trace-cmd: Add tracecmd_read_prev()

Add the tracecmd_read_prev(handle, record) that returns the record
before the given record.

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

2 files changed, 102 insertions, 0 deletions

diff --git a/trace-cmd.h b/trace-cmd.h
index b7cd5cc..7228a6d 100644
--- a/trace-cmd.h
+++ b/trace-cmd.h
@@ -64,6 +64,9 @@ struct record *
 tracecmd_read_data(struct tracecmd_input *handle, int cpu);
 
 struct record *
+tracecmd_read_prev(struct tracecmd_input *handle, struct record *record);
+
+struct record *
 tracecmd_read_next_data(struct tracecmd_input *handle, int *rec_cpu);
 
 struct record *
diff --git a/trace-input.c b/trace-input.c
index ce7bd09..279382a 100644
--- a/trace-input.c
+++ b/trace-input.c
@@ -1500,6 +1500,105 @@ tracecmd_read_next_data(struct tracecmd_input *handle, int *rec_cpu)
         return NULL;
 }
 
+/**
+ * tracecmd_read_prev - read the record before the given record
+ * @handle: input handle to the trace.dat file
+ * @record: the record to use to find the previous record.
+ *
+ * This returns the record before the @record on its CPU. If
+ * @record is the first record, NULL is returned. The cursor is set
+ * as if the previous record was read by tracecmd_read_data().
+ *
+ * @record can not be NULL, otherwise NULL is returned.
+ *
+ * Note, this is not that fast of an algorithm, since it needs
+ * to build the timestamp for the record.
+ *
+ * Note 2: This may free any record allocoted with tracecmd_peek_data().
+ *
+ * The record returned must be freed with free_record().
+ */
+struct record *
+tracecmd_read_prev(struct tracecmd_input *handle, struct record *record)
+{
+        unsigned long long offset, page_offset;;
+        struct cpu_data *cpu_data;
+        int index;
+        int cpu;
+
+        if (!record)
+                return NULL;
+
+        cpu = record->cpu;
+        offset = record->offset;
+        cpu_data = &handle->cpu_data[cpu];
+
+        page_offset = calc_page_offset(handle, offset);
+        index = offset - page_offset;
+
+        /* Note, the record passed in could have been a peek */
+        if (cpu_data->next) {
+                free_record(cpu_data->next);
+                cpu_data->next = NULL;
+        }
+
+        /* Reset the cursor */
+        /* Should not happen */
+        if (get_page(handle, cpu, page_offset) < 0)
+                return NULL;
+
+        update_page_info(handle, cpu);
+
+        /* Find the record before this record */
+        index = 0;
+        for (;;) {
+                record = tracecmd_read_data(handle, cpu);
+                /* Should not happen! */
+                if (!record)
+                        return NULL;
+                if (record->offset == offset)
+                        break;
+                index = record->offset - page_offset;
+                free_record(record);
+        }
+        free_record(record);
+
+        if (index)
+                /* we found our record */
+                return tracecmd_read_at(handle, page_offset + index, NULL);
+
+        /* The previous record is on the previous page */
+        for (;;) {
+                /* check if this is the first page */
+                if (page_offset == cpu_data->file_offset)
+                        return NULL;
+                page_offset -= handle->page_size;
+
+                /* Updating page to a new page will reset index to 0 */
+                get_page(handle, cpu, page_offset);
+
+                record = NULL;
+                index = 0;
+                do {
+                        if (record) {
+                                index = record->offset - page_offset;
+                                free_record(record);
+                        }
+                        record = tracecmd_read_data(handle, cpu);
+                        /* Should not happen */
+                        if (!record)
+                                return NULL;
+                } while (record->offset != offset);
+                free_record(record);
+
+                if (index)
+                        /* we found our record */
+                        return tracecmd_read_at(handle, page_offset + index, NULL);
+        }
+
+        /* Not reached */
+}
+
 static int init_cpu(struct tracecmd_input *handle, int cpu)
 {
         struct cpu_data *cpu_data = &handle->cpu_data[cpu];