9p2.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

		goto out;
	}
	if((p = getbuf(file->fs->dev, file->addr, Bread|Bmod)) == nil){
		error = Ealloc;
		goto out;
	}
	if((d = getdir(p, file->slot)) == nil || !(d->mode & DALLOC)){
		error = Ealloc;
		goto out;
	}
	if(error = mkqidcmp(&file->qid, d))
		goto out;
	if(t = file->tlock) {
		tim = time(0);
		if(t->time < tim || t->file != file){
			error = Ebroken;
			goto out;
		}
		/* renew the lock */
		t->time = tim + TLOCK;
	}
	accessdir(p, d, FWRITE);
	if(d->mode & DAPND)
		offset = d->size;
	if(offset+count > d->size)
		d->size = offset+count;
	while(count > 0){
		if(p == nil){
			p = getbuf(file->fs->dev, file->addr, Bread|Bmod);
			if((d = getdir(p, file->slot)) == nil || !(d->mode & DALLOC)){
				error = Ealloc;
				goto out;
			}
		}
		addr = offset / BUFSIZE;
		o = offset % BUFSIZE;
		n = BUFSIZE - o;
		if(n > count)
			n = count;
		qpath = d->qid.path;
		p1 = dnodebuf1(p, d, addr, Tfile);
		p = nil;
		if(p1 == nil) {
			error = Efull;
			goto out;
		}
		if(checktag(p1, Tfile, qpath)){
			putbuf(p1);
			error = Ephase;
			goto out;
		}
		memmove(p1->iobuf+o, f->data+nwrite, n);
		p1->flags |= Bmod;
		putbuf(p1);
		count -= n;
		nwrite += n;
		offset += n;
	}

out:
	if(p != nil)
		putbuf(p);
	if(file != nil)
		qunlock(file);
	r->count = nwrite;

	return error;
}

static int
_clunk(File* file, int remove, int wok)
{
	Tlock *t;
	int error;

	error = 0;
	if(t = file->tlock){
		if(t->file == file)
			t->time = 0;		/* free the lock */
		file->tlock = 0;
	}
	if(remove)
		error = doremove(file, wok);
	file->open = 0;
	freewp(file->wpath);
	freefp(file);
	qunlock(file);

	return error;
}

static int
fsclunk(Chan* chan, Fcall* f, Fcall*)
{
	File *file;

	if((file = filep(chan, f->fid, 0)) == nil)
		return Efid;

	_clunk(file, file->open & FREMOV, 0);
	return 0;
}

static int
fsremove(Chan* chan, Fcall* f, Fcall*)
{
	File *file;

	if((file = filep(chan, f->fid, 0)) == nil)
		return Efid;

	return _clunk(file, 1, chan == cons.chan);
}

static int
fsstat(Chan* chan, Fcall* f, Fcall* r, uchar* data)
{
	Dir dir;
	Iobuf *p;
	Dentry *d;
	File *file;
	int error, len;

	if((file = filep(chan, f->fid, 0)) == nil)
		return Efid;

	p = getbuf(file->fs->dev, file->addr, Bread);
	if(p == nil || checktag(p, Tdir, QPNONE)){
		error = Edir1;
		goto out;
	}
	if((d = getdir(p, file->slot)) == nil || !(d->mode & DALLOC)){
		error = Ealloc;
		goto out;
	}
	if(error = mkqidcmp(&file->qid, d))
		goto out;

	if(d->qid.path == QPROOT)	/* stat of root gives time */
		d->atime = time(0);

	len = dir9p2(&dir, d, data);
	data += len;
	if((r->nstat = convD2M(&dir, data, chan->msize - len)) == 0)
		error = Ersc;
	else
		r->stat = data;

out:
	if(p != nil)
		putbuf(p);
	if(file != nil)
		qunlock(file);

	return error;
}

static int
fswstat(Chan* chan, Fcall* f, Fcall*, char *strs)
{
	Iobuf *p, *p1;
	Dentry *d, *d1, xd;
	File *file;
	int error, slot, uid, gid, l;
	long addr;
	Dir dir;
	ulong mode;

	p = p1 = nil;
	d1 = nil;

	if((file = filep(chan, f->fid, 0)) == nil){
		error = Efid;
		goto out;
	}

	/*
	 * if user none,
	 * can't do anything
	 * unless allow.
	 */
	if(file->uid == 0 && !wstatallow){
		error = Eaccess;
		goto out;
	}

	if(isro(file->fs->dev) || (writegroup && !ingroup(file->uid, writegroup))){
		error = Eronly;
		goto out;
	}

