一般来说，进程创建过程为：

• 在进程列表中增加一项，从PCB池中申请一个空间PCB，为新进程分配唯一标识符；
• 为新进程的进程映像分配地址空间，以便容纳进程实体，由进程管理程序确定加载至进程地址空间中的程序；
• 为新进程分配各种资源；
• 初始化PCB，如进程标识符、处理器初始状态、进程优先级等；
• 把新进程的状态设置为就绪态，并将其移入就绪队列；
• 通知操作系统某些模块，如记账程序、性能监控程序等。

以由ELF文件建立一个可运行的进程单位为例，GeekOS中内核线程的建立流程如下：

1、 Spawn_Init_Process函数的功能是调用Start_Kernel_Thread()，它以Spawner函数为进程体建立一个核心级进程，并使之准备就绪。

Spawner函数运行过程为：通过Read_Fully函数将ELF可执行文件读入内存缓冲区；通过Parse_ELF_Executable函数解析ELF文件， 并通过Spawn_Program函数执行ELF文件。最后通过Free函数释放内存缓冲区。 geekos/main.c void Spawner(unsigned long arg); static void Spawn_Init_Process(void) { /* this thread will load&run ELF files, see the rest in lprog.c */ Print("Starting the Spawner thread... "); Start_Kernel_Thread( Spawner, 0, PRIORITY_NORMAL, true ); }

2、Start_Kernel_Thread函数通过调用Create_Thread函数、Setup_Kernel_Thread、Make_Runnable_Atomic来创建内核进程。

geekos/kthread.c /* * Start a kernel-mode-only thread, using given function as its body * and passing given argument as its parameter. Returns pointer * to the new thread if successful, null otherwise. * * startFunc - is the function to be called by the new thread * arg - is a paramter to pass to the new function * priority - the priority of this thread (use PRIORITY_NORMAL) for * most things * detached - use false for kernel threads */ struct Kernel_Thread* Start_Kernel_Thread( Thread_Start_Func startFunc, ulong_t arg, int priority, bool detached ) { struct Kernel_Thread* kthread = Create_Thread(priority, detached); if (kthread != 0) { /* * Create the initial context for the thread to make * it schedulable. */ Setup_Kernel_Thread(kthread, startFunc, arg); /* Atomically put the thread on the run queue. */ Make_Runnable_Atomic(kthread); } return kthread; }

1）Create_Thread函数主要功能为通过Alloc_Page函数为Kernel_Thread结构体和内核进程栈区分配内存空间，并通过Init_Thread函数初始化Kernel_Thread结构体。最后将该进程结构体通过Add_To_Back_Of_All_Thread_List函数加入进程队列末尾。

PS：Kernel_Thread结构体就是GeekOS中的PCB。 geekos/kthread.c /* * Create a new raw thread object. * Returns a null pointer if there isn't enough memory. */ static struct Kernel_Thread* Create_Thread(int priority, bool detached) { struct Kernel_Thread* kthread; void* stackPage = 0; /* * For now, just allocate one page each for the thread context * object and the thread's stack. */ kthread = Alloc_Page(); if (kthread != 0) stackPage = Alloc_Page(); /* Make sure that the memory allocations succeeded. */ if (kthread == 0) return 0; if (stackPage == 0) { Free_Page(kthread); return 0; } /*Print("New thread @ %x, stack @ %x ", kthread, stackPage); */ /* * Initialize the stack pointer of the new thread * and accounting info */ Init_Thread(kthread, stackPage, priority, detached); /* Add to the list of all threads in the system. */ Add_To_Back_Of_All_Thread_List(&s_allThreadList, kthread); return kthread; } geekos/mem.c /* * Allocate a page of physical memory. */ void* Alloc_Page(void) { struct Page* page; void *result = 0; bool iflag = Begin_Int_Atomic(); /* See if we have a free page */ if (!Is_Page_List_Empty(&s_freeList)) { /* Remove the first page on the freelist. */ page = Get_Front_Of_Page_List(&s_freeList); KASSERT((page->flags & PAGE_ALLOCATED) == 0); Remove_From_Front_Of_Page_List(&s_freeList); /* Mark page as having been allocated. */ page->flags |= PAGE_ALLOCATED; g_freePageCount--; result = (void*) Get_Page_Address(page); } End_Int_Atomic(iflag); return result; } geekos/kthread.c /* * Initialize a new Kernel_Thread. */ static void Init_Thread(struct Kernel_Thread* kthread, void* stackPage, int priority, bool detached) { static int nextFreePid = 1; struct Kernel_Thread* owner = detached ? (struct Kernel_Thread*)0 : g_currentThread; memset(kthread, '