exec.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

#include "rc.h"
#include "getflags.h"
#include "exec.h"
#include "io.h"
#include "fns.h"
/*
 * Start executing the given code at the given pc with the given redirection
 */
char *argv0="rc";

void
start(code *c, int pc, var *local)
{
	struct thread *p = new(struct thread);

	p->code = codecopy(c);
	p->pc = pc;
	p->argv = 0;
	p->redir = p->startredir = runq?runq->redir:0;
	p->local = local;
	p->cmdfile = 0;
	p->cmdfd = 0;
	p->eof = 0;
	p->iflag = 0;
	p->lineno = 1;
	p->ret = runq;
	runq = p;
}

word*
newword(char *wd, word *next)
{
	word *p = new(word);
	p->word = strdup(wd);
	p->next = next;
	return p;
}

void
pushword(char *wd)
{
	if(runq->argv==0)
		panic("pushword but no argv!", 0);
	runq->argv->words = newword(wd, runq->argv->words);
}

void
popword(void)
{
	word *p;
	if(runq->argv==0)
		panic("popword but no argv!", 0);
	p = runq->argv->words;
	if(p==0)
		panic("popword but no word!", 0);
	runq->argv->words = p->next;
	efree(p->word);
	efree((char *)p);
}

void
freelist(word *w)
{
	word *nw;
	while(w){
		nw = w->next;
		efree(w->word);
		efree((char *)w);
		w = nw;
	}
}

void
pushlist(void)
{
	list *p = new(list);
	p->next = runq->argv;
	p->words = 0;
	runq->argv = p;
}

void
poplist(void)
{
	list *p = runq->argv;
	if(p==0)
		panic("poplist but no argv", 0);
	freelist(p->words);
	runq->argv = p->next;
	efree((char *)p);
}

int
count(word *w)
{
	int n;
	for(n = 0;w;n++) w = w->next;
	return n;
}

void
pushredir(int type, int from, int to)
{
	redir * rp = new(redir);
	rp->type = type;
	rp->from = from;
	rp->to = to;
	rp->next = runq->redir;
	runq->redir = rp;
}

var*
newvar(char *name, var *next)
{
	var *v = new(var);
	v->name = name;
	v->val = 0;
	v->fn = 0;
	v->changed = 0;
	v->fnchanged = 0;
	v->next = next;
	return v;
}
/*
 * get command line flags, initialize keywords & traps.
 * get values from environment.
 * set $pid, $cflag, $*
 * fabricate bootstrap code and start it (*=(argv);. /usr/lib/rcmain $*)
 * start interpreting code
 */

void
main(int argc, char *argv[])
{
	code bootstrap[17];
	char num[12], *rcmain;
	int i;
	argc = getflags(argc, argv, "SsrdiIlxepvVc:1m:1[command]", 1);
	if(argc==-1)
		usage("[file [arg ...]]");
	if(argv[0][0]=='-')
		flag['l'] = flagset;
	if(flag['I'])
		flag['i'] = 0;
	else if(flag['i']==0 && argc==1 && Isatty(0)) flag['i'] = flagset;
	rcmain = flag['m']?flag['m'][0]:Rcmain; 
	err = openfd(2);
	kinit();
	Trapinit();
	Vinit();
	inttoascii(num, mypid = getpid());
	setvar("pid", newword(num, (word *)0));
	setvar("cflag", flag['c']?newword(flag['c'][0], (word *)0)
				:(word *)0);
	setvar("rcname", newword(argv[0], (word *)0));
	i = 0;
	bootstrap[i++].i = 1;
	bootstrap[i++].f = Xmark;
	bootstrap[i++].f = Xword;
	bootstrap[i++].s="*";
	bootstrap[i++].f = Xassign;
	bootstrap[i++].f = Xmark;
	bootstrap[i++].f = Xmark;
	bootstrap[i++].f = Xword;
	bootstrap[i++].s="*";
	bootstrap[i++].f = Xdol;
	bootstrap[i++].f = Xword;
	bootstrap[i++].s = rcmain;
	bootstrap[i++].f = Xword;
	bootstrap[i++].s=".";
	bootstrap[i++].f = Xsimple;
	bootstrap[i++].f = Xexit;
	bootstrap[i].i = 0;
	start(bootstrap, 1, (var *)0);
	/* prime bootstrap argv */
	pushlist();
	argv0 = strdup(argv[0]);
	for(i = argc-1;i!=0;--i) pushword(argv[i]);
	for(;;){
		if(flag['r'])
			pfnc(err, runq);
		runq->pc++;
		(*runq->code[runq->pc-1].f)();
		if(ntrap)
			dotrap();
	}
}
/*
 * Opcode routines
 * Arguments on stack (...)
 * Arguments in line [...]
 * Code in line with jump around {...}
 *
 * Xappend(file)[fd]			open file to append
 * Xassign(name, val)			assign val to name
 * Xasync{... Xexit}			make thread for {}, no wait
 * Xbackq{... Xreturn}			make thread for {}, push stdout
 * Xbang				complement condition
 * Xcase(pat, value){...}		exec code on match, leave (value) on
 * 					stack
 * Xclose[i]				close file descriptor
 * Xconc(left, right)			concatenate, push results
 * Xcount(name)				push var count
 * Xdelfn(name)				delete function definition
 * Xdeltraps(names)			delete named traps
 * Xdol(name)				get variable value
 * Xqdol(name)				concatenate variable components
 * Xdup[i j]				dup file descriptor
 * Xexit				rc exits with status
 * Xfalse{...}				execute {} if false
 * Xfn(name){... Xreturn}			define function
 * Xfor(var, list){... Xreturn}		for loop
 * Xjump[addr]				goto
 * Xlocal(name, val)			create local variable, assign value
 * Xmark				mark stack
 * Xmatch(pat, str)			match pattern, set status
 * Xpipe[i j]{... Xreturn}{... Xreturn}	construct a pipe between 2 new threads,
 * 					wait for both
 * Xpipefd[type]{... Xreturn}		connect {} to pipe (input or output,
 * 					depending on type), push /dev/fd/??
 * Xpopm(value)				pop value from stack
 * Xrdwr(file)[fd]			open file for reading and writing
 * Xread(file)[fd]			open file to read
 * Xsettraps(names){... Xreturn}		define trap functions
 * Xshowtraps				print trap list
 * Xsimple(args)			run command and wait
 * Xreturn				kill thread
 * Xsubshell{... Xexit}			execute {} in a subshell and wait
 * Xtrue{...}				execute {} if true
 * Xunlocal				delete local variable
 * Xword[string]			push string
 * Xwrite(file)[fd]			open file to write
 */