	/*
	 * first get parent
	 */
	if(file->wpath){
		p1 = getbuf(file->fs->dev, file->wpath->addr, Bread);
		if(p1 == nil){
			error = Ephase;
			goto out;
		}
		d1 = getdir(p1, file->wpath->slot);
		if(d1 == nil || checktag(p1, Tdir, QPNONE) || !(d1->mode & DALLOC)){
			error = Ephase;
			goto out;
		}
	}

	if((p = getbuf(file->fs->dev, file->addr, Bread)) == nil){
		error = Ealloc;
		goto out;
	}
	d = getdir(p, file->slot);
	if(d == nil || checktag(p, Tdir, QPNONE) || !(d->mode & DALLOC)){
		error = Ealloc;
		goto out;
	}
	if(error = mkqidcmp(&file->qid, d))
		goto out;

	/*
	 * Convert the message and fix up
	 * fields not to be changed.
	 */
	if(convM2D(f->stat, f->nstat, &dir, strs) == 0){
		print("9p2: convM2D returns 0\n");
		error = Econvert;
		goto out;
	}
	if(dir.uid == nil || strlen(dir.uid) == 0)
		uid = d->uid;
	else
		uid = strtouid(dir.uid);
	if(dir.gid == nil || strlen(dir.gid) == 0)
		gid = d->gid;
	else
		gid = strtouid(dir.gid);
	if(dir.name == nil || strlen(dir.name) == 0)
		dir.name = d->name;
	else{
		if((l = checkname9p2(dir.name)) == 0){
			error = Ename;
			goto out;
		}
		if(l > NAMELEN){
			error = Etoolong;
			goto out;
		}
	}

	/*
	 * Before doing sanity checks, find out what the
	 * new 'mode' should be:
	 * if 'type' and 'mode' are both defaults, take the
	 * new mode from the old directory entry;
	 * else if 'type' is the default, use the new mode entry;
	 * else if 'mode' is the default, create the new mode from
	 * 'type' or'ed with the old directory mode;
	 * else neither are defaults, use the new mode but check
	 * it agrees with 'type'.
	 */
	if(dir.qid.type == 0xFF && dir.mode == ~0){
		dir.mode = d->mode & 0777;
		if(d->mode & DLOCK)
			dir.mode |= DMEXCL;
		if(d->mode & DAPND)
			dir.mode |= DMAPPEND;
		if(d->mode & DDIR)
			dir.mode |= DMDIR;
	}
	else if(dir.qid.type == 0xFF){
		/* nothing to do */
	}
	else if(dir.mode == ~0)
		dir.mode = (dir.qid.type<<24)|(d->mode & 0777);
	else if(dir.qid.type != ((dir.mode>>24) & 0xFF)){
		error = Eqidmode;
		goto out;
	}

	/*
	 * Check for unknown type/mode bits
	 * and an attempt to change the directory bit.
	 */
	if(dir.mode & ~(DMDIR|DMAPPEND|DMEXCL|0777)){
		error = Enotm;
		goto out;
	}
	if(d->mode & DDIR)
		mode = DMDIR;
	else
		mode = 0;
	if((dir.mode^mode) & DMDIR){
		error = Enotd;
		goto out;
	}

	if(dir.mtime == ~0)
		dir.mtime = d->mtime;
	if(dir.length == ~0)
		dir.length = d->size;

	/*
	 * Currently, can't change length.
	 */
	if(dir.length != d->size){
		error = Enotl;
		goto out;
	}

	/*
	 * if chown,
	 * must be god
	 * wstatallow set to allow chown during boot
	 */
	if(uid != d->uid && !wstatallow) {
		error = Enotu;
		goto out;
	}

