new helper: __dentry_path()

builds path relative to fs root, called under dcache_lock,
doesn't append any nonsense to unlinked ones.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

@@ -2049,16 +2049,12 @@ char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
 /*
  * Write full pathname from the root of the filesystem into the buffer.
  */
-char *dentry_path(struct dentry *dentry, char *buf, int buflen)
+char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
 {
 	char *end = buf + buflen;
 	char *retval;
 
-	spin_lock(&dcache_lock);
 	prepend(&end, &buflen, "\0", 1);
-	if (d_unlinked(dentry) &&
-		(prepend(&end, &buflen, "//deleted", 9) != 0))
-			goto Elong;
 	if (buflen < 1)
 		goto Elong;
 	/* Get '/' right */
@@ -2076,7 +2072,28 @@ char *dentry_path(struct dentry *dentry, char *buf, int buflen)
 		retval = end;
 		dentry = parent;
 	}
+	return retval;
+Elong:
+	return ERR_PTR(-ENAMETOOLONG);
+}
+EXPORT_SYMBOL(__dentry_path);
+
+char *dentry_path(struct dentry *dentry, char *buf, int buflen)
+{
+	char *p = NULL;
+	char *retval;
+
+	spin_lock(&dcache_lock);
+	if (d_unlinked(dentry)) {
+		p = buf + buflen;
+		if (prepend(&p, &buflen, "//deleted", 10) != 0)
+			goto Elong;
+		buflen++;
+	}
+	retval = __dentry_path(dentry, buf, buflen);
 	spin_unlock(&dcache_lock);
+	if (!IS_ERR(retval) && p)
+		*p = '/';	/* restore '/' overriden with '\0' */
 	return retval;
 Elong:
 	spin_unlock(&dcache_lock);

include/linux/dcache.h

@@ -315,6 +315,7 @@ extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
 
 extern char *__d_path(const struct path *path, struct path *root, char *, int);
 extern char *d_path(const struct path *, char *, int);
+extern char *__dentry_path(struct dentry *, char *, int);
 extern char *dentry_path(struct dentry *, char *, int);
 
 /* Allocation counts.. */