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

	}
	else if(file->fs->dev->type == Devro){
		error = Eronly;
		goto out;
	}

	if ((p = getbuf(file->fs->dev, file->addr, Bread|Bmod)) == nil ||
	    (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 = toytime();
		if(t->time < tim || t->file != file){
			error = Ebroken;
			goto out;
		}
		/* renew the lock */
		t->time = tim + TLOCK;
	}
	accessdir(p, d, FWRITE, file->uid);
	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(p == nil){
				error = Ealloc;
				goto out;
			}
			d = getdir(p, file->slot);
			if(d == 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, file->uid);
		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 && (file->qid.type & QTAUTH) == 0)
		error = doremove(file, wok);
	file->open = 0;
	freewp(file->wpath);
	authfree(file->auth);
	freefp(file);
	qunlock(file);

	return error;
}

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

	error = 0;
	p = nil;
	if((file = filep(chan, f->fid, 0)) == nil)
		return Efid;
	if(file->qid.type & QTAUTH){
		memset(&dentry, 0, sizeof dentry);
		d = &dentry;
		mkqid9p1(&d->qid, &file->qid);
		strcpy(d->name, "#¿");
		d->uid = authuid(file->auth);
		d->gid = d->uid;
		d->muid = d->uid;
		d->atime = time();
		d->mtime = d->atime;
		d->size = 0;
	} else {
		p = getbuf(file->fs->dev, file->addr, Bread);
		if(p == nil || checktag(p, Tdir, QPNONE)){
			error = Edir1;
			goto out;
		}
		d = getdir(p, file->slot);
		if(d == 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();
	}
	len = mkdir9p2(&dir, d, data);
	data += len;

	if((r->nstat = convD2M(&dir, data, chan->msize - len)) == 0)
		error = Eedge;
	r->stat = data;

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

	return error;
}

static int
wstat(Chan* chan, Fcall* f, Fcall*, char* strs)
{
	Iobuf *p, *p1;
	Dentry *d, *d1;
	File *file;
	int error, err, gid, gl, muid, op, slot, tsync, uid;
	long addr;
	Dir dir;

	if(convM2D(f->stat, f->nstat, &dir, strs) == 0)
		return Econvert;

	/*
	 * Get the file.
	 * If user 'none' (uid == 0), can't do anything;
	 * if filesystem is read-only, can't change anything.
	 */
	if((file = filep(chan, f->fid, 0)) == nil)
		return Efid;
	p = p1 = nil;
	if(file->uid == 0){
		error = Eaccess;
		goto out;
	}
	if(file->fs->dev->type == Devro){
		error = Eronly;
		goto out;
	}
	if(file->qid.type & QTAUTH){
		error = Emode;
		goto out;
	}

	/*
	 * Get the current entry and check it is still valid.
	 */
	p = getbuf(file->fs->dev, file->addr, Bread);
	if(p == nil || checktag(p, Tdir, QPNONE)){
		error = Ealloc;
		goto out;
	}
	d = getdir(p, file->slot);
	if(d == nil || !(d->mode & DALLOC)){
		error = Ealloc;
		goto out;
	}
	if(error = mkqidcmp(&file->qid, d))
		goto out;

	/*
	 * Run through each of the (sub-)fields in the provided Dir
	 * checking for validity and whether it's a default:
	 * .type, .dev and .atime are completely ignored and not checked;
	 * .qid.path, .qid.vers and .muid are checked for validity but
	 * any attempt to change them is an error.
	 * .qid.type/.mode, .mtime, .name, .length, .uid and .gid can
	 * possibly be changed.
	 *
	 * 'Op' flags there are changed fields, i.e. it's not a no-op.
	 * 'Tsync' flags all fields are defaulted.
	 *
	 * Wstatallow and writeallow are set to allow changes during the
	 * fileserver bootstrap phase.
	 */
	tsync = 1;
	if(dir.qid.path != ~0){
		if(dir.qid.path != file->qid.path){
			error = Ewstatp;
			goto out;
		}
		tsync = 0;
	}
	if(dir.qid.vers != ~0){
		if(dir.qid.vers != file->qid.vers){
			error = Ewstatv;
			goto out;
		}
		tsync = 0;
	}
	if(dir.muid != nil && *dir.muid != '\0'){
		muid = strtouid(dir.muid);
		if(muid != d->muid && !wstatallow){
			error = Ewstatm;
			goto out;
		}
		tsync = 0;
	}

