【CSAPP】Shell Lab 外殼實驗
阿新 • • 發佈：2019-01-26
這個實驗的目的是為了更加熟悉程序控制和訊號處理。從給出到說明文件得知，實驗主要是按照tshref.out檔案的說明，一步一步往tsh.c新增相應的功能。同時還有tshref檔案作為我們要達到的目標。
這個實驗通過一個job_t結構體記錄相關作業的控制資訊。通過addjob，deletejob等函式對作業進行對應的操作。我們主要的注意力集中在：eval，do_bgfg，waitfg，還有3個訊號處理函式上。
可能用到的gdb相關操作：
（1）改變gdb訊號處理的設定 ：設定gdb接收到SIGINT時不要停止、列印、傳遞給除錯目標程式 。
(gdb) handle SIGINT nostop print pass
（2）使用gdb命令直接向除錯的應用程式傳送訊號 ：首先在你希望傳送訊號的語句處設定斷點，然後執行程式，當停止到斷點所在位置後，用gdb的signal命令傳送訊號給除錯目標程式 。
(gdb) signal SIGINT
（3）除錯多程序程式：mode到可選值為parent和child表示fork之後除錯父程序還是子程序。
(gdb) set follow-fork-mode mode
====================================================================================================================================
實驗開始，首先是eval函式：
下面到函式判斷是否是一個內建命令：void eval(char *cmdline) { char *argv[MAXARGS]; char buf[MAXLINE]; int bg; pid_t pid; sigset_t mask; strcpy(buf, cmdline); bg = parseline(buf, argv); if(argv[0] == NULL) return; /*防止addjob和deletejob衝突，先阻塞SIGCHLD訊號*/ sigemptyset(&mask); sigaddset(&mask, SIGCHLD); sigprocmask(SIG_BLOCK, &mask, NULL); if(!builtin_cmd(argv)){ if((pid = fork()) == 0){ sigprocmask(SIG_UNBLOCK, &mask, NULL); if(setpgid(0, 0) < 0) unix_error("eval: setgpid failed.\n"); if(execve(argv[0], argv, environ) < 0 ){ printf("%s: Command not found.\n", argv[0]); exit(0); } } /*前臺程式*/ if(!bg) addjob(jobs, pid, FG, cmdline); else addjob(jobs, pid, BG, cmdline); sigprocmask(SIG_UNBLOCK, &mask, NULL); /*若在前臺執行，阻塞到pid所代表到作業狀態state不是FG*/ if(!bg) waitfg(pid); else printf("[%d] (%d) %s\n", pid2jid(pid), pid, cmdline); } return; }
然後是較為簡單到SIGINT處理函式：int builtin_cmd(char **argv) { if(!strcmp(argv[0], "quit")) exit(0); if(!strcmp(argv[0], "jobs")){ listjobs(jobs); return 1; } /*後面到作業控制會用到*/ if(!strcmp(argv[0], "bg") || !strcmp(argv[0], "fg")){ do_bgfg(argv); return 1; } return 0; /* not a builtin command */ }
void sigint_handler(int sig)
{
pid_t pid = fgpid(jobs);
int jid = pid2jid(pid);
if(pid != 0){
printf("Job [%d] terminated by SIGINT.\n", jid);
deletejob(jobs, pid);
kill(-pid, sig);
}
return;
}void sigtstp_handler(int sig)
{
pid_t pid = fgpid(jobs);
int jid = pid2jid(pid);
if(pid != 0){
printf("Job[%d] stopped by SIGTSTP", jid);
(*getjobpid(jobs, pid)).state = ST;
kill(-pid, sig);
}
return;
}void sigchld_handler(int sig)
{
pid_t pid;
int status, child_sig;
while((pid = waitpid(-1, &status, WUNTRACED | WNOHANG)) > 0 ){
printf("Handling chlid proess %d\n", (int)pid);
/*handle SIGTSTP*/
if( WIFSTOPPED(status) )
sigtstp_handler( WSTOPSIG(status) );
/*handle child process interrupt by uncatched signal*/
else if( WIFSIGNALED(status) ) {
child_sig = WTERMSIG(status);
if(child_sig == SIGINT)
sigint_handler(child_sig);
}
else
deletejob(jobs, pid);
}
return;
}接下去是do_bgfg函式：
void do_bgfg(char **argv)
{
char *id = argv[1];
struct job_t *job;
int jobid;
if(id[0] == '%')
jobid = atoi(id+1);
if((job = getjobjid(jobs, jobid)) == NULL){
printf("Job is not exist.\n");
return;
}
if(!strcmp(argv[0], "bg")){
job->state = BG;
kill(-1* job->pid, SIGCONT);
}
if(!strcmp(argv[0], "fg")){
job->state = FG;
kill(-1 * job->pid, SIGCONT);
waitfg(job->pid);
}
return;
}
<span style="font-size:14px;">下面是waitfg：</span><pre name="code" class="cpp">void waitfg(pid_t pid)
{
while(pid == fgpid(jobs));
return;
}
pid_t fgpid(struct job_t *jobs) {
int i;
for (i = 0; i < MAXJOBS; i++)
if (jobs[i].state == FG)
return jobs[i].pid;
return 0;
}
==========================================================================================================================================================
完整的tsh.c如下：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
/* Misc manifest constants */
#define MAXLINE 1024 /* max line size */
#define MAXARGS 128 /* max args on a command line */
#define MAXJOBS 16 /* max jobs at any point in time */
#define MAXJID 1<<16 /* max job ID */
/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1 /* running in foreground */
#define BG 2 /* running in background */
#define ST 3 /* stopped */
/*
* Jobs states: FG (foreground), BG (background), ST (stopped)
* Job state transitions and enabling actions:
* FG -> ST : ctrl-z
* ST -> FG : fg command
* ST -> BG : bg command
* BG -> FG : fg command
* At most 1 job can be in the FG state.
