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

@@ -171,6 +171,17 @@ 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;
@@ -119,6 +120,7 @@ static int settings_zms_unlink_ll_node(struct settings_zms *cf, uint32_t name_ha
 
 	return rc;
 }
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
 
 static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
 {
@@ -132,6 +134,7 @@ static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
 		return rc;
 	}
 
+#ifndef CONFIG_SETTINGS_ZMS_NO_LL_DELETE
 	rc = settings_zms_unlink_ll_node(cf, name_hash);
 	if (rc < 0) {
 		return rc;
@@ -143,6 +146,7 @@ static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
 		return rc;
 	}
 
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
 	return rc;
 }
 
@@ -177,15 +181,27 @@ static int settings_zms_load(struct settings_store *cs, const struct settings_lo
 							       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's name or value is either missing or deleted.
+			 * Clean dirty entries to make space for future settings items.
 			 */
 			ret = settings_zms_delete(cf, ZMS_NAME_ID_FROM_LL_NODE(ll_hash_id));
 			if (ret < 0) {
 				return ret;
 			}
+#endif /* CONFIG_SETTINGS_ZMS_NO_LL_DELETE */
+
+			ret = zms_read(&cf->cf_zms, ll_hash_id, &settings_element,
+				       sizeof(struct settings_hash_linked_list));
+			if (ret < 0) {
+				return ret;
+			}
+			/* update next ll_hash_id */
+			ll_hash_id = settings_element.next_hash;
 			continue;
 		}
 
@@ -313,6 +329,17 @@ 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
+		/* 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.
@@ -342,7 +369,9 @@ 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 */
 	return 0;
 }