[PATCH v2 2/3] perf x86: Add compaction function for uncore attributes

[roman . sudarikov]

From: Roman Sudarikov <roman.sudarikov@xxxxxxxxxxxxxxx>

In current design, there is an implicit assumption that array of pointers
to uncore type attributes is NULL terminated. However, not all attributes
are mandatory for each Uncore unit type, e.g. "events" is required for
IMC but doesn't exist for CHA. That approach correctly supports only one
optional attribute which also must be the last in the row.
The patch removes limitation by safely removing embedded NULL elements.

Co-developed-by: Alexander Antonov <alexander.antonov@xxxxxxxxx>
Signed-off-by: Alexander Antonov <alexander.antonov@xxxxxxxxx>
Signed-off-by: Roman Sudarikov <roman.sudarikov@xxxxxxxxxxxxxxx>
---
 arch/x86/events/intel/uncore.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
index 24e120289018..a05352c4fc01 100644
--- a/arch/x86/events/intel/uncore.c
+++ b/arch/x86/events/intel/uncore.c
@@ -923,6 +923,22 @@ static void uncore_types_exit(struct intel_uncore_type **types)
 		uncore_type_exit(*types);
 }
 
+static void uncore_type_attrs_compaction(struct intel_uncore_type *type)
+{
+	int i, j;
+	int size = ARRAY_SIZE(type->attr_groups);
+
+	for (i = 0, j = 0; i < size; i++) {
+		if (!type->attr_groups[i])
+			continue;
+		if (i > j) {
+			type->attr_groups[j] = type->attr_groups[i];
+			type->attr_groups[i] = NULL;
+		}
+		j++;
+	}
+}
+
 static int __init uncore_type_init(struct intel_uncore_type *type, bool setid)
 {
 	struct intel_uncore_pmu *pmus;
@@ -980,6 +996,12 @@ static int __init uncore_type_init(struct intel_uncore_type *type, bool setid)
 		if (!type->get_topology(type) && !type->set_mapping(type))
 			type->mapping_group = &uncore_mapping_group;
 
+	/*
+	 * For optional attributes, we can safely remove embedded NULL
+	 * attr_groups elements.
+	 */
+	uncore_type_attrs_compaction(type);
+
 	return 0;
 
 err:
-- 
2.19.1