cmd/sharefs: reproduce vfs inode file attribute race

This happens in the vfs permissions check only and stale data appears to never reach userspace.

Signed-off-by: Ophestra <cat@gensokyo.uk>

test/interactive/raceattr.nix

@@ -0,0 +1,24 @@
+{ lib, pkgs, ... }:
+let
+  inherit (pkgs) buildGoModule;
+in
+{
+  environment.systemPackages = [
+    (buildGoModule rec {
+      name = "raceattr";
+      pname = name;
+      tags = [ "raceattr" ];
+
+      src = builtins.path {
+        name = "${pname}-src";
+        path = lib.cleanSource ../../cmd/sharefs/test;
+        filter = path: type: (type == "directory") || (type == "regular" && lib.hasSuffix ".go" path);
+      };
+      vendorHash = null;
+
+      preBuild = ''
+        go mod init hakurei.app/raceattr >& /dev/null
+      '';
+    })
+  ];
+}