lib9p: added functions for devshr

sys/include/9p.h

@@ -216,9 +216,12 @@ struct Srv {
 void		srv(Srv*);
 void		postmountsrv(Srv*, char*, char*, int);
 void		_postmountsrv(Srv*, char*, char*, int);
+void		postsharesrv(Srv*, char*, char*, char*, char*);
+void		_postsharesrv(Srv*, char*, char*, char*, char*);
 void		listensrv(Srv*, char*);
 void		_listensrv(Srv*, char*);
 int 		postfd(char*, int);
+int		sharefd(char*, char*, char*, int);
 int		chatty9p;
 void		respond(Req*, char*);
 void		responderror(Req*);

sys/src/lib9p/post.c

@@ -56,6 +56,56 @@ _postmountsrv(Srv *s, char *name, char *mtpt, int flag)
 		close(s->srvfd);
 }
 
+void
+_postsharesrv(Srv *s, char *name, char *mtpt, char *desc, char *flag)
+{
+	int fd[2];
+
+	if(!s->nopipe){
+		if(pipe(fd) < 0)
+			sysfatal("pipe: %r");
+		s->infd = s->outfd = fd[1];
+		s->srvfd = fd[0];
+	}
+	if(name)
+		if(postfd(name, s->srvfd) < 0)
+			sysfatal("postfd %s: %r", name);
+
+	if(_forker == nil)
+		sysfatal("no forker");
+	_forker(postproc, s, RFNAMEG);
+
+	/*
+	 * Normally the server is posting as the last thing it does
+	 * before exiting, so the correct thing to do is drop into
+	 * a different fd space and close the 9P server half of the
+	 * pipe before trying to mount the kernel half.  This way,
+	 * if the file server dies, we don't have a ref to the 9P server
+	 * half of the pipe.  Then killing the other procs will drop
+	 * all the refs on the 9P server half, and the mount will fail.
+	 * Otherwise the mount hangs forever.
+	 *
+	 * Libthread in general and acme win in particular make
+	 * it hard to make this fd bookkeeping work out properly,
+	 * so leaveinfdopen is a flag that win sets to opt out of this
+	 * safety net.
+	 */
+	if(!s->leavefdsopen){
+		rfork(RFFDG);
+		rendezvous(0, 0);
+		close(s->infd);
+		if(s->infd != s->outfd)
+			close(s->outfd);
+	}
+
+	if(mtpt){
+		if(sharefd(mtpt, desc, flag, s->srvfd) < 0)
+			sysfatal("sharefd %s: %r", mtpt);
+	}else
+		close(s->srvfd);
+}
+
+
 static void
 postproc(void *v)
 {

sys/src/lib9p/rfork.c

@@ -32,3 +32,9 @@ postmountsrv(Srv *s, char *name, char *mtpt, int flag)
 	_postmountsrv(s, name, mtpt, flag);
 }
 
+void
+postsharesrv(Srv *s, char *name, char *mtpt, char *desc, char *flag)
+{
+	_forker = rforker;
+	_postsharesrv(s, name, mtpt, desc, flag);
+}

sys/src/lib9p/srv.c

@@ -851,3 +851,29 @@ postfd(char *name, int pfd)
 	return 0;
 }
 
+int
+sharefd(char *name, char *desc, char *flags, int pfd)
+{
+	int fd;
+	char buf[80];
+
+	snprint(buf, sizeof buf, "#σc/%s", name);
+	if(chatty9p)
+		fprint(2, "sharefd %s\n", buf);
+	fd = create(buf, OWRITE, 0600);
+	if(fd < 0){
+		if(chatty9p)
+			fprint(2, "create fails: %r\n");
+		return -1;
+	}
+	if(fprint(fd, "%s %d %s\n", flags, pfd, desc) < 0){
+		if(chatty9p)
+			fprint(2, "write fails: %r\n");
+		close(fd);
+		return -1;
+	}
+	close(fd);
+	if(chatty9p)
+		fprint(2, "sharefd successful\n");
+	return 0;
+}