Services: Renamed from Servers

It didn't feel right to have a "DHCPClient" in a "Servers" directory.
Rename this to Services to better reflect the type of programs we'll
be putting in there.

Services/SystemServer/main.cpp

@@ -0,0 +1,139 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Service.h"
+#include <AK/Assertions.h>
+#include <AK/ByteBuffer.h>
+#include <LibCore/ConfigFile.h>
+#include <LibCore/Event.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/File.h>
+#include <errno.h>
+#include <signal.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+static void sigchld_handler(int)
+{
+    int status = 0;
+    pid_t pid = waitpid(-1, &status, WNOHANG);
+    if (!pid)
+        return;
+
+    dbg() << "Reaped child with pid " << pid;
+    Service* service = Service::find_by_pid(pid);
+    if (service == nullptr) {
+        dbg() << "There was no service with this pid, what is going on?";
+        return;
+    }
+
+    // Call service->did_exit(status) some time soon.
+    // We wouldn't want to run the complex logic, such
+    // as possibly spawning the service again, from the
+    // signal handler, so defer it.
+    Core::EventLoop::main().post_event(*service, make<Core::DeferredInvocationEvent>([=](auto&) {
+        service->did_exit(status);
+    }));
+    Core::EventLoop::wake();
+}
+
+static void check_for_test_mode()
+{
+    auto f = Core::File::construct("/proc/cmdline");
+    if (!f->open(Core::IODevice::ReadOnly)) {
+        dbg() << "Failed to read command line: " << f->error_string();
+        ASSERT(false);
+    }
+    const String cmd = String::copy(f->read_all());
+    dbg() << "Read command line: " << cmd;
+    if (cmd.matches("*testmode=1*")) {
+        // Eventually, we should run a test binary and wait for it to finish
+        // before shutting down. But this is good enough for now.
+        dbg() << "Waiting for testmode shutdown...";
+        sleep(5);
+        dbg() << "Shutting down due to testmode...";
+        if (fork() == 0) {
+            execl("/bin/shutdown", "/bin/shutdown", "-n", nullptr);
+            ASSERT_NOT_REACHED();
+        }
+    } else {
+        dbg() << "Continuing normally";
+    }
+}
+
+static void mount_all_filesystems()
+{
+    dbg() << "Spawning mount -a to mount all filesystems.";
+    pid_t pid = fork();
+
+    if (pid < 0) {
+        perror("fork");
+        ASSERT_NOT_REACHED();
+    } else if (pid == 0) {
+        execl("/bin/mount", "mount", "-a", nullptr);
+        perror("exec");
+        ASSERT_NOT_REACHED();
+    } else {
+        wait(nullptr);
+    }
+}
+
+int main(int, char**)
+{
+    if (pledge("stdio proc exec tty accept unix rpath wpath cpath chown fattr id", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    mount_all_filesystems();
+
+    struct sigaction sa = {
+        .sa_handler = sigchld_handler,
+        .sa_mask = 0,
+        .sa_flags = SA_RESTART
+    };
+    sigaction(SIGCHLD, &sa, nullptr);
+
+    Core::EventLoop event_loop;
+
+    // Read our config and instantiate services.
+    // This takes care of setting up sockets.
+    NonnullRefPtrVector<Service> services;
+    auto config = Core::ConfigFile::get_for_system("SystemServer");
+    for (auto name : config->groups())
+        services.append(Service::construct(*config, name));
+
+    // After we've set them all up, activate them!
+    for (auto& service : services)
+        service.activate();
+
+    // This won't return if we're in test mode.
+    check_for_test_mode();
+
+    return event_loop.exec();
+}