Feather-Trace: add platform independent implementation

This patch adds the simple fallback implementation and creates dummy
hooks in the x86 and ARM Kconfig files.

3 files changed, 70 insertions, 0 deletions

diff --git a/litmus/Kconfig b/litmus/Kconfig
index 382b2e426437..70ddbaddc06f 100644
--- a/litmus/Kconfig
+++ b/litmus/Kconfig
@@ -1,3 +1,28 @@
 menu "LITMUS^RT"
 
+menu "Tracing"
+
+config FEATHER_TRACE
+        bool "Feather-Trace Infrastructure"
+        default y
+        help
+          Feather-Trace basic tracing infrastructure. Includes device file
+          driver and instrumentation point support.
+
+          There are actually two implementations of Feather-Trace.
+          1) A slower, but portable, default implementation.
+          2) Architecture-specific implementations that rewrite kernel .text at runtime.
+
+          If enabled, Feather-Trace will be based on 2) if available (currently only for x86).
+          However, if DEBUG_RODATA=y, then Feather-Trace will choose option 1) in any case
+          to avoid problems with write-protected .text pages.
+
+          Bottom line: to avoid increased overheads, choose DEBUG_RODATA=n.
+
+          Note that this option only enables the basic Feather-Trace infrastructure;
+          you still need to enable SCHED_TASK_TRACE and/or SCHED_OVERHEAD_TRACE to
+          actually enable any events.
+
+endmenu
+
 endmenu
diff --git a/litmus/Makefile b/litmus/Makefile
index f0ed31faf582..4c6130b58bae 100644
--- a/litmus/Makefile
+++ b/litmus/Makefile
@@ -1,3 +1,5 @@
 #
 # Makefile for LITMUS^RT
 #
+
+obj-$(CONFIG_FEATHER_TRACE) += ft_event.o
diff --git a/litmus/ft_event.c b/litmus/ft_event.c
new file mode 100644
index 000000000000..399a07becca5
--- /dev/null
+++ b/litmus/ft_event.c
@@ -0,0 +1,43 @@
+#include <linux/types.h>
+
+#include <litmus/feather_trace.h>
+
+#if !defined(CONFIG_ARCH_HAS_FEATHER_TRACE) || defined(CONFIG_DEBUG_RODATA)
+/* provide dummy implementation */
+
+int ft_events[MAX_EVENTS];
+
+int ft_enable_event(unsigned long id)
+{
+        if (id < MAX_EVENTS) {
+                ft_events[id]++;
+                return 1;
+        } else
+                return 0;
+}
+
+int ft_disable_event(unsigned long id)
+{
+        if (id < MAX_EVENTS && ft_events[id]) {
+                ft_events[id]--;
+                return 1;
+        } else
+                return 0;
+}
+
+int ft_disable_all_events(void)
+{
+        int i;
+
+        for (i = 0; i < MAX_EVENTS; i++)
+                ft_events[i] = 0;
+
+        return MAX_EVENTS;
+}
+
+int ft_is_event_enabled(unsigned long id)
+{
+        return  id < MAX_EVENTS && ft_events[id];
+}
+
+#endif