void
Xappend(void)
{
	char *file;
	int f;
	switch(count(runq->argv->words)){
	default:
		Xerror1(">> requires singleton");
		return;
	case 0:
		Xerror1(">> requires file");
		return;
	case 1:
		break;
	}
	file = runq->argv->words->word;
	if((f = open(file, 1))<0 && (f = Creat(file))<0){
		pfmt(err, "%s: ", file);
		Xerror("can't open");
		return;
	}
	Seek(f, 0L, 2);
	pushredir(ROPEN, f, runq->code[runq->pc].i);
	runq->pc++;
	poplist();
}

void
Xsettrue(void)
{
	setstatus("");
}

void
Xbang(void)
{
	setstatus(truestatus()?"false":"");
}

void
Xclose(void)
{
	pushredir(RCLOSE, runq->code[runq->pc].i, 0);
	runq->pc++;
}

void
Xdup(void)
{
	pushredir(RDUP, runq->code[runq->pc].i, runq->code[runq->pc+1].i);
	runq->pc+=2;
}

void
Xeflag(void)
{
	if(eflagok && !truestatus()) Xexit();
}

void
Xexit(void)
{
	struct var *trapreq;
	struct word *starval;
	static int beenhere = 0;
	if(getpid()==mypid && !beenhere){
		trapreq = vlook("sigexit");
		if(trapreq->fn){
			beenhere = 1;
			--runq->pc;
			starval = vlook("*")->val;
			start(trapreq->fn, trapreq->pc, (struct var *)0);
			runq->local = newvar(strdup("*"), runq->local);
			runq->local->val = copywords(starval, (struct word *)0);
			runq->local->changed = 1;
			runq->redir = runq->startredir = 0;
			return;
		}
	}
	Exit(getstatus());
}

void
Xfalse(void)
{
	if(truestatus()) runq->pc = runq->code[runq->pc].i;
	else runq->pc++;
}
int ifnot;		/* dynamic if not flag */

void
Xifnot(void)
{
	if(ifnot)
		runq->pc++;
	else
		runq->pc = runq->code[runq->pc].i;
}

void
Xjump(void)
{
	runq->pc = runq->code[runq->pc].i;
}

void
Xmark(void)
{
	pushlist();
}

void
Xpopm(void)
{
	poplist();
}

void
Xread(void)
{
	char *file;
	int f;
	switch(count(runq->argv->words)){
	default:
		Xerror1("< requires singleton\n");
		return;
	case 0:
		Xerror1("< requires file\n");
		return;
	case 1:
		break;
	}
	file = runq->argv->words->word;
	if((f = open(file, 0))<0){
		pfmt(err, "%s: ", file);
		Xerror("can't open");
		return;
	}
	pushredir(ROPEN, f, runq->code[runq->pc].i);
	runq->pc++;
	poplist();
}

void
Xrdwr(void)
{
	char *file;
	int f;

	switch(count(runq->argv->words)){
	default:
		Xerror1("<> requires singleton\n");
		return;
	case 0:
		Xerror1("<> requires file\n");
		return;
	case 1:
		break;
	}
	file = runq->argv->words->word;
	if((f = open(file, ORDWR))<0){
		pfmt(err, "%s: ", file);
		Xerror("can't open");
		return;
	}
	pushredir(ROPEN, f, runq->code[runq->pc].i);
	runq->pc++;
	poplist();
}

void
turfredir(void)
{
	while(runq->redir!=runq->startredir)
		Xpopredir();
}

void
Xpopredir(void)
{
	struct redir *rp = runq->redir;
	if(rp==0)
		panic("turfredir null!", 0);
	runq->redir = rp->next;
	if(rp->type==ROPEN)
		close(rp->from);
	efree((char *)rp);
}

void
Xreturn(void)
{
	struct thread *p = runq;
	turfredir();
	while(p->argv) poplist();
	codefree(p->code);
	runq = p->ret;
	efree((char *)p);
	if(runq==0)
		Exit(getstatus());
}

void
Xtrue(void)
{
	if(truestatus()) runq->pc++;
	else runq->pc = runq->code[runq->pc].i;
}

void
Xif(void)
{
	ifnot = 1;
	if(truestatus()) runq->pc++;
	else runq->pc = runq->code[runq->pc].i;
}

void
Xwastrue(void)
{
	ifnot = 0;
}

void
Xword(void)
{
	pushword(runq->code[runq->pc++].s);
}

void
Xwrite(void)
{
	char *file;
	int f;
	switch(count(runq->argv->words)){
	default:
		Xerror1("> requires singleton\n");
		return;
	case 0:
		Xerror1("> requires file\n");
		return;
	case 1:
		break;
	}
	file = runq->argv->words->word;
	if((f = Creat(file))<0){
		pfmt(err, "%s: ", file);