settings: zms: add option to disable updating linked list

When deleting a settings entry the linked list is updated by removing
the deleted node. This operation is time consuming and add some delays.
For applications that use almost the same set of Setting entries, add an
option to make this operation faster at a cost of having some empty
nodes in the linked list.
These empty nodes can be used later when the deleted entry is written
again.
Each empty node occupies 16B of storage.

Signed-off-by: Riadh Ghaddab <[email protected]>

Author: rghaddab

subsys/settings/Kconfig

@@ -190,6 +190,17 @@ config SETTINGS_ZMS_MAX_COLLISIONS_BITS
 	  The maximum number of hash collisions needs to be well sized depending
 	  on the data that is going to be stored in ZMS and its hash values
 
+config SETTINGS_ZMS_NO_LL_DELETE
+	bool "Disable deletion of Linked list hashes"
+	help
+	  For some applications, the Settings delete operation is too long for
+	  ZMS because of the linked list update.
+	  As a tradeoff for performance the linked list is not updated. As a
+	  result, some nodes will be unused and will occupy some space in the
+	  storage.
+	  These nodes will be used again when the same Settings element that has
+	  been deleted is created again.
+
 config SETTINGS_SHELL
 	bool "Settings shell"
 	depends on SHELL

subsys/settings/src/settings_zms.c

@@ -61,6 +61,7 @@ static int settings_zms_dst(struct settings_zms *cf)
 	return 0;
 }
 
+#ifndef CONFIG_SETTINGS_ZMS_NO_LL_DELETE
 static int settings_zms_unlink_ll_node(struct settings_zms *cf, uint32_t name_hash)
 {
 	int rc = 0;
@@ -119,32 +120,7 @@ static int settings_zms_unlink_ll_node(struct settings_zms *cf, uint32_t name_ha
 
 	return rc;
 }
-
-static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
-{
-	int rc = 0;
-
-	rc = zms_delete(&cf->cf_zms, name_hash);
-	if (rc >= 0) {
-		rc = zms_delete(&cf->cf_zms, name_hash + ZMS_DATA_ID_OFFSET);
-	}
-	if (rc < 0) {
-		return rc;
-	}
-
-	rc = settings_zms_unlink_ll_node(cf, name_hash);
-	if (rc < 0) {
-		return rc;
-	}
-
-	/* Now delete the current linked list element */
-	rc = zms_delete(&cf->cf_zms, name_hash | 1);
-	if (rc < 0) {
-		return rc;
-	}
-
-	return rc;
-}
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
 
 #if CONFIG_SETTINGS_ZMS_NAME_CACHE
 static void settings_zms_cache_add(struct settings_zms *cf, uint32_t name_hash, uint8_t flags)
@@ -194,6 +170,7 @@ static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
 	if (rc < 0) {
 		return rc;
 	}
+#ifndef CONFIG_SETTINGS_ZMS_NO_LL_DELETE
 	rc = settings_zms_unlink_ll_node(cf, name_hash);
 	if (rc < 0) {
 		return rc;
@@ -204,15 +181,16 @@ static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
 	if (rc < 0) {
 		return rc;
 	}
-
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
 #ifdef CONFIG_SETTINGS_ZMS_NAME_CACHE
 	/* Update the flag of the Settings entry in cache. */
 	uint8_t cache_flags = 0;
 
 	if (ZMS_COLLISION_NUM(name_hash) > 0) {
+		/* indicates that it has a hash collision */
 		cache_flags |= BIT(1);
 	}
-	/* set the delete BIT(1) indicating that the entry is deleted. */
+	/* set the delete BIT(2) indicating that the entry is deleted. */
 	cache_flags |= BIT(2);
 	settings_zms_cache_add(cf, name_hash & ZMS_HASH_MASK, cache_flags);
 #endif
@@ -249,15 +227,26 @@ static int settings_zms_load(struct settings_store *cs, const struct settings_lo
 					  ZMS_NAME_HASH_ID(ll_hash_id) + ZMS_DATA_ID_OFFSET);
 
 		if ((rc1 <= 0) || (rc2 <= 0)) {
-			/* Settings item is not stored correctly in the ZMS.
-			 * ZMS entry for its name or value is either missing
-			 * or deleted. Clean dirty entries to make space for
-			 * future settings item.
+			/* In case we are not updating the linked list, this is an empty mode
+			 * Just continue
+			 */
+#ifndef CONFIG_SETTINGS_ZMS_NO_LL_DELETE
+			/* Otherwise, Settings item is not stored correctly in the ZMS.
+			 * ZMS entry for its name or value is either missing or deleted.
+			 * Clean dirty entries to make space for future settings item.
 			 */
 			ret = settings_zms_delete(cf, ZMS_NAME_HASH_ID(ll_hash_id));
 			if (ret < 0) {
 				return ret;
 			}
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
+			/* update next ll_hash_id */
+			ret = zms_read(&cf->cf_zms, ll_hash_id, &settings_element,
+				       sizeof(struct settings_hash_linked_list));
+			if (ret < 0) {
+				return ret;
+			}
+			ll_hash_id = settings_element.next_hash;
 			continue;
 		}
 
@@ -305,6 +294,9 @@ static int settings_zms_save(struct settings_store *cs, const char *name, const
 	bool write_name;
 	int rc = 0;
 	int first_available_hash_index = -1;
+#ifdef CONFIG_SETTINGS_ZMS_NO_LL_DELETE
+	bool ll_node_exist = false;
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
 
 	if (!name) {
 		return -EINVAL;
@@ -327,11 +319,18 @@ static int settings_zms_save(struct settings_store *cs, const char *name, const
 		} else {
 			write_name = false;
 		}
+#ifdef CONFIG_SETTINGS_ZMS_NO_LL_DELETE
+		/* In this case the settings entry is deleted, which means that
+		 * its linked list node still exist in this case and do not need
+		 * to be updated.
+		 */
+		ll_node_exist = true;
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
 		goto no_hash_collision;
 	}
 #endif
 
-	/* Let's find out if there is no hash collisions in the storage */
+	/* Let's find out if there are hash collisions in the storage */
 	write_name = true;
 
 	for (int i = 0; i <= cf->hash_collision_num; i++) {
@@ -405,6 +404,20 @@ static int settings_zms_save(struct settings_store *cs, const char *name, const
 		if (rc < 0) {
 			return rc;
 		}
+#ifdef CONFIG_SETTINGS_ZMS_NO_LL_DELETE
+		if (ll_node_exist) {
+			goto no_ll_update;
+		}
+		/* verify that the ll_node doesn't exist otherwise do not update it */
+		rc = zms_read(&cf->cf_zms, name_hash | 1, &settings_element,
+			      sizeof(struct settings_hash_linked_list));
+		if (rc >= 0) {
+			goto no_ll_update;
+		} else if (rc != -ENOENT) {
+			return rc;
+		}
+		/* else the LL node doesn't exist let's update it */
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
 		/* write linked list structure element */
 		settings_element.next_hash = 0;
 		/* Verify first that the linked list last element is not broken.
@@ -434,6 +447,9 @@ static int settings_zms_save(struct settings_store *cs, const char *name, const
 		cf->second_to_last_hash_id = cf->last_hash_id;
 		cf->last_hash_id = name_hash | 1;
 	}
+#ifdef CONFIG_SETTINGS_ZMS_NO_LL_DELETE
+no_ll_update:
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
 #ifdef CONFIG_SETTINGS_ZMS_NAME_CACHE
 	/* Add the flags of the written settings entry in cache */
 	cache_flags = 0;