[PATCH v3 14/16] ovl: fix du --one-file-system on overlay mount

[Amir Goldstein <amir73il@gmail.com>]

Overlay directory inodes report overlay bdev to stat(2).
Overlay non-dir inodes report real bdev and real ino to stat(2).

Due to the different bdev values for dir and non-dir inodes, when executing
the command du -x on an overlay mount, the result is wrong because non-dirs
are not accounted for in the overlay bdev usage.

The reasons for this bdev inconsistecy is:
1. The overlay ino is not persistent, so real ino is used for non-dirs
2. The tupple overlay bdev and real ino is not unique, so real bdev is
   used for non-dirs

In case all overlay layers are on the same underlying fs, the tupple
from reason 2 above is unique, so use this tupple for non-dirs to get
the correct result from du -x.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/overlayfs/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 3615a52..39c3bb0 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -78,6 +78,13 @@ static int ovl_getattr(const struct path *path, struct kstat *stat,
 		stat->dev = lower->d_sb->s_dev;
 		stat->ino = lower->d_inode->i_ino;
 	}
+	/*
+	 * When all layers are on same fs, the tupple overlay bdev
+	 * and real inode ino is unique, so it is preferred to expose
+	 * overlay bdev for overlay inodes for things like du -x.
+	 */
+	if (ovl_same_sb(dentry->d_sb))
+		stat->dev = dentry->d_sb->s_dev;
 
 	return err;
 }
-- 
2.7.4