LibWebView: Collect memory and cpu usage for helpers on Linux

Meta/gn/secondary/Userland/Libraries/LibWebView/BUILD.gn

@@ -152,6 +152,8 @@ shared_library("LibWebView") {
       "OutOfProcessWebView.cpp",
       "Platform/ProcessStatisticsSerenity.cpp",
     ]
+  } else if (current_os == "linux") {
+    sources += [ "Platform/ProcessStatisticsLinux.cpp" ]
   } else {
     sources += [ "Platform/ProcessStatisticsNoop.cpp" ]
   }

Userland/Libraries/LibWebView/CMakeLists.txt

@@ -27,6 +27,10 @@ if (SERENITYOS)
         OutOfProcessWebView.cpp
         Platform/ProcessStatisticsSerenity.cpp
     )
+elseif(LINUX AND NOT ANDROID)
+    list(APPEND SOURCES
+        Platform/ProcessStatisticsLinux.cpp
+    )
 else()
     list(APPEND SOURCES
         Platform/ProcessStatisticsNoop.cpp

Userland/Libraries/LibWebView/Platform/ProcessStatisticsLinux.cpp

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2024, Andrew Kaster <akaster@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/String.h>
+#include <LibCore/File.h>
+#include <LibWebView/Platform/ProcessStatistics.h>
+#include <unistd.h>
+
+namespace WebView {
+
+static auto user_hz = sysconf(_SC_CLK_TCK);
+static auto page_size = sysconf(_SC_PAGESIZE);
+static auto ncpu_online = sysconf(_SC_NPROCESSORS_ONLN);
+
+ErrorOr<void> update_process_statistics(ProcessStatistics& statistics)
+{
+    // Read the total time scheduled from /proc/stat, and each process's usage from /proc/pid/stat
+    // Calculate the CPU percentage for each process based on the total time scheduled and the time spent in the process
+
+    static auto proc_stat = TRY(Core::File::open("/proc/stat"sv, Core::File::OpenMode::Read));
+    TRY(proc_stat->seek(0, SeekMode::SetPosition));
+
+    char buf[1024] = {};
+    auto buffer = Bytes { buf, sizeof(buf) };
+    auto line = TRY(proc_stat->read_some(buffer));
+
+    int user_time = 0;
+    int system_time = 0;
+    int idle_time = 0;
+    int irq_time = 0;
+    int softirq_time = 0;
+
+    // user, nice (ignored), system, idle, iowait (ignored), irq, softirq, steal (ignored), guest (ignored), guest_nice (ignored)
+    int res = sscanf(reinterpret_cast<char const*>(line.data()), "cpu %d %*d %d %d %*d %d %d", &user_time, &system_time, &idle_time, &irq_time, &softirq_time);
+    if (res != 5)
+        return Error::from_string_literal("Failed to parse /proc/stat");
+
+    u64 const total_time_scheduled = user_time + system_time + idle_time + irq_time + softirq_time;
+    float const total_time_scheduled_diff = static_cast<float>(total_time_scheduled) - statistics.total_time_scheduled;
+    statistics.total_time_scheduled = total_time_scheduled;
+
+    for (auto& process : statistics.processes) {
+        auto proc_pid_stat_or_error = Core::File::open(MUST(String::formatted("/proc/{}/stat", process.pid)), Core::File::OpenMode::Read);
+        if (proc_pid_stat_or_error.is_error()) {
+            // FIXME: Remove stale process from process list?
+            continue;
+        }
+        auto proc_pid_stat = proc_pid_stat_or_error.release_value();
+        line = TRY(proc_pid_stat->read_some(buffer));
+
+        // We only care about fields 14 (utime), 15 (stime), and 24 (rss)
+        unsigned long utime = 0;
+        unsigned long stime = 0;
+        long rss = 0;
+        //                                                        1   2   3   4   5   6   7   8   9   10  11  12  13  14* 15* 16  17  18  19  20  21  22  23  24*
+        res = sscanf(reinterpret_cast<char const*>(line.data()), "%*d %*s %*c %*d %*d %*d %*d %*d %*u %*u %*u %*u %*u %lu %lu %*d %*d %*d %*d %*d %*d %*u %*u %ld", &utime, &stime, &rss);
+        if (res != 3)
+            return Error::from_string_literal("Failed to parse /proc/pid/stat");
+
+        process.memory_usage_bytes = rss * page_size;
+
+        u64 const time_process = utime + stime;
+        float const time_scheduled_diff = static_cast<float>(time_process) - process.time_spent_in_process;
+        process.time_spent_in_process = time_process;
+
+        process.cpu_percent = 0.0;
+        if (total_time_scheduled_diff > 0) {
+            process.cpu_percent = time_scheduled_diff / (total_time_scheduled_diff / ncpu_online) * 100.0f;
+        }
+    }
+
+    return {};
+}
+
+}