs/overlayfs.c
> index 0fe3944..0ddfeec 100644
> --- a/fs/overlayfs/overlayfs.c
> +++ b/fs/overlayfs/overlayfs.c
> @@ -495,7 +495,8 @@ static struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
>  				dput(upperdentry);
>  				upperdentry = NULL;
>  				ue->opaque = true;
> -			}
> +			} else if (!S_ISDIR(upperdentry->d_inode->i_mode))
> +				ue->opaque = true;

Setting opaque unconditionally, without checking whether the lower
file exists or not, means on unlink we'll create a whiteout even when
not necessary.

Thanks,
Miklos
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