cobalt/kernel: fixup for v3.19+ (trace_seq)

kernel/cobalt/include/asm-generic/xenomai/wrappers.h

@@ -116,6 +116,16 @@ devm_hwmon_device_register_with_groups(struct device *dev, const char *name,
 #error "Xenomai/cobalt requires Linux kernel 3.10 or above"
 #endif /* < 3.10 */
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(3,17,0)
+#include <linux/trace_seq.h>
+ 
+static inline unsigned char *
+trace_seq_buffer_ptr(struct trace_seq *s)
+{
+	return s->buffer + s->len;
+}
+#endif
+
 #if LINUX_VERSION_CODE < KERNEL_VERSION(3,19,0)
 #define user_msghdr msghdr
 #endif

kernel/cobalt/trace/cobalt-posix.h

@@ -92,7 +92,7 @@ DECLARE_EVENT_CLASS(syscall_exit,
 
 #define cobalt_print_sched_params(__policy, __p_ex)			\
 ({									\
-  	const char *__ret = p->buffer + p->len;				\
+	const unsigned char *__ret = trace_seq_buffer_ptr(p);		\
 	switch (__policy) {						\
 	case SCHED_QUOTA:						\
 		trace_seq_printf(p, "priority=%d, group=%d",		\