[PATCH i-g-t 2/6] tests/cgroup_dmem: add dmem cgroup controller test

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

Add a test that exercises the cgroup v2 dmem controller interface using
the new igt_cgroup library.

The test uses igt_simple_main and:
  - Skips if no dmem regions are registered (no cgroup v2 or no
   dmem-capable device).
  - Creates a sub-cgroup and moves the test process into it.
  - Enumerates all registered device memory regions and prints their
   capacity, system-wide current usage, per-cgroup current usage, and
   configured min, low and max limits.
  - Destroys the cgroup on completion.

Assisted-by: GitHub Copilot:claude-sonnet-4.6
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 tests/cgroup_dmem.c | 92 +++++++++++++++++++++++++++++++++++++++++++++
 tests/meson.build   |  1 +
 2 files changed, 93 insertions(+)
 create mode 100644 tests/cgroup_dmem.c

diff --git a/tests/cgroup_dmem.c b/tests/cgroup_dmem.c
new file mode 100644
index 000000000..442c965f9
--- /dev/null
+++ b/tests/cgroup_dmem.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2025 Intel Corporation
+ */
+
+/**
+ * TEST: cgroup dmem
+ * Description: Exercises the cgroup v2 dmem controller interface.  Creates a
+ *              cgroup, moves the process into it, enumerates all dmem regions,
+ *              prints their capacity, system-wide current usage, per-cgroup
+ *              current usage and configured limits, then destroys the cgroup.
+ * Category: Core
+ * Mega feature: General Core features
+ * Sub-category: uapi
+ * Functionality: cgroup
+ * Feature: dmem
+ * Test category: uapi
+ */
+
+#include <inttypes.h>
+
+#include "igt.h"
+#include "igt_cgroup.h"
+
+IGT_TEST_DESCRIPTION("Exercises the cgroup v2 dmem controller interface.");
+
+static void fmt_bytes(uint64_t v, char *buf, size_t len)
+{
+	if (v == IGT_CGROUP_DMEM_MAX)
+		snprintf(buf, len, "max");
+	else
+		snprintf(buf, len, "%" PRIu64, v);
+}
+
+int igt_simple_main()
+{
+	struct igt_cgroup *cg;
+	const char *region;
+	char **regions;
+	uint64_t capacity, sys_current, cg_current, min, low, max;
+	char cap_s[32], sys_s[32], cg_s[32];
+	char min_s[32], low_s[32], max_s[32];
+	int i;
+
+	igt_require_f(igt_cgroup_dmem_available(),
+		      "No dmem regions found; is cgroup v2 with the "
+		      "dmem controller available?\n");
+
+	cg = igt_cgroup_new("igt-cgroup-dmem-test");
+	igt_assert_f(cg, "Failed to create cgroup\n");
+
+	igt_cgroup_move_current(cg);
+
+	regions = igt_cgroup_dmem_regions();
+	igt_assert_f(regions, "Failed to enumerate dmem regions\n");
+
+	igt_info("%-40s %16s %16s %16s %16s %16s %16s\n",
+		 "region", "capacity", "system-current",
+		 "cgroup-current", "min", "low", "max");
+	igt_info("%-40s %16s %16s %16s %16s %16s %16s\n",
+		 "------", "--------", "--------------",
+		 "--------------", "---", "---", "---");
+
+	for (i = 0; regions[i]; i++) {
+		region = regions[i];
+
+		igt_cgroup_dmem_get_capacity(region, &capacity);
+		fmt_bytes(capacity, cap_s, sizeof(cap_s));
+
+		igt_cgroup_dmem_get_system_current(region, &sys_current);
+		fmt_bytes(sys_current, sys_s, sizeof(sys_s));
+
+		igt_cgroup_dmem_get_current(cg, region, &cg_current);
+		fmt_bytes(cg_current, cg_s, sizeof(cg_s));
+
+		igt_cgroup_dmem_get_min(cg, region, &min);
+		fmt_bytes(min, min_s, sizeof(min_s));
+
+		igt_cgroup_dmem_get_low(cg, region, &low);
+		fmt_bytes(low, low_s, sizeof(low_s));
+
+		igt_cgroup_dmem_get_max(cg, region, &max);
+		fmt_bytes(max, max_s, sizeof(max_s));
+
+		igt_info("%-40s %16s %16s %16s %16s %16s %16s\n",
+			 region, cap_s, sys_s, cg_s,
+			 min_s, low_s, max_s);
+	}
+
+	igt_cgroup_dmem_regions_free(regions);
+	igt_cgroup_free(cg);
+}
diff --git a/tests/meson.build b/tests/meson.build
index 60cea3aa8..02fbb8c4e 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -1,4 +1,5 @@
 test_progs = [
+	'cgroup_dmem',
 	'core_auth',
 	'core_debugfs',
 	'core_getclient',
-- 
2.53.0