litmus: synchronous task release API

This adds the internals for two new systems calls:
	- sys_wait_for_ts_release()
	- sys_release_ts()

The first system call  suspends a task until the task systems is
released with the second system call.

2 files changed, 86 insertions, 0 deletions

diff --git a/include/litmus/rt_param.h b/include/litmus/rt_param.h
index 9fb5b19b78..1f94e45578 100644
--- a/include/litmus/rt_param.h
+++ b/include/litmus/rt_param.h
@@ -30,6 +30,7 @@ typedef enum {
 struct rt_task {
         lt_t            exec_cost;
         lt_t            period;
+        lt_t            phase;
         unsigned int    cpu;
         task_class_t    cls;
 };
diff --git a/litmus/sync.c b/litmus/sync.c
new file mode 100644
index 0000000000..fccde19236
--- /dev/null
+++ b/litmus/sync.c
@@ -0,0 +1,85 @@
+/* litmus/sync.c - Support for synchronous and asynchronous task system releases.
+ *
+ *
+ */
+
+#include <asm/atomic.h>
+#include <asm/uaccess.h>
+#include <linux/spinlock.h>
+#include <linux/list.h>
+#include <linux/sched.h>
+#include <linux/completion.h>
+
+#include <litmus/litmus.h>
+#include <litmus/jobs.h>
+
+static DECLARE_COMPLETION(ts_release);
+
+static long do_wait_for_ts_release(void)
+{
+        long ret = 0;
+
+        /* If the interruption races with a release, the completion object
+         * may have a non-zero counter. To avoid this problem, this should
+         * be replaced by wait_for_completion().
+         *
+         * For debugging purposes, this is interruptible for now.
+         */
+        ret = wait_for_completion_interruptible(&ts_release);
+
+        return ret;
+}
+
+
+static long do_release_ts(lt_t start)
+{
+        long ret = 0;
+        int  task_count = 0;
+        long flags;
+        struct list_head        *pos;
+        struct task_struct      *t;
+
+
+        spin_lock_irqsave(&ts_release.wait.lock, flags);
+
+        list_for_each(pos, &ts_release.wait.task_list) {
+                t = (struct task_struct*) list_entry(pos,
+                                                     struct __wait_queue,
+                                                     task_list)->private;
+                task_count++;
+                release_at(t, start + t->rt_param.task_params.phase);
+        }
+
+        spin_unlock_irqrestore(&ts_release.wait.lock, flags);
+
+        complete_n(&ts_release, task_count);
+
+        return ret;
+}
+
+
+asmlinkage long sys_wait_for_ts_release(void)
+{
+        long ret = -EPERM;
+        struct task_struct *t = current;
+
+        if (is_realtime(t))
+                ret = do_wait_for_ts_release();
+
+        return ret;
+}
+
+
+asmlinkage long sys_release_ts(lt_t __user *__delay)
+{
+        long ret;
+        lt_t delay;
+
+        /* FIXME: check capabilities... */
+
+        ret = copy_from_user(&delay, __delay, sizeof(lt_t));
+        if (ret == 0)
+                ret = do_release_ts(sched_clock() + delay);
+
+        return ret;
+}