Replace checkPermBits error-return with hasPermBits bool

- hasPermBits uses a 4-entry mask array indexed by mode&3 to select
  the required permission bits: OREAD→4, OWRITE→2, ORDWR→6, OEXEC→1
- Zero branches, zero error paths — returns bits&mask == mask
- open() uses OR semantics: checks owner, group, world independently;
  any tier granting access is sufficient
- checkPerm removed entirely; permission logic is pure boolean math

cmd/olliesrv/server.go

@@ -144,35 +144,11 @@ func fileOwnerGroup(root *fs.Tree, path string) (uid, gid string) {
 	return "ollie", "agent"
 }
 
-func checkPerm(uname string, mode uint8, uid string, perm uint32, inGroup bool) error {
-	var bits uint32
-	if uname == uid {
-		bits = (perm >> 6) & 7
-	} else if inGroup {
-		bits = (perm >> 3) & 7
-	} else {
-		bits = perm & 7
-	}
-	omode := mode & 3
-	switch omode {
-	case plan9.OREAD:
-		if bits&4 == 0 {
-			return fmt.Errorf("permission denied")
-		}
-	case plan9.OWRITE:
-		if bits&2 == 0 {
-			return fmt.Errorf("permission denied")
-		}
-	case plan9.ORDWR:
-		if bits&6 != 6 {
-			return fmt.Errorf("permission denied")
-		}
-	case plan9.OEXEC:
-		if bits&1 == 0 {
-			return fmt.Errorf("permission denied")
-		}
-	}
-	return nil
+var permMask = [4]uint32{4, 2, 6, 1} // OREAD, OWRITE, ORDWR, OEXEC
+
+func hasPermBits(mode uint8, bits uint32) bool {
+	m := permMask[mode&3]
+	return bits&m == m
 }
 
 const readTimeout = 10 * time.Second
@@ -413,8 +389,20 @@ func (s *Server) open(cs *connState, fc *plan9.Fcall) *plan9.Fcall {
 		return errFcall(fc, "bad fid")
 	}
 	uid, gid := fileOwnerGroup(s.rootTree, f.path)
-	if err := checkPerm(cs.uname, fc.Mode, uid, uint32(makeStat(s.rootTree, f.path).Mode)&0777, s.InGroup(gid, cs.uname)); err != nil {
-		return errFcall(fc, err.Error())
+	perm := uint32(makeStat(s.rootTree, f.path).Mode) & 0777
+
+	allowed := false
+	if cs.uname == uid {
+		allowed = hasPermBits(fc.Mode, perm>>6)
+	}
+	if !allowed && s.InGroup(gid, cs.uname) {
+		allowed = hasPermBits(fc.Mode, perm>>3)
+	}
+	if !allowed {
+		allowed = hasPermBits(fc.Mode, perm)
+	}
+	if !allowed {
+		return errFcall(fc, "permission denied")
 	}
 	f.mode = fc.Mode
 	return &plan9.Fcall{Type: plan9.Ropen, Tag: fc.Tag, Qid: f.qid}