src.ctf.fs: deterministically sort trace's DS file groups

This patch makes a `src.ctf.fs` component deterministically sort its
trace's DS file groups. The order of the DS file group array directly
influences:

* The order of the output ports.
* Which DS file group gets which stream ID if the trace's packet headers
  do not contain a `stream_instance_id` field (automatic stream IDs).

It's important that, whatever the build or file system, the component
always assigns the same IDs to the same DS file group for a given trace.
This can help debugging and testing.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I105f44e7885a2974ace4d62abe0ee5384316b350
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2079
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>

diff --git a/src/plugins/ctf/fs-src/fs.c b/src/plugins/ctf/fs-src/fs.c
index f82ef74cafb38099050166a45639157641c51b27..cf3cc7145c7ccbd73b7143de70230c3c313f57c5 100644 (file)
--- a/src/plugins/ctf/fs-src/fs.c
+++ b/src/plugins/ctf/fs-src/fs.c
@@ -1969,6 +1969,22 @@ end:
        return ret;
 }
 
+static
+gint compare_ds_file_groups_by_first_path(gconstpointer a, gconstpointer b)
+{
+       struct ctf_fs_ds_file_group * const *ds_file_group_a = a;
+       struct ctf_fs_ds_file_group * const *ds_file_group_b = b;
+       const struct ctf_fs_ds_file_info *first_ds_file_info_a;
+       const struct ctf_fs_ds_file_info *first_ds_file_info_b;
+
+       BT_ASSERT((*ds_file_group_a)->ds_file_infos->len > 0);
+       BT_ASSERT((*ds_file_group_b)->ds_file_infos->len > 0);
+       first_ds_file_info_a = (*ds_file_group_a)->ds_file_infos->pdata[0];
+       first_ds_file_info_b = (*ds_file_group_b)->ds_file_infos->pdata[0];
+       return strcmp(first_ds_file_info_a->path->str,
+               first_ds_file_info_b->path->str);
+}
+
 int ctf_fs_component_create_ctf_fs_trace(
                struct ctf_fs_component *ctf_fs,
                const bt_value *paths_value,
@@ -2065,6 +2081,20 @@ int ctf_fs_component_create_ctf_fs_trace(
                        "Failed to fix packet index tracer bugs.");
        }
 
+       /*
+        * Sort data stream file groups by first data stream file info
+        * path to get a deterministic order. This order influences the
+        * order of the output ports. It also influences the order of
+        * the automatic stream IDs if the trace's packet headers do not
+        * contain a `stream_instance_id` field, in which case the data
+        * stream file to stream ID association is always the same,
+        * whatever the build and the system.
+        *
+        * Having a deterministic order here can help debugging and
+        * testing.
+        */
+       g_ptr_array_sort(ctf_fs->trace->ds_file_groups,
+               compare_ds_file_groups_by_first_path);
        goto end;
 error:
        ret = -1;