process: derive AppID from /proc/$pid/cgroup instead of walking the process tree

.github/workflows/main.yml

@@ -44,7 +44,7 @@ jobs:
           export CC=gcc CXX=g++
           meson configure -Db_coverage=true build-gcc
           meson test -C build-gcc --suite gamescope -v
-          gcovr -f src --xml -o coverage.xml -s build-gcc
+          gcovr -f src -e src/reshade --xml -o coverage.xml -s build-gcc
       - name: Upload coverage report
         uses: actions/upload-artifact@v7
         with:

src/Backends/OpenVRBackend.cpp

@@ -20,6 +20,7 @@
 #include "edid.h"
 #include "Ratio.h"
 #include "LibInputHandler.h"
+#include "Utils/Process.h"
 
 #include <signal.h>
 #include <string.h>
@@ -124,8 +125,6 @@ namespace vr
 
 extern std::atomic<uint32_t> g_unCurrentVRSceneAppId;
 
-uint32_t get_appid_from_pid( pid_t pid );
-
 ///////////////////////////////////////////////
 // Josh:
 // GetVulkanInstanceExtensionsRequired and GetVulkanDeviceExtensionsRequired return *space separated* exts :(
@@ -1179,7 +1178,7 @@ namespace gamescope
                     if (m_uCurrentScenePid != vrEvent.data.process.pid)
                     {
                         m_uCurrentScenePid = vrEvent.data.process.pid;
-                        m_uCurrentSceneAppId = get_appid_from_pid(m_uCurrentScenePid);
+                        m_uCurrentSceneAppId = gamescope::Process::GetAppIdFromPid(m_uCurrentScenePid);
                         g_unCurrentVRSceneAppId = m_uCurrentSceneAppId;
 
                         openvr_log.debugf("SceneApplicationChanged -> pid: %u appid: %u", m_uCurrentScenePid, m_uCurrentSceneAppId);

src/Utils/Process.cpp

@@ -1,11 +1,15 @@
 #include "Process.h"
-#include "../Utils/Algorithm.h"
+#include "Algorithm.h"
 #include "../convar.h"
 #include "../log.hpp"
 #include "../Utils/Defer.h"
 
-#include <algorithm>
 #include <array>
+#include <cstdio>
+#include <cstring>
+#include <fstream>
+#include <istream>
+#include <string>
 
 #include <errno.h>
 #include <pthread.h>
@@ -538,4 +542,43 @@ namespace gamescope::Process
         return __progname;
     }
 
+    uint32_t GetAppIdFromCgroup( std::istream &stream )
+    {
+        std::string line;
+        while ( std::getline( stream, line ) )
+        {
+            // cgroup line format: hierarchy-ID:controller-list:cgroup-path
+            size_t first_colon = line.find( ':' );
+            if ( first_colon == std::string::npos )
+                continue;
+            size_t second_colon = line.find( ':', first_colon + 1 );
+            if ( second_colon == std::string::npos )
+                continue;
+
+            const char *path = line.c_str() + second_colon + 1;
+            const char *last_slash = strrchr( path, '/' );
+            const char *scope = last_slash ? last_slash + 1 : path;
+
+            pid_t reaperpid = 0;
+            uint32_t appid = 0;
+            if ( sscanf( scope, "app-steam-app%u-%d.scope", &appid, &reaperpid ) == 2 && appid != 0 )
+                return appid;
+        }
+        return 0;
+    }
+
+    uint32_t GetAppIdFromPid( pid_t pid )
+    {
+        char filename[256];
+        snprintf( filename, sizeof( filename ), "/proc/%i/cgroup", pid );
+        std::ifstream cgroup_file( filename );
+
+        if ( !cgroup_file.is_open() || cgroup_file.bad() )
+            return 0;
+
+        uint32_t appid = GetAppIdFromCgroup( cgroup_file );
+        if ( appid != 0 )
+            s_ProcessLog.debugf( "AppID %u derived from cgroup for pid %d", appid, pid );
+        return appid;
+    }
 }

src/Utils/Process.h

@@ -1,7 +1,9 @@
 #pragma once
 
-#include <optional>
+#include <cstdint>
 #include <functional>
+#include <iosfwd>
+#include <optional>
 #include <span>
 
 #include <sys/types.h>
@@ -43,4 +45,6 @@ namespace gamescope::Process
 
     const char *GetProcessName();
 
