LITMUS^RT Core: add get_current_budget() system call

Allow userspace to figure out the used-up and remaining budget
of a task.

2 files changed, 56 insertions, 0 deletions

diff --git a/litmus/budget.c b/litmus/budget.c
index 47bf78a19f87..d67f4b387862 100644
--- a/litmus/budget.c
+++ b/litmus/budget.c
@@ -1,9 +1,11 @@
 #include <linux/sched.h>
 #include <linux/percpu.h>
 #include <linux/hrtimer.h>
+#include <linux/uaccess.h>
 
 #include <litmus/litmus.h>
 #include <litmus/preempt.h>
+#include <litmus/sched_plugin.h>
 
 #include <litmus/budget.h>
 
@@ -113,4 +115,54 @@ static int __init init_budget_enforcement(void)
         return 0;
 }
 
+void litmus_current_budget(lt_t *used_so_far, lt_t *remaining)
+{
+        struct task_struct *t = current;
+        unsigned long flags;
+        s64 delta;
+
+        local_irq_save(flags);
+
+        delta = sched_clock_cpu(smp_processor_id()) - t->se.exec_start;
+        if (delta < 0)
+                delta = 0;
+
+        TRACE_CUR("current_budget: sc:%llu start:%llu lt_t:%llu delta:%lld exec-time:%llu rem:%llu\n",
+                sched_clock_cpu(smp_processor_id()), t->se.exec_start,
+                litmus_clock(), delta,
+                tsk_rt(t)->job_params.exec_time,
+                budget_remaining(t));
+
+        if (used_so_far)
+                *used_so_far = tsk_rt(t)->job_params.exec_time + delta;
+
+        if (remaining) {
+                *remaining = budget_remaining(t);
+                if (*remaining > delta)
+                        *remaining -= delta;
+                else
+                        *remaining = 0;
+        }
+
+        local_irq_restore(flags);
+}
+
+asmlinkage long sys_get_current_budget(
+        lt_t __user * _expended,
+        lt_t __user *_remaining)
+{
+        lt_t expended = 0, remaining = 0;
+
+        if (is_realtime(current))
+                litmus->current_budget(&expended, &remaining);
+
+        if (_expended && put_user(expended, _expended))
+                return -EFAULT;
+
+        if (_remaining && put_user(remaining, _remaining))
+                return -EFAULT;
+
+        return 0;
+}
+
 module_init(init_budget_enforcement);
diff --git a/litmus/sched_plugin.c b/litmus/sched_plugin.c
index edd91e9bf773..7b1eba0de75c 100644
--- a/litmus/sched_plugin.c
+++ b/litmus/sched_plugin.c
@@ -13,6 +13,7 @@
 #include <litmus/sched_plugin.h>
 #include <litmus/preempt.h>
 #include <litmus/jobs.h>
+#include <litmus/budget.h>
 
 /*
  * Generic function to trigger preemption on either local or remote cpu
@@ -197,6 +198,9 @@ int register_sched_plugin(struct sched_plugin* plugin)
         if (!plugin->wait_for_release_at)
                 plugin->wait_for_release_at = default_wait_for_release_at;
 
+        if (!plugin->current_budget)
+                plugin->current_budget = litmus_current_budget;
+
         raw_spin_lock(&sched_plugins_lock);
         list_add(&plugin->list, &sched_plugins);
         raw_spin_unlock(&sched_plugins_lock);