kernel+libc: Add getpid()

apps/app.c

@@ -12,7 +12,7 @@ void bye()
 int main()
 {
     atexit(bye);
-    printf("Welcome to %s from userspace!\n", "Luna");
+    printf("Welcome to %s from userspace (pid %d)!\n", "Luna", getpid());
 
     int fd = open("/etc/motd", 0);
     if (fd < 0)

initrd/etc/motd

@@ -1 +1 @@
-G'day mate!
+Hello, world!

kernel/CMakeLists.txt

@@ -28,6 +28,7 @@ set(SOURCES
     src/sys/usleep.cpp
     src/sys/open.cpp
     src/sys/file.cpp
+    src/sys/id.cpp
     src/fs/VFS.cpp
     src/fs/tmpfs/FileSystem.cpp
     src/InitRD.cpp

kernel/src/sys/id.cpp

@@ -0,0 +1,7 @@
+#include "sys/Syscall.h"
+#include "thread/Scheduler.h"
+
+Result<u64> sys_getpid(Registers*, SyscallArgs)
+{
+    return Scheduler::current()->id;
+}

libc/include/unistd.h

@@ -15,7 +15,9 @@ extern "C"
 #endif
 
     pid_t fork();
-    pid_t getpid();
+
+    /* Returns the current process' process ID. */
+    pid_t getpid(void);
 
     int execv(const char*, char* const*);
     int execve(const char*, char* const*, char* const*);

libc/src/unistd.cpp

@@ -8,6 +8,11 @@ extern "C" long arch_invoke_syscall(long, uintptr_t, uintptr_t, uintptr_t, uintp
 
 extern "C"
 {
+    pid_t getpid(void)
+    {
+        return (pid_t)syscall(SYS_getpid);
+    }
+
     long syscall(long num, ...)
     {
         va_list ap;

libluna/include/luna/Syscall.h

@@ -2,7 +2,7 @@
 
 #define enumerate_syscalls(_e)                                                                                         \
     _e(exit) _e(console_write) _e(clock_gettime) _e(allocate_memory) _e(deallocate_memory) _e(usleep) _e(open)         \
-        _e(close) _e(read)
+        _e(close) _e(read) _e(getpid)
 
 enum Syscalls
 {