libperf cpumap: Refactor perf_cpu_map__merge()

The perf_cpu_map__merge() function has two arguments, 'orig' and
'other'.  The function definition might cause confusion as it could give
the impression that the CPU maps in the two arguments are copied into a
new allocated structure, which is then returned as the result.

The purpose of the function is to merge the CPU map 'other' into the CPU
map 'orig'.  This commit changes the 'orig' argument to a pointer to
pointer, so the new result will be updated into 'orig'.

The return value is changed to an int type, as an error number or 0 for
success.

Update callers and tests for the new function definition.

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20241107125308.41226-2-leo.yan@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 30 insertions, 25 deletions

diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
index cae799ad44e1..a36e90d38142 100644
--- a/tools/lib/perf/cpumap.c
+++ b/tools/lib/perf/cpumap.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0-only
+#include <errno.h>
 #include <perf/cpumap.h>
 #include <stdlib.h>
 #include <linux/refcount.h>
@@ -436,46 +437,49 @@ bool perf_cpu_map__is_subset(const struct perf_cpu_map *a, const struct perf_cpu
 }
 
 /*
- * Merge two cpumaps
+ * Merge two cpumaps.
  *
- * orig either gets freed and replaced with a new map, or reused
- * with no reference count change (similar to "realloc")
- * other has its reference count increased.
+ * If 'other' is subset of '*orig', '*orig' keeps itself with no reference count
+ * change (similar to "realloc").
+ *
+ * If '*orig' is subset of 'other', '*orig' reuses 'other' with its reference
+ * count increased.
+ *
+ * Otherwise, '*orig' gets freed and replaced with a new map.
  */
-
-struct perf_cpu_map *perf_cpu_map__merge(struct perf_cpu_map *orig,
-					 struct perf_cpu_map *other)
+int perf_cpu_map__merge(struct perf_cpu_map **orig, struct perf_cpu_map *other)
 {
 	struct perf_cpu *tmp_cpus;
 	int tmp_len;
 	int i, j, k;
 	struct perf_cpu_map *merged;
 
-	if (perf_cpu_map__is_subset(orig, other))
-		return orig;
-	if (perf_cpu_map__is_subset(other, orig)) {
-		perf_cpu_map__put(orig);
-		return perf_cpu_map__get(other);
+	if (perf_cpu_map__is_subset(*orig, other))
+		return 0;
+	if (perf_cpu_map__is_subset(other, *orig)) {
+		perf_cpu_map__put(*orig);
+		*orig = perf_cpu_map__get(other);
+		return 0;
 	}
 
-	tmp_len = __perf_cpu_map__nr(orig) + __perf_cpu_map__nr(other);
+	tmp_len = __perf_cpu_map__nr(*orig) + __perf_cpu_map__nr(other);
 	tmp_cpus = malloc(tmp_len * sizeof(struct perf_cpu));
 	if (!tmp_cpus)
-		return NULL;
+		return -ENOMEM;
 
 	/* Standard merge algorithm from wikipedia */
 	i = j = k = 0;
-	while (i < __perf_cpu_map__nr(orig) && j < __perf_cpu_map__nr(other)) {
-		if (__perf_cpu_map__cpu(orig, i).cpu <= __perf_cpu_map__cpu(other, j).cpu) {
-			if (__perf_cpu_map__cpu(orig, i).cpu == __perf_cpu_map__cpu(other, j).cpu)
+	while (i < __perf_cpu_map__nr(*orig) && j < __perf_cpu_map__nr(other)) {
+		if (__perf_cpu_map__cpu(*orig, i).cpu <= __perf_cpu_map__cpu(other, j).cpu) {
+			if (__perf_cpu_map__cpu(*orig, i).cpu == __perf_cpu_map__cpu(other, j).cpu)
 				j++;
-			tmp_cpus[k++] = __perf_cpu_map__cpu(orig, i++);
+			tmp_cpus[k++] = __perf_cpu_map__cpu(*orig, i++);
 		} else
 			tmp_cpus[k++] = __perf_cpu_map__cpu(other, j++);
 	}
 
-	while (i < __perf_cpu_map__nr(orig))
-		tmp_cpus[k++] = __perf_cpu_map__cpu(orig, i++);
+	while (i < __perf_cpu_map__nr(*orig))
+		tmp_cpus[k++] = __perf_cpu_map__cpu(*orig, i++);
 
 	while (j < __perf_cpu_map__nr(other))
 		tmp_cpus[k++] = __perf_cpu_map__cpu(other, j++);
@@ -483,8 +487,9 @@ struct perf_cpu_map *perf_cpu_map__merge(struct perf_cpu_map *orig,
 
 	merged = cpu_map__trim_new(k, tmp_cpus);
 	free(tmp_cpus);
-	perf_cpu_map__put(orig);
-	return merged;
+	perf_cpu_map__put(*orig);
+	*orig = merged;
+	return 0;
 }
 
 struct perf_cpu_map *perf_cpu_map__intersect(struct perf_cpu_map *orig,
diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
index c6d67fc9e57e..94b7369f3efe 100644
--- a/tools/lib/perf/evlist.c
+++ b/tools/lib/perf/evlist.c
@@ -75,7 +75,7 @@ static void __perf_evlist__propagate_maps(struct perf_evlist *evlist,
 		evsel->threads = perf_thread_map__get(evlist->threads);
 	}
 
-	evlist->all_cpus = perf_cpu_map__merge(evlist->all_cpus, evsel->cpus);
+	perf_cpu_map__merge(&evlist->all_cpus, evsel->cpus);
 }
 
 static void perf_evlist__propagate_maps(struct perf_evlist *evlist)
diff --git a/tools/lib/perf/include/perf/cpumap.h b/tools/lib/perf/include/perf/cpumap.h
index 90457d17fb2f..c83bfb2c36ff 100644
--- a/tools/lib/perf/include/perf/cpumap.h
+++ b/tools/lib/perf/include/perf/cpumap.h
@@ -39,8 +39,8 @@ LIBPERF_API struct perf_cpu_map *perf_cpu_map__new_online_cpus(void);
 LIBPERF_API struct perf_cpu_map *perf_cpu_map__new(const char *cpu_list);
 LIBPERF_API struct perf_cpu_map *perf_cpu_map__read(FILE *file);
 LIBPERF_API struct perf_cpu_map *perf_cpu_map__get(struct perf_cpu_map *map);
-LIBPERF_API struct perf_cpu_map *perf_cpu_map__merge(struct perf_cpu_map *orig,
-						     struct perf_cpu_map *other);
+LIBPERF_API int perf_cpu_map__merge(struct perf_cpu_map **orig,
+				    struct perf_cpu_map *other);
 LIBPERF_API struct perf_cpu_map *perf_cpu_map__intersect(struct perf_cpu_map *orig,
 							 struct perf_cpu_map *other);
 LIBPERF_API void perf_cpu_map__put(struct perf_cpu_map *map);