linux-kernel - Re: [PATCH v2] fs: add file

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Message-ID: <CAJ75kXZ+QFait-h--dAixE462XL00frBCxnvSBN+rQo3nSXrEw@mail.gmail.com>
Date:	Wed, 23 Mar 2016 15:06:20 +0100
From:	William Dauchy <wdauchy@...il.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	linux-unionfs@...r.kernel.org, David Howells <dhowells@...hat.com>,
	Goldwyn Rodrigues <rgoldwyn@...e.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"Theodore Ts'o" <tytso@....edu>, Daniel Axtens <dja@...ens.net>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] fs: add file_dentry()

Hello Miklos,

On Wed, Mar 23, 2016 at 2:36 PM, Miklos Szeredi <miklos@...redi.hu> wrote:
> This series fixes bugs in nfs and ext4 due to 4bacc9c9234c ("overlayfs:
> Make f_path always point to the overlay and f_inode to the underlay").
>
> Regular files opened on overlayfs will result in the file being opened on
> the underlying filesystem, while f_path points to the overlayfs
> mount/dentry.
>
> This confuses filesystems which get the dentry from struct file and assume
> it's theirs.
>
> Add a new helper, file_dentry() [*], to get the filesystem's own dentry
> from the file.  This checks file->f_path.dentry->d_flags against
> DCACHE_OP_REAL, and returns file->f_path.dentry if DCACHE_OP_REAL is not
> set (this is the common, non-overlayfs case).
>
> In the uncommon case it will call into overlayfs's ->d_real() to get the
> underlying dentry, matching file_inode(file).
>
> The reason we need to check against the inode is that if the file is copied
> up while being open, d_real() would return the upper dentry, while the open
> file comes from the lower dentry.
>
> [*] If possible, it's better simply to use file_inode() instead.
>
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> Tested-by: Goldwyn Rodrigues <rgoldwyn@...e.com>
> Reviewed-by: Trond Myklebust <trond.myklebust@...marydata.com>
> Cc: <stable@...r.kernel.org> # v4.2

4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and
f_inode to the underlay").
This commit is from v4.1 if I am not wrong. So the stable tag might be wrong.

Am I missing something?
-- 
William