tsh.c

/* 
 * tsh - A tiny shell program with job control
 * 
 * Dilluti0n
 */
#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);

/* my helper functions */
void listbgjobs(struct job_t *jobs);
int Sigprocmask(int how, const sigset_t *restrict set,
                sigset_t *restrict oset);
int Kill(pid_t pid, int sig);
void printjobpid(pid_t pid);
int parsebgfgarg(const char *argv1, int *id);
int bg2fg(struct job_t *bgjob);

/* 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]; /* array that we will store pointers to args */
    int isbg; /* is background job? 1:0 */
    
    isbg = parseline(cmdline, argv); /* parse cmdline to arg list */
    if (argv[0] == NULL)
        return;                 /* invalid format of cmdline */
    
    if (builtin_cmd(argv) == 1)
        return; /* argv[0] is builtin cmd (jobs, fg, bg) */

    /* set sigset mask for SIGCHLD */
    sigset_t mask;
    sigemptyset(&mask);
    sigaddset(&mask, SIGCHLD);
    Sigprocmask(SIG_BLOCK, &mask, NULL); /* Block SIGCHLD */
    
    /* now argv[0] is not builtin cmd, try to fork and execute */
    pid_t cpid;
    if ((cpid = fork()) < 0)
        unix_error("fork error");

    /* child process */
    if (cpid == 0) {
        /* set process group id to child process's pid.
         * now each child process's pgid are unique. */
        if (setpgid(0, 0) < 0)
            unix_error("setpgid error");
        Sigprocmask(SIG_UNBLOCK, &mask, NULL); /* Unblock SIGCHLD */
        if (execve(argv[0], argv, environ) < 0) { /* Execute `argv[0]` */
            printf("%s: Command not found\n", argv[0]);
            exit(0);
        }
        /* useless space */
    }

    /* parant process(shell) */
    int state = isbg ? BG : FG;
    if (addjob(jobs, cpid, state, cmdline) == 0) /* too many job */
        Kill(cpid, SIGKILL); /* addjob failed. kill the job */
    if (state == FG) {
        /* shell shall wait until foreground job stoped or terminated */
        waitfg(cpid);        
    } else { /* state == BG */
        printjobpid(cpid); /* print [jid] (pid) cmdline for background job */
    }
    Sigprocmask(SIG_UNBLOCK, &mask, NULL); /* Unblock SIGCHLD */
}

/* 
 * 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) 
{
    const char *cmd = argv[0];
    if (!strcmp("quit", cmd)) {
        fflush(stdout);
        exit(0);
    } else if (!strcmp("jobs", cmd)) {
        listbgjobs(jobs);
        return 1;  /* is a builtin command */
    } else if (!strcmp("bg", cmd) || !strcmp("fg", cmd)) {
        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) 
{
    const char *arg = argv[1];
    if (!strcmp("fg", argv[0])) {
        if (arg == NULL) {      /* no argument for command fg */
            printf("fg command requires PID or %%jobid argument\n");
            return;
        }
        int id, ispid;
        if ((ispid = parsebgfgarg(arg, &id)) < 0) { /* invalid argument */
            printf("fg: argument must be a PID or %%jobid\n");
            return;
        }
        if (ispid) {
            if (bg2fg(getjobpid(jobs, (pid_t) id)) == 0) {
                printf("(%d): no such process\n", id);
                return;
            }
        } else {
            if (bg2fg(getjobjid(jobs, id)) == 0) {
                printf("%%%d: no such job\n", id);
                return;
            }
        }
    } else if (!strcmp("bg", argv[0])) {
        if (arg == NULL) {      /* no argument for command bg */
            printf("bg command requires PID or %%jobid argument\n");
            return;
        }
        int id, ispid;
        struct job_t *job;                          /* target job */

        if ((ispid = parsebgfgarg(arg, &id)) < 0) { /* invalid argument */
            printf("bg: argument must be a PID or %%jobid\n");
            return;
        }
        if (ispid) {
            if ((job = getjobpid(jobs, (pid_t) id)) == NULL) {
                printf("(%d): no such process\n", id);
                return;
            }
            if (job->state == ST) {
                job->state = BG;
                Kill(job->pid, SIGCONT);
            }
            printf("[%d] (%d) %s", job->jid, job->pid, job->cmdline);
        } else { /* id is jid */
            if ((job = getjobjid(jobs, id)) == NULL) {
                printf("%%%d: no such job\n", id);
                return;
            }
            if (job->state == ST) {
                job->state = BG;
                Kill(job->pid, SIGCONT);
            }
            printf("[%d] (%d) %s", job->jid, job->pid, job->cmdline);
        }
    }   
}

/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{
    struct job_t *job; /* pointer to job struct of pid */
    int state;
    if ((job = getjobpid(jobs, pid)) == NULL)
        return; /* there is no job with corresponding pid */
    if ((state = job->state) != FG)
        return; /* do not do useless things when pid is not fg process */
    
    sigset_t mask;
    sigfillset(&mask);
    sigdelset(&mask, SIGCHLD); /* mask is set to only recieve SIGCHLD */
    sigdelset(&mask, SIGINT);  /* ... and SIGINT */
    sigdelset(&mask, SIGTSTP); /* ... and SIGTSTP */
    sigdelset(&mask, SIGSTOP);  /* ... and also SIGSTOP */

    while (state == FG) {
        sigsuspend(&mask); /* suspend current process until recieve SIGCHLD */
        if (errno != EINTR)
            unix_error("sigsuspend error");
        state = job->state; /* if job has been deleted, state is set to UNDEF
                             * or job has been stopped, state is set to ST */
    }
}

