[nrf fromtree] 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 <[email protected]>
(cherry picked from commit ef4e8dd)

Author: rghaddab

subsys/settings/Kconfig

@@ -32,13 +32,21 @@ 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
+	select SYS_HASH_FUNC32
+	help
+	  Use ZMS as settings storage backend.
+
 config SETTINGS_FCB
 	bool "FCB"
 	depends on FCB
@@ -132,6 +140,37 @@ 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_CUSTOM_SECTOR_COUNT
+	bool "Customize the sector count of the ZMS settings partition"
+	depends on SETTINGS_ZMS
+	help
+	  The number of sectors used by default is the maximum value that can
+	  fit in the settings storage partition.
+	  Enabling this config allows to customize the number of used sectors.
+
+config SETTINGS_ZMS_SECTOR_COUNT
+	int "Sector count of the ZMS settings area"
+	default 8
+	depends on SETTINGS_ZMS && SETTINGS_ZMS_CUSTOM_SECTOR_COUNT
+	help
+	  Number of sectors used for the ZMS settings area
+
+config SETTINGS_ZMS_MAX_COLLISIONS_BITS
+	int "number of bits reserved to handle collisions between hash numbers"
+	default 4
+	depends on SETTINGS_ZMS
+	help
+	  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_SHELL
 	bool "Settings shell"
 	depends on SHELL

subsys/settings/include/settings/settings_zms.h

@@ -0,0 +1,89 @@
+/* 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 is hashed into 29 bits minus hash_collisions_bits.
+ * The 2 MSB_bits have always the same value 10, the LL_bit for the name's hash is 0
+ * and the hash_collisions_bits is configurable through CONFIG_SETTINGS_ZMS_MAX_COLLISIONS_BITS.
+ * The resulted 32 bits is the ZMS_ID of the Setting's name.
+ * If we detect a collision between ZMS_IDs we increment the value within hash_collision_bits
+ * until we find a free ZMS_ID.
+ * Separately, we store a linked list using the Setting's name ZMS_ID but setting the lsb to 1.
+ *
+ * The linked list is used to maintain a relation between all ZMS_IDs. This is necessary to load
+ * all settings at initialization.
+ * The linked list contains at least a header followed by multiple linked list elements that
+ * we can refer to as LL_x (where x is the order of that element in that list).
+ * This is a representation of the Linked List that is stored in the storage.
+ * LL_header <--> LL_0 <--> LL_1 <--> LL_2.
+ * The "next_hash" pointer of each LL element refers to the next element in the linked list.
+ * The "previous_hash" pointer is referring the previous element in the linked list.
+ *
+ * The bit representation of the 32 bits ZMS_ID is the following:
+ * --------------------------------------------------------------
+ * | MSB_bits | hash (truncated) | hash_collision_bits | LL_bit |
+ * --------------------------------------------------------------
+ * Where:
+ * MSB_bits (2 bits width) : = 10 for Name IDs
+ *			     = 11 for Data IDs
+ * hash (29 bits - hash_collision_bits) : truncated hash obtained from sys_hash32
+ * hash_collision_bits (configurable width) : used to handle hash collisions
+ * LL_bit : = 0 when this is a name's ZMS_ID
+ *	    = 1 when this is the linked list ZMS_ID corresponding to the name
+ *
+ * if a settings element is deleted it won't be found.
+ */
+
+#define ZMS_LL_HEAD_HASH_ID 0x80000000
+#define ZMS_DATA_ID_OFFSET  0x40000000
+#define ZMS_HASH_MASK       GENMASK(29, CONFIG_SETTINGS_ZMS_MAX_COLLISIONS_BITS + 1)
+#define ZMS_COLLISIONS_MASK GENMASK(CONFIG_SETTINGS_ZMS_MAX_COLLISIONS_BITS, 1)
+#define ZMS_HASH_TOTAL_MASK GENMASK(29, 1)
+#define ZMS_MAX_COLLISIONS  (BIT(CONFIG_SETTINGS_ZMS_MAX_COLLISIONS_BITS) - 1)
+#define ZMS_HEADER_HASH     0x80000000
+
+/* some useful macros */
+#define ZMS_NAME_HASH_ID(x) (x & ZMS_HASH_TOTAL_MASK)
+#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)
+
+struct settings_zms {
+	struct settings_store cf_store;
+	struct zms_fs cf_zms;
+	const struct device *flash_dev;
+	uint32_t last_hash_id;
+	uint32_t second_to_last_hash_id;
+	uint8_t hash_collision_num;
+};
+
+struct settings_hash_linked_list {
+	uint32_t previous_hash;
+	uint32_t next_hash;
+};
+
+#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)