Audited use of append.

The ramfs used append incorrectly in one place.
This was fixed by an explicit allocation.

Signed-off-by: David M. Rogers <predictivestatmech@gmail.com>

cfilesys.go

@@ -277,6 +277,7 @@ func (ent cEnt) Walk(ctx context.Context,
 	// drop part of ent.path
 	//steps = steps[:len(qids)]
 	//remain := len(ent.path) - bsp
+	// Note: potentially dangerous use of append [may modify ent.path]
 	//next.path = append(ent.path[:remain], steps[bsp:]...)
 	if len(qids) > 0 {
 		next.qid = qids[len(qids)-1]

cmd/9pr/main.go

@@ -84,9 +84,10 @@ func main() {
 	}
 
 	completer := readline.NewPrefixCompleter(
-		readline.PcItem("ls"),
 		readline.PcItem("cat"),
 		readline.PcItem("cd"),
+		readline.PcItem("exit"),
+		readline.PcItem("ls"),
 		readline.PcItem("mkdir"),
 		readline.PcItem("pwd"),
 		readline.PcItem("rm"),
@@ -122,6 +123,9 @@ func main() {
 		var cmd func(ctx context.Context, args ...string) error
 
 		switch name {
+		case "exit":
+			csession.Stop(nil)
+			return
 		case "ls":
 			cmd = commander.cmdls
 		case "cd":

ramfs/dirent.go

@@ -53,7 +53,7 @@ func (h FileHandle) OpenDir(ctx context.Context) (p9p.ReadNext, error) {
 
 func (h FileHandle) Clunk(ctx context.Context) error {
 	h.ent.decref()
-	for i := range(h.parents) {
+	for i := range h.parents {
 		h.parents[len(h.parents)-i-1].decref()
 	}
 	return nil
@@ -163,12 +163,25 @@ func (h FileHandle) Walk(ctx context.Context, names ...string) ([]p9p.Qid, p9p.D
 		// ref = /
 		// rh.ent = /
 		// rh.parents = []
-		rh.parents = append(append(
+		rh.parents = make([]*FileEnt, len(h.parents)-ndel + 1 + len(ans)-ndel)
+
+		// would use append, but append mutates its input
+		/*rh.parents = append(append(
 							h.parents[:len(h.parents)-ndel],
 							ref),
-							ans[ndel:]...)
-		for _, p := range(rh.parents) {
+							ans[ndel:]...)*/
+		i0 := len(h.parents)-ndel + 1
+		for i := range rh.parents {
+			var p *FileEnt
+			if i < len(h.parents)-ndel {
+				p = h.parents[i]
+			} else if i >= i0 {
+				p = ans[ndel+i-i0]
+			} else {
+				p = ref
+			}
 			p.incref()
+			rh.parents[i] = p
 		}
 		rh.ent = rh.parents[len(rh.parents)-1]
 		rh.parents = rh.parents[:len(rh.parents)-1]
@@ -177,7 +190,7 @@ func (h FileHandle) Walk(ctx context.Context, names ...string) ([]p9p.Qid, p9p.D
 	}
 
 	qids = make([]p9p.Qid, len(ans))
-	for i, a := range(ans) {
+	for i, a := range ans {
 		qids[i] = a.Info.Qid
 	}