srv.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

	r->fid->qid = r->ofcall.qid;
	if(r->ofcall.qid.type&QTDIR)
		r->fid->diroffset = 0;
}

static void
screate(Srv *srv, Req *r)
{
	if((r->fid = lookupfid(srv->fpool, r->ifcall.fid)) == nil)
		respond(r, Eunknownfid);
	else if(r->fid->omode != -1)
		respond(r, Ebotch);
	else if(!(r->fid->qid.type&QTDIR))
		respond(r, Ecreatenondir);
	else if(r->fid->file && !hasperm(r->fid->file, r->fid->uid, AWRITE))
		respond(r, Eperm);
	else if(srv->create)
		srv->create(r);
	else
		respond(r, Enocreate);
}
static void
rcreate(Req *r, char *error)
{
	if(error)
		return;
	r->fid->omode = r->ifcall.mode;
	r->fid->qid = r->ofcall.qid;
}

static void
sread(Srv *srv, Req *r)
{
	int o;

	if((r->fid = lookupfid(srv->fpool, r->ifcall.fid)) == nil){
		respond(r, Eunknownfid);
		return;
	}
	if((int)r->ifcall.count < 0){
		respond(r, Ebotch);
		return;
	}
	if(r->ifcall.offset < 0
	|| ((r->fid->qid.type&QTDIR) && r->ifcall.offset != 0 && r->ifcall.offset != r->fid->diroffset)){
		respond(r, Ebadoffset);
		return;
	}

	if(r->ifcall.count > srv->msize - IOHDRSZ)
		r->ifcall.count = srv->msize - IOHDRSZ;
	r->rbuf = emalloc9p(r->ifcall.count);
	r->ofcall.data = r->rbuf;
	o = r->fid->omode & 3;
	if(o != OREAD && o != ORDWR && o != OEXEC){
		respond(r, Ebotch);
		return;
	}
	if((r->fid->qid.type&QTDIR) && r->fid->file){
		r->ofcall.count = readdirfile(r->fid->rdir, r->rbuf, r->ifcall.count);
		respond(r, nil);
		return;
	}
	if(srv->read)
		srv->read(r);
	else
		respond(r, "no srv->read");
}
static void
rread(Req *r, char *error)
{
	if(error==nil && (r->fid->qid.type&QTDIR))
		r->fid->diroffset += r->ofcall.count;
}

static void
swrite(Srv *srv, Req *r)
{
	int o;
	char e[ERRMAX];

	if((r->fid = lookupfid(srv->fpool, r->ifcall.fid)) == nil){
		respond(r, Eunknownfid);
		return;
	}
	if((int)r->ifcall.count < 0){
		respond(r, Ebotch);
		return;
	}
	if(r->ifcall.offset < 0){
		respond(r, Ebotch);
		return;
	}
	if(r->ifcall.count > srv->msize - IOHDRSZ)
		r->ifcall.count = srv->msize - IOHDRSZ;
	o = r->fid->omode & 3;
	if(o != OWRITE && o != ORDWR){
		snprint(e, sizeof e, "write on fid with open mode 0x%ux", r->fid->omode);
		respond(r, e);
		return;
	}
	if(srv->write)
		srv->write(r);
	else
		respond(r, "no srv->write");
}
static void
rwrite(Req *r, char *error)
{
	if(error)
		return;
	if(r->fid->file)
		r->fid->file->qid.vers++;
}

static void
sclunk(Srv *srv, Req *r)
{
	if((r->fid = removefid(srv->fpool, r->ifcall.fid)) == nil)
		respond(r, Eunknownfid);
	else
		respond(r, nil);
}
static void
rclunk(Req*, char*)
{
}

static void
sremove(Srv *srv, Req *r)
{
	if((r->fid = removefid(srv->fpool, r->ifcall.fid)) == nil){
		respond(r, Eunknownfid);
		return;
	}
	/* BUG RACE */
	if(r->fid->file && !hasperm(r->fid->file->parent, r->fid->uid, AWRITE)){
		respond(r, Eperm);
		return;
	}
	if(srv->remove)
		srv->remove(r);
	else
		respond(r, r->fid->file ? nil : Enoremove);
}
static void
rremove(Req *r, char *error, char *errbuf)
{
	if(error)
		return;
	if(r->fid->file){
		if(removefile(r->fid->file) < 0){
			snprint(errbuf, ERRMAX, "remove %s: %r", 
				r->fid->file->name);
			r->error = errbuf;
		}
		r->fid->file = nil;
	}
}

