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CSAPP(深入理解计算机系统) 实验——实现shell

 
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/* 
 * tsh - A tiny shell program with job control
 * rommel @copyright
 */
#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);
sigset_t mask_signal(int how, int sig);
int send_signal(pid_t pid, int sig);
/* Here are helper routines that we've provided for you */
void do_echo(char **argv);
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 */

	/* 信号处理函数 */
	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);

	/* Shell输入程序 */
	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;

	strcpy(buf, cmdline);
	bg = parseline(buf, argv);
	if (argv[0] == NULL) {
		return;
	}

	if (bg != -1 && !builtin_cmd(argv)) {
		//处理addjob与子进程结束的竞争条件
		mask_signal(SIG_BLOCK, SIGCHLD);
		if ((pid = fork()) == 0) {
			//child
			mask_signal(SIG_UNBLOCK, SIGCHLD);
			if (setpgid(0, 0) < 0) { /* put the child in a new process group */
				unix_error("eval: setpgid failed");
			}
			if (execve(argv[0], argv, environ) < 0) {
				printf("%s: Command not found.\n", argv[0]);
				exit(0);
			}
		} else {
			//addjob
			if (!bg) {
				//fg
				addjob(jobs, pid, FG, cmdline);
			} else {
				//bg
				addjob(jobs, pid, BG, cmdline);
			}
			mask_signal(SIG_UNBLOCK, SIGCHLD); /* 添加完成,解除阻塞 */
			//wait foreground to stop
			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], "quit")) {
		exit(0);
	}
	if (!strcmp(argv[0], "&")) {
		return 1;
	}
	if (!strcmp(argv[0], "echo")) {
		do_echo(argv);
		return 1;
	}
	if (!strcmp("bg", argv[0]) || !(strcmp("fg", argv[0]))) {
		printf("bg/fg \n");
		do_bgfg(argv);
		return 1;
	}
	if (!strcmp("jobs", argv[0])) {
		listjobs(jobs);
		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;
	//获得jobid
	int jobid;
	if (id[0] == '%') {
		jobid = atoi(id += sizeof(char));
	}
	if ((job = getjobjid(jobs, jobid)) == NULL) {
		printf("job is not exist");
		return;
	}
	if (!strcmp(argv[0], "bg")) {
		//bg task
		job->state = BG;
		//唤醒job
		send_signal(-1 * job->pid, SIGCONT);

	} else if (!strcmp(argv[0], "fg")) {
		job->state = FG;
		send_signal(-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)) {
		sleep(0);
	}
	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("Handler child %d\n", (int) pid);
		sigint_handler(sig);
		if (
		WIFSTOPPED(status)) {
			/* handle stop signals (this assumes all stop signals are
			 equivalent to SIGTSTP) */
			sigtstp_handler(
			WSTOPSIG(status));
		} else if (WIFSIGNALED(status)) {
			/* 处理异常终止 */
			child_sig =
			WTERMSIG(status);
			if (child_sig == SIGINT)
				sigint_handler(child_sig);
			else
				unix_error("sigchld_handler: uncaught signal/n");
		} else
			deletejob(jobs, pid); /* remove the job under normal conditions */
	}
	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);//get fgid
	int jid = pid2jid(pid);
	if (pid != 0) {
		printf("Job %d terminated by signal: Interrupt", jid);
		deletejob(jobs, pid);
		send_signal(-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) {
	printf("stop sig\n");
	pid_t pid = fgpid(jobs); /* get pid of the fg job */
	int jid = pid2jid(pid);
	/* if there is a fg job, send it the signal */
	if (pid != 0) {
		printf("Job [%d] (%d) stopped by signal %d/n", jid, pid, sig);
		(*(getjobpid(jobs, pid))).state = ST; /* job's state is "stopped" */
		send_signal(-pid, sig); /* forward the signal to the process group */
	}
	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);
}

/*
 * echo function
 */
void do_echo(char **argv) {
	int i = 0;
	while (1) {
		if (argv[i + 1] != NULL) {
			printf("%s ", argv[i + 1]);
			i++;
		} else {
			break;
		}
	}
}

/*
 #  * mask the indicated signal according to "how"
 #  */
sigset_t mask_signal(int how, int sig) {
	sigset_t signals, result;
	if (sigemptyset(&signals) < 0)
		unix_error("mask_signal: sigemptyset failed");
	if (sigaddset(&signals, sig) < 0)
		unix_error("mask_signal: sigaddset failed");
	if (sigprocmask(how, &signals, &result) < 0)
		unix_error("mask_signal: sigprocmask failed");
	return result;
}

/*
 * error-handling wrapper for kill()
 */
int send_signal(pid_t pid, int sig) {
	if (kill(pid, sig) < 0) {
		/* fail silently if pid doesn't exist -- this keeps handlers that
		 are called too close together from complaining */
		if (errno != ESRCH)
			unix_error("send_signal: kill failed");
	}
	return 0;
}


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