[PATCH v6 4/9] ovl: return anonymous st_dev for lower inodes

[Amir Goldstein <amir73il@gmail.com>]

From: Chandan Rajendra <chandan@linux.vnet.ibm.com>

For non-samefs setup, to make sure that st_dev/st_ino pair
is unique across the system, we return a unique anonymous
st_dev for stat(2) of lower layer inode.

We need to make this change before fixing constant st_dev/st_ino across
copy up for non-samefs. Otherwise, we can end up with two objects
in the system, the real lower inode and the overlay inode which
have same st_dev/st_ino value, but different content.

[amir: simplify ovl_get_pseudo_dev()
       split from allocate anonymous bdev patch]

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/overlayfs/inode.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index b772e5a2a730..607a50c50042 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -15,6 +15,14 @@
 #include <linux/ratelimit.h>
 #include "overlayfs.h"
 
+
+static dev_t ovl_get_pseudo_dev(struct dentry *dentry)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+
+	return oe->lowerstack[0].layer->pseudo_dev;
+}
+
 int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 {
 	int err;
@@ -121,6 +129,13 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 		 */
 		stat->dev = dentry->d_sb->s_dev;
 		stat->ino = dentry->d_inode->i_ino;
+	} else if (!OVL_TYPE_UPPER(type)) {
+		/*
+		 * For non-samefs setup, to make sure that st_dev/st_ino pair
+		 * is unique across the system, we use a unique anonymous
+		 * st_dev for lower layer inode.
+		 */
+		stat->dev = ovl_get_pseudo_dev(dentry);
 	}
 
 	/*
-- 
2.7.4