static void
sstat(Srv *srv, Req *r)
{
	if((r->fid = lookupfid(srv->fpool, r->ifcall.fid)) == nil){
		respond(r, Eunknownfid);
		return;
	}
	if(r->fid->file){
		/* should we rlock the file? */
		r->d = r->fid->file->Dir;
		if(r->d.name)
			r->d.name = estrdup9p(r->d.name);
		if(r->d.uid)
			r->d.uid = estrdup9p(r->d.uid);
		if(r->d.gid)
			r->d.gid = estrdup9p(r->d.gid);
		if(r->d.muid)
			r->d.muid = estrdup9p(r->d.muid);
	}
	if(srv->stat)	
		srv->stat(r);	
	else if(r->fid->file)
		respond(r, nil);
	else
		respond(r, Enostat);
}
static void
rstat(Req *r, char *error)
{
	int n;
	uchar *statbuf;
	uchar tmp[BIT16SZ];

	if(error)
		return;
	if(convD2M(&r->d, tmp, BIT16SZ) != BIT16SZ){
		r->error = "convD2M(_,_,BIT16SZ) did not return BIT16SZ";
		return;
	}
	n = GBIT16(tmp)+BIT16SZ;
	statbuf = emalloc9p(n);
	if(statbuf == nil){
		r->error = "out of memory";
		return;
	}
	r->ofcall.nstat = convD2M(&r->d, statbuf, n);
	r->ofcall.stat = statbuf;	/* freed in closereq */
	if(r->ofcall.nstat <= BIT16SZ){
		r->error = "convD2M fails";
		free(statbuf);
		return;
	}
}

static void
swstat(Srv *srv, Req *r)
{
	if((r->fid = lookupfid(srv->fpool, r->ifcall.fid)) == nil){
		respond(r, Eunknownfid);
		return;
	}
	if(srv->wstat == nil){
		respond(r, Enowstat);
		return;
	}
	if(convM2D(r->ifcall.stat, r->ifcall.nstat, &r->d, (char*)r->ifcall.stat) != r->ifcall.nstat){
		respond(r, Ebaddir);
		return;
	}
	if((ushort)~r->d.type){
		respond(r, "wstat -- attempt to change type");
		return;
	}
	if((uint)~r->d.dev){
		respond(r, "wstat -- attempt to change dev");
		return;
	}
	if((uchar)~r->d.qid.type || (ulong)~r->d.qid.vers || (uvlong)~r->d.qid.path){
		respond(r, "wstat -- attempt to change qid");
		return;
	}
	if(r->d.muid && r->d.muid[0]){
		respond(r, "wstat -- attempt to change muid");
		return;
	}
	if((ulong)~r->d.mode && ((r->d.mode&DMDIR)>>24) != (r->fid->qid.type&QTDIR)){
		respond(r, "wstat -- attempt to change DMDIR bit");
		return;
	}
	srv->wstat(r);
}
static void
rwstat(Req*, char*)
{
}

void
srv(Srv *srv)
{
	Req *r;

	fmtinstall('D', dirfmt);
	fmtinstall('F', fcallfmt);

	if(srv->fpool == nil)
		srv->fpool = allocfidpool(srv->destroyfid);
	if(srv->rpool == nil)
		srv->rpool = allocreqpool(srv->destroyreq);
	if(srv->msize == 0)
		srv->msize = 8192+IOHDRSZ;

	changemsize(srv, srv->msize);

	srv->fpool->srv = srv;
	srv->rpool->srv = srv;

