mount: Add comment to is_root_xxx checks

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

mount.c

@@ -50,11 +50,20 @@ static inline int is_root(char *p)
 	return p[0] == '/' && p[1] == '\0';
 }
 
+/* True for the root mount (the topmost one) */
 static inline int is_root_mount(struct mount_info *mi)
 {
 	return is_root(mi->mountpoint);
 }
 
+/*
+ * True if the mountpoint target is root on its FS.
+ *
+ * This is used to determine whether we need to postpone
+ * mounting. E.g. one can bind mount some subdir from a
+ * disk, and in this case we'll have to get the root disk
+ * mount first, then bind-mount it. See do_mount_one().
+ */
 static inline int fsroot_mounted(struct mount_info *mi)
 {
 	return is_root(mi->root);