一步一步教你写SHELL
这个LAB 是上完CMU CSAPP的14-15 LECTURE之后，就可以做了。
csapp 课程观看地址：https://search.bilibili.com/all?keyword=csapp&from_source=banner_search
lab 5 下载地址: http://csapp.cs.cmu.edu/3e/shlab-handout.tar
LAB 要求：http://csapp.cs.cmu.edu/3e/cachelab.pdf
课件PPT 在（需要抄代码）https://www.cs.cmu.edu/~213/lectures/15-ecf-signals.pdf
这个lab要求我们实现一个简易的unix shell程序，内容依托CSAPP第八章的异常控制流.
这个LAB 就按照TRACE 文件来一点点实现。 读WRITES UP很重要，理解课本里的每段代码也很重要是前置功课。
所给的文件中已经有了大致的框架，我们要做的就是完成一下几个函数：
函数原型 作用
void eval(char *cmdline) 分析命令，并派生子进程执行
int builtin_cmd(char **argv) 执行内建的命令
void do_bgfg(char **argv) 执行bg和fg命令
void waitfg(pid_t pid) 阻塞知道一个进程不在前台运行
void sigchld_handler(int sig) SIGCHID信号处理函数
void sigint_handler(int sig) SIGINT信号处理函数
void sigtstp_handler(int sig) SIGTSTP信号处理函数
TSH.C辅助函数
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STEP 1
理解书本的SHELL基本代码，搭一个框架。因为PPT上有讲，我就不解释了，PPT逐步解释的很清楚了
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因为这页PPT说了，这个代码有个问题，没有回收僵尸子进程。我们稍后来做。
有了这个框架，我们就可以填充我们的builtin_command， 书上也很友好的给了例子。
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代码里用到了Fork,这是为了简洁代码，把出错的情况包装起来的，下面所有的Code,可能都会用到这种首字母大写的方法。根据PPT 找到CSAPP.C
http://csapp.cs.cmu.edu/3e/ics3/code/src/csapp.c
把需要的方法都抄出来。
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这2个代码写好，TRACE2,3 应该可以过了。是测QUIT的。
TRACE4,需要修改下输出格式。也就过了。
printf("[%d] (%d) %s",pid2jid(pid), pid, cmdline);
TRACE5，因为辅助函数已经提供LISTJOBS所以很快可以实现。加在builtin_command
if (!strcmp(argv[0], "jobs")){/* jobs command */
listjobs(jobs);
return 1;
}
发现JOB没有打出来，看来是需要维护JOB LIST。根据PPT上的代码，有对应的，需要控制BLOCK。来保证父进程先ADD，子进程再DELETE。这里需要弄懂下面几个方法，可以MAN 方法名查看。
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STEP 2
把下面的逻辑接进我们的EVAL，和CHILD HANDLER
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大概代码如下图。
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然后写CHD_HANLDER，如果子进程结束，需要去DELETE JOB
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跑了之后发现都在打FRONTEND，这是为什么呢？
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经过分析，是因为在EVAL，和SIGCHLD_HANDLER里有WAITPID的阻塞等待子进程退出的逻辑。
当时前端进程的时候，EVAL里的WAITPID 会抢到这个线程退出的状态，然后就没有DELETEJOBS。而后端进程，因为在EVAL中只是做了PRINT，所以会在CHLD_HANDLER里被DELETE。
这就解释了为什么只打印了前端进程。
解决方案是可以2块地方都加上DELETEJOB 的逻辑。
不过看write up里面有一句
image.png
实现代码
/*
* waitfg - Block until process pid is no longer the foreground process
*/
void waitfg(pid_t pid)
{
while (fgpid(jobs)) {
usleep(1000);
}
return;
}
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改了之后，运行MAKE TEST05，发现这次是啥也没打出来。
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分析TRACE_05做的事。
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代码是SIG_CHLD HANDLER里
会BLOCK WAITING，这个时候前端进程打印出那个TSH> JOBS，会BLOCK，一直等到所有子进程都被回收后，那么就等价于等到2个后端进程都做好，也DELETE，才会离开HANDLER。
那么最后JOBS就当然没有东西可以打印。
所以WAITPID要改成非阻塞的。
同时因为不阻塞了，所以ERRNO ！= ECHILD的判断可以删了。
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SETP 3
从TRACE06 开始就是要实现SIGINT 和 SIGSTOP。