	/*
	 * if chgroup,
	 * must be either
	 *	a) owner and in new group
	 *	b) leader of both groups
	 * wstatallow and writeallow are set to allow chgrp during boot
	 */
	while(gid != d->gid) {
		if(wstatallow || writeallow)
			break;
		if(d->uid == file->uid && ingroup(file->uid, gid))
			break;
		if(leadgroup(file->uid, gid))
			if(leadgroup(file->uid, d->gid))
				break;
		error = Enotg;
		goto out;
	}

	/*
	 * if rename,
	 * must have write permission in parent
	 */
	while(strncmp(d->name, dir.name, sizeof(d->name)) != 0) {
		if(checkname(dir.name) || d1 == nil) {
			error = Ename;
			goto out;
		}
		if(strcmp(dir.name, ".") == 0 || strcmp(xd.name, "..") == 0) {
			error = Ename;
			goto out;
		}

		/*
		 * drop entry to prevent lock, then
		 * check that destination name is unique,
		 */
		putbuf(p);
		for(addr = 0; ; addr++) {
			if((p = dnodebuf(p1, d1, addr, 0)) == nil)
				break;
			if(checktag(p, Tdir, d1->qid.path)) {
				putbuf(p);
				continue;
			}
			for(slot = 0; slot < DIRPERBUF; slot++) {
				d = getdir(p, slot);
				if(!(d->mode & DALLOC))
					continue;
				if(strncmp(dir.name, d->name, sizeof(d->name)) == 0) {
					error = Eexist;
					goto out;
				}
			}
			putbuf(p);
		}

		/*
		 * reacquire entry
		 */
		if((p = getbuf(file->fs->dev, file->addr, Bread)) == nil){
			error = Ephase;
			goto out;
		}
		d = getdir(p, file->slot);
		if(d == nil || checktag(p, Tdir, QPNONE) || !(d->mode & DALLOC)) {
			error = Ephase;
			goto out;
		}

		if(wstatallow || writeallow) /* set to allow rename during boot */
			break;
		if(d1 == nil || iaccess(file, d1, DWRITE)) {
			error = Eaccess;
			goto out;
		}
		break;
	}

	/*
	 * if mode/time, either
	 *	a) owner
	 *	b) leader of either group
	 */
	mode = dir.mode & 0777;
	if(dir.mode & DMAPPEND)
		mode |= DAPND;
	if(dir.mode & DMEXCL)
		mode |= DLOCK;
	while(d->mtime != dir.mtime || ((d->mode^mode) & (DAPND|DLOCK|0777))) {
		if(wstatallow)			/* set to allow chmod during boot */
			break;
		if(d->uid == file->uid)
			break;
		if(leadgroup(file->uid, gid))
			break;
		if(leadgroup(file->uid, d->gid))
			break;
		error = Enotu;
		goto out;
	}
	d->mtime = dir.mtime;
	d->uid = uid;
	d->gid = gid;
	d->mode = (mode & (DAPND|DLOCK|0777)) | (d->mode & (DALLOC|DDIR));

	strncpy(d->name, dir.name, sizeof(d->name));
	accessdir(p, d, FWSTAT);

out:
	if(p != nil)
		putbuf(p);
	if(p1 != nil)
		putbuf(p1);
	if(file != nil)
		qunlock(file);

	return error;
}

static int
recv(Chan *c, uchar *buf, int n)
{
	int fd, m, len;

	fd = c->chan;
	/* read count */
	qlock(&c->rlock);
	m = readn(fd, buf, BIT32SZ);
	if(m != BIT32SZ){
		qunlock(&c->rlock);
		if(m < 0){
			print("readn(BIT32SZ) fails: %r\n");
			return -1;
		}
		print("readn(BIT32SZ) returns %d: %r\n", m);
		return 0;
	}

