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aux/listen: removing service script sholud kill listener (thanks mischief)

mischief spotted that the only way for listeners to go away was
truncating (but not removing) a service script. this is wrong and
not as described in the manpage.

this change makes removing (or truncating) a listen script stop
the listener.

scandir() first marks all current announces, then reads the service
directory adding announces which will clear the marks for the ones
already there or add a new unmarked one. finally, we shoot down and
remove all still marked announces.

--- a/sys/src/cmd/aux/listen.c

+++ b/sys/src/cmd/aux/listen.c

@@ -16,9 +16,10 @@

 struct Announce

 {

 	Announce	*next;

-	char	*a;

 	int	announced;

-	int	whined;

+	char	whined;

+	char	mark;

+	char	a[];

 };

 int	readstr(char*, char*, char*, int);

@@ -292,66 +293,33 @@

 	/* look for duplicate */

 	l = &announcements;

 	for(a = announcements; a; a = a->next){

-		if(strcmp(str, a->a) == 0)

+		if(strcmp(str, a->a) == 0){

+			a->mark = 0;

 			return;

+		}

 		l = &a->next;

 	}

 	/* accept it */

 	a = mallocz(sizeof(*a) + strlen(str) + 1, 1);

-	if(a == 0)

+	if(a == nil)

 		return;

-	a->a = ((char*)a)+sizeof(*a);

 	strcpy(a->a, str);

-	a->announced = 0;

 	*l = a;

 }

-/*

- *  delete a service for announcement list

- */

 void

-delannounce(char *str)

-{

-	Announce *a, **l;

-

-	/* look for service */

-	l = &announcements;

-	for(a = announcements; a; a = a->next){

-		if(strcmp(str, a->a) == 0)

-			break;

-		l = &a->next;

-	}

-	if (a == nil)

-		return;

-	*l = a->next;			/* drop from the list */

-	if (a->announced > 0)

-		postnote(PNPROC, a->announced, "die");

-	a->announced = 0;

-	free(a);

-}

-

-static int

-ignore(char *srvdir, char *name)

-{

-	int rv;

-	char *file = smprint("%s/%s", srvdir, name);

-	Dir *d = dirstat(file);

-

-	rv = !d || d->length <= 0;	/* ignore unless it's non-empty */

-	free(d);

-	free(file);

-	return rv;

-}

-

-void

 scandir(char *proto, char *protodir, char *dname)

 {

+	Announce *a, **l;

 	int fd, i, n, nlen;

 	char *nm;

 	char ds[128];

 	Dir *db;

+	for(a = announcements; a != nil; a = a->next)

+		a->mark = 1;

+

 	fd = open(dname, OREAD);

 	if(fd < 0)

 		return;

@@ -360,20 +328,31 @@

 	while((n=dirread(fd, &db)) > 0){

 		for(i=0; i<n; i++){

 			nm = db[i].name;

-			if(!(db[i].qid.type&QTDIR) &&

-			    strncmp(nm, proto, nlen) == 0) {

-				snprint(ds, sizeof ds, "%s!*!%s", protodir,

-					nm + nlen);

-				if (ignore(dname, nm))

-					delannounce(ds);

-				else

-					addannounce(ds);

-			}

+			if(db[i].qid.type&QTDIR)

+				continue;

+			if(db[i].length <= 0)

+				continue;

+			if(strncmp(nm, proto, nlen) != 0)

+				continue;

+			snprint(ds, sizeof ds, "%s!*!%s", protodir, nm + nlen);

+			addannounce(ds);

 		}

 		free(db);

 	}

 	close(fd);

+

+	l = &announcements;

+	while((a = *l) != nil){

+		if(a->mark){

+			*l = a->next;

+			if (a->announced > 0)

+				postnote(PNPROC, a->announced, "die");

+			free(a);

+			continue;

+		}

+		l = &a->next;

+	}

 }

 void