MDEV-34358 Detect config changes during encryption iteration

Problem:
=======
When innodb_encrypt_tables or innodb_encryption_rotate_key_age is
changed during encryption thread iteration, threads continue with
stale configuration values, potentially missing tablespaces that
should be encrypted or rotated under the new settings.

Solution:
========
Added atomic version counter fil_crypt_settings_version that is
incremented whenever innodb_encrypt_tables or
innodb_encryption_rotate_key_age changes. Encryption threads capture
the version at iteration start and check for changes during iteration.
If config changed, threads immediately restart iteration from the
beginning to ensure complete coverage with new settings.

fil_crypt_settings_version: Atomic counter to track the
innodb_encrypt_tables or innodb_encryption_rotate_key_age changes

rotate_thread_t::settings_version: To compare the
existing fil_crypt_settings_version to restart the
encryption from the beginning

Author: Thirunarayanan

storage/innobase/fil/fil0crypt.cc

@@ -46,6 +46,12 @@ static bool fil_crypt_threads_inited = false;
 /** Is encryption enabled/disabled */
 ulong srv_encrypt_tables;
 
+/** Version counter for innodb_encrypt_tables changes.
+Incremented each time innodb_encrypt_tables or
+innodb_encryption_rotate_key_age is modified to signal
+encryption threads to restart iteration */
+static Atomic_counter<uint16_t> fil_crypt_settings_version;
+
 /** No of key rotation threads requested */
 uint srv_n_fil_crypt_threads;
 
@@ -1029,7 +1035,8 @@ static bool fil_crypt_start_encrypting_space(fil_space_t* space)
 
 /** State of a rotation thread */
 struct rotate_thread_t {
-  explicit rotate_thread_t(uint no) : thread_no(no) {}
+  explicit rotate_thread_t(uint no) : thread_no(no),
+    settings_version(fil_crypt_settings_version) {}
 
   bool first = true;              /*!< is position before first space */
 
@@ -1052,6 +1059,11 @@ struct rotate_thread_t {
   when woken by signal or when work is found. */
   uint16_t sleep_timeout_ms= 5000;
 
+  /** Config version when thread started current iteration.
+  Used to detect innodb_encrypt_tables changes during iteration
+  and restart from beginning to ensure complete encryption coverage. */
+  uint16_t settings_version;
+
   uint thread_no;
   uint32_t offset = 0;            /*!< current page number */
   uint min_key_version_found = 0; /*!< min key version found but not rotated */
@@ -1083,6 +1095,12 @@ struct rotate_thread_t {
 	timed_wait_count = 0;
   }
 
+	/** Check if innodb_encrypt_tables config has changed.
+	@return true if config changed, requiring iteration restart */
+	bool settings_changed() const {
+		return settings_version != fil_crypt_settings_version;
+	}
+
 	/** @return whether this thread should terminate */
 	bool should_shutdown() const {
 		mysql_mutex_assert_owner(&fil_crypt_threads_mutex);
@@ -2137,23 +2155,39 @@ static void fil_crypt_thread()
 		/* if we find a tablespace that is starting, skip over it
 		and recheck it later */
 		bool recheck = false;
-
 wait_for_work:
 		thr.wait_for_work(recheck);
 
+restart_iteration:
 		recheck = false;
 		thr.first = true;      // restart from first tablespace
+		thr.settings_version = fil_crypt_settings_version;
 		key_state_t new_state;
 
 		/* iterate all spaces searching for those needing rotation */
 		while (fil_crypt_find_space_to_rotate(&new_state, &thr,
 						      &recheck)) {
+#if 0
+			/* Check if innodb_encrypt_tables or
+			innodb_encryption_rotate_key_age changed during
+			iteration. If changed, restart immediately */
+			if (thr.settings_changed()) {
+
+				if (thr.space != fil_system.space_list.end() &&
+				    thr.space != space_list_t::iterator(
+							fil_system.temp_space)) {
+					thr.space->release();
+				}
 
+				thr.space = fil_system.space_list.end();
+				goto restart_iteration;
+			}
+#endif
 			if (thr.space == fil_system.space_list.end()) {
 				/* When iterating fil_system.space_list,
 				reaching .end(), it could mean all spaces
 				are encrypted, or some spaces were temporarily
-                                unacquirable (CLOSING flag, DDL in progress).
+				unacquirable (CLOSING flag, DDL in progress).
 
 				For default_encrypt_list: Spaces exist but
 				none are acquirable. Wake other threads
@@ -2329,6 +2363,10 @@ void fil_crypt_set_rotate_key_age(uint val)
   if (val == 0)
     fil_crypt_default_encrypt_tables_fill();
   mysql_mutex_unlock(&fil_system.mutex);
+
+  /* Increment version to signal threads to restart iteration */
+  fil_crypt_settings_version++;
+
   pthread_cond_broadcast(&fil_crypt_threads_cond);
   mysql_mutex_unlock(&fil_crypt_threads_mutex);
 }
@@ -2383,6 +2421,9 @@ void fil_crypt_set_encrypt_tables(ulong val)
 
   mysql_mutex_unlock(&fil_system.mutex);
 
+  /* Increment version to signal threads to restart iteration */
+  fil_crypt_settings_version++;
+
   pthread_cond_broadcast(&fil_crypt_threads_cond);
   mysql_mutex_unlock(&fil_crypt_threads_mutex);
 }