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upas/fs: remove useless syncsem, make sure mbox is locked when fetching / syncing

--- a/sys/src/cmd/upas/fs/dat.h

+++ b/sys/src/cmd/upas/fs/dat.h

@@ -149,7 +149,6 @@

 struct Mailbox {

 	QLock;

 	long	idxsem;		/* abort on concurrent index access */

-	long	syncsem;		/* abort on concurrent syncs */

 	int	refs;

 	Mailbox	*next;

 	int	id;

--- a/sys/src/cmd/upas/fs/fs.c

+++ b/sys/src/cmd/upas/fs/fs.c

@@ -1244,6 +1244,7 @@

 		return nil;

 	}

+	qlock(f->mb);

 	switch(t){

 	case Qctl:

 		rhdr.count = 0;

@@ -1251,7 +1252,6 @@

 	case Qmboxctl:

 		i = mboxctlread(f->mb, &p);

 		goto output;

-		break;

 	case Qheader:

 		cacheheaders(f->mb, f->m);

 		rhdr.count = readheader(f->m, (char*)mbuf, off, cnt);

@@ -1287,6 +1287,7 @@

 		}

 		break;

 	}

+	qunlock(f->mb);

 	return nil;

 }

@@ -1410,7 +1411,10 @@

 			argc = tokenize(thdr.data, argv, nelem(argvbuf));

 			if(argc == 0)

 				return Ebadctl;

-			return f->mb->ctl(f->mb, argc, argv);

+			qlock(f->mb);

+			err = f->mb->ctl(f->mb, argc, argv);

+			qunlock(f->mb);

+			return err;

 		}

 		break;

 	case Qflags:

@@ -1419,11 +1423,10 @@

 		 */

 		if(!f->mb || !f->m)

 			break;

+		qlock(f->mb);

 		m = gettopmsg(f->mb, f->m);

 		err = modflags(f->mb, m, thdr.data);

-//		premature optimization?  flags not written immediately.

-//		if(err == nil && f->m->cstate&Cidxstale)

-//			wridxfile(f->mb);		/* syncmbox(f->mb, 1); */

+		qunlock(f->mb);

 		return err;

 	}

 	return Eperm;

@@ -1607,28 +1610,24 @@

 		t = time(0);

 		qlock(&mbllock);

 		for(mb = mbl; mb != nil; mb = mb->next){

-			assert(mb->refs > 0);

+			if(!canqlock(mb))

+				continue;

 			if(mb->waketime != 0 && t >= mb->waketime){

-				qlock(mb);

 				mb->waketime = 0;

 				break;

 			}

-

-			if(mb->d == nil || mb->d->name == nil)

-				continue;

-			d = dirstat(mb->path);

-			if(d == nil)

-				continue;

-

-			qlock(mb);

-			if(mb->d)

-			if(d->qid.path != mb->d->qid.path

-			   || d->qid.vers != mb->d->qid.vers){

-				free(d);

-				break;

+			if(mb->d != nil && mb->d->name != nil){

+				d = dirstat(mb->path);

+				if(d != nil){

+					if(d->qid.path != mb->d->qid.path

+					|| d->qid.vers != mb->d->qid.vers){

+						free(d);

+						break;

+					}

+					free(d);

+				}

 			}

 			qunlock(mb);

-			free(d);

 		}

 		qunlock(&mbllock);

 		if(mb != nil){

--- a/sys/src/cmd/upas/fs/mbox.c

+++ b/sys/src/cmd/upas/fs/mbox.c

@@ -66,15 +66,12 @@

 	int n, d, y, a;

 	Message *m, *next;

-	if(semacquire(&mb->syncsem, 0) <= 0)

-		return nil;

+	assert(canqlock(mb) == 0);

 	a = mb->root->subname;

 	if(rdidxfile(mb, doplumb) == -2)

 		wridxfile(mb);

-	if(s = mb->sync(mb, doplumb, &n)){

-		semrelease(&mb->syncsem, 1);

+	if(s = mb->sync(mb, doplumb, &n))

 		return s;

-	}

 	d = 0;

 	y = 0;

 	for(m = mb->root->part; m; m = next){

@@ -102,7 +99,6 @@

 		henter(PATH(0, Qtop), mb->name,

 			(Qid){PATH(mb->id, Qmbox), mb->vers, QTDIR}, nil, mb);

 	}

-	semrelease(&mb->syncsem, 1);

 	return nil;

 }

@@ -182,7 +178,6 @@

 	initheaders();

 	mb = emalloc(sizeof *mb);

 	mb->idxsem = 1;

-	mb->syncsem = 1;

 	mb->flags = flags;

 	strncpy(mb->path, path, sizeof mb->path - 1);

 	p = name;

@@ -1184,8 +1179,8 @@

 void

 mboxdecref(Mailbox *mb)

 {

-	assert(mb->refs > 0);

 	qlock(mb);

+	assert(mb->refs > 0);

 	mb->refs--;

 	if(mb->refs == 0){

 		syncmbox(mb, 1);