Feather-Trace: support draining of trace buffer

1 files changed, 12 insertions, 3 deletions

diff --git a/litmus/trace.c b/litmus/trace.c
index 489e23e8a6..67e40d623b 100644
--- a/litmus/trace.c
+++ b/litmus/trace.c
@@ -88,6 +88,9 @@ static void free_ft_buffer(struct ft_buffer* buf)
 static DECLARE_MUTEX(feather_lock);
 static int use_count = 0;
 
+/* used for draining the FT buffers */
+static int enabled_events = 0;
+
 static int trace_release(struct inode *in, struct file *filp)
 {
         int err                 = -EINVAL;
@@ -104,6 +107,7 @@ static int trace_release(struct inode *in, struct file *filp)
         if (use_count == 1) {
                 /* disable events */
                 ft_disable_all_events();
+                enabled_events = 0;
 
                 /* wait for any pending events to complete */
                 set_current_state(TASK_UNINTERRUPTIBLE);
@@ -125,7 +129,6 @@ out:
         return err;
 }
 
-
 static ssize_t trace_read(struct file *filp, char __user *to, size_t len,
                       loff_t *f_pos)
 {
@@ -141,6 +144,7 @@ static ssize_t trace_read(struct file *filp, char __user *to, size_t len,
 
         while (len >= sizeof(struct timestamp)) {
                 if (ft_buffer_read(trace_ts_buf, &ts)) {
+                        /* FIXME: avoid double copy */
                         if (copy_to_user(to, &ts, sizeof(struct timestamp))) {
                                 error = -EFAULT;
                                 break;
@@ -149,14 +153,17 @@ static ssize_t trace_read(struct file *filp, char __user *to, size_t len,
                                 to     += sizeof(struct timestamp);
                                 error  += sizeof(struct timestamp);
                         }
-                } else {
+                } else if (enabled_events) {
+                        /* only wait if there are any events enabled */
                         set_current_state(TASK_INTERRUPTIBLE);
                         schedule_timeout(50);
                         if (signal_pending(current)) {
                                 error = -ERESTARTSYS;
                                 break;
                         }
-                }
+                } else
+                        /* nothing left to get, return to user space */
+                        break;
         }
         up(&feather_lock);
 out:
@@ -203,10 +210,12 @@ static ssize_t trace_write(struct file *filp, const char __user *from,
                         printk(KERN_INFO
                                "Disabling feather-trace event %lu.\n", id);
                         ft_disable_event(id);
+                        enabled_events--;
                 } else {
                         printk(KERN_INFO
                                "Enabling feather-trace event %lu.\n", id);
                         ft_enable_event(id);
+                        enabled_events++;
                 }
                 error += sizeof(long);
         }