From 16ba8bc7733e5cd9a6d88331499cd8f2d764e4cd Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bvanassche@google.com>
Date: Tue, 15 Feb 2022 23:39:33 +0000
Subject: [PATCH] statslog: Make this library compatible with the cgroups v2
 hierarchy

Call memcg_apps_dir() instead of hard-coding the top-level directory of
the memcg controller.

Bug: 213617178
Test: Verified lmkd operation inside Cuttlefish.
Change-Id: I659610ebdabe3b69b0b1097aa5cf248d6f3273c5
Signed-off-by: Bart Van Assche <bvanassche@google.com>
---
 Android.bp   |  1 +
 statslog.cpp | 18 ++++++++++++------
 statslog.h   |  1 -
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/Android.bp b/Android.bp
index 5a079c9..0481c96 100644
--- a/Android.bp
+++ b/Android.bp
@@ -55,6 +55,7 @@ cc_library_static {
     defaults: ["stats_defaults"],
     shared_libs: [
         "liblog",
+        "libprocessgroup",
     ],
 }
 
diff --git a/statslog.cpp b/statslog.cpp
index 6568f73..26a6d86 100644
--- a/statslog.cpp
+++ b/statslog.cpp
@@ -30,6 +30,10 @@
 #include <time.h>
 #include <unistd.h>
 
+#include <string>
+
+#include <processgroup/processgroup.h>
+
 #ifdef LMKD_LOG_STATS
 
 #define STRINGIFY(x) STRINGIFY_INTERNAL(x)
@@ -85,18 +89,20 @@ static void memory_stat_parse_line(char* line, struct memory_stat* mem_st) {
         mem_st->swap_in_bytes = value;
 }
 
-static int memory_stat_from_cgroup(struct memory_stat* mem_st, int pid, uid_t uid) {
-    FILE *fp;
-    char buf[PATH_MAX];
+static int memory_stat_from_cgroup(struct memory_stat* mem_st, int pid, uid_t uid __unused) {
+    std::string path;
+    if (!CgroupGetAttributePathForTask("MemStats", pid, &path)) {
+        ALOGE("Querying MemStats path failed");
+        return -1;
+    }
 
-    snprintf(buf, sizeof(buf), MEMCG_PROCESS_MEMORY_STAT_PATH, uid, pid);
-
-    fp = fopen(buf, "r");
+    FILE* fp = fopen(path.c_str(), "r");
 
     if (fp == NULL) {
         return -1;
     }
 
+    char buf[PAGE_SIZE];
     while (fgets(buf, PAGE_SIZE, fp) != NULL) {
         memory_stat_parse_line(buf, mem_st);
     }
diff --git a/statslog.h b/statslog.h
index 89e4d2e..e3f8b72 100644
--- a/statslog.h
+++ b/statslog.h
@@ -92,7 +92,6 @@ enum lmk_state {
 
 #ifdef LMKD_LOG_STATS
 
-#define MEMCG_PROCESS_MEMORY_STAT_PATH "/dev/memcg/apps/uid_%u/pid_%d/memory.stat"
 #define PROC_STAT_FILE_PATH "/proc/%d/stat"
 #define PROC_STAT_BUFFER_SIZE 1024
 #define BYTES_IN_KILOBYTE 1024