code: plan9front

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gefs: correctly serialize updates to mounts

we don't need a lock free list, we just need an
rwlock; this isn't a high contention data structure.

--- a/sys/src/cmd/gefs/blk.c

+++ b/sys/src/cmd/gefs/blk.c

@@ -928,9 +928,6 @@

 		case DFtree:

 			free(p->t);

 			break;

-		case DFmnt:

-			free(p->m);

-			break;

 		case DFblk:

 			a = getarena(p->bp.addr);

 			qe.op = Qfree;

--- a/sys/src/cmd/gefs/dat.h

+++ b/sys/src/cmd/gefs/dat.h

@@ -433,7 +433,6 @@

 enum {

 	DFblk,

-	DFmnt,

 	DFtree,

 };

@@ -517,6 +516,7 @@

 	QLock	synclk;

 	Rendez	syncrz;

+	RWLock	mountlk;

 	Mount	*mounts;

 	Mount	*snapmnt;

 	Lock	connlk;

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

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

@@ -96,8 +96,10 @@

          */

 	qlock(&fs->mutlk);

 	tracem("packb");

-	for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next)

+	rlock(&fs->mountlk);

+	for(mnt = fs->mounts; mnt != nil; mnt = mnt->next)

 		updatesnap(&mnt->root, mnt->root, mnt->name, mnt->flag);

+	runlock(&fs->mountlk);

 	/*

 	 * Now that we've updated the snaps, we can sync the

 	 * dlist; the snap tree will not change from here.

@@ -199,7 +201,8 @@

 	}

 	t = nil;

 	*tp = nil;

-	for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next){

+	rlock(&fs->mountlk);

+	for(mnt = fs->mounts; mnt != nil; mnt = mnt->next){

 		if(strcmp(a->old, mnt->name) == 0){

 			updatesnap(&mnt->root, mnt->root, mnt->name, mnt->flag);

 			t = agetp(&mnt->root);

@@ -207,6 +210,7 @@

 			break;

 		}

 	}

+	runlock(&fs->mountlk);

 	if(t == nil && (t = opensnap(a->old, nil)) == nil){

 		if(a->fd != -1)

 			fprint(a->fd, "snap: open '%s': does not exist\n", a->old);

@@ -623,13 +627,13 @@

 		return fs->snapmnt;

 	}

-	for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next){

+	wlock(&fs->mountlk);

+	for(mnt = fs->mounts; mnt != nil; mnt = mnt->next){

 		if(strcmp(name, mnt->name) == 0){

 			ainc(&mnt->ref);

 			goto Out;

 		}

 	}

-

 	if((mnt = mallocz(sizeof(*mnt), 1)) == nil)

 		error(Enomem);

 	if(waserror()){

@@ -644,10 +648,11 @@

 	mnt->flag = flg;

 	mnt->root = t;

 	mnt->next = fs->mounts;

-	asetp(&fs->mounts, mnt);

+	fs->mounts = mnt;

 	poperror();

 Out:

+	wunlock(&fs->mountlk);

 	return mnt;

 }

@@ -654,22 +659,22 @@

 void

 clunkmount(Mount *mnt)

 {

-	Mount *me, **p;

-	Bfree *f;

+	Mount *e, **p;

 	if(mnt == nil)

 		return;

 	if(adec(&mnt->ref) == 0){

-		for(p = &fs->mounts; (me = *p) != nil; p = &me->next){

-			if(me == mnt)

+		wlock(&fs->mountlk);

+		p = &fs->mounts;

+		for(e = fs->mounts; e != nil; e = e->next){

+			if(e == mnt)

 				break;

+			p = &e->next;

 		}

-		assert(me != nil);

-		f = emalloc(sizeof(Bfree), 0);

-		f->op = DFmnt;

-		f->m = mnt;

-		*p = me->next;

-		limbo(f);

+		assert(e != nil);

+		*p = e->next;

+		free(mnt);

+		wunlock(&fs->mountlk);

 	}

 }

@@ -2673,7 +2678,8 @@

 		chsend(fs->admchan, a);

 		tmnow(&now, nil);

-		for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next){

+		rlock(&fs->mountlk);

+		for(mnt = fs->mounts; mnt != nil; mnt = mnt->next){

 			if(!(mnt->flag & Ltsnap))

 				continue;

 			if(now.yday != then.yday){

@@ -2696,6 +2702,7 @@

 				snapmsg("main", mnt->minutely[m], Lauto);

 			}

 		}

+		runlock(&fs->mountlk);

 		if(now.hour != then.hour)

 			h = (h+1)%24;

 		if(now.min != then.min)

--- a/sys/src/cmd/gefs/snap.c

+++ b/sys/src/cmd/gefs/snap.c

@@ -348,12 +348,14 @@

 	btupsert(&fs->snap, m, nm);

 	if(deltree){

 		reclaimblocks(t->gen, succ, t->pred);

-		for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next){

+		rlock(&fs->mountlk);

+		for(mnt = fs->mounts; mnt != nil; mnt = mnt->next){

 			if(mnt->root->gen == t->succ)

 				mnt->root->pred = t->pred;

 			if(mnt->root->gen == t->pred)

 				mnt->root->succ = t->succ;

 		}

+		runlock(&fs->mountlk);

 	}

 }