WRITEUP 里的一个HINT很重要。
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实现如下代码
/*
* 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 fg = fgpid(jobs);
printf("Job [%d] (%d) terminated by signal %d \n",
pid2jid(fg), fg, sig);
deletejob(jobs, fg);
Kill(-fg,sig);
}
image.png
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TRACE06,07都可以过了
同样方式，实现SIGSTOP, pass trace08
/*
* 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 fg = fgpid(jobs);
printf("Job [%d] (%d) stopped by signal %d \n",
pid2jid(fg), fg, sig);
(*getjobpid(jobs, fg)).state = ST;
Kill(-fg,sig);
}
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STEP 4
之后的TRACE，发现要求要实现FG,BG了
那么思路是首先要在BUILTIN_CMD 里把这个命令加上，随后实现DO_FGBG
image.png
在实现DO_FGBG，就是按照这个命令的功能，首先解析参数，拿到第二个看有没有%，如果有，从JID拿到PID。然后就是发送SIG_CONG的命令，让程序做起来（如果STOP的话，如果没STOP这个命令会被忽略掉（幂等））
最后别忘记要模仿EVAL的对前后端进程的处理，前端要调用WAITFG进行阻塞，后端要打印。
大概代码
/*
* do_bgfg - Execute the builtin bg and fg commands
*/
void do_bgfg(char **argv)
{
char* next_arg = argv[1];
int pid;
struct job_t *cur;
if (next_arg[0] == '%') {
int jid = atoi(((char *)next_arg) + 1);
cur = getjobjid(jobs,jid);
pid = cur->pid;
}else {
pid = atoi(next_arg);
cur = getjobpid(jobs,pid);
}
Kill(-pid,SIGCONT);
if (!strcmp(argv[0], "bg")) {
cur->state = BG;
printf("[%d] (%d) %s",pid2jid(pid), pid, cur->cmdline);
} else {
cur->state = FG;
waitfg(pid);
}
return;
}
到这里TRACE9和10就过了。TRACE 11，12，13是另外一个SIGINT和SIGSTOP的CASE，我们之前的代码似乎也能过，不需要作啥修改。
STEP 5
根据TRACE 14，需要对FG,BG 做一些ERROR HANDLING，就是各种JID,PID不合法的CORNER CASE 做输出处理。
/*
* do_bgfg - Execute the builtin bg and fg commands
*/
void do_bgfg(char **argv)
{
char* next_arg = argv[1];
if (next_arg == NULL) {
printf("%s command requires PID or %%jobid argument\n",argv[0]);
return;
}
int pid;
struct job_t *cur;
if (next_arg[0] == '%') {
int jid = atoi(((char *)next_arg) + 1);
if (jid == 0 && strcmp(((char *)next_arg) + 1, "0")) {
printf("%s: argument must be a PID or %%jobid\n",argv[0]);
return;
}
cur = getjobjid(jobs,jid);
pid = cur->pid;
if (cur == NULL) {
printf("%s: No such job\n",next_arg);
return;
}
}else {
pid = atoi(next_arg);
if (pid == 0 && strcmp(next_arg, "0")) {
printf("%s: argument must be a PID or %%jobid\n",argv[0]);
return;
}
cur = getjobpid(jobs,pid);
if (cur == NULL) {
printf("(%d): No such process\n",pid);
return;
}
}
Kill(-pid,SIGCONT);
if (!strcmp(argv[0], "bg")) {
cur->state = BG;
printf("[%d] (%d) %s",pid2jid(pid), pid, cur->cmdline);
} else {
cur->state = FG;
waitfg(pid);
}
return;
}
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TRACE 15 也赠送过了。之前代码写的可以哈
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TRACE 16 失败了。发现我们的SHELL 没法停止。
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看一下TRACE 16在干嘛
STEP 6
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原来是程序里面在即调了SIG_INT 和 SIG_STOP。因为这个程序用代码发的，我们无法用HANDLER机制去捕捉到。并且因为是STOP状态，所以我们的SIGCHLD HANDLER里面是会忽略的。那么就没有HANDLER去DELETE JOB 或者去修改进程的状态从FG变为ST，那么WAIT FG就会无限等待。
