main.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#endif /* KSH */
	} else
		Flag(FTRACKALL) = 1;	/* set after ENV */

	shell(s, TRUE);	/* doesn't return */
	return 0;
}

int
include(name, argc, argv, intr_ok)
	const char *name;
	int argc;
	char **argv;
	int intr_ok;
{
	register Source *volatile s = NULL;
	Source *volatile sold;
	struct shf *shf;
	char **volatile old_argv;
	volatile int old_argc;
	int i;

	shf = shf_open(name, O_RDONLY, 0, SHF_MAPHI|SHF_CLEXEC);
	if (shf == NULL)
		return -1;

	if (argv) {
		old_argv = e->loc->argv;
		old_argc = e->loc->argc;
	} else {
		old_argv = (char **) 0;
		old_argc = 0;
	}
	sold = source;
	newenv(E_INCL);
	i = ksh_sigsetjmp(e->jbuf, 0);
	if (i) {
		source = sold;
		if (s) /* Do this before quitenv(), which frees the memory */
			shf_close(s->u.shf);
		quitenv();
		if (old_argv) {
			e->loc->argv = old_argv;
			e->loc->argc = old_argc;
		}
		switch (i) {
		  case LRETURN:
		  case LERROR:
			return exstat & 0xff; /* see below */
		  case LINTR:
			/* intr_ok is set if we are including .profile or $ENV.
			 * If user ^C's out, we don't want to kill the shell...
			 */
			if (intr_ok && (exstat - 128) != SIGTERM)
				return 1;
			/* fall through... */
		  case LEXIT:
		  case LLEAVE:
		  case LSHELL:
			unwind(i);
			/*NOREACHED*/
		  default:
			internal_errorf(1, "include: %d", i);
			/*NOREACHED*/
		}
	}
	if (argv) {
		e->loc->argv = argv;
		e->loc->argc = argc;
	}
	s = pushs(SFILE, ATEMP);
	s->u.shf = shf;
	s->file = str_save(name, ATEMP);
	i = shell(s, FALSE);
	source = sold;
	shf_close(s->u.shf);
	quitenv();
	if (old_argv) {
		e->loc->argv = old_argv;
		e->loc->argc = old_argc;
	}
	return i & 0xff;	/* & 0xff to ensure value not -1 */
}

int
command(comm)
	const char *comm;
{
	register Source *s;

	s = pushs(SSTRING, ATEMP);
	s->start = s->str = comm;
	return shell(s, FALSE);
}

/*
 * run the commands from the input source, returning status.
 */
int
shell(s, toplevel)
	Source *volatile s;		/* input source */
	int volatile toplevel;
{
	struct op *t;
	volatile int wastty = s->flags & SF_TTY;
	volatile int attempts = 13;
	volatile int interactive = Flag(FTALKING) && toplevel;
	int i;

	newenv(E_PARSE);
	if (interactive)
		really_exit = 0;
	i = ksh_sigsetjmp(e->jbuf, 0);
	if (i) {
		s->start = s->str = null;
		switch (i) {
		  case LINTR: /* we get here if SIGINT not caught or ignored */
		  case LERROR:
		  case LSHELL:
			if (interactive) {
				if (i == LINTR)
					shellf(newline);
				/* Reset any eof that was read as part of a
				 * multiline command.
				 */
				if (Flag(FIGNOREEOF) && s->type == SEOF
				    && wastty)
					s->type = SSTDIN;
				/* Used by exit command to get back to
				 * top level shell.  Kind of strange since
				 * interactive is set if we are reading from
				 * a tty, but to have stopped jobs, one only
				 * needs FMONITOR set (not FTALKING/SF_TTY)...
				 */
				break;
			}
			/* fall through... */
		  case LEXIT:
		  case LLEAVE:
		  case LRETURN:
			quitenv();
			unwind(i);	/* keep on going */
			/*NOREACHED*/
		  default:
			quitenv();
			internal_errorf(1, "shell: %d", i);
			/*NOREACHED*/
		}
	}

	while (1) {
		if (trap)
			runtraps(0);

		if (s->next == NULL)
			if (Flag(FVERBOSE))
				s->flags |= SF_ECHO;
			else
				s->flags &= ~SF_ECHO;

		if (interactive) {
			j_notify();
#ifdef KSH
			mcheck();
#endif /* KSH */
			set_prompt(PS1, s);
		}

		t = compile(s);
		if (t != NULL && t->type == TEOF) {
			if (wastty && Flag(FIGNOREEOF) && --attempts > 0) {
				shellf("Use `exit' to leave ksh\n");
				s->type = SSTDIN;
			} else if (wastty && !really_exit
				   && j_stopped_running())
			{
				really_exit = 1;
				s->type = SSTDIN;
			} else {
				/* this for POSIX, which says EXIT traps
				 * shall be taken in the environment
				 * immediately after the last command
				 * executed.
				 */
				if (toplevel)
					unwind(LEXIT);
				break;
			}
		}

		if (t && (!Flag(FNOEXEC) || (s->flags & SF_TTY)))
			exstat = execute(t, 0);

		if (t != NULL && t->type != TEOF && interactive && really_exit)
			really_exit = 0;

		reclaim();
	}
	quitenv();
	return exstat;
}

/* return to closest error handler or shell(), exit if none found */
void
unwind(i)
	int i;
{
	/* ordering for EXIT vs ERR is a bit odd (this is what at&t ksh does) */
	if (i == LEXIT || (Flag(FERREXIT) && (i == LERROR || i == LINTR)
			   && sigtraps[SIGEXIT_].trap))
	{
		runtrap(&sigtraps[SIGEXIT_]);
		i = LLEAVE;
	} else if (Flag(FERREXIT) && (i == LERROR || i == LINTR)) {
		runtrap(&sigtraps[SIGERR_]);
		i = LLEAVE;
	}
	while (1) {
		switch (e->type) {
		  case E_PARSE:
		  case E_FUNC:
		  case E_INCL:
		  case E_LOOP:
		  case E_ERRH:
			ksh_siglongjmp(e->jbuf, i);
			/*NOTREACHED*/

