Get rid of the 'mount read: i/o on hungup channel' 
errors when unmounting some common file servers

Reference: /n/sources/patch/sorry/grumble-on-dismount
Date: Wed Feb 23 16:47:45 CET 2005

--- /sys/src/cmd/ramfs.c	Wed Feb 23 16:46:10 2005
+++ /sys/src/cmd/ramfs.c	Wed Feb 23 16:46:06 2005
@@ -745,7 +745,7 @@
 void
 io(void)
 {
-	char *err, buf[20];
+	char *err, buf[40];
 	int n, pid, ctl;
 
 	pid = getpid();
@@ -771,6 +771,12 @@
 		 * so we wait for the error.
 		 */
 		n = read9pmsg(mfd[0], mdata, messagesize);
+		if(n < 0){
+			errstr(buf, sizeof buf);
+			if (buf[0]=='\0' || strncmp(buf, "i/o on hungup channel", 22)==0)
+				exits("");
+			error("mount read");
+		}
 		if(n < 0)
 			error("mount read");
 		if(n == 0)
--- /sys/src/cmd/ip/ftpfs/ftpfs.c	Wed Feb 23 16:46:22 2005
+++ /sys/src/cmd/ip/ftpfs/ftpfs.c	Wed Feb 23 16:46:19 2005
@@ -247,15 +247,19 @@
 void
 io(void)
 {
-	char *err;
+	char *err, buf[ERRMAX];
 	int n;
 
 	kapid = kaproc();
 
 	while(!dying){
 		n = read9pmsg(mfd, mdata, messagesize);
-		if(n <= 0)
-			fatal("mount read");
+		if(n <= 0){
+			errstr(buf, sizeof buf);
+			if (buf[0]=='\0' || strncmp(buf, "i/o on hungup channel", 22)==0)
+				exits("");
+			fatal("mount read: %s\n", buf);
+		}
 		if(convM2S(mdata, n, &thdr) == 0)
 			continue;
 
--- /sys/src/cmd/tapefs/fs.c	Wed Feb 23 16:46:40 2005
+++ /sys/src/cmd/tapefs/fs.c	Wed Feb 23 16:46:37 2005
@@ -18,6 +18,7 @@
 int	replete;
 int	verbose;
 int	newtap;		/* tap with time in sec */
+uchar	statbuf[STATMAX];
 
 Fid *	newfid(int);
 int	ramstat(Ram*, uchar*, int);
@@ -301,8 +302,11 @@
 		thdr.qid = r->qid;
 		return 0;
 	}
-	if(mode & ORCLOSE)
-		return Eperm;
+	if(mode & ORCLOSE){
+		if(r->qid.path==0)
+			return Eperm;
+		f->rclose = 1;
+	}
 	trunc = mode & OTRUNC;
 	mode &= OPERM;
 	if(mode==OWRITE || mode==ORDWR || trunc)
@@ -416,14 +420,16 @@
 	f->busy = 0;
 	f->open = 0;
 	f->ram = 0;
-	return 0;
+	return nil;
 }
 
 char *
 rremove(Fid *f)
 {
-	USED(f);
-	return Eperm;
+	if(f->ram->qid.path == 0)
+		return Eperm;
+	f->ram->busy = 0;
+	return nil;
 }
 
 char *
@@ -435,12 +441,56 @@
 	return 0;
 }
 
+static Ram *
+firstent(Ram *r)
+{
+	Ram *s, *t;
+	for(s = r->parent; s; s = s->next)
+		if (s->child)
+			for (t = s->child; t; t = t->next)
+				if (t == r)
+					return s->child;
+	sysfatal("firstent: internal error - can't ever happen\n");
+	return nil;
+}
+
 char *
 rwstat(Fid *f)
 {
+	Ram *r, *s;
+	Dir dir;
+
 	if(f->ram->busy == 0)
 		return Enotexist;
-	return Eperm;
+
+	convM2D(rhdr.stat, rhdr.nstat, &dir, (char*)statbuf);
+	r = f->ram;
+
+	if(dir.length!=~0 && dir.length!=r->ndata)
+		return Eperm;
+
+	if (dir.name[0] != '\0' && strcmp(dir.name, r->name) != 0)
+		for(s = firstent(f->ram); s; s = s->next)
+			if(s->busy && strcmp(dir.name, s->name)==0)
+				return Eexist;
+
+
+	/* all valid, now do it */
+
+	if(dir.mode != ~0){
+		dir.mode &= ~DMDIR;	/* cannot change dir bit */
+		dir.mode |= r->perm&DMDIR;
+		r->perm = dir.mode;
+	}
+	if(dir.name[0] != '\0'){
+		free(r->name);
+		r->name = estrdup(dir.name);
+	}
+	if(dir.uid[0] != '\0')
+		r->user = estrdup(dir.uid);
+	if(dir.gid[0] != '\0')
+		r->group = estrdup(dir.gid);
+	return 0;
 }
 
 int
@@ -541,7 +591,7 @@
 		if(write(mfd[1], mdata, n) != n)
 			error("mount write");
 	}
-	if (buf[0]=='\0' || strncmp(buf, "write to hung", 13)==0)
+	if (buf[0]=='\0' || strncmp(buf, "i/o on hungup channel", 22)==0)
 		exits("");
 	fprint(2, "%s: mount read: %s\n", argv0, buf);
 	exits(buf);