思考了一下，这下WUNTRACED需要登场了。这个可以监听到STOP的子进程的情况，这下问题就变成，我们必须用不同分支去隔离开STOP还是TERMINATE的。
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这个时候发现SIG INT 会堵住。
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看来还需要加个判断，因为我们的代码只判断了正常退出，没有判断SIG_INT的退出。
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最后发现有2句话没打印，就补一下，
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但是再做REGRESSION TEST的时候，发现，这样的话SIG_INT（SIG_STOP）的提示语言 会被打印2次，一次是SIG_INT（SIG_STOP） HANDLER里，一次在SIG_CHLD HANDLER里。
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但是我们可以看到JID，一次是2，一次是0。我们可以用JID是否为0来过滤。当然我们也可以去掉SIG_INT HANDLER里的那次打印。同时要把DELETE也移动过去，因为我们要确保，先打印后DELETE JOB，不然JID会变成0.
最终代码
/*
* tsh - A tiny shell program with job control
*
*
*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
/* 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 error handling function defined by yixuaz */
pid_t Fork(void);
void Execve(const char *filename, char *const argv[], char *const envp[]);
void Sigemptyset(sigset_t *set);
void Sigaddset(sigset_t *set, int signum);
void Sigfillset(sigset_t *set);
void Kill(pid_t pid, int signum);
void Setpgid(pid_t pid, pid_t pgid);
void Sigprocmask(int how, sigset_t *set, sigset_t *oldset);
/* 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]; /* Argument list execve() */
char buf[MAXLINE]; /* Holds modified command line */
int bg; /* Should the job run in bg or fg? */
pid_t pid; /* Process id */
sigset_t mask_all, mask_one, prev_one;
strcpy(buf, cmdline);
bg = parseline(buf, argv);
if (argv[0] == NULL)
return; /* Ignore empty lines */
Sigfillset(&mask_all);
Sigemptyset(&mask_one);
Sigaddset(&mask_one, SIGCHLD);
if (!builtin_cmd(argv)) {
Sigprocmask(SIG_BLOCK, &mask_one, &prev_one); /* Block SIGCHLD */
if ((pid = Fork()) == 0) { /* Child runs user job */
Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
Setpgid(0,0);
Execve(argv[0],argv,environ);
}
Sigprocmask(SIG_BLOCK, &mask_all, NULL); /* Parent process */
addjob(jobs, pid, bg + 1, cmdline); /* Add the child to the job list FG 1 BG 2*/
Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
/* Parent waits for foreground job to terminate */
if (!bg) {
waitfg(pid);
}
else
printf("[%d] (%d) %s",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], "jobs")){/* jobs command */
listjobs(jobs);
return 1;
}
if (!strcmp(argv[0], "bg") || !strcmp(argv[0], "fg")){/* bg/fg command */
do_bgfg(argv);
return 1;
}
if (!strcmp(argv[0], "quit")) /* quit command */
exit(0);
if (!strcmp(argv[0], "&")) /* Ignore singleton & */
return 1;
return 0; /* not a builtin command */
}
/*
* do_bgfg - Execute the builtin bg and fg commands
*/
void do_bgfg(char **argv)
{
char* next_arg = argv[1];
if (next_arg == NULL) {
printf("%s command requires PID or %%jobid argument\n",argv[0]);