	/*
	 * .qid.type and .mode have some bits in common. Only .mode
	 * is currently needed for comparisons with the old mode but
	 * if there are changes to the bits also encoded in .qid.type
	 * then file->qid must be updated appropriately later.
	 */
	if(dir.qid.type == (uchar)~0){
		if(dir.mode == ~0)
			dir.qid.type = mktype9p2(d->mode);
		else
			dir.qid.type = dir.mode>>24;
	}
	else
		tsync = 0;
	if(dir.mode == ~0)
		dir.mode = mkmode9p2(d->mode);
	else
		tsync = 0;

	/*
	 * Check dir.qid.type and dir.mode agree, check for any unknown
	 * type/mode bits, check for an attempt to change the directory bit.
	 */
	if(dir.qid.type != ((dir.mode>>24) & 0xFF)){
		error = Ewstatq;
		goto out;
	}
	if(dir.mode & ~(DMDIR|DMAPPEND|DMEXCL|0777)){
		error = Ewstatb;
		goto out;
	}

	op = dir.mode^mkmode9p2(d->mode);
	if(op & DMDIR){
		error = Ewstatd;
		goto out;
	}

	if(dir.mtime != ~0){
		if(dir.mtime != d->mtime)
			op = 1;
		tsync = 0;
	}
	else
		dir.mtime = d->mtime;

	if(dir.length == ~(Off)0)
		dir.length = d->size;
	else {
		if (dir.length < 0) {
			error = Ewstatl;
			goto out;
		} else if(dir.length != d->size)
			op = 1;
		tsync = 0;
	}

	/*
	 * Check for permission to change .mode, .mtime or .length,
	 * must be owner or leader of either group, for which test gid
	 * is needed; permission checks on gid will be done later.
	 * 'Gl' counts whether neither, one or both groups are led.
	 */
	if(dir.gid != nil && *dir.gid != '\0'){
		gid = strtouid(dir.gid);
		tsync = 0;
	}
	else
		gid = d->gid;
	gl = leadgroup(file->uid, gid) != 0;
	gl += leadgroup(file->uid, d->gid) != 0;

	if(op && !wstatallow && d->uid != file->uid && !gl){
		error = Ewstato;
		goto out;
	}

	/*
	 * Rename.
	 * Check .name is valid and different to the current.
	 */
	if(dir.name != nil && *dir.name != '\0'){
		if(error = checkname9p2(dir.name))
			goto out;
		if(strncmp(dir.name, d->name, NAMELEN))
			op = 1;
		else
			dir.name = d->name;
		tsync = 0;
	}
	else
		dir.name = d->name;

	/*
	 * If the name is really to be changed check it's unique
	 * and there is write permission in the parent.
	 */
	if(dir.name != d->name){
		/*
		 * First get parent.
		 * Must drop current entry to prevent
		 * deadlock when searching that new name
		 * already exists below.
		 */
		putbuf(p);
		p = nil;

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

		/*
		 * Check entries in parent for new name.
		 */
		for(addr = 0; ; addr++){
			if((p = dnodebuf(p1, d1, addr, 0, file->uid)) == 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) ||
				   strncmp(dir.name, d->name, sizeof d->name))
					continue;
				error = Eexist;
				goto out;
			}
			putbuf(p);
		}

		/*
		 * Reacquire entry and check it's still OK.
		 */
		p = getbuf(file->fs->dev, file->addr, Bread);
		if(p == nil || checktag(p, Tdir, QPNONE)){
			error = Ephase;
			goto out;
		}
		d = getdir(p, file->slot);
		if(d == nil || !(d->mode & DALLOC)){
			error = Ephase;
			goto out;
		}

		/*
		 * Check write permission in the parent.
		 */
		if(!wstatallow && !writeallow && iaccess(file, d1, DWRITE)){
			error = Eaccess;
			goto out;
		}
	}

	/*
	 * Check for permission to change owner - must be god.
	 */
	if(dir.uid != nil && *dir.uid != '\0'){
		uid = strtouid(dir.uid);
		if(uid != d->uid){
			if(!wstatallow){
				error = Ewstatu;
				goto out;
			}
			op = 1;
		}
		tsync = 0;
	}
	else
		uid = d->uid;

	/*
	 * Check for permission to change group, must be
	 * either owner and in new group or leader of both groups.
	 */
	if(gid != d->gid){
		if(!(wstatallow || writeallow)
		&& !(d->uid == file->uid && ingroup(file->uid, gid))
		&& !(gl == 2)){
			error = Ewstatg;
			goto out;
		}
		op = 1;
	}

