Don't mask out sticky bit to/from gofer

RELNOTES: sticky bit propagates to gofers now.
PiperOrigin-RevId: 231822453
Change-Id: I73426170b9457350480a3b144a2baf937e7cb477

pkg/p9/buffer.go

@@ -144,7 +144,7 @@ func (b *buffer) ReadGID() GID {
 
 // ReadPermissions reads a file mode value and applies the mask for permissions.
 func (b *buffer) ReadPermissions() FileMode {
-	return b.ReadFileMode() & PermissionsMask
+	return b.ReadFileMode() & permissionsMask
 }
 
 // ReadFileMode reads a file mode value.
@@ -230,7 +230,7 @@ func (b *buffer) WriteGID(gid GID) {
 
 // WritePermissions applies a permissions mask and writes the FileMode.
 func (b *buffer) WritePermissions(perm FileMode) {
-	b.WriteFileMode(perm & PermissionsMask)
+	b.WriteFileMode(perm & permissionsMask)
 }
 
 // WriteFileMode writes a FileMode.

pkg/p9/p9.go

@@ -130,8 +130,12 @@ const (
 	// Exec is a mode bit indicating exec permission.
 	Exec FileMode = 01
 
-	// PermissionsMask is the mask to apply to FileModes for permissions.
-	PermissionsMask FileMode = 0777
+	// AllPermissions is a mask with rwx bits set for user, group and others.
+	AllPermissions FileMode = 0777
+
+	// permissionsMask is the mask to apply to FileModes for permissions. It
+	// includes rwx bits for user, group and others, and sticky bit (01000).
+	permissionsMask FileMode = 01777
 )
 
 // QIDType is the most significant byte of the FileMode word, to be used as the
@@ -157,7 +161,7 @@ func (m FileMode) FileType() FileMode {
 
 // Permissions returns just the permission bits of the mode.
 func (m FileMode) Permissions() FileMode {
-	return m & PermissionsMask
+	return m & permissionsMask
 }
 
 // Writable returns the mode with write bits added.
@@ -987,7 +991,7 @@ func (s *SetAttr) Encode(b *buffer) {
 // Apply applies this to the given Attr.
 func (a *Attr) Apply(mask SetAttrMask, attr SetAttr) {
 	if mask.Permissions {
-		a.Mode = a.Mode&^PermissionsMask | (attr.Permissions & PermissionsMask)
+		a.Mode = a.Mode&^permissionsMask | (attr.Permissions & permissionsMask)
 	}
 	if mask.UID {
 		a.UID = attr.UID