cpu.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

static int
srvp9auth(int fd, char *user)
{
	uchar key[16];
	uchar digest[SHA1dlen];
	char fromclientsecret[21];
	char fromserversecret[21];
	int i;
	AuthInfo *ai;

	ai = auth_proxy(0, nil, "proto=%q role=server %s", p9authproto, keyspec);
	if(ai == nil)
		return -1;
	if(auth_chuid(ai, nil) < 0)
		return -1;
	strecpy(user, user+MaxStr, ai->cuid);
	memmove(key+4, ai->secret, ai->nsecret);

	if(ealgs == nil)
		return fd;

	/* exchange random numbers */
	srand(truerand());
	for(i = 0; i < 4; i++)
		key[i+12] = rand();
	if(readn(fd, key, 4) != 4)
		return -1;
	if(write(fd, key+12, 4) != 4)
		return -1;

	/* scramble into two secrets */
	sha1(key, sizeof(key), digest, nil);
	mksecret(fromclientsecret, digest);
	mksecret(fromserversecret, digest+10);

	/* set up encryption */
	i = pushssl(fd, ealgs, fromserversecret, fromclientsecret, nil);
	if(i < 0)
		werrstr("can't establish ssl connection: %r");
	return i;
}

/*
 *  set authentication mechanism
 */
int
setam(char *name)
{
	for(am = authmethod; am->name != nil; am++)
		if(strcmp(am->name, name) == 0)
			return 0;
	am = authmethod;
	return -1;
}

/*
 *  set authentication mechanism and encryption/hash algs
 */
int
setamalg(char *s)
{
	ealgs = strchr(s, ' ');
	if(ealgs != nil)
		*ealgs++ = 0;
	return setam(s);
}

char *rmtnotefile = "/mnt/term/dev/cpunote";

/*
 *  loop reading /mnt/term/dev/note looking for notes.
 *  The child returns to start the shell.
 */
void
rmtnoteproc(void)
{
	int n, fd, pid, notepid;
	char buf[256];

	/* new proc returns to start shell */
	pid = rfork(RFPROC|RFFDG|RFNOTEG|RFNAMEG|RFMEM);
	switch(pid){
	case -1:
		syslog(0, "cpu", "cpu -R: can't start noteproc: %r");
		return;
	case 0:
		return;
	}

	/* new proc reads notes from other side and posts them to shell */
	switch(notepid = rfork(RFPROC|RFFDG|RFMEM)){
	case -1:
		syslog(0, "cpu", "cpu -R: can't start wait proc: %r");
		_exits(0);
	case 0:
		fd = open(rmtnotefile, OREAD);
		if(fd < 0){
			syslog(0, "cpu", "cpu -R: can't open %s", rmtnotefile);
			_exits(0);
		}
	
		for(;;){
			n = read(fd, buf, sizeof(buf)-1);
			if(n <= 0){
				postnote(PNGROUP, pid, "hangup");
				_exits(0);
			}
			buf[n] = 0;
			postnote(PNGROUP, pid, buf);
		}
	}

	/* original proc waits for shell proc to die and kills note proc */
	for(;;){
		n = waitpid();
		if(n < 0 || n == pid)
			break;
	}
	postnote(PNPROC, notepid, "kill");
	_exits(0);
}

enum
{
	Qdir,
	Qcpunote,

	Nfid = 32,
};

struct {
	char	*name;
	Qid	qid;
	ulong	perm;
} fstab[] =
{
	[Qdir]		{ ".",		{Qdir, 0, QTDIR},	DMDIR|0555	},
	[Qcpunote]	{ "cpunote",	{Qcpunote, 0},		0444		},
};

typedef struct Note Note;
struct Note
{
	Note *next;
	char msg[ERRMAX];
};

typedef struct Request Request;
struct Request
{
	Request *next;
	Fcall f;
};

typedef struct Fid Fid;
struct Fid
{
	int	fid;
	int	file;
	int	omode;
};
Fid fids[Nfid];

struct {
	Lock;
	Note *nfirst, *nlast;
	Request *rfirst, *rlast;
} nfs;

int
fsreply(int fd, Fcall *f)
{
	uchar buf[IOHDRSZ+Maxfdata];
	int n;

	if(dbg)
		fprint(2, "<-%F\n", f);
	n = convS2M(f, buf, sizeof buf);
	if(n > 0){
		if(write(fd, buf, n) != n){
			close(fd);
			return -1;
		}
	}
	return 0;
}

