daemon: read-copy-update the daemon config

Ensure data-race-free access to the daemon configuration without
locking by mutating a deep copy of the config and atomically storing
a pointer to the copy into the daemon-wide configStore value. Any
operations which need to read from the daemon config must capture the
configStore value only once and pass it around to guarantee a consistent
view of the config.

Signed-off-by: Cory Snider <csnider@mirantis.com>

daemon/inspect_test.go

@@ -19,16 +19,18 @@ func TestGetInspectData(t *testing.T) {
 	}
 
 	d := &Daemon{
-		linkIndex:   newLinkIndex(),
-		configStore: &config.Config{},
+		linkIndex: newLinkIndex(),
 	}
 	if d.UsesSnapshotter() {
 		t.Skip("does not apply to containerd snapshotters, which don't have RWLayer set")
 	}
-	_, err := d.getInspectData(c)
+	cfg := &config.Config{}
+	d.configStore.Store(cfg)
+
+	_, err := d.getInspectData(cfg, c)
 	assert.Check(t, is.ErrorContains(err, "RWLayer of container inspect-me is unexpectedly nil"))
 
 	c.Dead = true
-	_, err = d.getInspectData(c)
+	_, err = d.getInspectData(cfg, c)
 	assert.Check(t, err)
 }