[PATCH i-g-t 3/6] lib/xe: add xe_cgroup_region_name() helper

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

Add xe_cgroup_region_name(fd, region) which constructs the dmem cgroup
region path for a given xe memory region.  The returned string has the
form "drm/<pci-slot>/<region>" (e.g. "drm/0000:03:00.0/vram0"),
matching the name registered by the kernel via drmm_cgroup_register_region().

Only VRAM regions are tracked by the dmem controller; system and stolen
memory regions return NULL.

Assisted-by: GitHub Copilot:claude-sonnet-4.6
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 lib/xe/xe_query.c | 32 ++++++++++++++++++++++++++++++++
 lib/xe/xe_query.h |  2 ++
 2 files changed, 34 insertions(+)

diff --git a/lib/xe/xe_query.c b/lib/xe/xe_query.c
index 3286a3b37..ad8b16f74 100644
--- a/lib/xe/xe_query.c
+++ b/lib/xe/xe_query.c
@@ -7,6 +7,7 @@
  */
 
 #include <fcntl.h>
+#include <limits.h>
 #include <stdlib.h>
 #include <pthread.h>
 
@@ -21,6 +22,7 @@
 
 #include "drmtest.h"
 #include "igt_debugfs.h"
+#include "igt_device.h"
 #include "ioctl_wrappers.h"
 #include "igt_map.h"
 #include "intel_pat.h"
@@ -1270,6 +1272,36 @@ int xe_query_eu_thread_count(int fd, int gt)
 		xe_hwconfig_lookup_value_u32(fd, INTEL_HWCONFIG_NUM_THREADS_PER_EU);
 }
 
+/**
+ * xe_cgroup_region_name() - Build the dmem cgroup region name for an xe memory region.
+ * @fd: xe device fd.
+ * @region: Region mask (as used by xe_mem_region(), xe_region_name(), etc.).
+ *
+ * Constructs the full dmem cgroup region path for @region on the device
+ * identified by @fd.  The returned string has the form
+ * ``drm/<pci-slot>/<region>`` (e.g. ``drm/0000:03:00.0/vram0``), matching
+ * the name registered by the kernel driver via drmm_cgroup_register_region().
+ *
+ * Only VRAM regions are registered with the dmem controller; passing a
+ * system-memory region returns %NULL.
+ *
+ * Return: A newly allocated string that the caller must free(), or %NULL if
+ * @region is not tracked by the dmem cgroup controller.
+ */
+char *xe_cgroup_region_name(int fd, uint64_t region)
+{
+	char pci_slot[NAME_MAX];
+	char *name;
+
+	if (xe_region_class(fd, region) != DRM_XE_MEM_REGION_CLASS_VRAM)
+		return NULL;
+
+	igt_device_get_pci_slot_name(fd, pci_slot);
+
+	igt_assert(asprintf(&name, "drm/%s/%s", pci_slot, xe_region_name(region)) > 0);
+	return name;
+}
+
 igt_constructor
 {
 	xe_device_cache_init();
diff --git a/lib/xe/xe_query.h b/lib/xe/xe_query.h
index 8815c6c66..b01a5dac1 100644
--- a/lib/xe/xe_query.h
+++ b/lib/xe/xe_query.h
@@ -204,4 +204,6 @@ void xe_device_put(int fd);
 int xe_query_eu_count(int fd, int gt);
 int xe_query_eu_thread_count(int fd, int gt);
 
+char *xe_cgroup_region_name(int fd, uint64_t region);
+
 #endif	/* XE_QUERY_H */
-- 
2.53.0