	/*
	 * Checks all done, update if necessary.
	 */
	if(op){
		d->mode = mkmode9p1(dir.mode);
		file->qid.type = mktype9p2(d->mode);
		d->mtime = dir.mtime;
		if (dir.length < d->size) {
			err = dtrunclen(p, d, dir.length, uid);
			if (error == 0)
				error = err;
		}
		d->size = dir.length;
		if(dir.name != d->name)
			strncpy(d->name, dir.name, sizeof(d->name));
		d->uid = uid;
		d->gid = gid;
	}
	if(!tsync)
		accessdir(p, d, FREAD, file->uid);

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

	return error;
}

int
serve9p2(Msgbuf* mb)
{
	Chan *chan;
	Fcall f, r;
	Msgbuf *data, *rmb;
	char ename[64];
	int error, n, type;
	static int once;

	if(once == 0){
		fmtinstall('F', fcallfmt);
		once = 1;
	}

	/*
	 * 0 return means i don't understand this message,
	 * 1 return means i dealt with it, including error
	 * replies.
	 */
	if(convM2S(mb->data, mb->count, &f) != mb->count)
{
print("didn't like %d byte message\n", mb->count);
		return 0;
}
	type = f.type;
	if(type < Tversion || type >= Tmax || (type & 1) || type == Terror)
		return 0;

	chan = mb->chan;
	if(CHAT(chan))
		print("9p2: f %F\n", &f);
	r.type = type+1;
	r.tag = f.tag;
	error = 0;
	data = nil;

	switch(type){
	default:
		r.type = Rerror;
		snprint(ename, sizeof(ename), "unknown message: %F", &f);
		r.ename = ename;
		break;
	case Tversion:
		error = version(chan, &f, &r);
		break;
	case Tauth:
		error = auth(chan, &f, &r);
		break;
	case Tattach:
		error = attach(chan, &f, &r);
		break;
	case Tflush:
		error = flush(chan, &f, &r);
		break;
	case Twalk:
		error = walk(chan, &f, &r);
		break;
	case Topen:
		error = open(chan, &f, &r);
		break;
	case Tcreate:
		error = create(chan, &f, &r);
		break;
	case Tread:
		data = mballoc(chan->msize, chan, Mbreply1);
		error = read(chan, &f, &r, data->data);
		break;
	case Twrite:
		error = write(chan, &f, &r);
		break;
	case Tclunk:
		error = clunk(chan, &f, &r);
		break;
	case Tremove:
		error = remove(chan, &f, &r);
		break;
	case Tstat:
		data = mballoc(chan->msize, chan, Mbreply1);
		error = stat(chan, &f, &r, data->data);
		break;
	case Twstat:
		data = mballoc(chan->msize, chan, Mbreply1);
		error = wstat(chan, &f, &r, (char*)data->data);
		break;
	}

	if(error != 0){
		r.type = Rerror;
		if(error >= MAXERR){
			snprint(ename, sizeof(ename), "error %d", error);
			r.ename = ename;
		}
		else
			r.ename = errstr9p[error];
	}
	if(CHAT(chan))
		print("9p2: r %F\n", &r);

	rmb = mballoc(chan->msize, chan, Mbreply2);
	n = convS2M(&r, rmb->data, chan->msize);
	if(data != nil)
		mbfree(data);
	if(n == 0){
		type = r.type;
		r.type = Rerror;

		/*
		 * If a Tversion has not been seen on the chan then
		 * chan->msize will be 0. In that case craft a special
		 * Rerror message. It's fortunate that the mballoc above
		 * for rmb will have returned a Msgbuf of MAXMSG size
		 * when given a request with count of 0...
		 */
		if(chan->msize == 0){
			r.ename = "Tversion not seen";
			n = convS2M(&r, rmb->data, MAXMSG);
		}
		else{
			snprint(ename, sizeof(ename), "9p2: convS2M: type %d", type);
			r.ename = ename;
			n = convS2M(&r, rmb->data, chan->msize);
		}
		print("%s\n", r.ename);
		if(n == 0){
			/*
			 * What to do here, the failure notification failed?
			 */
			mbfree(rmb);
			return 1;
		}
	}
	rmb->count = n;
	rmb->param = mb->param;
	send(chan->reply, rmb);

	return 1;
}