Don't needlessly refresh fileserver backends during Pillar rendering

This uses the opts key that masterless runs use to limit fileserver
backend refreshes to a single refresh. Adding it to the master opts
ensures that FSChan instances created on the master do not trigger
fileserver backend refreshes.

changelog/65990.fixed.md

@@ -0,0 +1,2 @@
+Fixed an issue where fileclient requests during Pillar rendering cause
+fileserver backends to be needlessly refreshed.

salt/config/__init__.py

@@ -3948,6 +3948,14 @@ def apply_master_config(overrides=None, defaults=None):
 
     opts = defaults.copy()
     opts["__role"] = "master"
+
+    # Suppress fileserver update in FSChan, for LocalClient instances generated
+    # during Pillar compilation. The master daemon already handles FS updates
+    # in its maintenance thread. Refreshing during Pillar compilation slows
+    # down Pillar considerably (even to the point of timeout) when there are
+    # many gitfs remotes.
+    opts["__fs_update"] = True
+
     _adjust_log_file_override(overrides, defaults["log_file"])
     if overrides:
         opts.update(overrides)

tests/unit/test_fileclient.py

@@ -0,0 +1,62 @@
+"""
+    :codeauthor: Erik Johnson <palehose@gmail.com>
+"""
+
+import salt.config
+from salt import fileclient
+from tests.support.mock import MagicMock, patch
+from tests.support.unit import TestCase
+
+
+class FSClientTestCase(TestCase):
+    def _get_defaults(self, **kwargs):
+        """
+        master/minion config defaults
+        """
+        ret = {
+            "saltenv": kwargs.pop("saltenv", None),
+            "id": "test",
+            "cachedir": "/A",
+            "sock_dir": "/B",
+            "root_dir": "/C",
+            "fileserver_backend": "roots",
+            "open_mode": False,
+            "auto_accept": False,
+            "file_roots": {},
+            "pillar_roots": {},
+            "file_ignore_glob": [],
+            "file_ignore_regex": [],
+            "worker_threads": 5,
+            "hash_type": "sha256",
+            "log_file": "foo.log",
+            "ssl": True,
+            "file_client": "local",
+        }
+        ret.update(kwargs)
+        return ret
+
+    def test_master_no_fs_update(self):
+        """
+        Test that an FSClient spawned from the master does not cause fileserver
+        backends to be refreshed on instantiation. The master already has the
+        maintenance thread for that.
+        """
+        opts = salt.config.apply_master_config(defaults=self._get_defaults())
+        fileserver = MagicMock()
+
+        with patch("salt.fileserver.Fileserver", fileserver):
+            client = fileclient.FSClient(opts)
+            assert client.channel.fs.update.call_count == 0
+
+    def test_masterless_no_fs_update(self):
+        """
+        Test that an FSClient spawned from a masterless run refreshes the
+        fileserver backends. This is necessary to ensure that a masterless run
+        can access any configured gitfs remotes.
+        """
+        opts = salt.config.apply_minion_config(defaults=self._get_defaults())
+        fileserver = MagicMock()
+
+        with patch("salt.fileserver.Fileserver", fileserver):
+            client = fileclient.FSClient(opts)
+            assert client.channel.fs.update.call_count == 1