*/
/* Global variables */
extern char **environ; /* defined in libc */
char prompt[] = "tsh> "; /* command line prompt (DO NOT CHANGE) */
int verbose = 0; /* if true, print additional output */
int nextjid = 1; /* next job ID to allocate */
char sbuf[MAXLINE]; /* for composing sprintf messages */
struct job_t { /* The job struct */
pid_t pid; /* job PID */
int jid; /* job ID [1, 2, ...] */
int state; /* UNDEF, BG, FG, or ST */
char cmdline[MAXLINE]; /* command line */
};
struct job_t jobs[MAXJOBS]; /* The job list */
/* End global variables */
/* Function prototypes */
/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv);
void do_bgfg(char **argv);
void waitfg(pid_t pid);
void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);
/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv);
void sigquit_handler(int sig);
void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int maxjid(struct job_t *jobs);
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
int deletejob(struct job_t *jobs, pid_t pid);
pid_t fgpid(struct job_t *jobs);
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid);
int pid2jid(pid_t pid);
void listjobs(struct job_t *jobs);
void usage(void);
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);
/*
* main - The shell's main routine
*/
int main(int argc, char **argv)
{
char c;
char cmdline[MAXLINE];
int emit_prompt = 1; /* emit prompt (default) */
/* Redirect stderr to stdout (so that driver will get all output
* on the pipe connected to stdout) */
dup2(1, 2);
/* Parse the command line */
while ((c = getopt(argc, argv, "hvp")) != EOF) {
switch (c) {
case 'h': /* print help message */
usage();
break;
case 'v': /* emit additional diagnostic info */
verbose = 1;
break;
case 'p': /* don't print a prompt */
emit_prompt = 0; /* handy for automatic testing */
break;
default:
usage();
}
}
/* Install the signal handlers */
/* These are the ones you will need to implement */
Signal(SIGINT, sigint_handler); /* ctrl-c */
Signal(SIGTSTP, sigtstp_handler); /* ctrl-z */
Signal(SIGCHLD, sigchld_handler); /* Terminated or stopped child */
/* This one provides a clean way to kill the shell */
Signal(SIGQUIT, sigquit_handler);
/* Initialize the job list */
initjobs(jobs);
/* Execute the shell's read/eval loop */
while (1) {
/* Read command line */
if (emit_prompt) {
printf("%s", prompt);
fflush(stdout);
}
if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
app_error("fgets error");
if (feof(stdin)) { /* End of file (ctrl-d) */
fflush(stdout);
exit(0);
}
/* Evaluate the command line */
eval(cmdline);
fflush(stdout);
fflush(stdout);
}
exit(0); /* control never reaches here */
}
/*
* eval - Evaluate the command line that the user has just typed in
*
* If the user has requested a built-in command (quit, jobs, bg or fg)
* then execute it immediately. Otherwise, fork a child process and
* run the job in the context of the child. If the job is running in
* the foreground, wait for it to terminate and then return. Note:
* each child process must have a unique process group ID so that our
* background children don't receive SIGINT (SIGTSTP) from the kernel
* when we type ctrl-c (ctrl-z) at the keyboard.
