[PATCH 06/11] UBUNTU: ubuntu: overlayfs -- overlayfs: add statfs support

[Paolo Pisati]

From: Andy Whitcroft <apw at canonical.com>

Add support for statfs to the overlayfs filesystem.  As the upper layer
is the target of all write operations assume that the space in that
filesystem is the space in the overlayfs.  There will be some inaccuracy as
overwriting a file will copy it up and consume space we were not expecting,
but it is better than nothing.

Use the upper layer dentry and mount from the overlayfs root inode,
passing the statfs call to that filesystem.

Signed-off-by: Andy Whitcroft <apw at canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi at suse.cz>
Signed-off-by: Andy Whitcroft <apw at canonical.com>
(cherry picked from commit 3a375b0e617e3f8a54619d0d569fb2918c379289)

BugLink: http://bugs.launchpad.net/bugs/1076317

Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 fs/overlayfs/super.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 18042cf..8091f76 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -404,9 +404,29 @@ static int ovl_remount_fs(struct super_block *sb, int *flagsp, char *data)
 		return mnt_want_write(ufs->upper_mnt);
 }
 
+/**
+ * ovl_statfs
+ * @sb: The overlayfs super block
+ * @buf: The struct kstatfs to fill in with stats
+ *
+ * Get the filesystem statistics.  As writes always target the upper layer
+ * filesystem pass the statfs to the same filesystem.
+ */
+static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
+{
+	struct dentry *root_dentry = dentry->d_sb->s_root;
+	struct path path;
+	ovl_path_upper(root_dentry, &path);
+
+	if (!path.dentry->d_sb->s_op->statfs)
+		return -ENOSYS;
+	return path.dentry->d_sb->s_op->statfs(path.dentry, buf);
+}
+
 static const struct super_operations ovl_super_operations = {
 	.put_super	= ovl_put_super,
 	.remount_fs	= ovl_remount_fs,
+	.statfs		= ovl_statfs,
 };
 
 struct ovl_config {
-- 
1.7.10.4