Re: [PATCH 1/4] vfs: add file_dentry()

[Theodore Ts'o <tytso@mit.edu>]

On Thu, Mar 17, 2016 at 10:02:00AM +0100, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@redhat.com>
> 
> 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 simply compares file_inode(file->f_path.dentry) to
> file_inode(file) and if they are equal returns file->f_path.dentry (this is
> the common, non-overlayfs case).
> 
> In the uncommon case (regular file on overlayfs) it will call into
> overlayfs's ->d_native_dentry() to get the underlying dentry matching
> file_inode(file).
> 
> [*] If possible, it's better simply to use file_inode() instead.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> Tested-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> Reviewed-by: Trond Myklebust <trond.myklebust@primarydata.com>
> Cc: <stable@vger.kernel.org> # v4.2
> Cc: David Howells <dhowells@redhat.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Daniel Axtens <dja@axtens.net>
> ---
>  fs/open.c              | 11 +++++++++++
>  fs/overlayfs/super.c   | 16 ++++++++++++++++
>  include/linux/dcache.h |  1 +
>  include/linux/fs.h     |  2 ++
>  4 files changed, 30 insertions(+)

I have this patch in the ext4.git tree, but I'd like to get an
Acked-by from Al before I send a pull request to Linus.

Al?  Any objections to my sending in this change via the ext4 tree?

						- Ted

> 
> diff --git a/fs/open.c b/fs/open.c
> index 55bdc75e2172..6326c11eda78 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -831,6 +831,17 @@ char *file_path(struct file *filp, char *buf, int buflen)
>  }
>  EXPORT_SYMBOL(file_path);
>  
> +struct dentry *file_dentry(const struct file *file)
> +{
> +	struct dentry *dentry = file->f_path.dentry;
> +
> +	if (likely(d_inode(dentry) == file_inode(file)))
> +		return dentry;
> +	else
> +		return dentry->d_op->d_native_dentry(dentry, file_inode(file));
> +}
> +EXPORT_SYMBOL(file_dentry);
> +
>  /**
>   * vfs_open - open the file at the given path
>   * @path: path to open
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 619ad4b016d2..5142aa2034c4 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -336,14 +336,30 @@ static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
>  	return ret;
>  }
>  
> +static struct dentry *ovl_d_native_dentry(struct dentry *dentry,
> +					 struct inode *inode)
> +{
> +	struct ovl_entry *oe = dentry->d_fsdata;
> +	struct dentry *realentry = ovl_upperdentry_dereference(oe);
> +
> +	if (realentry && inode == d_inode(realentry))
> +		return realentry;
> +	realentry = __ovl_dentry_lower(oe);
> +	if (realentry && inode == d_inode(realentry))
> +		return realentry;
> +	BUG();
> +}
> +
>  static const struct dentry_operations ovl_dentry_operations = {
>  	.d_release = ovl_dentry_release,
>  	.d_select_inode = ovl_d_select_inode,
> +	.d_native_dentry = ovl_d_native_dentry,
>  };
>  
>  static const struct dentry_operations ovl_reval_dentry_operations = {
>  	.d_release = ovl_dentry_release,
>  	.d_select_inode = ovl_d_select_inode,
> +	.d_native_dentry = ovl_d_native_dentry,
>  	.d_revalidate = ovl_dentry_revalidate,
>  	.d_weak_revalidate = ovl_dentry_weak_revalidate,
>  };
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index c4b5f4b3f8f8..99ecb6de636c 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -161,6 +161,7 @@ struct dentry_operations {
>  	struct vfsmount *(*d_automount)(struct path *);
>  	int (*d_manage)(struct dentry *, bool);
>  	struct inode *(*d_select_inode)(struct dentry *, unsigned);
> +	struct dentry *(*d_native_dentry)(struct dentry *, struct inode *);
>  } ____cacheline_aligned;
>  
>  /*
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index ae681002100a..1091d9f43271 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1234,6 +1234,8 @@ static inline struct inode *file_inode(const struct file *f)
>  	return f->f_inode;
>  }
>  
> +extern struct dentry *file_dentry(const struct file *file);
> +
>  static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
>  {
>  	return locks_lock_inode_wait(file_inode(filp), fl);
> -- 
> 2.1.4
>