@@ -35,16 +40,16 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen)
  *
  * Load acquire is needed to make sure that we see that terminating NUL.
  */
-static int prepend_name(char **buffer, int *buflen, const struct qstr *name)
+static int prepend_name(struct prepend_buffer *b, const struct qstr *name)
 {
 	const char *dname = smp_load_acquire(&name->name); /* ^^^ */
 	u32 dlen = READ_ONCE(name->len);
 	char *p;
 
-	*buflen -= dlen + 1;
-	if (*buflen < 0)
+	b->len -= dlen + 1;
+	if (b->len < 0)
 		return -ENAMETOOLONG;
-	p = *buffer -= dlen + 1;
+	p = b->ptr -= dlen + 1;
 	*p++ = '/';
 	while (dlen--) {
 		char c = *dname++;

@@ -55,6 +60,50 @@ static int prepend_name(char **buffer, int *buflen, const struct qstr *name)
 	return 0;
 }
 
+static inline int prepend_entries(struct prepend_buffer *b, const struct path *path, const struct path *root, struct mount *mnt)
+{
+	struct dentry *dentry = path->dentry;
+	struct vfsmount *vfsmnt = path->mnt;
+
+	while (dentry != root->dentry || vfsmnt != root->mnt) {
+		int error;
+		struct dentry * parent;
+
+		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
+			struct mount *parent = READ_ONCE(mnt->mnt_parent);
+			struct mnt_namespace *mnt_ns;
+
+			/* Escaped? */
+			if (dentry != vfsmnt->mnt_root)
+				return 3;
+
+			/* Global root? */
+			if (mnt != parent) {
+				dentry = READ_ONCE(mnt->mnt_mountpoint);
+				mnt = parent;
+				vfsmnt = &mnt->mnt;
+				continue;
+			}
+			mnt_ns = READ_ONCE(mnt->mnt_ns);
+			/* open-coded is_mounted() to use local mnt_ns */
+			if (!IS_ERR_OR_NULL(mnt_ns) && !is_anon_ns(mnt_ns))
+				return 1;	// absolute root
+
+			return 2;		// detached or not attached yet
+			break;
+		}
+		parent = dentry->d_parent;
+		prefetch(parent);
+		error = prepend_name(b, &dentry->d_name);
+		if (error)
+			break;
+
+		dentry = parent;
+	}
+	return 0;
+}

+
 /**
  * prepend_path - Prepend path string to a buffer
  * @path: the dentry/vfsmount to report

@@ -74,15 +123,12 @@ static int prepend_name(char **buffer, int *buflen, const struct qstr *name)
  */
 static int prepend_path(const struct path *path,
 			const struct path *root,
-			char **buffer, int *buflen)
+			struct prepend_buffer *orig)
 {
-	struct dentry *dentry;
-	struct vfsmount *vfsmnt;
 	struct mount *mnt;
 	int error = 0;
 	unsigned seq, m_seq = 0;
-	char *bptr;
-	int blen;
+	struct prepend_buffer b;
 
 	rcu_read_lock();
 restart_mnt:

@@ -90,50 +136,12 @@ static int prepend_path(const struct path *path,
 	seq = 0;
 	rcu_read_lock();
 restart:
-	bptr = *buffer;
-	blen = *buflen;
-	error = 0;
-	dentry = path->dentry;
-	vfsmnt = path->mnt;
-	mnt = real_mount(vfsmnt);
+	b = *orig;
+	mnt = real_mount(path->mnt);
 	read_seqbegin_or_lock(&rename_lock, &seq);
-	while (dentry != root->dentry || vfsmnt != root->mnt) {
-		struct dentry * parent;
 
-		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
-			struct mount *parent = READ_ONCE(mnt->mnt_parent);
-			struct mnt_namespace *mnt_ns;
+	error = prepend_entries(&b, path, root, mnt);
 
-			/* Escaped? */
-			if (dentry != vfsmnt->mnt_root) {
-				bptr = *buffer;
-				blen = *buflen;
-				error = 3;
-				break;
-			}
-			/* Global root? */
-			if (mnt != parent) {
-				dentry = READ_ONCE(mnt->mnt_mountpoint);
-				mnt = parent;
-				vfsmnt = &mnt->mnt;
-				continue;
-			}
-			mnt_ns = READ_ONCE(mnt->mnt_ns);
-			/* open-coded is_mounted() to use local mnt_ns */
-			if (!IS_ERR_OR_NULL(mnt_ns) && !is_anon_ns(mnt_ns))
-				error = 1;	// absolute root
-			else
-				error = 2;	// detached or not attached yet
-			break;
-		}
-		parent = dentry->d_parent;
-		prefetch(parent);
-		error = prepend_name(&bptr, &blen, &dentry->d_name);
-		if (error)
-			break;
-
-		dentry = parent;
-	}
 	if (!(seq & 1))
 		rcu_read_unlock();
 	if (need_seqretry(&rename_lock, seq)) {

@@ -150,14 +158,17 @@ static int prepend_path(const struct path *path,
 	}
 	done_seqretry(&mount_lock, m_seq);
 
-	if (error >= 0 && bptr == *buffer) {
-		if (--blen < 0)
+	// Escaped? No path
+	if (error == 3)
+		b = *orig;
+
+	if (error >= 0 && b.ptr == orig->ptr) {
+		if (--b.len < 0)
 			error = -ENAMETOOLONG;
 		else
-			*--bptr = '/';
+			*--b.ptr = '/';
 	}
-	*buffer = bptr;
-	*buflen = blen;
+	*orig = b;
 	return error;
 }
 

@@ -181,34 +192,34 @@ char *__d_path(const struct path *path,
 	       const struct path *root,
 	       char *buf, int buflen)
 {
-	char *res = buf + buflen;
+	struct prepend_buffer b = { buf + buflen, buflen };
 	int error;
 
-	prepend(&res, &buflen, "\0", 1);
-	error = prepend_path(path, root, &res, &buflen);
+	prepend(&b, "\0", 1);
+	error = prepend_path(path, root, &b);