linux-kernel - Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount

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Date:   Thu, 2 Mar 2017 12:06:57 -0500
From:   Vivek Goyal <vgoyal@...hat.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Djalal Harouni <tixxdz@...il.com>, Chris Mason <clm@...com>,
        Theodore Tso <tytso@....edu>,
        Josh Triplett <josh@...htriplett.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andy Lutomirski <luto@...nel.org>,
        Seth Forshee <seth.forshee@...onical.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Dongsu Park <dongsu@...ocode.com>,
        David Herrmann <dh.herrmann@...glemail.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Alban Crequy <alban.crequy@...il.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Phil Estes <estesp@...il.com>,
        Amir Goldstein <amir73il@...il.com>
Subject: Re: [RFC v2 1/1] shiftfs: uid/gid shifting bind mount

On Mon, Feb 20, 2017 at 04:47:05PM -0800, James Bottomley wrote:

[..]
> +static int shiftfs_readlink(struct dentry *dentry, char __user *data,
> +			    int flags)
> +{
> +	struct dentry *real = dentry->d_fsdata;
> +	const struct inode_operations *iop = real->d_inode->i_op;
> +
> +	if (iop->readlink)
> +		return iop->readlink(real, data, flags);
> +
> +	return -EINVAL;
> +}
> +

Hi James,

I was testing shiftfs on top of xfs and noticed readlink() is failing as
xfs does not define readlink. 

Following patch fixes it for me.

Vivek

---
 fs/shiftfs.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

Index: rhvgoyal-linux/fs/shiftfs.c
===================================================================
--- rhvgoyal-linux.orig/fs/shiftfs.c	2017-02-28 11:07:04.360579594 -0500
+++ rhvgoyal-linux/fs/shiftfs.c	2017-03-02 11:59:17.484345405 -0500
@@ -179,12 +179,8 @@ static int shiftfs_readlink(struct dentr
 			    int flags)
 {
 	struct dentry *real = dentry->d_fsdata;
-	const struct inode_operations *iop = real->d_inode->i_op;
 
-	if (iop->readlink)
-		return iop->readlink(real, data, flags);
-
-	return -EINVAL;
+	return vfs_readlink(real, data, flags);
 }
 
 static const char *shiftfs_get_link(struct dentry *dentry, struct inode *inode,