/* match a note read request with a note, reply to the request */
int
kick(int fd)
{
	Request *rp;
	Note *np;
	int rv;

	for(;;){
		lock(&nfs);
		rp = nfs.rfirst;
		np = nfs.nfirst;
		if(rp == nil || np == nil){
			unlock(&nfs);
			break;
		}
		nfs.rfirst = rp->next;
		nfs.nfirst = np->next;
		unlock(&nfs);

		rp->f.type = Rread;
		rp->f.count = strlen(np->msg);
		rp->f.data = np->msg;
		rv = fsreply(fd, &rp->f);
		free(rp);
		free(np);
		if(rv < 0)
			return -1;
	}
	return 0;
}

void
flushreq(int tag)
{
	Request **l, *rp;

	lock(&nfs);
	for(l = &nfs.rfirst; *l != nil; l = &(*l)->next){
		rp = *l;
		if(rp->f.tag == tag){
			*l = rp->next;
			unlock(&nfs);
			free(rp);
			return;
		}
	}
	unlock(&nfs);
}

Fid*
getfid(int fid)
{
	int i, freefid;

	freefid = -1;
	for(i = 0; i < Nfid; i++){
		if(freefid < 0 && fids[i].file < 0)
			freefid = i;
		if(fids[i].fid == fid)
			return &fids[i];
	}
	if(freefid >= 0){
		fids[freefid].fid = fid;
		return &fids[freefid];
	}
	return nil;
}

int
fsstat(int fd, Fid *fid, Fcall *f)
{
	Dir d;
	uchar statbuf[256];

	memset(&d, 0, sizeof(d));
	d.name = fstab[fid->file].name;
	d.uid = user;
	d.gid = user;
	d.muid = user;
	d.qid = fstab[fid->file].qid;
	d.mode = fstab[fid->file].perm;
	d.atime = d.mtime = time(0);
	f->stat = statbuf;
	f->nstat = convD2M(&d, statbuf, sizeof statbuf);
	return fsreply(fd, f);
}

int
fsread(int fd, Fid *fid, Fcall *f)
{
	Dir d;
	uchar buf[256];
	Request *rp;

	switch(fid->file){
	default:
		return -1;
	case Qdir:
		if(f->offset == 0 && f->count >0){
			memset(&d, 0, sizeof(d));
			d.name = fstab[Qcpunote].name;
			d.uid = user;
			d.gid = user;
			d.muid = user;
			d.qid = fstab[Qcpunote].qid;
			d.mode = fstab[Qcpunote].perm;
			d.atime = d.mtime = time(0);
			f->count = convD2M(&d, buf, sizeof buf);
			f->data = (char*)buf;
		} else
			f->count = 0;
		return fsreply(fd, f);
	case Qcpunote:
		rp = mallocz(sizeof(*rp), 1);
		if(rp == nil)
			return -1;
		rp->f = *f;
		lock(&nfs);
		if(nfs.rfirst == nil)
			nfs.rfirst = rp;
		else
			nfs.rlast->next = rp;
		nfs.rlast = rp;
		unlock(&nfs);
		return kick(fd);;
	}
}

char Eperm[] = "permission denied";
char Enofile[] = "out of files";
char Enotdir[] = "not a directory";

void
notefs(int fd)
{
	uchar buf[IOHDRSZ+Maxfdata];
	int i, j, n, ncpunote;
	char err[ERRMAX];
	Fcall f;
	Fid *fid, *nfid;
	int doreply;

	rfork(RFNOTEG);
	fmtinstall('F', fcallfmt);

	for(n = 0; n < Nfid; n++){
		fids[n].file = -1;
		fids[n].omode = -1;
	}

	ncpunote = 0;
	for(;;){
		n = read9pmsg(fd, buf, sizeof(buf));
		if(n <= 0){
			if(dbg)
				fprint(2, "read9pmsg(%d) returns %d: %r\n", fd, n);
			break;
		}
		if(convM2S(buf, n, &f) <= BIT16SZ)
			break;
		if(dbg)
			fprint(2, "->%F\n", &f);
		doreply = 1;
		fid = getfid(f.fid);
		if(fid == nil){
nofids:
			f.type = Rerror;
			f.ename = Enofile;
			fsreply(fd, &f);
			continue;
		}
		switch(f.type++){
		default:
			f.type = Rerror;
			f.ename = "unknown type";
			break;
		case Tflush:
			flushreq(f.oldtag);
			break;
		case Tversion:
			if(f.msize > IOHDRSZ+Maxfdata)
				f.msize = IOHDRSZ+Maxfdata;
			break;
		case Tauth:
			f.type = Rerror;
			f.ename = "cpu: authentication not required";
			break;
		case Tattach:
			f.qid = fstab[Qdir].qid;
			fid->file = Qdir;
			break;
		case Twalk:
			nfid = nil;
			if(f.newfid != f.fid){
				nfid = getfid(f.newfid);
				if(nfid == nil)
					goto nofids;
				nfid->file = fid->file;
				fid = nfid;
			}