-}
+    uint32_t GetAppIdFromCgroup( std::istream &stream );
+    uint32_t GetAppIdFromPid( pid_t pid );
+}

src/steamcompmgr.cpp

@@ -43,15 +43,11 @@
 #include <condition_variable>
 #include <mutex>
 #include <atomic>
-#include <vector>
 #include <algorithm>
 #include <array>
-#include <iostream>
 #include <fstream>
 #include <string>
-#include <queue>
 #include <filesystem>
-#include <variant>
 #include <unordered_set>
 
 #include <assert.h>
@@ -97,7 +93,6 @@
 #include "reshade_effect_manager.hpp"
 #include "BufferMemo.h"
 #include "Utils/Process.h"
-#include "Utils/Algorithm.h"
 
 #include "wlr_begin.hpp"
 #include "wlr/types/wlr_pointer_constraints_v1.h"
@@ -4932,98 +4927,6 @@ get_name_from_pid( pid_t pid )
 	return procNameStr;
 }
 
-uint32_t
-get_appid_from_pid( pid_t pid )
-{
-	uint32_t unFoundAppId = 0;
-
-	char filename[256];
-	pid_t next_pid = pid;
-
-	while ( 1 )
-	{
-		snprintf( filename, sizeof( filename ), "/proc/%i/stat", next_pid );
-		std::ifstream proc_stat_file( filename );
-
-		if (!proc_stat_file.is_open() || proc_stat_file.bad())
-			break;
-
-		std::string proc_stat;
-
-		std::getline( proc_stat_file, proc_stat );
-
-		char *procName = nullptr;
-		char *lastParens = nullptr;
-
-		for ( uint32_t i = 0; i < proc_stat.length(); i++ )
-		{
-			if ( procName == nullptr && proc_stat[ i ] == '(' )
-			{
-				procName = &proc_stat[ i + 1 ];
-			}
-
-			if ( proc_stat[ i ] == ')' )
-			{
-				lastParens = &proc_stat[ i ];
-			}
-		}
-
-		if (!lastParens)
-			break;
-
-		*lastParens = '\0';
-		char state;
-		int parent_pid = -1;
-
-		sscanf( lastParens + 1, " %c %d", &state, &parent_pid );
-
-		if ( strcmp( "reaper", procName ) == 0 )
-		{
-			snprintf( filename, sizeof( filename ), "/proc/%i/cmdline", next_pid );
-			std::ifstream proc_cmdline_file( filename );
-			std::string proc_cmdline;
-
-			bool bSteamLaunch = false;
-			uint32_t unAppId = 0;
-
-			std::getline( proc_cmdline_file, proc_cmdline );
-
-			for ( uint32_t j = 0; j < proc_cmdline.length(); j++ )
-			{
-				if ( proc_cmdline[ j ] == '\0' && j + 1 < proc_cmdline.length() )
-				{
-					if ( strcmp( "SteamLaunch", &proc_cmdline[ j + 1 ] ) == 0 )
-					{
-						bSteamLaunch = true;
-					}
-					else if ( sscanf( &proc_cmdline[ j + 1 ], "AppId=%u", &unAppId ) == 1 && unAppId != 0 )
-					{
-						if ( bSteamLaunch == true )
-						{
-							unFoundAppId = unAppId;
-						}
-					}
-					else if ( strcmp( "--", &proc_cmdline[ j + 1 ] ) == 0 )
-					{
-						break;
-					}
-				}
-			}
-		}
-
-		if ( parent_pid == -1 || parent_pid == 0 )
-		{
-			break;
-		}
-		else
-		{
-			next_pid = parent_pid;
-		}
-	}
-
-	return unFoundAppId;
-}
-
 static pid_t
 get_win_pid(xwayland_ctx_t *ctx, Window id)
 {
@@ -5113,7 +5016,7 @@ add_win(xwayland_ctx_t *ctx, Window id, Window prev, unsigned long sequence)
 	{
 		if ( new_win->pid != -1 )
 		{
-			new_win->appID = get_appid_from_pid( new_win->pid );
+			new_win->appID = gamescope::Process::GetAppIdFromPid( new_win->pid );
 		}
 		else
 		{

src/wlserver.cpp

@@ -66,7 +66,7 @@
 #include "InputEmulation.h"
 #include "commit.h"
 #include "Timeline.h"
-#include "Utils/NonCopyable.h"
+#include "Utils/Process.h"
 