		  case E_NONE:
			if (i == LINTR)
				e->flags |= EF_FAKE_SIGDIE;
			/* Fall through... */

		  default:
			quitenv();
		}
	}
}

void
newenv(type)
	int type;
{
	register struct env *ep;

	ep = (struct env *) alloc(sizeof(*ep), ATEMP);
	ep->type = type;
	ep->flags = 0;
	ainit(&ep->area);
	ep->loc = e->loc;
	ep->savefd = NULL;
	ep->oenv = e;
	ep->temps = NULL;
	e = ep;
}

void
quitenv()
{
	register struct env *ep = e;
	register int fd;

	if (ep->oenv && ep->oenv->loc != ep->loc)
		popblock();
	if (ep->savefd != NULL) {
		for (fd = 0; fd < NUFILE; fd++)
			/* if ep->savefd[fd] < 0, means fd was closed */
			if (ep->savefd[fd])
				restfd(fd, ep->savefd[fd]);
		if (ep->savefd[2]) /* Clear any write errors */
			shf_reopen(2, SHF_WR, shl_out);
	}
	reclaim();

	/* Bottom of the stack.
	 * Either main shell is exiting or cleanup_parents_env() was called.
	 */
	if (ep->oenv == NULL) {
		if (ep->type == E_NONE) {	/* Main shell exiting? */
			if (Flag(FTALKING))
				hist_finish();
			j_exit();
			if (ep->flags & EF_FAKE_SIGDIE) {
				int sig = exstat - 128;

				/* ham up our death a bit (at&t ksh
				 * only seems to do this for SIGTERM)
				 * Don't do it for SIGQUIT, since we'd
				 * dump a core..
				 */
				if (sig == SIGINT || sig == SIGTERM) {
					setsig(&sigtraps[sig], SIG_DFL,
						SS_RESTORE_CURR|SS_FORCE);
					kill(0, sig);
				}
			}
#ifdef MEM_DEBUG
			chmem_allfree();
#endif /* MEM_DEBUG */
		}
		exit(exstat);
	}

	e = e->oenv;
	afree(ep, ATEMP);
}

/* Called after a fork to cleanup stuff left over from parents environment */
void
cleanup_parents_env()
{
	struct env *ep;
	int fd;

	/* Don't clean up temporary files - parent will probably need them.
	 * Also, can't easily reclaim memory since variables, etc. could be
	 * anywyere.
	 */

	/* close all file descriptors hiding in savefd */
	for (ep = e; ep; ep = ep->oenv) {
		if (ep->savefd) {
			for (fd = 0; fd < NUFILE; fd++)
				if (ep->savefd[fd] > 0)
					close(ep->savefd[fd]);
			afree(ep->savefd, &ep->area);
			ep->savefd = (short *) 0;
		}
	}
	e->oenv = (struct env *) 0;
}

/* Called just before an execve cleanup stuff temporary files */
void
cleanup_proc_env()
{
	struct env *ep;

	for (ep = e; ep; ep = ep->oenv)
		remove_temps(ep->temps);
}

/* remove temp files and free ATEMP Area */
static void
reclaim()
{
	remove_temps(e->temps);
	e->temps = NULL;
	afreeall(&e->area);
}

static void
remove_temps(tp)
	struct temp *tp;
{
#ifdef OS2
	static struct temp *delayed_remove;
	struct temp *t, **tprev;

	if (delayed_remove) {
		for (tprev = &delayed_remove, t = delayed_remove; t; t = *tprev)
			/* No need to check t->pid here... */
			if (unlink(t->name) >= 0 || errno == ENOENT) {
				*tprev = t->next;
				afree(t, APERM);
			} else
				tprev = &t->next;
	}
#endif /* OS2 */

	for (; tp != NULL; tp = tp->next)
		if (tp->pid == procpid) {
#ifdef OS2
			/* OS/2 (and dos) do not allow files that are currently
			 * open to be removed, so we cache it away for future
			 * removal.
			 * XXX should only do this if errno
			 *     is Efile-still-open-can't-remove
			 *     (but I don't know what that is...)
			 */
			if (unlink(tp->name) < 0 && errno != ENOENT) {
				t = (struct temp *) alloc(
				    sizeof(struct temp) + strlen(tp->name) + 1,
				    APERM);
				memset(t, 0, sizeof(struct temp));
				t->name = (char *) &t[1];
				strcpy(t->name, tp->name);
				t->next = delayed_remove;
				delayed_remove = t;
			}
#else /* OS2 */
			unlink(tp->name);
#endif /* OS2 */
		}
}

/* Returns true if name refers to a restricted shell */
static int
is_restricted(name)
	char *name;
{
	char *p;

	/* this silly function prevents you running a command called runconf.sh. */
	/* we don't care about restricted shells, which aren't very restricted anyway */
	/* and introduce a false sense of security */
	return 0;
#ifdef dumbidea
	if ((p = ksh_strrchr_dirsep(name)))
		name = p;
	/* accepts rsh, rksh, rpdksh, pdrksh, etc. */
	return (p = strchr(name, 'r')) && strstr(p, "sh");
#endif
}

void
aerror(ap, msg)
	Area *ap;
	const char *msg;
{
	internal_errorf(1, "alloc: %s", msg);
	errorf(null); /* this is never executed - keeps gcc quiet */
	/*NOTREACHED*/
}