exec.c

早期freebsd实现

/* exec.c */
#include <signal.h>
#include <errno.h>
#include <setjmp.h>
#include "rc.h"
#include "jbwrap.h"

/*
   Takes an argument list and does the appropriate thing (calls a
   builtin, calls a function, etc.)
*/

extern void exec(List *s, bool parent) {
	char **av, **ev = NULL;
	int pid, stat;
	builtin_t *b;
	char *path = NULL;
	bool didfork, returning, saw_exec, saw_builtin;
	av = list2array(s, dashex);
	saw_builtin = saw_exec = FALSE;
	do {
		if (*av == NULL	|| isabsolute(*av))
			b = NULL;
		else if (!saw_builtin && fnlookup(*av) != NULL)
			b = funcall;
		else
			b = isbuiltin(*av);

		/*
		   a builtin applies only to the immmediately following
		   command, e.g., builtin exec echo hi
		*/
		saw_builtin = FALSE;

		if (b == b_exec) {
			av++;
			saw_exec = TRUE;
			parent = FALSE;
		} else if (b == b_builtin) {
			av++;
			saw_builtin = TRUE;
		}
	} while (b == b_exec || b == b_builtin);
	if (*av == NULL && saw_exec) { /* do redirs and return on a null exec */
		doredirs();
		return;
	}
	/* force an exit on exec with any rc_error, but not for null commands as above */
	if (saw_exec)
		rc_pid = -1;
	if (b == NULL) {
		path = which(*av, TRUE);
		if (path == NULL && *av != NULL) { /* perform null commands for redirections */
			set(FALSE);
			redirq = NULL;
			if (parent)
				return;
			rc_exit(1);
		}
		ev = makeenv(); /* environment only needs to be built for execve() */
	}
	/*
	   If parent & the redirq is nonnull, builtin or not it has to fork.
	   If the fifoq is nonnull, then it must be emptied at the end so we
	   must fork no matter what.
	 */
	if ((parent && (b == NULL || redirq != NULL)) || outstanding_cmdarg()) {
		pid = rc_fork();
		didfork = TRUE;
	} else {
		pid = 0;
		didfork = FALSE;
	}
	returning = (!didfork && parent);
	switch (pid) {
	case -1:
		uerror("fork");
		rc_error(NULL);
		/* NOTREACHED */
	case 0:
		if (!returning)
			setsigdefaults(FALSE);
		pop_cmdarg(FALSE);
		doredirs();

		/* null commands performed for redirections */
		if (*av == NULL || b != NULL) {
			if (b != NULL)
				(*b)(av);
			if (returning)
				return;
			rc_exit(getstatus());
		}
		execve(path, (char * const *) av, (char * const *) ev);
		uerror(*av);
		rc_exit(1);
		/* NOTREACHED */
	default:
		redirq = NULL;
		rc_wait4(pid, &stat, TRUE);
		setstatus(-1, stat);
		if ((stat & 0xff) == 0)
			nl_on_intr = FALSE;
		SIGCHK;
		nl_on_intr = TRUE;
		pop_cmdarg(TRUE);
	}
}