			f.ename = nil;
			for(i=0; i<f.nwname; i++){
				if(i > MAXWELEM){
					f.type = Rerror;
					f.ename = "too many name elements";
					break;
				}
				if(fid->file != Qdir){
					f.type = Rerror;
					f.ename = Enotdir;
					break;
				}
				if(strcmp(f.wname[i], "cpunote") == 0){
					fid->file = Qcpunote;
					f.wqid[i] = fstab[Qcpunote].qid;
					continue;
				}
				f.type = Rerror;
				f.ename = err;
				strcpy(err, "cpu: file \"");
				for(j=0; j<=i; j++){
					if(strlen(err)+1+strlen(f.wname[j])+32 > sizeof err)
						break;
					if(j != 0)
						strcat(err, "/");
					strcat(err, f.wname[j]);
				}
				strcat(err, "\" does not exist");
				break;
			}
			if(nfid != nil && (f.ename != nil || i < f.nwname))
				nfid ->file = -1;
			if(f.type != Rerror)
				f.nwqid = i;
			break;
		case Topen:
			if(f.mode != OREAD){
				f.type = Rerror;
				f.ename = Eperm;
			}
			fid->omode = f.mode;
			if(fid->file == Qcpunote)
				ncpunote++;
			f.qid = fstab[fid->file].qid;
			break;
		case Tcreate:
			f.type = Rerror;
			f.ename = Eperm;
			break;
		case Tread:
			if(fsread(fd, fid, &f) < 0)
				goto err;
			doreply = 0;
			break;
		case Twrite:
			f.type = Rerror;
			f.ename = Eperm;
			break;
		case Tclunk:
			if(fid->omode != -1 && fid->file == Qcpunote){
				ncpunote--;
				if(ncpunote == 0)	/* remote side is done */
					goto err;
			}
			fid->file = -1;
			fid->omode = -1;
			break;
		case Tremove:
			f.type = Rerror;
			f.ename = Eperm;
			break;
		case Tstat:
			if(fsstat(fd, fid, &f) < 0)
				goto err;
			doreply = 0;
			break;
		case Twstat:
			f.type = Rerror;
			f.ename = Eperm;
			break;
		}
		if(doreply)
			if(fsreply(fd, &f) < 0)
				break;
	}
err:
	if(dbg)
		fprint(2, "notefs exiting: %r\n");
	werrstr("success");
	postnote(PNGROUP, exportpid, "kill");
	if(dbg)
		fprint(2, "postnote PNGROUP %d: %r\n", exportpid);
	close(fd);
}

char 	notebuf[ERRMAX];

void
catcher(void*, char *text)
{
	int n;

	n = strlen(text);
	if(n >= sizeof(notebuf))
		n = sizeof(notebuf)-1;
	memmove(notebuf, text, n);
	notebuf[n] = '\0';
	noted(NCONT);
}

/*
 *  mount in /dev a note file for the remote side to read.
 */
void
lclnoteproc(int netfd)
{
	Waitmsg *w;
	Note *np;
	int pfd[2];
	int pid;

	if(pipe(pfd) < 0){
		fprint(2, "cpu: can't start note proc: pipe: %r\n");
		return;
	}

	/* new proc mounts and returns to start exportfs */
	switch(pid = rfork(RFPROC|RFNAMEG|RFFDG|RFMEM)){
	default:
		exportpid = pid;
		break;
	case -1:
		fprint(2, "cpu: can't start note proc: rfork: %r\n");
		return;
	case 0:
		close(pfd[0]);
		if(mount(pfd[1], -1, "/dev", MBEFORE, "") < 0)
			fprint(2, "cpu: can't mount note proc: %r\n");
		close(pfd[1]);
		return;
	}

	close(netfd);
	close(pfd[1]);

	/* new proc listens for note file system rpc's */
	switch(rfork(RFPROC|RFNAMEG|RFMEM)){
	case -1:
		fprint(2, "cpu: can't start note proc: rfork1: %r\n");
		_exits(0);
	case 0:
		notefs(pfd[0]);
		_exits(0);
	}

	/* original proc waits for notes */
	notify(catcher);
	w = nil;
	for(;;) {
		*notebuf = 0;
		free(w);
		w = wait();
		if(w == nil) {
			if(*notebuf == 0)
				break;
			np = mallocz(sizeof(Note), 1);
			if(np != nil){
				strcpy(np->msg, notebuf);
				lock(&nfs);
				if(nfs.nfirst == nil)
					nfs.nfirst = np;
				else
					nfs.nlast->next = np;
				nfs.nlast = np;
				unlock(&nfs);
				kick(pfd[0]);
			}
			unlock(&nfs);
		} else if(w->pid == exportpid)
			break;
	}

	if(w == nil)
		exits(nil);
	exits(0);
/*	exits(w->msg); */
}