	while(r = getreq(srv)){
		if(r->error){
			respond(r, r->error);
			continue;	
		}
		switch(r->ifcall.type){
		default:
			respond(r, "unknown message");
			break;
		case Tversion:	sversion(srv, r);	break;
		case Tauth:	sauth(srv, r);	break;
		case Tattach:	sattach(srv, r);	break;
		case Tflush:	sflush(srv, r);	break;
		case Twalk:	swalk(srv, r);	break;
		case Topen:	sopen(srv, r);	break;
		case Tcreate:	screate(srv, r);	break;
		case Tread:	sread(srv, r);	break;
		case Twrite:	swrite(srv, r);	break;
		case Tclunk:	sclunk(srv, r);	break;
		case Tremove:	sremove(srv, r);	break;
		case Tstat:	sstat(srv, r);	break;
		case Twstat:	swstat(srv, r);	break;
		}
	}

	free(srv->rbuf);
	srv->rbuf = nil;
	free(srv->wbuf);
	srv->wbuf = nil;
	srv->msize = 0;
	freefidpool(srv->fpool);
	srv->fpool = nil;
	freereqpool(srv->rpool);
	srv->rpool = nil;

	if(srv->end)
		srv->end(srv);
}

void
respond(Req *r, char *error)
{
	int i, m, n;
	char errbuf[ERRMAX];
	Srv *srv;

	srv = r->srv;
	assert(srv != nil);

	assert(r->responded == 0);
	r->error = error;

	switch(r->ifcall.type){
	default:
		assert(0);
	/*
	 * Flush is special.  If the handler says so, we return
	 * without further processing.  Respond will be called
	 * again once it is safe.
	 */
	case Tflush:
		if(rflush(r, error)<0)
			return;
		break;
	case Tversion:	rversion(r, error);	break;
	case Tauth:	rauth(r, error);	break;
	case Tattach:	rattach(r, error);	break;
	case Twalk:	rwalk(r, error);	break;
	case Topen:	ropen(r, error);	break;
	case Tcreate:	rcreate(r, error);	break;
	case Tread:	rread(r, error);	break;
	case Twrite:	rwrite(r, error);	break;
	case Tclunk:	rclunk(r, error);	break;
	case Tremove:	rremove(r, error, errbuf);	break;
	case Tstat:	rstat(r, error);	break;
	case Twstat:	rwstat(r, error);	break;
	}

	r->ofcall.tag = r->ifcall.tag;
	r->ofcall.type = r->ifcall.type+1;
	if(r->error)
		setfcallerror(&r->ofcall, r->error);

if(chatty9p)
	fprint(2, "-%d-> %F\n", srv->outfd, &r->ofcall);

	qlock(&srv->wlock);
	n = convS2M(&r->ofcall, srv->wbuf, srv->msize);
	if(n <= 0){
		fprint(2, "n = %d %F\n", n, &r->ofcall);
		abort();
	}
	assert(n > 2);
	if(r->pool)	/* not a fake */
		closereq(removereq(r->pool, r->ifcall.tag));
	m = write(srv->outfd, srv->wbuf, n);
	if(m != n)
		sysfatal("lib9p srv: write %d returned %d on fd %d: %r", n, m, srv->outfd);
	qunlock(&srv->wlock);

	qlock(&r->lk);	/* no one will add flushes now */
	r->responded = 1;
	qunlock(&r->lk);

	for(i=0; i<r->nflush; i++)
		respond(r->flush[i], nil);
	free(r->flush);
	r->flush = nil;
	r->nflush = 0;

	if(r->pool)
		closereq(r);
	else
		free(r);
}

void
responderror(Req *r)
{
	char errbuf[ERRMAX];
	
	rerrstr(errbuf, sizeof errbuf);
	respond(r, errbuf);
}

int
postfd(char *name, int pfd)
{
	int fd;
	char buf[80];

	snprint(buf, sizeof buf, "/srv/%s", name);
	if(chatty9p)
		fprint(2, "postfd %s\n", buf);
	fd = create(buf, OWRITE|ORCLOSE|OCEXEC, 0600);
	if(fd < 0){
		if(chatty9p)
			fprint(2, "create fails: %r\n");
		return -1;
	}
	if(fprint(fd, "%d", pfd) < 0){
		if(chatty9p)
			fprint(2, "write fails: %r\n");
		close(fd);
		return -1;
	}
	if(chatty9p)
		fprint(2, "postfd successful\n");
	return 0;
}