[PATCH v11 12/18] ovl: Get and install lower most data dentry in stack

[Vivek Goyal <vgoyal@redhat.com>]

Now we want to support midlayer metacopy dentry as well. To support that
we need to find out lowest data dentry and keep track of that too so that
later it can be used for data copy up.

Introduce logic to traverse through metacopies and find and install the
lowest data ovl_path in stack.

This patch does it only for upper dentry at this point of time. Next patch
will introduce this logic for the cases when upper does not exist.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 fs/overlayfs/namei.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 77 insertions(+), 3 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index ddb73b5a06d4..e26c0bdf0381 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -205,7 +205,7 @@ static int ovl_check_metacopy_xattr(struct dentry *dentry)
 }
 
 static int ovl_check_metacopy(struct ovl_fs *ofs, struct dentry *dentry,
-			      unsigned int ctr)
+			      unsigned int numlower, bool is_upper)
 {
 	int metacopy;
 
@@ -213,7 +213,7 @@ static int ovl_check_metacopy(struct ovl_fs *ofs, struct dentry *dentry,
 	if (metacopy <= 0 )
 		return metacopy;
 
-	if (!ctr) {
+	if (is_upper && !numlower) {
 		/*
 		 * Found a upper dentry with metacopy set but at the same
 		 * time there is no corresponding origin dentry. Something
@@ -236,6 +236,77 @@ static int ovl_check_metacopy(struct ovl_fs *ofs, struct dentry *dentry,
 	return metacopy;
 }
 
+/*
+ * Returns < 0 upon error, 0 if dentry does not have metacopy xattr, 1 if
+ * dentry has metacopy xattr.
+ */
+static int ovl_get_metacopy_chain(struct ovl_fs *ofs,
+			      struct dentry *upperdentry,
+			      struct ovl_path *lower, unsigned int numlower,
+			      struct ovl_path *stackp, unsigned int *ctrp)
+{
+	int metacopy = 0, i, err;
+	struct dentry *origin = NULL, *parent;
+	struct vfsmount *mnt;
+
+	if (upperdentry) {
+		metacopy = ovl_check_metacopy(ofs, upperdentry, *ctrp, true);
+		if (metacopy <= 0 )
+			return metacopy;
+	}
+
+	/*
+	 * Expecting one dentry in stackp[0] and lowest data will be installed
+	 * at stackp[1], if appropriate./
+	 */
+	BUG_ON(*ctrp != 1);
+	err = ovl_check_metacopy(ofs, stackp[0].dentry, *ctrp, false);
+	if (err < 0)
+		return err;
+
+	if (!err)
+		return metacopy;
+
+	parent = stackp[0].dentry;
+	dget(parent);
+
+	/* Get the data dentry corresponding to metacopy dentry */
+	for (i = 0; i < numlower; i++) {
+		mnt = lower[i].layer->mnt;
+		origin = ovl_get_origin(parent, mnt);
+		if (IS_ERR(origin)) {
+			dput(parent);
+			return PTR_ERR(origin);
+		}
+
+		if (origin) {
+			err = ovl_check_metacopy_xattr(origin);
+			if (err < 0) {
+				dput(parent);
+				dput(origin);
+				return err;
+			}
+
+			if (err) {
+				dput(parent);
+				parent = origin;
+				origin = NULL;
+				continue;
+			}
+			break;
+		}
+	}
+
+	dput(parent);
+	if (!origin)
+		return -ESTALE;
+
+	stackp[1].dentry = origin;
+	stackp[1].layer = lower[i].layer;
+	*ctrp += 1;
+	return 1;
+}
+
 static bool ovl_is_opaquedir(struct dentry *dentry)
 {
 	return ovl_check_dir_xattr(dentry, OVL_XATTR_OPAQUE);
@@ -699,7 +770,10 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			if (err)
 				goto out_put_upper;
 
-			err = ovl_check_metacopy(ofs, upperdentry, ctr);
+			err = ovl_get_metacopy_chain(ofs, upperdentry,
+						     roe->lowerstack,
+						     roe->numlower, stack,
+						     &ctr);
 			metacopy = err;
 			if (err < 0)
 				goto out_put_upper;
-- 
2.13.6