Kernel: Implement the alarm() syscall.

Kernel/Process.cpp

@@ -1207,8 +1207,16 @@ int Process::sys$setgid(gid_t gid)
 
 unsigned Process::sys$alarm(unsigned seconds)
 {
-    (void) seconds;
-    ASSERT_NOT_REACHED();
+    unsigned previous_alarm_remaining = 0;
+    if (m_alarm_deadline && m_alarm_deadline > g_uptime) {
+        previous_alarm_remaining = (m_alarm_deadline - g_uptime) / TICKS_PER_SECOND;
+    }
+    if (!seconds) {
+        m_alarm_deadline = 0;
+        return previous_alarm_remaining;
+    }
+    m_alarm_deadline = g_uptime + seconds * TICKS_PER_SECOND;
+    return previous_alarm_remaining;
 }
 
 int Process::sys$uname(utsname* buf)

Kernel/Process.h

@@ -351,6 +351,8 @@ private:
     OwnPtr<ELFLoader> m_elf_loader;
 
     Lock m_big_lock { "Process" };
+
+    qword m_alarm_deadline { 0 };
 };
 
 class ProcessInspectionHandle {
@@ -396,7 +398,7 @@ inline void Process::for_each(Callback callback)
     ASSERT_INTERRUPTS_DISABLED();
     for (auto* process = g_processes->head(); process;) {
         auto* next_process = process->next();
-        if (!callback(*process))
+        if (callback(*process) == IterationDecision::Abort)
             break;
         process = next_process;
     }

Kernel/Scheduler.cpp

@@ -188,8 +188,13 @@ bool Scheduler::pick_next()
                 auto exit_status = Process::reap(process);
                 dbgprintf("reaped unparented process %s(%u), exit status: %u\n", name.characters(), pid, exit_status);
             }
+            return IterationDecision::Continue;
         }
-        return true;
+        if (process.m_alarm_deadline && g_uptime > process.m_alarm_deadline) {
+            process.m_alarm_deadline = 0;
+            process.send_signal(SIGALRM, nullptr);
+        }
+        return IterationDecision::Continue;
     });
 
     // Dispatch any pending signals.