*/
void eval(char *cmdline)
{
char *argv[MAXARGS];
char buf[MAXLINE];
int bg;
pid_t pid;
sigset_t mask;
strcpy(buf, cmdline);
bg = parseline(buf, argv);
if(argv[0] == NULL)
return;
sigemptyset(&mask);
sigaddset(&mask, SIGCHLD);
sigprocmask(SIG_BLOCK, &mask, NULL);
if(!builtin_cmd(argv)){
if((pid = fork()) == 0){
sigprocmask(SIG_UNBLOCK, &mask, NULL);
if(setpgid(0, 0) < 0)
unix_error("eval: setgpid failed.\n");
if(execve(argv[0], argv, environ) < 0 ){
printf("%s: Command not found.\n", argv[0]);
exit(0);
}
}
if(!bg)
addjob(jobs, pid, FG, cmdline);
else
addjob(jobs, pid, BG, cmdline);
sigprocmask(SIG_UNBLOCK, &mask, NULL);
if(!bg)
waitfg(pid);
else
printf("[%d] (%d) %s\n", pid2jid(pid), pid, cmdline);
}
return;
}
/*
* parseline - Parse the command line and build the argv array.
*
* Characters enclosed in single quotes are treated as a single
* argument. Return true if the user has requested a BG job, false if
* the user has requested a FG job.
*/
int parseline(const char *cmdline, char **argv)
{
static char array[MAXLINE]; /* holds local copy of command line */
char *buf = array; /* ptr that traverses command line */
char *delim; /* points to first space delimiter */
int argc; /* number of args */
int bg; /* background job? */
strcpy(buf, cmdline);
buf[strlen(buf)-1] = ' '; /* replace trailing '\n' with space */
while (*buf && (*buf == ' ')) /* ignore leading spaces */
buf++;
/* Build the argv list */
argc = 0;
if (*buf == '\'') {
buf++;
delim = strchr(buf, '\'');
}
else {
delim = strchr(buf, ' ');
}
while (delim) {
argv[argc++] = buf;
*delim = '\0';
buf = delim + 1;
while (*buf && (*buf == ' ')) /* ignore spaces */
buf++;
if (*buf == '\'') {
buf++;
delim = strchr(buf, '\'');
}
else {
delim = strchr(buf, ' ');
}
}
argv[argc] = NULL;
if (argc == 0) /* ignore blank line */
return 1;
/* should the job run in the background? */
if ((bg = (*argv[argc-1] == '&')) != 0) {
argv[--argc] = NULL;
}
return bg;
}
/*
* builtin_cmd - If the user has typed a built-in command then execute
* it immediately.
*/
int builtin_cmd(char **argv)
{
if(!strcmp(argv[0], "quit"))
exit(0);
if(!strcmp(argv[0], "jobs")){
listjobs(jobs);
return 1;
}
if(!strcmp(argv[0], "bg") || !strcmp(argv[0], "fg")){
do_bgfg(argv);
return 1;
}
return 0; /* not a builtin command */
}
/*
* do_bgfg - Execute the builtin bg and fg commands
*/
void do_bgfg(char **argv)
{
char *id = argv[1];
struct job_t *job;
int jobid;
if(id[0] == '%')
jobid = atoi(id+1);
if((job = getjobjid(jobs, jobid)) == NULL){
printf("Job is not exist.\n");
return;
}
if(!strcmp(argv[0], "bg")){
job->state = BG;
kill(-1* job->pid, SIGCONT);
}
if(!strcmp(argv[0], "fg")){
job->state = FG;
kill(-1 * job->pid, SIGCONT);
waitfg(job->pid);
}
return;
}
/*
* waitfg - Block until process pid is no longer the foreground process
*/
void waitfg(pid_t pid)
{
while(pid == fgpid(jobs));
return;
}
/*****************
* Signal handlers
*****************/
/*
* sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
* a child job terminates (becomes a zombie), or stops because it
* received a SIGSTOP or SIGTSTP signal. The handler reaps all
* available zombie children, but doesn't wait for any other
* currently running children to terminate.
*/
void sigchld_handler(int sig)
{
pid_t pid;
int status, child_sig;
while((pid = waitpid(-1, &status, WUNTRACED | WNOHANG)) > 0 ){
printf("Handling chlid proess %d\n", (int)pid);
/*handle SIGTSTP*/
if( WIFSTOPPED(status) )
sigtstp_handler( WSTOPSIG(status) );
/*handle child process interrupt by uncatched signal*/
else if( WIFSIGNALED(status) ) {
child_sig = WTERMSIG(status);
if(child_sig == SIGINT)
sigint_handler(child_sig);
}
else
deletejob(jobs, pid);
}
return;
}
/*
* sigint_handler - The kernel sends a SIGINT to the shell whenver the
* user types ctrl-c at the keyboard. Catch it and send it along
* to the foreground job.
*/
void sigint_handler(int sig)
{
pid_t pid = fgpid(jobs);
int jid = pid2jid(pid);
if(pid != 0){
printf("Job [%d] terminated by SIGINT.\n", jid);
deletejob(jobs, pid);
kill(-pid, sig);
}
return;
}
/*
* sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
* the user types ctrl-z at the keyboard. Catch it and suspend the
* foreground job by sending it a SIGTSTP.
