295 lines
13 KiB
TeX
295 lines
13 KiB
TeX
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\documentclass[a4paper]{ctexart}
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\input{mypreamble}
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\renewcommand{\mychapternum}{4}
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\renewcommand{\mylabname}{内核线程管理}
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\renewcommand{\mydate}{2024年5月17日}
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\begin{document}
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\mytitle
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\begin{enumerate}
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\item{\textbf{研读理解相关代码后，回答以下问题：}}
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\begin{enumerate}
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\questionandanswer[]{
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请简单说明\mintinline{C}{proc_struct}中各个成员变量含义以及作用。它与理论课中讲述的PCB结构有何不同之处？
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}{}
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{\kaishu
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\setlength{\parskip}{2em}
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\begin{minted}[]{C}
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struct proc_struct {
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enum proc_state state; // Process state
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int pid; // Process ID
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int runs; // the running times of Proces
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uintptr_t kstack; // Process kernel stack
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volatile bool need_resched; // bool value: need to be rescheduled to release CPU?
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struct proc_struct *parent; // the parent process
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struct mm_struct *mm; // Process's memory management field
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struct context context; // Switch here to run process
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struct trapframe *tf; // Trap frame for current interrupt
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uintptr_t cr3; // CR3 register: the base addr of Page Directroy Table(PDT)
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uint32_t flags; // Process flag
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char name[PROC_NAME_LEN + 1]; // Process name
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list_entry_t list_link; // Process link list
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list_entry_t hash_link; // Process hash list
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};
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\end{minted}
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\mintinline{C}{state}是进程的状态，\mintinline{C}{pid}是进程的ID，\mintinline{C}{runs}是进程的被调度到的次数，\mintinline{C}{kstack}是进程的堆栈，\mintinline{C}{need_resched}用于非抢占式调度，表示进程是否运行结束可以把CPU重新调度给其他进程，\mintinline{C}{parent}是进程的父进程，\mintinline{C}{mm}是进程的内存管理的部分的指针，\mintinline{C}{context}是进程的上下文，即
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\begin{minted}{C}
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struct context {
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uint32_t eip;
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uint32_t esp;
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uint32_t ebx;
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uint32_t ecx;
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uint32_t edx;
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uint32_t esi;
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uint32_t edi;
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uint32_t ebp;
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};
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\end{minted}
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\mintinline{C}{tf}是进程的中断帧，记录了中断的相关信息，\mintinline{C}{cr3}是进程的页目录表的指针，\mintinline{C}{flags}是进程的各种标志位，\mintinline{C}{name}是进程的名称，\mintinline{C}{list_link}是所有进程的链表表项，\mintinline{C}{hash_link}是具有同一个哈希值的进程的链表表项。
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它与理论课中讲述的PCB结构的不同之处在于没有优先级、进程组、进程运行时间、进程使用的CPU时间、进程的子进程的CPU时间、文件管理（因为还没实现文件系统？）。
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}
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\questionandanswer[]{
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试简单分析 uCore中 内核线程的创建过程。（要求说明处理流程，相关的主要函数、它们的功能以及调用关系。）
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}{}
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{\kaishu
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\setlength{\parskip}{2em}
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\begin{center}
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\includegraphics[width=1\linewidth]{imgs/2024-05-17-19-18-00.png}
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\end{center}
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\begin{minted}{C}
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// proc_init - set up the first kernel thread idleproc "idle" by itself and
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// - create the second kernel thread init_main
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void
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proc_init(void) {
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int i;
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list_init(&proc_list);
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for (i = 0; i < HASH_LIST_SIZE; i ++) {
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list_init(hash_list + i);
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}
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if ((idleproc = alloc_proc()) == NULL) {
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panic("cannot alloc idleproc.\n");
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}
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idleproc->pid = 0;
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idleproc->state = PROC_RUNNABLE;
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idleproc->kstack = (uintptr_t)bootstack;
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idleproc->need_resched = 1;
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set_proc_name(idleproc, "idle");
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nr_process ++;
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current = idleproc;
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int pid = kernel_thread(init_main, "Hello world!!", 0);
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if (pid <= 0) {
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panic("create init_main failed.\n");
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}
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initproc = find_proc(pid);
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set_proc_name(initproc, "init");
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assert(idleproc != NULL && idleproc->pid == 0);
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assert(initproc != NULL && initproc->pid == 1);
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}
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\end{minted}