 #if HAVE_PIPEWIRE
 #include "pipewire.hpp"
@@ -1845,8 +1845,6 @@ void xdg_toplevel_new(struct wl_listener *listener, void *data)
 {
 }
 
-uint32_t get_appid_from_pid( pid_t pid );
-
 wlserver_xdg_surface_info* waylandy_type_surface_new(struct wl_client *client, struct wlr_surface *surface)
 {
 	wlserver_wl_surface_info *wlserver_surface = get_wl_surface_info(surface);
@@ -1868,7 +1866,7 @@ wlserver_xdg_surface_info* waylandy_type_surface_new(struct wl_client *client, s
 	{
 		pid_t nPid = 0;
 		wl_client_get_credentials( client, &nPid, nullptr, nullptr );
-		window->appID = get_appid_from_pid( nPid );
+		window->appID = gamescope::Process::GetAppIdFromPid( nPid );
 	}
 	window->_window_types.emplace<steamcompmgr_xdg_win_t>();
 

tests/meson.build

@@ -1,16 +1,28 @@
 catch2_dep = dependency('catch2-with-main', required: true)
 
 srcdir = '../src'
-unittest_src = []
+
+convar_unittest_src = []
 foreach src : gamescope_core_src + ['Script/Script.cpp', 'convar_script.cpp']
-	unittest_src += srcdir / src
+	convar_unittest_src += srcdir / src
 endforeach
-
 test_convar = executable(
 	'test_convar',
-	unittest_src + ['test_convar.cpp'],
+	convar_unittest_src + ['test_convar.cpp'],
 	include_directories: [srcdir, sol2_include],
 	dependencies: [catch2_dep, luajit_dep, cap_dep, drm_dep, glm_dep, wlroots_dep],
 	cpp_args: gamescope_cpp_args,
 )
 test('convar', test_convar)
+
+utils_process_unittest_src = []
+foreach src : gamescope_core_src
+	utils_process_unittest_src += srcdir / src
+endforeach
+test_utils_process = executable(
+	'test_utils_process',
+	utils_process_unittest_src + ['test_utils_process.cpp'],
+	include_directories: [srcdir],
+	dependencies: [catch2_dep, cap_dep],
+)
+test('utils/process', test_utils_process)

tests/test_utils_process.cpp

@@ -0,0 +1,44 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include <sstream>
+
+#include "Utils/Process.h"
+
+using namespace gamescope;
+
+TEST_CASE("GetAppIdFromCgroup", "[appid]") {
+    SECTION("steam app scope") {
+        std::istringstream stream("0::/user.slice/user-1000.slice/user@1000.service/app.slice/app-steam-app12345-9876.scope\n");
+        REQUIRE(Process::GetAppIdFromCgroup(stream) == 12345u);
+    }
+
+    SECTION("no matching scope") {
+        std::istringstream stream("0::/user.slice/user-1000.slice/session.scope\n");
+        REQUIRE(Process::GetAppIdFromCgroup(stream) == 0u);
+    }
+
+    SECTION("multiple lines, one matching") {
+        std::istringstream stream(
+            "12:devices:/user.slice\n"
+            "11:memory:/user.slice/user-1000.slice/session-1.scope\n"
+            "0::/user.slice/user-1000.slice/user@1000.service/app.slice/app-steam-app567-42.scope\n"
+        );
+        REQUIRE(Process::GetAppIdFromCgroup(stream) == 567u);
+    }
+
+    SECTION("empty stream") {
+        std::istringstream stream("");
+        REQUIRE(Process::GetAppIdFromCgroup(stream) == 0u);
+    }
+
+    SECTION("malformed lines") {
+        std::istringstream stream("not-a-valid-cgroup-line\n");
+        REQUIRE(Process::GetAppIdFromCgroup(stream) == 0u);
+
+        stream = std::istringstream("not-a-valid:cgroup-line\n");
+        REQUIRE(Process::GetAppIdFromCgroup(stream) == 0u);
+
+        stream = std::istringstream("not-a-valid:cgroup-line:\n");
+        REQUIRE(Process::GetAppIdFromCgroup(stream) == 0u);
+    }
+}