linux-kernel - Re: [PATCH 07/38] whiteout: Set S_OPAQUE inode flag when creating directories

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Date:	Tue, 13 Jul 2010 12:05:56 +0800
From:	Ian Kent <raven@...maw.net>
To:	Valerie Aurora <vaurora@...hat.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	Jan Blunck <jblunck@...e.de>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 07/38] whiteout: Set S_OPAQUE inode flag when creating
 directories

On Tue, Jun 15, 2010 at 11:39:37AM -0700, Valerie Aurora wrote:
> From: Jan Blunck <jblunck@...e.de>
> 
> In case of an union directory we don't want that the directories on lower
> layers of the union "show through". So to prevent that the contents of
> underlying directories magically shows up after a mkdir() we set the S_OPAQUE
> flag if directories are created where a whiteout existed before.

I found this hard to understand.

Do you mean:

For directories within a union that are whiteouts we don't want the entries of
lower layer file system to "show through". To achieve this we set the S_OPAQUE
flag after a mkdir() on directories that are whiteouts.

> 
> Signed-off-by: Jan Blunck <jblunck@...e.de>
> Signed-off-by: Valerie Aurora <vaurora@...hat.com>
> ---
>  fs/namei.c         |   11 ++++++++++-
>  include/linux/fs.h |    3 +++
>  2 files changed, 13 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 2c723e2..8c67636 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -2107,6 +2107,7 @@ SYSCALL_DEFINE3(mknod, const char __user *, filename, int, mode, unsigned, dev)
>  int vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
>  {
>  	int error = may_create(dir, dentry);
> +	int opaque = 0;
>  
>  	if (error)
>  		return error;
> @@ -2119,9 +2120,17 @@ int vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
>  	if (error)
>  		return error;
>  
> +	if (d_is_whiteout(dentry))
> +		opaque = 1;
> +
>  	error = dir->i_op->mkdir(dir, dentry, mode);
> -	if (!error)
> +	if (!error) {
>  		fsnotify_mkdir(dir, dentry);
> +		if (opaque) {
> +			dentry->d_inode->i_flags |= S_OPAQUE;
> +			mark_inode_dirty(dentry->d_inode);
> +		}
> +	}
>  	return error;
>  }
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 7afdbd4..e9aa650 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -236,6 +236,7 @@ struct inodes_stat_t {
>  #define S_NOCMTIME	128	/* Do not update file c/mtime */
>  #define S_SWAPFILE	256	/* Do not truncate: swapon got its bmaps */
>  #define S_PRIVATE	512	/* Inode is fs-internal */
> +#define S_OPAQUE	1024	/* Directory is opaque */
>  
>  /*
>   * Note that nosuid etc flags are inode-specific: setting some file-system
> @@ -271,6 +272,8 @@ struct inodes_stat_t {
>  #define IS_SWAPFILE(inode)	((inode)->i_flags & S_SWAPFILE)
>  #define IS_PRIVATE(inode)	((inode)->i_flags & S_PRIVATE)
>  
> +#define IS_OPAQUE(inode)	((inode)->i_flags & S_OPAQUE)
> +
>  /* the read-only stuff doesn't really belong here, but any other place is
>     probably as bad and I don't want to create yet another include file. */
>  
> -- 
> 1.6.3.3
> 
> --
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