trace-cmd library: Add tracecmd_iterate_reset()

Currently there's no easy way to reset iterating over a trace.dat file if a
tracecmd_iterate_events() was called. Add a helper function to do that:

 tracecmd_iterate_reset()

Link: https://lore.kernel.org/linux-trace-devel/20231229031138.68313-4-rostedt@goodmis.org

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

4 files changed, 44 insertions, 1 deletions

diff --git a/Documentation/libtracecmd/libtracecmd-iterate.txt b/Documentation/libtracecmd/libtracecmd-iterate.txt
index 12c54b2c..dc053ccb 100644
--- a/Documentation/libtracecmd/libtracecmd-iterate.txt
+++ b/Documentation/libtracecmd/libtracecmd-iterate.txt
@@ -4,7 +4,7 @@ libtracecmd(3)
 NAME
 ----
 tracecmd_iterate_events, tracecmd_iterate_events_multi, tracecmd_follow_event,
-tracecmd_follow_missed_events, tracecmd_filter_add - Read events from a trace file
+tracecmd_follow_missed_events, tracecmd_filter_add, tracecmd_iterate_reset - Read events from a trace file
 
 SYNOPSIS
 --------
@@ -45,6 +45,7 @@ int *tracecmd_follow_missed_events*(struct tracecmd_input pass:[*]_handle_,
 				   void pass:[*]_callback_data_);
 struct tracecmd_filter pass:[*]*tracecmd_filter_add*(struct tracecmd_input *_handle_,
 					    const char pass:[*]_filter_str_, bool _neg_);
+int *tracecmd_iterate_reset*(struct tracecmd_input pass:[*]_handle_);
 --
 
 DESCRIPTION
@@ -140,6 +141,10 @@ is defined by *tep_filter_add_filter_str(3)*. If _neg_ is true, then the events
 that match the filter will be skipped, otherwise the events that match will execute
 the _callback()_ function in the iterators.
 
+The *tracecmd_iterate_reset()* sets the _handle_ back to start at the beginning, so that
+the next call to *tracecmd_iterate_events()* starts back at the first event again, instead
+of continuing where it left off.
+
 RETURN VALUE
 ------------
 Both *tracecmd_iterate_events()*, *tracecmd_iterate_events_reverse()* and
@@ -147,6 +152,9 @@ Both *tracecmd_iterate_events()*, *tracecmd_iterate_events_reverse()* and
 (handling the follow and filters appropriately). Or an error value, which can include
 returning a non-zero result from the _callback()_ function.
 
+*tracecmd_iterate_reset()* returns 0 on success and -1 if an error occurred. Note,
+if -1 is returned, a partial reset may have also happened.
+
 EXAMPLE
 -------
 [source,c]
diff --git a/Documentation/libtracecmd/libtracecmd.txt b/Documentation/libtracecmd/libtracecmd.txt
index bbe6cc78..52d4e599 100644
--- a/Documentation/libtracecmd/libtracecmd.txt
+++ b/Documentation/libtracecmd/libtracecmd.txt
@@ -61,6 +61,7 @@ Iterating over events in a trace file:
 					   void pass:[*]_callback_data_);
 	struct tracecmd_filter pass:[*]*tracecmd_filter_add*(struct tracecmd_input *_handle_,
 						    const char pass:[*]_filter_str_, bool _neg_);
+	int *tracecmd_iterate_reset*(struct tracecmd_input pass:[*]_handle_);
 
 Read tracing instances from a trace file:
 	int *tracecmd_buffer_instances*(struct tracecmd_input pass:[*]_handle_);
diff --git a/include/trace-cmd/trace-cmd.h b/include/trace-cmd/trace-cmd.h
index e6527b71..55a0c518 100644
--- a/include/trace-cmd/trace-cmd.h
+++ b/include/trace-cmd/trace-cmd.h
@@ -72,6 +72,8 @@ int tracecmd_follow_missed_events(struct tracecmd_input *handle,
 						  int, void *),
 				  void *callback_data);
 
+int tracecmd_iterate_reset(struct tracecmd_input *handle);
+
 int tracecmd_iterate_events(struct tracecmd_input *handle,
 			    cpu_set_t *cpus, int cpu_size,
 			    int (*callback)(struct tracecmd_input *handle,
diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
index bf070f05..88bef83f 100644
--- a/lib/trace-cmd/trace-input.c
+++ b/lib/trace-cmd/trace-input.c
@@ -2114,6 +2114,38 @@ tracecmd_read_cpu_first(struct tracecmd_input *handle, int cpu)
 }
 
 /**
+ * tracecmd_iterate_reset - Set the handle to iterate from the beginning
+ * @handle: input handle for the trace.dat file
+ *
+ * This causes tracecmd_iterate_events*() to start from the beginning
+ * of the trace.dat file.
+ */
+int tracecmd_iterate_reset(struct tracecmd_input *handle)
+{
+	unsigned long long page_offset;
+	int cpu;
+	int ret = 0;
+	int r;
+
+	for (cpu = 0; cpu < handle->cpus; cpu++) {
+		page_offset = calc_page_offset(handle, handle->cpu_data[cpu].file_offset);
+
+		r = get_page(handle, cpu, page_offset);
+		if (r < 0) {
+			ret = -1;
+			continue; /* ?? */
+		}
+
+		/* If the page was already mapped, we need to reset it */
+		if (r)
+			update_page_info(handle, cpu);
+
+		free_next(handle, cpu);
+	}
+	return ret;
+}
+
+/**
  * tracecmd_read_cpu_last - get the last record in a CPU
  * @handle: input handle for the trace.dat file
  * @cpu: the CPU to search