libc: implement fork

lib/libc/core/CMakeLists.txt

@@ -1,4 +1,4 @@
-set(source_dirs assert stdio stdlib string errno ctype wctype)
+set(source_dirs assert stdio stdlib string errno ctype wctype unistd)
 
 foreach (dir ${source_dirs})
 	file(GLOB dir_sources ${CMAKE_CURRENT_SOURCE_DIR}/${dir}/*.c)

lib/libc/core/unistd/fork.c

@@ -0,0 +1,24 @@
+#include <errno.h>
+#include <magenta/task.h>
+#include <sys/types.h>
+
+pid_t fork(void)
+{
+	kern_handle_t new_task = KERN_HANDLE_INVALID,
+		      new_space = KERN_HANDLE_INVALID;
+	kern_status_t status = task_duplicate(&new_task, &new_space);
+	if (status != KERN_OK) {
+		return __set_errno(__errno_from_kern_status(status));
+	}
+
+	if (new_task == KERN_HANDLE_INVALID) {
+		/* child task */
+		return 0;
+	}
+
+	tid_t child = 0;
+	task_config_get(new_task, TASK_CFG_ID, &child, sizeof child);
+
+	/* parent task */
+	return child;
+}