/*****************
 * 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 cstat; /* status when child terminated */
    int olderrno = errno;
    pid_t pid;
    sigset_t mask_all, prev;

    sigfillset(&mask_all);      /* block all signals while processing */
    
    /* note: we shouldn't block call of waitpid because if we block it and
     * child terminates while the last call of waitpid (return value -1 and
     * errno = ECHILD) our shell has no informantion about terminated process
     */
    while ((pid = waitpid((pid_t) -1, &cstat, WNOHANG | WUNTRACED)) > 0) {
        Sigprocmask(SIG_BLOCK, &mask_all, &prev);
        struct job_t *job;
        if ((job = getjobpid(jobs, pid)) == NULL) { /* this should not happen */
            Sigprocmask(SIG_SETMASK, &prev, NULL);
            break;
        }
        if (WIFSTOPPED(cstat)) { /* job is stopped */
            printf("Job [%d] (%d) stopped by signal %d\n", job->jid,
                   job->pid, WSTOPSIG(cstat));
            job->state = ST;        
        } else { /* job is terminated */
            if (WIFSIGNALED(cstat)) { /* process terminated by signal */
                printf("Job [%d] (%d) terminated by signal %d\n", job->jid,
                       job->pid, WTERMSIG(cstat));
            }
            /* no need to call deletejob() and do one more search for pid
             * since we already have job entry by getjobpid() */
            clearjob(job);
            nextjid = maxjid(jobs) + 1;
        }
        Sigprocmask(SIG_SETMASK, &prev, NULL);
    }
    if (pid < 0 && errno != ECHILD && errno != EINTR)
        unix_error("waitpid error");
    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) 
{
    int olderrno = errno;
    pid_t pid;                  /* pid of foreground process */
    sigset_t mask, prev;

    sigemptyset(&mask);
    sigaddset(&mask, SIGINT);   /* SIGINT should not be nested */
    Sigprocmask(SIG_BLOCK, &mask, &prev);
    if((pid = fgpid(jobs)) != 0)
        Kill(-pid, SIGINT);     /* send SIGINT to the foreground process */
    Sigprocmask(SIG_SETMASK, &prev, NULL);

    errno = olderrno;
}

/*
 * 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) 
{
    int olderrno = errno;
    pid_t pid;                   /* pid of foreground process */
    sigset_t mask, prev;

    sigemptyset(&mask);
    sigaddset(&mask, SIGTSTP);   /* SIGTSTP should not be nested */
    Sigprocmask(SIG_BLOCK, &mask, &prev);
    if((pid = fgpid(jobs)) != 0)
        Kill(-pid, SIGTSTP);     /* send SIGTSTP to the foreground process */
    Sigprocmask(SIG_SETMASK, &prev, NULL);

    errno = olderrno;
}

/*********************
 * End signal handlers
 *********************/

/********************
 * My helper routines
 ********************/

void listbgjobs(struct job_t *jobs)
{
    int i;
    
    for (i = 0; i < MAXJOBS; i++) {
        if (jobs[i].pid != 0 && jobs[i].state != FG) {
            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("%s: Internal error: job[%d].state=%d ", 
                       __func__, i, jobs[i].state);
            }
            printf("%s", jobs[i].cmdline);
        }
    }
}

int Sigprocmask(int how, const sigset_t *restrict set,
                sigset_t *restrict oset)
{
    int res;
    if ((res = sigprocmask(how, set, oset)) == 1)
        unix_error("sigprocmask error");
    return res;
}

int Kill(pid_t pid, int sig)
{
    int res;
    if ((res = kill(pid, sig)) < 0)
        unix_error("kill error");
    return res;
}

/* printjobpid - print job by pid */
void printjobpid(pid_t pid)
{
    struct job_t *job; /* pointer to process's job structure */

    if ((job = getjobpid(jobs, pid)) != NULL) {
        printf("[%d] (%d) ", job->jid, job->pid);
        printf("%s", job->cmdline);
    }
}

/*
 * parsebgfgarg - parse argument for internal command fg, bg
 *         return -1 if argv1 is invalid, 0 if %<jid>, 1 if <pid>
 */
int parsebgfgarg(const char *argv1, int *id)
{
    if (argv1 == NULL || id == NULL)
        return -1;

    int ispid = 1;
    if (*argv1 == '%') { /* jid */
        ispid = 0;
        argv1++;
    }
    if (!isdigit(*argv1)) /* invalid */
        return -1;

    /* parse the number from argv */
    char buf[MAXLINE];          /* buffer to store <id> */
    int bufp = 0, c;
    const int lim = MAXLINE - 1;
    while (isdigit(c = *argv1++) && bufp < lim)
        buf[bufp++] = c;
    buf[bufp] = '\0';

    /* store it to id */
    *id = atoi(buf);
    return ispid;
}
/*
 * bg2fg - switch background job to foregrond. retrun 0 if bgjob is NULL,
 *       return -1 if fatal error(bgjob is foreground job),
 *       return positive if no error.
 */
int bg2fg(struct job_t *bgjob)
{
    if (bgjob == NULL)
        return 0;
    if (bgjob->state == FG)
        return -1; /* fatal error */
    
    switch(bgjob->state) {
    case FG: /* this should not happen */
        break;
    case ST:
        bgjob->state = FG;
        Kill(-bgjob->pid, SIGCONT);
        break;
    case BG:
        bgjob->state = FG;
        break;
    default:
        break;
    }
    waitfg(bgjob->pid);         /* suspend shell for foreground job */
    return 1;
}

/************************
 * End My helper routines
 ************************/

/***********************************************
 * 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);
}