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主要的内核线程创建过程在\mintinline{C}{proc_init}中，首先调用\mintinline{C}{list_init}初始化全部进程的链表和相同哈希的进程列表，然后调用 \mintinline{C}{alloc_proc}给当前进程分配一个进程控制块，并且设置相关属性，其中调用\mintinline{C}{set_proc_name}设置当前进程的名称为\mintinline{C}{"idle"}，之后调用\mintinline{C}{kernel_thread}创建一个\mintinline{C}{init_main}进程，并调用\mintinline{C}{find_proc}，再调用\mintinline{C}{set_proc_name}将其名称设置为\mintinline{C}{init}。
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\begin{minted}{C}
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// kernel_thread - create a kernel thread using "fn" function
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// NOTE: the contents of temp trapframe tf will be copied to
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// proc->tf in do_fork-->copy_thread function
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int
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kernel_thread(int (*fn)(void *), void *arg, uint32_t clone_flags) {
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struct trapframe tf;
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memset(&tf, 0, sizeof(struct trapframe));
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tf.tf_cs = KERNEL_CS;
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tf.tf_ds = tf.tf_es = tf.tf_ss = KERNEL_DS;
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tf.tf_regs.reg_ebx = (uint32_t)fn;
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tf.tf_regs.reg_edx = (uint32_t)arg;
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tf.tf_eip = (uint32_t)kernel_thread_entry;
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return do_fork(clone_flags | CLONE_VM, 0, &tf);
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}
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\end{minted}
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\mintinline{C}{kernel_thread}的功能是通过调用一个函数创建一个新的线程，由于新的线程是由当前线程创建的，这里就调用了\mintinline{C}{do_fork}函数。
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\begin{minted}{C}
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/* do_fork - parent process for a new child process
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* @clone_flags: used to guide how to clone the child process
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* @stack: the parent's user stack pointer. if stack==0, It means to fork a kernel thread.
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* @tf: the trapframe info, which will be copied to child process's proc->tf
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*/
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int
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do_fork(uint32_t clone_flags, uintptr_t stack, struct trapframe *tf) {
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int ret = -E_NO_FREE_PROC;
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struct proc_struct *proc;
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if (nr_process >= MAX_PROCESS) {
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goto fork_out;
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}
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ret = -E_NO_MEM;
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//LAB4:EXERCISE2 YOUR CODE
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/*
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* Some Useful MACROs, Functions and DEFINEs, you can use them in below implementation.
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* MACROs or Functions:
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* alloc_proc: create a proc struct and init fields (lab4:exercise1)
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* setup_kstack: alloc pages with size KSTACKPAGE as process kernel stack
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* copy_mm: process "proc" duplicate OR share process "current"'s mm according clone_flags
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* if clone_flags & CLONE_VM, then "share" ; else "duplicate"
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* copy_thread: setup the trapframe on the process's kernel stack top and
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* setup the kernel entry point and stack of process
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* hash_proc: add proc into proc hash_list
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* get_pid: alloc a unique pid for process
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* wakeup_proc: set proc->state = PROC_RUNNABLE
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* VARIABLES:
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* proc_list: the process set's list
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* nr_process: the number of process set
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*/
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// 1. call alloc_proc to allocate a proc_struct
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// 2. call setup_kstack to allocate a kernel stack for child process
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// 3. call copy_mm to dup OR share mm according clone_flag
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// 4. call copy_thread to setup tf & context in proc_struct
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// 5. insert proc_struct into hash_list && proc_list
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// 6. call wakeup_proc to make the new child process RUNNABLE
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// 7. set ret vaule using child proc's pid
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if ((proc = alloc_proc()) == NULL) {
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goto fork_out;
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}
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proc->parent = current;
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if (setup_kstack(proc) != 0) {
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goto bad_fork_cleanup_proc;
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}
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if (copy_mm(clone_flags, proc) != 0) {
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goto bad_fork_cleanup_kstack;
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}
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copy_thread(proc, stack, tf);
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bool intr_flag;
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local_intr_save(intr_flag);
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{
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proc->pid = get_pid();
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hash_proc(proc);
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list_add(&proc_list, &(proc->list_link));
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nr_process ++;
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}
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local_intr_restore(intr_flag);
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wakeup_proc(proc);
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ret = proc->pid;
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fork_out:
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return ret;
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bad_fork_cleanup_kstack:
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put_kstack(proc);
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bad_fork_cleanup_proc:
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kfree(proc);
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goto fork_out;
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}
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\end{minted}
