vfs: check i_nlink limits in vfs_{mkdir,rename_dir,link}

New field of struct super_block - ->s_max_links.  Maximal allowed
value of ->i_nlink or 0; in the latter case all checks still need
to be done in ->link/->mkdir/->rename instances.  Note that this
limit applies both to directoris and to non-directories.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ext2/namei.c b/fs/ext2/namei.c
index 0804198..dffb865 100644
--- a/fs/ext2/namei.c
+++ b/fs/ext2/namei.c
@@ -195,9 +195,6 @@
 	struct inode *inode = old_dentry->d_inode;
 	int err;
 
-	if (inode->i_nlink >= EXT2_LINK_MAX)
-		return -EMLINK;
-
 	dquot_initialize(dir);
 
 	inode->i_ctime = CURRENT_TIME_SEC;
@@ -217,10 +214,7 @@
 static int ext2_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
 {
 	struct inode * inode;
-	int err = -EMLINK;
-
-	if (dir->i_nlink >= EXT2_LINK_MAX)
-		goto out;
+	int err;
 
 	dquot_initialize(dir);
 
@@ -346,11 +340,6 @@
 			drop_nlink(new_inode);
 		inode_dec_link_count(new_inode);
 	} else {
-		if (dir_de) {
-			err = -EMLINK;
-			if (new_dir->i_nlink >= EXT2_LINK_MAX)
-				goto out_dir;
-		}
 		err = ext2_add_link(new_dentry, old_inode);
 		if (err)
 			goto out_dir;