xen/sched: only allow schedulers with all mandatory functions available

Some functions of struct scheduler are mandatory. Test those in the
scheduler initialization loop to be present and drop schedulers not
complying.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>

xen/common/schedule.c

@@ -1727,9 +1727,33 @@ void __init scheduler_init(void)
 
     for ( i = 0; i < NUM_SCHEDULERS; i++)
     {
+#define sched_test_func(f)                               \
+        if ( !schedulers[i]->f )                         \
+        {                                                \
+            printk("scheduler %s misses .%s, dropped\n", \
+                   schedulers[i]->opt_name, #f);         \
+            schedulers[i] = NULL;                        \
+        }
+
+        sched_test_func(init);
+        sched_test_func(deinit);
+        sched_test_func(pick_cpu);
+        sched_test_func(alloc_vdata);
+        sched_test_func(free_vdata);
+        sched_test_func(switch_sched);
+        sched_test_func(do_schedule);
+
+#undef sched_test_func
+
         if ( schedulers[i]->global_init && schedulers[i]->global_init() < 0 )
+        {
+            printk("scheduler %s failed initialization, dropped\n",
+                   schedulers[i]->opt_name);
             schedulers[i] = NULL;
-        else if ( !ops.name && !strcmp(schedulers[i]->opt_name, opt_sched) )
+        }
+
+        if ( schedulers[i] && !ops.name &&
+             !strcmp(schedulers[i]->opt_name, opt_sched) )
             ops = *schedulers[i];
     }