Move prefork, postfork, and thread-exit hooks into subsys

So far, crypto is the only module that uses them, but others are
likely to do so in the future.

src/app/config/config.c

@@ -64,6 +64,7 @@
 #include "app/config/confparse.h"
 #include "app/config/statefile.h"
 #include "app/main/main.h"
+#include "app/main/subsysmgr.h"
 #include "core/mainloop/connection.h"
 #include "core/mainloop/cpuworker.h"
 #include "core/mainloop/mainloop.h"
@@ -1393,10 +1394,10 @@ options_act_reversible(const or_options_t *old_options, char **msg)
    * processes. */
   if (running_tor && options->RunAsDaemon) {
     if (! start_daemon_has_been_called())
-      crypto_prefork();
+      subsystems_prefork();
     /* No need to roll back, since you can't change the value. */
     if (start_daemon())
-      crypto_postfork();
+      subsystems_postfork();
   }
 
 #ifdef HAVE_SYSTEMD

src/app/main/subsysmgr.c

@@ -128,3 +128,60 @@ subsystems_shutdown_downto(int target_level)
     sys_initialized[i] = false;
   }
 }
+
+/**
+ * Run pre-fork code on all subsystems that declare any
+ **/
+void
+subsystems_prefork(void)
+{
+  check_and_setup();
+
+  for (int i = (int)n_tor_subsystems - 1; i >= 0; --i) {
+    const subsys_fns_t *sys = tor_subsystems[i];
+    if (!sys->supported)
+      continue;
+    if (! sys_initialized[i])
+      continue;
+    if (sys->prefork)
+      sys->prefork();
+  }
+}
+
+/**
+ * Run post-fork code on all subsystems that declare any
+ **/
+void
+subsystems_postfork(void)
+{
+  check_and_setup();
+
+  for (unsigned i = 0; i < n_tor_subsystems; ++i) {
+    const subsys_fns_t *sys = tor_subsystems[i];
+    if (!sys->supported)
+      continue;
+    if (! sys_initialized[i])
+      continue;
+    if (sys->postfork)
+      sys->postfork();
+  }
+}
+
+/**
+ * Run thread-clanup code on all subsystems that declare any
+ **/
+void
+subsystems_thread_cleanup(void)
+{
+  check_and_setup();
+
+  for (int i = (int)n_tor_subsystems - 1; i >= 0; --i) {
+    const subsys_fns_t *sys = tor_subsystems[i];
+    if (!sys->supported)
+      continue;
+    if (! sys_initialized[i])
+      continue;
+    if (sys->thread_cleanup)
+      sys->thread_cleanup();
+  }
+}

src/app/main/subsysmgr.h

@@ -17,4 +17,8 @@ int subsystems_init_upto(int level);
 void subsystems_shutdown(void);
 void subsystems_shutdown_downto(int level);
 
+void subsystems_prefork(void);
+void subsystems_postfork(void);
+void subsystems_thread_cleanup(void);
+
 #endif

src/lib/crypt_ops/crypto_init.c

@@ -227,4 +227,7 @@ const struct subsys_fns_t sys_crypto = {
   .level = -60,
   .initialize = init_crypto_sys,
   .shutdown = shutdown_crypto_sys,
+  .prefork = crypto_prefork,
+  .postfork = crypto_postfork,
+  .thread_cleanup = crypto_thread_cleanup,
 };

src/lib/subsys/subsys.h

@@ -53,6 +53,22 @@ typedef struct subsys_fns_t {
    **/
   int (*add_pubsub)(struct dispatch_connector_t *);
 
+  /**
+   * Perform any necessary pre-fork cleanup.  This function may not fail.
+   */
+  void (*prefork)(void);
+
+  /**
+   * Perform any necessary post-fork setup. This function may not fail.
+   */
+  void (*postfork)(void);
+
+  /**
+   * Free any thread-local resources held by this subsystem. Called before
+   * the thread exits.
+   */
+  void (*thread_cleanup)(void);
+
   /**
    * Free all resources held by this subsystem.
    *

src/test/testing_common.c

@@ -232,12 +232,12 @@ void
 tinytest_prefork(void)
 {
   free_pregenerated_keys();
-  crypto_prefork();
+  subsystems_prefork();
 }
 void
 tinytest_postfork(void)
 {
-  crypto_postfork();
+  subsystems_postfork();
   init_pregenerated_keys();
 }