ftrace: new continue entry - separate out from trace_entry

Some tracers will need to work with more than one entry. In order to do this
the trace_entry structure was split into two fields. One for the start of
all entries, and one to continue an existing entry.

The trace_entry structure now has a "field" entry that consists of the previous
content of the trace_entry, and a "cont" entry that is just a string buffer
the size of the "field" entry.

Thanks to Andrew Morton for suggesting this idea.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.h

@@ -61,13 +61,12 @@ struct stack_entry {
 };
 
 /*
- * The trace entry - the most basic unit of tracing. This is what
+ * The trace field - the most basic unit of tracing. This is what
  * is printed in the end as a single line in the trace output, such as:
  *
  *     bash-15816 [01]   235.197585: idle_cpu <- irq_enter
  */
-struct trace_entry {
-	char			type;
+struct trace_field {
 	char			cpu;
 	char			flags;
 	char			preempt_count;
@@ -83,6 +82,18 @@ struct trace_entry {
 	};
 };
 
+struct trace_field_cont {
+	char				buf[sizeof(struct trace_field)];
+};
+
+struct trace_entry {
+	char 				type;
+	union {
+		struct trace_field	field;
+		struct trace_field_cont	cont;
+	};
+};
+
 #define TRACE_ENTRY_SIZE	sizeof(struct trace_entry)
 
 /*

kernel/trace/trace_mmiotrace.c

@@ -174,14 +174,14 @@ static ssize_t mmio_read(struct trace_iterator *iter, struct file *filp,
 static int mmio_print_rw(struct trace_iterator *iter)
 {
 	struct trace_entry *entry = iter->ent;
-	struct mmiotrace_rw *rw	= &entry->mmiorw;
+	struct mmiotrace_rw *rw	= &entry->field.mmiorw;
 	struct trace_seq *s	= &iter->seq;
-	unsigned long long t	= ns2usecs(entry->t);
+	unsigned long long t	= ns2usecs(entry->field.t);
 	unsigned long usec_rem	= do_div(t, 1000000ULL);
 	unsigned secs		= (unsigned long)t;
 	int ret = 1;
 
-	switch (entry->mmiorw.opcode) {
+	switch (entry->field.mmiorw.opcode) {
 	case MMIO_READ:
 		ret = trace_seq_printf(s,
 			"R %d %lu.%06lu %d 0x%llx 0x%lx 0x%lx %d\n",
@@ -216,14 +216,14 @@ static int mmio_print_rw(struct trace_iterator *iter)
 static int mmio_print_map(struct trace_iterator *iter)
 {
 	struct trace_entry *entry = iter->ent;
-	struct mmiotrace_map *m	= &entry->mmiomap;
+	struct mmiotrace_map *m	= &entry->field.mmiomap;
 	struct trace_seq *s	= &iter->seq;
-	unsigned long long t	= ns2usecs(entry->t);
+	unsigned long long t	= ns2usecs(entry->field.t);
 	unsigned long usec_rem	= do_div(t, 1000000ULL);
 	unsigned secs		= (unsigned long)t;
 	int ret = 1;
 
-	switch (entry->mmiorw.opcode) {
+	switch (entry->field.mmiorw.opcode) {
 	case MMIO_PROBE:
 		ret = trace_seq_printf(s,
 			"MAP %lu.%06lu %d 0x%llx 0x%lx 0x%lx 0x%lx %d\n",