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\mintinline{C}{do_fork}函数中，先调用\mintinline{C}{alloc_proc}分配一个进程控制块，再调用\mintinline{C}{setup_kstack}分配一个内核堆栈，再调用\mintinline{C}{copy_mm}将父进程的内存空间复制或者共享给子进程，再调用\mintinline{C}{copy_thread}设置子进程的中断处理，并设置上下文的变量。之后关中断，将新的进程控制块插入到全部进程链表与相同哈希链表中，再开中断。然后把子进程设置成状态为\mintinline{C}{RUNNABLE}，返回子进程的\mintinline{C}{pid}。
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}
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\questionandanswer[]{
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试简单分析 uCore中 内核线程的切换过程。（要求说明处理流程，相关的主要函数、它们的功能以及调用关系。）
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}{}
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{\kaishu
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\setlength{\parskip}{2em}
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切换线程主要使用的是\mintinline{C}{schedule}函数。
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\begin{minted}{C}
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void
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schedule(void) {
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bool intr_flag;
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list_entry_t *le, *last;
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struct proc_struct *next = NULL;
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local_intr_save(intr_flag);
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{
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current->need_resched = 0;
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last = (current == idleproc) ? &proc_list : &(current->list_link);
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le = last;
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do {
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if ((le = list_next(le)) != &proc_list) {
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next = le2proc(le, list_link);
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if (next->state == PROC_RUNNABLE) {
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break;
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}
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}
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} while (le != last);
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if (next == NULL || next->state != PROC_RUNNABLE) {
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next = idleproc;
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}
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next->runs ++;
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if (next != current) {
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proc_run(next);
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}
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}
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local_intr_restore(intr_flag);
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}
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\end{minted}
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在\mintinline{C}{schedule}中，我们要找到下一次调度的线程，即找到状态为\mintinline{C}{RUNNABLE}的线程，如果当前的线程为\mintinline{C}{idleproc}即CPU空闲的线程则从线进程链表头开始找（因为\mintinline{C}{idleproc}线程不在线程链表中），否则从当前线程的下一个线程开始找。找到需要调度的\mintinline{C}{RUNNABLE}线程后，如果新的线程和老的线程不是同一个线程，则需要调用\mintinline{C}{proc_run}进行切换。
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\begin{minted}{C}
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// proc_run - make process "proc" running on cpu
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// NOTE: before call switch_to, should load base addr of "proc"'s new PDT
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void
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proc_run(struct proc_struct *proc) {
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if (proc != current) {
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bool intr_flag;
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struct proc_struct *prev = current, *next = proc;
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local_intr_save(intr_flag);
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{
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current = proc;
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load_esp0(next->kstack + KSTACKSIZE);
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lcr3(next->cr3);
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switch_to(&(prev->context), &(next->context));
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}
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local_intr_restore(intr_flag);
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}
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}
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\end{minted}
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在\mintinline{C}{proc_run}中，调用\mintinline{C}{load_esp0}设置任务状态段，调用\mintinline{C}{lcr3}加载新的进程的页表，之后调用\mintinline{C}{switch_to}保存老的进程的上下文，恢复新的进程的上下文。
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\begin{minted}{asm}
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switch_to: # switch_to(from, to)
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# save from's registers
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movl 4(%esp), %eax # eax points to from
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popl 0(%eax) # save eip !popl
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movl %esp, 4(%eax)
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movl %ebx, 8(%eax)
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movl %ecx, 12(%eax)
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movl %edx, 16(%eax)
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movl %esi, 20(%eax)
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movl %edi, 24(%eax)
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movl %ebp, 28(%eax)
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# restore to's registers
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movl 4(%esp), %eax # not 8(%esp): popped return address already
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# eax now points to to
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movl 28(%eax), %ebp
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movl 24(%eax), %edi
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movl 20(%eax), %esi
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movl 16(%eax), %edx
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movl 12(%eax), %ecx
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movl 8(%eax), %ebx
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movl 4(%eax), %esp
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pushl 0(%eax) # push eip
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ret
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\end{minted}
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在\mintinline{C}{switch_to}中，从\mintinline{C}{esp+4}的位置加载\mintinline{C}{eax}指针（即\mintinline{C}{&(prev->context)}），并把老的线程中当前的寄存器中的值都放到这个指针所在的\mintinline{C}{context}结构体中，再从\mintinline{C}{esp+8}的位置加载\mintinline{C}{eax}指针（即\mintinline{C}{&(next->context)}），并从这个指针的位置加载新的线程中的上下文寄存器的值，其中\mintinline{C}{eip}需要用\mintinline{C}{popl}和\mintinline{C}{pushl}来设置，不能使用\mintinline{C}{movl}来设置。
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}
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\end{enumerate}
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\end{enumerate}
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\end{document}
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