*/
void sigtstp_handler(int sig)
{
pid_t pid = fgpid(jobs);
int jid = pid2jid(pid);
if(pid != 0){
printf("Job[%d] stopped by SIGTSTP", jid);
(*getjobpid(jobs, pid)).state = ST;
kill(-pid, sig);
}
return;
}
/*********************
* End signal handlers
*********************/
/***********************************************
* Helper routines that manipulate the job list
**********************************************/
/* clearjob - Clear the entries in a job struct */
void clearjob(struct job_t *job) {
job->pid = 0;
job->jid = 0;
job->state = UNDEF;
job->cmdline[0] = '\0';
}
/* initjobs - Initialize the job list */
void initjobs(struct job_t *jobs) {
int i;
for (i = 0; i < MAXJOBS; i++)
clearjob(&jobs[i]);
}
/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs)
{
int i, max=0;
for (i = 0; i < MAXJOBS; i++)
if (jobs[i].jid > max)
max = jobs[i].jid;
return max;
}
/* addjob - Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
{
int i;
if (pid < 1)
return 0;
for (i = 0; i < MAXJOBS; i++) {
if (jobs[i].pid == 0) {
jobs[i].pid = pid;
jobs[i].state = state;
jobs[i].jid = nextjid++;
if (nextjid > MAXJOBS)
nextjid = 1;
strcpy(jobs[i].cmdline, cmdline);
if(verbose){
printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
}
return 1;
}
}
printf("Tried to create too many jobs\n");
return 0;
}
/* deletejob - Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid)
{
int i;
if (pid < 1)
return 0;
for (i = 0; i < MAXJOBS; i++) {
if (jobs[i].pid == pid) {
clearjob(&jobs[i]);
nextjid = maxjid(jobs)+1;
return 1;
}
}
return 0;
}
/* fgpid - Return PID of current foreground job, 0 if no such job */
pid_t fgpid(struct job_t *jobs) {
int i;
for (i = 0; i < MAXJOBS; i++)
if (jobs[i].state == FG)
return jobs[i].pid;
return 0;
}
/* getjobpid - Find a job (by PID) on the job list */
struct job_t *getjobpid(struct job_t *jobs, pid_t pid) {
int i;
if (pid < 1)
return NULL;
for (i = 0; i < MAXJOBS; i++)
if (jobs[i].pid == pid)
return &jobs[i];
return NULL;
}
/* getjobjid - Find a job (by JID) on the job list */
struct job_t *getjobjid(struct job_t *jobs, int jid)
{
int i;
if (jid < 1)
return NULL;
for (i = 0; i < MAXJOBS; i++)
if (jobs[i].jid == jid)
return &jobs[i];
return NULL;
}
/* pid2jid - Map process ID to job ID */
int pid2jid(pid_t pid)
{
int i;
if (pid < 1)
return 0;
for (i = 0; i < MAXJOBS; i++)
if (jobs[i].pid == pid) {
return jobs[i].jid;
}
return 0;
}
/* listjobs - Print the job list */
void listjobs(struct job_t *jobs)
{
int i;
for (i = 0; i < MAXJOBS; i++) {
if (jobs[i].pid != 0) {
printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
switch (jobs[i].state) {
case BG:
printf("Running ");
break;
case FG:
printf("Foreground ");
break;
case ST:
printf("Stopped ");
break;
default:
printf("listjobs: Internal error: job[%d].state=%d ",
i, jobs[i].state);
}
printf("%s", jobs[i].cmdline);
}
}
}
/******************************
* end job list helper routines
******************************/
/***********************
* Other helper routines
***********************/
/*
* usage - print a help message
*/
void usage(void)
{
printf("Usage: shell [-hvp]\n");
printf(" -h print this message\n");
printf(" -v print additional diagnostic information\n");
printf(" -p do not emit a command prompt\n");
exit(1);
}
/*
* unix_error - unix-style error routine
*/
void unix_error(char *msg)
{
fprintf(stdout, "%s: %s\n", msg, strerror(errno));
exit(1);
}
/*
* app_error - application-style error routine
*/
void app_error(char *msg)
{
fprintf(stdout, "%s\n", msg);
exit(1);
}
/*
* Signal - wrapper for the sigaction function
*/
handler_t *Signal(int signum, handler_t *handler)
{
struct sigaction action, old_action;
action.sa_handler = handler;
sigemptyset(&action.sa_mask); /* block sigs of type being handled */
action.sa_flags = SA_RESTART; /* restart syscalls if possible */
if (sigaction(signum, &action, &old_action) < 0)
unix_error("Signal error");
return (old_action.sa_handler);
}
/*
* sigquit_handler - The driver program can gracefully terminate the
* child shell by sending it a SIGQUIT signal.
*/
void sigquit_handler(int sig)
{
printf("Terminating after receipt of SIGQUIT signal\n");
exit(1);
}