	len = GBIT32(buf);
	if(len <= BIT32SZ || len > n){
		print("recv bad length %d\n", len);
		werrstr("bad length in 9P2000 message header");
		qunlock(&c->rlock);
		return -1;
	}
	len -= BIT32SZ;
	m = readn(fd, buf+BIT32SZ, len);
	qunlock(&c->rlock);
	if(m < len){
		print("recv wanted %d got %d\n", len, m);
		return 0;
	}
	return BIT32SZ+m;
}

static void
send(Chan *c, uchar *buf, int n)
{
	int fd, m;

	fd = c->chan;
	qlock(&c->wlock);
	m = write(fd, buf, n);
	qunlock(&c->wlock);
	if(m == n)
		return;
	panic("write failed");
}

void
serve9p2(Chan *chan, uchar *ib, int nib)
{
	uchar inbuf[MSIZE+IOHDRSZ], outbuf[MSIZE+IOHDRSZ];
	Fcall f, r;
	char ename[64];
	int error, n, type;

	chan->msize = MSIZE;
	fmtinstall('F', fcallfmt);

	for(;;){
		if(nib){
			memmove(inbuf, ib, nib);
			n = nib;
			nib = 0;
		}else
			n = recv(chan, inbuf, sizeof inbuf);
		if(chat){
			print("read msg %d (fd %d)\n", n, chan->chan);
			if(n <= 0)
				print("\terr: %r\n");
		}
		if(n == 0 && (chan == cons.srvchan || chan == cons.chan))
			continue;
		if(n <= 0)
			break;
		if(convM2S(inbuf, n, &f) != n){
			print("9p2: cannot decode\n");
			continue;
		}

		type = f.type;
		if(type < Tversion || type >= Tmax || (type&1) || type == Terror){
			print("9p2: bad message type %d\n", type);
			continue;
		}

		if(CHAT(chan))
			print("9p2: f %F\n", &f);

		r.type = type+1;
		r.tag = f.tag;
		error = 0;

		rlock(&mainlock);
		rlock(&chan->reflock);
		switch(type){
		default:
			r.type = Rerror;
			snprint(ename, sizeof ename, "unknown message: %F", &f);
			r.ename = ename;
			break;
		case Tversion:
			error = fsversion(chan, &f, &r);
			break;
		case Tauth:
			error = fsauth(chan, &f, &r);
			break;
		case Tattach:
			error = fsattach(chan, &f, &r);
			break;
		case Tflush:
			error = fsflush(chan, &f, &r);
			break;
		case Twalk:
			error = fswalk(chan, &f, &r);
			break;
		case Topen:
			error = fsopen(chan, &f, &r);
			break;
		case Tcreate:
			error = fscreate(chan, &f, &r);
			break;
		case Tread:
			r.data = (char*)inbuf;
			error = fsread(chan, &f, &r);
			break;
		case Twrite:
			error = fswrite(chan, &f, &r);
			break;
		case Tclunk:
			error = fsclunk(chan, &f, &r);
			break;
		case Tremove:
			error = fsremove(chan, &f, &r);
			break;
		case Tstat:
			error = fsstat(chan, &f, &r, inbuf);
			break;
		case Twstat:
			error = fswstat(chan, &f, &r, (char*)outbuf);
			break;
		}
		runlock(&chan->reflock);
		runlock(&mainlock);

		if(error != 0){
			r.type = Rerror;
			if(error >= MAXERR){
				snprint(ename, sizeof(ename), "error %d", error);
				r.ename = ename;
			}
			else
				r.ename = errstring[error];
		}
		if(CHAT(chan))
			print("9p2: r %F\n", &r);
	
		n = convS2M(&r, outbuf, sizeof outbuf);
		if(n == 0){
			type = r.type;
			r.type = Rerror;
			snprint(ename, sizeof(ename), "9p2: convS2M: type %d", type);
			r.ename = ename;
			print(ename);
			n = convS2M(&r, outbuf, sizeof outbuf);
			if(n == 0){
				/*
				 * What to do here, the failure notification failed?
				 */
				panic("can't write anything at all");
			}
		}
		send(chan, outbuf, n);
	}
	fileinit(chan);
	close(chan->chan);
	if(chan == cons.srvchan || chan == cons.chan)
		print("console chan read error");
}