return;
}
int pid;
struct job_t *cur;
if (next_arg[0] == '%') {
int jid = atoi(((char *)next_arg) + 1);
if (jid == 0 && strcmp(((char *)next_arg) + 1, "0")) {
printf("%s: argument must be a PID or %%jobid\n",argv[0]);
return;
}
cur = getjobjid(jobs,jid);
pid = cur->pid;
if (cur == NULL) {
printf("%s: No such job\n",next_arg);
return;
}
}else {
pid = atoi(next_arg);
if (pid == 0 && strcmp(next_arg, "0")) {
printf("%s: argument must be a PID or %%jobid\n",argv[0]);
return;
}
cur = getjobpid(jobs,pid);
if (cur == NULL) {
printf("(%d): No such process\n",pid);
return;
}
}
Kill(-pid,SIGCONT);
if (!strcmp(argv[0], "bg")) {
cur->state = BG;
printf("[%d] (%d) %s",pid2jid(pid), pid, cur->cmdline);
} else {
cur->state = FG;
waitfg(pid);
}
return;
}
/*
* waitfg - Block until process pid is no longer the foreground process
*/
void waitfg(pid_t pid)
{
while (fgpid(jobs)) {
usleep(1000);
}
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)
{
int olderrno = errno;
sigset_t mask_all, prev_all;
pid_t pid;
Sigfillset(&mask_all);
int status;
while ((pid = waitpid(-1, &status, WNOHANG|WUNTRACED)) > 0) { /* Reap a zombie child */
Sigprocmask(SIG_BLOCK, &mask_all, &prev_all);
if (WIFEXITED(status)) {
deletejob(jobs, pid);
} else if (WIFSTOPPED(status)) {
printf("Job [%d] (%d) stopped by signal %d \n",
pid2jid(fg), fg, sig);
(*getjobpid(jobs, fg)).state = ST;
} else if (WIFSIGNALED(status)) {
printf("Job [%d] (%d) terminated by signal %d \n",
pid2jid(pid), pid, WTERMSIG(status));
deletejob(jobs, pid);
}
Sigprocmask(SIG_SETMASK, &prev_all, NULL);
}
errno = olderrno;
}
/*
* 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 fg = fgpid(jobs);
Kill(-fg,sig);
}
/*
* 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 fg = fgpid(jobs);
Kill(-fg,sig);
}
/*********************
* 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);
}
/* error handling function defined by yixuaz */
void Execve(const char *filename, char *const argv[], char *const environ[])
{
if (execve(filename, argv, environ) < 0) {
printf("%s: Command not found.\n", argv[0]);
exit(0);
}
}
pid_t Fork(void)
{
pid_t pid;
if ((pid = fork()) < 0)
unix_error("Fork error");
return pid;
}
void Sigemptyset(sigset_t *set)
{
if(sigemptyset(set)<0)
unix_error("Sigemptyset error");
return;
}
void Sigaddset(sigset_t *set,int sign)
{
if(sigaddset(set,sign)<0)
unix_error("Sigaddset error");
return;
}
void Sigprocmask(int how, sigset_t *set, sigset_t *oldset)
{
if(sigprocmask(how,set,oldset)<0)
unix_error("Sigprocmask error");
return;
}
void Sigfillset(sigset_t *set)
{
if(sigfillset(set)<0)
unix_error("Sigfillset error");
return;
}
void Kill(pid_t pid, int signum)
{
int rc;
if ((rc = kill(pid, signum)) < 0)
unix_error("Kill error");
}
void Setpgid(pid_t pid, pid_t pgid) {
int rc;
if ((rc = setpgid(pid, pgid)) < 0)
unix_error("Setpgid error");
return;
}