settings: ZMS: add a backend for ZMS (Zephyr Memory Storage)

This adds the initial backend support for the ZMS storage system.

Signed-off-by: Riadh Ghaddab <rghaddab@baylibre.com>

subsys/settings/Kconfig

@@ -32,13 +32,38 @@ config SETTINGS_ENCODE_LEN
 
 choice SETTINGS_BACKEND
 	prompt "Storage back-end"
+	default SETTINGS_ZMS if ZMS
 	default SETTINGS_NVS if NVS
 	default SETTINGS_FCB if FCB
 	default SETTINGS_FILE if FILE_SYSTEM
 	default SETTINGS_NONE
 	help
 	  Storage back-end to be used by the settings subsystem.
 
+config SETTINGS_ZMS
+	bool "ZMS (Zephyr Memory Storage)"
+	depends on ZMS
+	help
+	  Use ZMS as settings storage backend.
+
+if SETTINGS_ZMS
+
+config SETTINGS_ZMS_NAME_CACHE
+	bool "ZMS name lookup cache"
+	help
+	  Enable ZMS name lookup cache, used to reduce the Settings name
+	  lookup time.
+
+config SETTINGS_ZMS_NAME_CACHE_SIZE
+	int "ZMS name lookup cache size"
+	default 128
+	range 1 $(UINT32_MAX)
+	depends on SETTINGS_ZMS_NAME_CACHE
+	help
+	  Number of entries in Settings ZMS name cache.
+
+endif # SETTINGS_ZMS
+
 config SETTINGS_FCB
 	bool "FCB"
 	depends on FCB
@@ -132,6 +157,20 @@ config SETTINGS_NVS_SECTOR_COUNT
 	help
 	  Number of sectors used for the NVS settings area
 
+config SETTINGS_ZMS_SECTOR_SIZE_MULT
+	int "Sector size of the ZMS settings area"
+	default 1
+	depends on SETTINGS_ZMS
+	help
+	  The sector size to use for the ZMS settings area as a multiple of
+	  FLASH_ERASE_BLOCK_SIZE.
+
+config SETTINGS_ZMS_SECTOR_COUNT
+	int "Sector count of the ZMS settings area"
+	default 8
+	help
+	  Number of sectors used for the ZMS settings area
+
 config SETTINGS_SHELL
 	bool "Settings shell"
 	depends on SHELL

subsys/settings/include/settings/settings_zms.h

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2024 BayLibre SAS
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef __SETTINGS_ZMS_H_
+#define __SETTINGS_ZMS_H_
+
+#include <zephyr/fs/zms.h>
+#include <zephyr/settings/settings.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* In the ZMS backend, each setting is stored in two ZMS entries:
+ *	1. setting's name
+ *	2. setting's value
+ *
+ * The ZMS entry ID for the setting's value is determined implicitly based on
+ * the ID of the ZMS entry for the setting's name, once that is found. The
+ * difference between name and value ID is constant and equal to
+ * ZMS_NAME_ID_OFFSET.
+ *
+ * Setting's name entries start from ZMS_NAMECNT_ID + 1.
+ * The entry with ID == ZMS_NAMECNT_ID is used to store the largest name ID in use.
+ *
+ * Deleted records will not be found, only the last record will be read.
+ */
+#define ZMS_NAMECNT_ID     0x80000000
+#define ZMS_NAME_ID_OFFSET 0x40000000
+
+struct settings_zms {
+	struct settings_store cf_store;
+	struct zms_fs cf_zms;
+	uint32_t last_name_id;
+	const struct device *flash_dev;
+#if CONFIG_SETTINGS_ZMS_NAME_CACHE
+	struct {
+		uint32_t name_hash;
+		uint32_t name_id;
+	} cache[CONFIG_SETTINGS_ZMS_NAME_CACHE_SIZE];
+
+	uint32_t cache_next;
+	uint32_t cache_total;
+	bool loaded;
+#endif
+};
+
+/* register zms to be a source of settings */
+int settings_zms_src(struct settings_zms *cf);
+
+/* register zms to be the destination of settings */
+int settings_zms_dst(struct settings_zms *cf);
+
+/* Initialize a zms backend. */
+int settings_zms_backend_init(struct settings_zms *cf);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __SETTINGS_ZMS_H_ */

subsys/settings/src/CMakeLists.txt

@@ -13,3 +13,4 @@ zephyr_sources_ifdef(CONFIG_SETTINGS_FCB settings_fcb.c)
 zephyr_sources_ifdef(CONFIG_SETTINGS_NVS settings_nvs.c)
 zephyr_sources_ifdef(CONFIG_SETTINGS_NONE settings_none.c)
 zephyr_sources_ifdef(CONFIG_SETTINGS_SHELL settings_shell.c)
+zephyr_sources_ifdef(CONFIG_SETTINGS_ZMS settings_zms.c)