trace-cmd: Add new tracecmd_set_cursor() function

The tracecmd_set_cursor() takes an offset that will cause the next
tracecmd_peek_data() or tracecmd_read_data() to return a record at
that offset (given that the CPU matches). This is useful when
iterating with tracecmd_read_data() and then needing to read a
record out of sequence. One can do:

	while ((record = tracecmd_read_data(h, cpu))) {
		/* ... */
		free_record(record);
		record = tracecmd_peek_data(h, cpu);
		save_offset = record->offset;
		free_record(record);
		record = tracecmd_read_at(h, o, NULL);
		/* ... */
		tracecmd_set_cursor(h, cpu, save_offset);
	}

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

2 files changed, 85 insertions, 12 deletions

diff --git a/trace-cmd.h b/trace-cmd.h
index eda7181..b7cd5cc 100644
--- a/trace-cmd.h
+++ b/trace-cmd.h
@@ -82,6 +82,9 @@ int tracecmd_refresh_record(struct tracecmd_input *handle,
 int tracecmd_set_cpu_to_timestamp(struct tracecmd_input *handle,
                                   int cpu, unsigned long long ts);
 
+int tracecmd_set_cursor(struct tracecmd_input *handle,
+                        int cpu, unsigned long long offset);
+
 int tracecmd_ftrace_overrides(struct tracecmd_input *handle);
 struct pevent *tracecmd_get_pevent(struct tracecmd_input *handle);
 
diff --git a/trace-input.c b/trace-input.c
index 884dd2f..3191510 100644
--- a/trace-input.c
+++ b/trace-input.c
@@ -816,13 +816,13 @@ read_old_format(struct tracecmd_input *handle, void **ptr, int cpu)
 }
 
 static struct record *
-read_event(struct tracecmd_input *handle, unsigned long long offset,
+peek_event(struct tracecmd_input *handle, unsigned long long offset,
            int cpu)
 {
         struct record *record = NULL;
 
         /*
-         * Since the timestamp is calculated from the beginnnig
+         * Since the timestamp is calculated from the beginning
          * of the page and through each event, we reset the
          * page to the beginning. This is just used by
          * tracecmd_read_at.
@@ -834,21 +834,30 @@ read_event(struct tracecmd_input *handle, unsigned long long offset,
         }
 
         do {
-                if (record)
-                        free_record(record);
-                /* Make sure peek returns new data */
-                if (handle->cpu_data[cpu].next) {
-                        free_record(handle->cpu_data[cpu].next);
-                        handle->cpu_data[cpu].next = NULL;
-                }
+                free_record(record);
+                record = tracecmd_peek_data(handle, cpu);
+                if (record && (record->offset + record->record_size) > offset)
+                        break;
                 record = tracecmd_read_data(handle, cpu);
-        } while (record && (record->offset + record->record_size) <= offset);
+        } while (record);
 
         return record;
 }
 
 static struct record *
-find_and_read_event(struct tracecmd_input *handle, unsigned long long offset,
+read_event(struct tracecmd_input *handle, unsigned long long offset,
+           int cpu)
+{
+        struct record *record;
+
+        record = peek_event(handle, offset, cpu);
+        if (record)
+                record = tracecmd_read_data(handle, cpu);
+        return record;
+}
+
+static struct record *
+find_and_peek_event(struct tracecmd_input *handle, unsigned long long offset,
                     int *pcpu)
 {
         unsigned long long page_offset;
@@ -875,7 +884,24 @@ find_and_read_event(struct tracecmd_input *handle, unsigned long long offset,
         if (pcpu)
                 *pcpu = cpu;
 
-        return read_event(handle, offset, cpu);
+        return peek_event(handle, offset, cpu);
+}
+
+
+static struct record *
+find_and_read_event(struct tracecmd_input *handle, unsigned long long offset,
+                    int *pcpu)
+{
+        struct record *record;
+        int cpu;
+
+        record = find_and_peek_event(handle, offset, &cpu);
+        if (record) {
+                record = tracecmd_read_data(handle, cpu);
+                if (pcpu)
+                        *pcpu = cpu;
+        }
+        return record;
 }
 
 /**
@@ -1147,6 +1173,50 @@ tracecmd_set_cpu_to_timestamp(struct tracecmd_input *handle, int cpu,
         return 0;
 }
 
+/**
+ * tracecmd_set_cursor - set the offset for the next tracecmd_read_data
+ * @handle: input handle for the trace.dat file
+ * @cpu: the CPU pointer to set
+ * @offset: the offset to place the cursor
+ *
+ * Set the pointer to the next read or peek. This is useful when
+ * needing to read sequentially and then look at another record
+ * out of sequence without breaking the iteration. This is done with:
+ *
+ *  record = tracecmd_peek_data()
+ *  offset = record->offset;
+ *  record = tracecmd_read_at();
+ *   - do what ever with record -
+ *  tracecmd_set_cursor(handle, cpu, offset);
+ *
+ *  Now the next tracecmd_peek_data or tracecmd_read_data will return
+ *  the original record.
+ */
+int tracecmd_set_cursor(struct tracecmd_input *handle,
+                        int cpu, unsigned long long offset)
+{
+        struct cpu_data *cpu_data = &handle->cpu_data[cpu];
+        unsigned long long page_offset;
+
+        if (cpu < 0 || cpu >= handle->cpus)
+                return -1;
+
+        if (offset < cpu_data->file_offset ||
+            offset > cpu_data->file_offset + cpu_data->file_size)
+                return -1;      /* cpu does not have this offset. */
+
+        /* Move this cpu index to point to this offest */
+        page_offset = offset & ~(handle->page_size - 1);
+
+        if (get_page(handle, cpu, page_offset) < 0)
+                return -1;
+
+        peek_event(handle, offset, cpu);
+
+        return 0;
+}
+
+
 static unsigned int
 translate_data(struct tracecmd_input *handle,
                void **ptr, unsigned long long *delta, int *length)