[nrf fromlist] settings: zms: load only subtree in the argument

If the subtree argument is not NULL in the settings_load function, load
only the setting entry that corresponds to that subtree.
If the subtree argument is NULL or it is not found in the storage, load
all the existing entries in the storage.

Upstream PR #: 87792

Signed-off-by: Riadh Ghaddab <[email protected]>
(cherry picked from commit ee9df348f12e0e395f017110243ce338e04204b1)

Author: rghaddab

subsys/settings/Kconfig

@@ -201,6 +201,16 @@ config SETTINGS_ZMS_NO_LL_DELETE
 	  These nodes will be used again when the same Settings element that has
 	  been deleted is created again.
 
+config SETTINGS_ZMS_LOAD_SUBTREE_PATH
+	bool "Load only subtree path if provided"
+	help
+	  Some applications use the settings_load_subtree to load only one
+	  settings entry instead of a all entries under that path.
+	  Enabling this config will allow the ZMS backend to try to load that
+	  path first.
+	  If the callback handler returns a zero value it will
+	  continue to look for all the keys under that subtree path.
+
 config SETTINGS_SHELL
 	bool "Settings shell"
 	depends on SHELL

subsys/settings/include/settings/settings_zms.h

@@ -74,7 +74,8 @@ extern "C" {
 #define ZMS_NAME_ID_FROM_LL_NODE(x) (x & ~BIT(0))
 #define ZMS_UPDATE_COLLISION_NUM(x, y)                                                             \
 	((x & ~ZMS_COLLISIONS_MASK) | ((y << 1) & ZMS_COLLISIONS_MASK))
-#define ZMS_COLLISION_NUM(x) ((x & ZMS_COLLISIONS_MASK) >> 1)
+#define ZMS_COLLISION_NUM(x)     ((x & ZMS_COLLISIONS_MASK) >> 1)
+#define ZMS_NAME_ID_FROM_HASH(x) ((x & ZMS_HASH_TOTAL_MASK) | BIT(31))
 
 struct settings_zms {
 	struct settings_store cf_store;

subsys/settings/src/settings_zms.c

@@ -196,6 +196,58 @@ static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
 	return rc;
 }
 
+#ifdef CONFIG_SETTINGS_ZMS_LOAD_SUBTREE_PATH
+/* Loads only the key which is defined by the name found in "subtree".
+ * This function doesn't look for all the subtrees under the path defined by "subtree".
+ * It is used to accelerate reads for applications using settings_load_subtree to load
+ * only one key instead of the whole subtree.
+ */
+static int settings_zms_load_subtree(struct settings_store *cs, const struct settings_load_arg *arg)
+{
+	struct settings_zms *cf = CONTAINER_OF(cs, struct settings_zms, cf_store);
+	struct settings_zms_read_fn_arg read_fn_arg;
+	char name[SETTINGS_MAX_NAME_LEN + SETTINGS_EXTRA_LEN + 1];
+	ssize_t rc1;
+	ssize_t rc2;
+	uint32_t name_hash;
+	int ret = 0;
+
+	name_hash = sys_hash32(arg->subtree, strlen(arg->subtree)) & ZMS_HASH_MASK;
+	for (int i = 0; i <= cf->hash_collision_num; i++) {
+		name_hash = ZMS_UPDATE_COLLISION_NUM(name_hash, i);
+		/* Get the name entry from ZMS */
+		rc1 = zms_read(&cf->cf_zms, ZMS_NAME_ID_FROM_HASH(name_hash), &name,
+			       sizeof(name) - 1);
+		/* get the length of data and verify that it exists */
+		rc2 = zms_get_data_length(&cf->cf_zms,
+					  ZMS_NAME_ID_FROM_HASH(name_hash) + ZMS_DATA_ID_OFFSET);
+		if ((rc1 <= 0) || (rc2 <= 0)) {
+			/* Name or data doesn't exist */
+			continue;
+		}
+		/* Found a name, this might not include a trailing \0 */
+		name[rc1] = '\0';
+		if (strcmp(arg->subtree, name)) {
+			/* Names are not equal let's continue to the next collision hash
+			 * if it exists.
+			 */
+			continue;
+		}
+		/* At this steps the names are equal, let's set the handler */
+		read_fn_arg.fs = &cf->cf_zms;
+		read_fn_arg.id = ZMS_NAME_ID_FROM_HASH(name_hash) + ZMS_DATA_ID_OFFSET;
+
+		ret = settings_call_set_handler(arg->subtree, rc2, settings_zms_read_fn, &read_fn_arg,
+						(void *)arg);
+		/* We should return here as there are no need to look for the next
+		 * hash collision */
+		return ret;
+	}
+
+	return 0;
+}
+#endif /* CONFIG_SETTINGS_ZMS_LOAD_SUBTREE_PATH */
+
 static int settings_zms_load(struct settings_store *cs, const struct settings_load_arg *arg)
 {
 	int ret = 0;
@@ -206,6 +258,15 @@ static int settings_zms_load(struct settings_store *cs, const struct settings_lo
 	ssize_t rc1;
 	ssize_t rc2;
 	uint32_t ll_hash_id;
+#ifdef CONFIG_SETTINGS_ZMS_LOAD_SUBTREE_PATH
+	/* If arg->subtree is not null we must load settings in that subtree */
+	if (arg->subtree != NULL) {
+		ret = settings_zms_load_subtree(cs, arg);
+		if (ret) {
+			return ret;
+		}
+	}
+#endif /* CONFIG_SETTINGS_ZMS_LOAD_SUBTREE_PATH */
 
 	ret = zms_read(&cf->cf_zms, ZMS_LL_HEAD_HASH_ID, &settings_element,
 		       sizeof(struct settings_hash_linked_list));
@@ -214,6 +275,7 @@ static int settings_zms_load(struct settings_store *cs, const struct settings_lo
 	}
 	ll_hash_id = settings_element.next_hash;
 
+	/* If subtree is NULL then we must load all found Settings */
 	while (ll_hash_id) {
 
 		/* In the ZMS backend, each setting item is stored in two ZMS