libdm: add statistics groups

Add a grouping facility to the libdm-stats library that allows the
user to bind several regions together as a group. Groups may be
used to aggregate data from several regions for reporting, or to
select and sort among large sets of regions.

A textual descriptor ("group tag") is associated with each group
and is stored in the first group member's aux_data field. The
tag contains the group member list and an optional alias for the
group, allowing the user to assign meaningful names to groups of
regions.

These descriptors are parsed in @stats_list message responses and
populate the resulting region and area tables with the group
structure.

Groups with overlapping regions are permitted but since this will
result in some events being counted more than once a warning is
printed in this case.

Nested and overlapping groups are not currently supported and
attempting to create these configurations results in error.

1 files changed, 74 insertions, 0 deletions

diff --git a/libdm/libdevmapper.h b/libdm/libdevmapper.h
index 68f119294..17f88a831 100644
--- a/libdm/libdevmapper.h
+++ b/libdm/libdevmapper.h
@@ -715,6 +715,19 @@ void dm_stats_buffer_destroy(struct dm_stats *dms, char *buffer);
 uint64_t dm_stats_get_nr_regions(const struct dm_stats *dms);
 
 /*
+ * Determine the number of groups contained in a dm_stats handle
+ * following a dm_stats_list() or dm_stats_populate() call.
+ *
+ * The value returned is the number of registered groups visible with the
+ * progam_id value used for the list or populate operation and may not be
+ * equal to the highest present group_id (either due to program_id
+ * filtering or gaps in the sequence of group_id values).
+ *
+ * Always returns zero on an empty handle.
+ */
+uint64_t dm_stats_get_nr_groups(const struct dm_stats *dms);
+
+/*
  * Test whether region_id is present in this dm_stats handle.
  */
 int dm_stats_region_present(const struct dm_stats *dms, uint64_t region_id);
@@ -733,6 +746,11 @@ uint64_t dm_stats_get_region_nr_areas(const struct dm_stats *dms,
 uint64_t dm_stats_get_nr_areas(const struct dm_stats *dms);
 
 /*
+ * Test whether group_id is present in this dm_stats handle.
+ */
+int dm_stats_group_present(const struct dm_stats *dms, uint64_t group_id);
+
+/*
  * Return the number of bins in the histogram configuration for the
  * specified region or zero if no histogram specification is configured.
  * Valid following a dm_stats_list() or dm_stats_populate() operation.
@@ -1080,6 +1098,62 @@ const char *dm_stats_get_current_region_program_id(const struct dm_stats *dms);
 const char *dm_stats_get_current_region_aux_data(const struct dm_stats *dms);
 
 /*
+ * Statistics groups and data aggregation.
+ */
+
+/*
+ * Create a new group in stats handle dms from the group descriptor
+ * passed in group. The group descriptor is a string containing a list
+ * of region_id values that will be included in the group. The first
+ * region_id found will be the group leader. Ranges of identifiers may
+ * be expressed as "M-N", where M and N are the start and end region_id
+ * values for the range.
+ */
+int dm_stats_create_group(struct dm_stats *dms, const char *group,
+			  const char *alias, uint64_t *group_id);
+
+/*
+ * Remove the specified group_id.
+ */
+int dm_stats_delete_group(struct dm_stats *dms, uint64_t group_id);
+
+/*
+ * Set an alias for this group or region. The alias will be returned
+ * instead of the normal dm-stats name for this region or group.
+ */
+int dm_stats_set_alias(struct dm_stats *dms, uint64_t group_id,
+		       const char *alias);
+
+/*
+ * Returns a pointer to the currently configured alias for id, or the
+ * name of the dm device the handle is bound to if no alias has been
+ * set. The pointer will be freed automatically when a new alias is set
+ * or when the stats handle is cleared.
+ */
+const char *dm_stats_get_alias(const struct dm_stats *dms, uint64_t id);
+
+/*
+ * Return the group_id that the specified region_id belongs to, or the
+ * special value DM_STATS_GROUP_NONE if the region does not belong
+ * to any group.
+ */
+uint64_t dm_stats_get_group_id(const struct dm_stats *dms, uint64_t region_id);
+
+/*
+ * Store a pointer to a string describing the regions that are members
+ * of the group specified by group_id in the memory pointed to by buf.
+ * The string is in the same format as the 'group' argument to
+ * dm_stats_create_group().
+ *
+ * The pointer does not need to be freed explicitly by the caller: it
+ * will become invalid following a subsequent dm_stats_list(),
+ * dm_stats_populate() or dm_stats_destroy() of the corresponding
+ * dm_stats handle.
+ */
+int dm_stats_get_group_descriptor(const struct dm_stats *dms,
+				  uint64_t group_id, char **buf);
+
+/*
  * Call this to actually run the ioctl.
  */
 int dm_task_run(struct dm_task *dmt);