非易失性存储库

[English]

简介

非易失性存储 (NVS) 库主要用于在 flash 中存储键值格式的数据。本文档将详细介绍 NVS 常用的一些概念。

底层存储

NVS 通过调用 spi_flash_{read|write|erase} API 对主 flash 的部分空间进行读、写、擦除操作,包括 data 类型和 nvs 子类型的所有分区。应用程序可调用 nvs_open API 选择使用带有 nvs 标签的分区,也可以通过调用 nvs_open_from_part API 选择使用指定名称的任意分区。

NVS 库后续版本可能会增加其他存储器后端,实现将数据保存至其他 flash 芯片(SPI 或 I2C 接口)、RTC 或 FRAM 中。

注解

如果 NVS 分区被截断(例如,更改分区表布局时),则应擦除分区内容。可以使用 ESP-IDF 构建系统中的 idf.py erase_flash 命令擦除 flash 上的所有内容。

注解

NVS 最适合存储一些较小的数据,而非字符串或二进制大对象 (BLOB) 等较大的数据。如需存储较大的 BLOB 或者字符串,请考虑使用基于磨损均衡库的 FAT 文件系统。

键值对

NVS 的操作对象为键值对,其中键是 ASCII 字符串,当前支持最大键长为 15 个字符,值可以为以下几种类型:

  • 整数型:uint8_tint8_tuint16_tint16_tuint32_tint32_tuint64_tint64_t
  • \0 结尾的字符串;
  • 可变长度的二进制数据 (BLOB)

注解

字符串值当前上限为 4000 字节,其中包括空终止符。BLOB 值上限为 508,000 字节或分区大小减去 4000 字节的 97.6%,以较低值为准。

后续可能会增加对 floatdouble 等其他类型数据的支持。

键必须唯一。为现有的键写入新的值可能产生如下结果:

  • 如果新旧值数据类型相同,则更新值;
  • 如果新旧值数据类型不同,则返回错误。

读取值时也会执行数据类型检查。如果读取操作的数据类型与该值的数据类型不匹配,则返回错误。

命名空间

为了减少不同组件之间键名的潜在冲突,NVS 将每个键值对分配给一个命名空间。命名空间的命名规则遵循键名的命名规则,即最多可占 15 个字符。命名空间的名称在调用 nvs_opennvs_open_from_part 中指定,调用后将返回一个不透明句柄,用于后续调用 nvs_read_*nvs_write_*nvs_commit 函数。这样,一个句柄关联一个命名空间,键名便不会与其他命名空间中相同键名冲突。请注意,不同 NVS 分区中具有相同名称的命名空间将被视为不同的命名空间。

安全性、篡改性及鲁棒性

NVS 与 ESP32 flash 加密系统不直接兼容。但如果 NVS 加密与 ESP32 flash 加密一起使用时,数据仍可以加密形式存储。更多详情请参阅 NVS 加密

如果未启用 NVS 加密,任何对 flash 芯片有物理访问权限的人都可以修改、擦除或添加键值对。NVS 加密启用后,如果不知道相应的 NVS 加密密钥,则无法修改或添加键值对并将其识别为有效键值。但是,针对擦除操作没有相应的防篡改功能。

当 flash 处于不一致状态时,NVS 库会尝试恢复。在任何时间点关闭设备电源,然后重新打开电源,不会导致数据丢失;但如果关闭设备电源时正在写入新的键值对,这一键值对可能会丢失。该库还应当能对 flash 中的任意数据进行正确初始化。

内部实现

键值对日志

NVS 按顺序存储键值对,新的键值对添加在最后。因此,如需更新某一键值对,实际是在日志最后增加一对新的键值对,同时将旧的键值对标记为已擦除。

页面和条目

NVS 库在其操作中主要使用两个实体:页面和条目。页面是一个逻辑结构,用于存储部分的整体日志。逻辑页面对应 flash 的一个物理扇区,正在使用中的页面具有与之相关联的序列号。序列号赋予了页面顺序,较高的序列号对应较晚创建的页面。页面有以下几种状态:

空或未初始化
页面对应的 flash 扇区为空白状态(所有字节均为 0xff)。此时,页面未存储任何数据且没有关联的序列号。
活跃状态
此时 flash 已完成初始化,页头部写入 flash,页面已具备有效序列号。页面中存在一些空条目,可写入数据。任意时刻,至多有一个页面处于活跃状态。
写满状态
Flash 已写满键值对,状态不再改变。用户无法向写满状态下的页面写入新键值对,但仍可将一些键值对标记为已擦除。
擦除状态
未擦除的键值对将移至其他页面,以便擦除当前页面。这一状态仅为暂时性状态,即 API 调用返回时,页面应脱离这一状态。如果设备突然断电,下次开机时,设备将继续把未擦除的键值对移至其他页面,并继续擦除当前页面。
损坏状态
页头部包含无效数据,无法进一步解析该页面中的数据,因此之前写入该页面的所有条目均无法访问。相应的 flash 扇区并不会被立即擦除,而是与其他处于未初始化状态的扇区一起等待后续使用。这一状态可能对调试有用。

Flash 扇区映射至逻辑页面并没有特定的顺序,NVS 库会检查存储在 flash 扇区的页面序列号,并根据序列号组织页面。

+--------+     +--------+     +--------+     +--------+
| Page 1 |     | Page 2 |     | Page 3 |     | Page 4 |
| Full   +---> | Full   +---> | Active |     | Empty  |   <- 状态
| #11    |     | #12    |     | #14    |     |        |   <- 序列号
+---+----+     +----+---+     +----+---+     +---+----+
    |               |              |             |
    |               |              |             |
    |               |              |             |
+---v------+  +-----v----+  +------v---+  +------v---+
| Sector 3 |  | Sector 0 |  | Sector 2 |  | Sector 1 |    <- 物理扇区
+----------+  +----------+  +----------+  +----------+

页面结构

当前,我们假设 flash 扇区大小为 4096 字节,并且 ESP32 flash 加密硬件在 32 字节块上运行。未来有可能引入一些编译时可配置项(可通过 menuconfig 进行配置),以适配具有不同扇区大小的 flash 芯片。但目前尚不清楚 SPI flash 驱动和 SPI flash cache 之类的系统组件是否支持其他扇区大小。

页面由头部、条目状态位图和条目三部分组成。为了实现与 ESP32 flash 加密功能兼容,条目大小设置为 32 字节。如果键值为整数型,条目则保存一个键值对;如果键值为字符串或 BLOB 类型,则条目仅保存一个键值对的部分内容(更多信息详见条目结构描述)。

页面结构如下图所示,括号内数字表示该部分的大小(以字节为单位):

+-----------+--------------+-------------+-------------------------+
| State (4) | Seq. no. (4) | version (1) | Unused (19) | CRC32 (4) |   页头部 (32)
+-----------+--------------+-------------+-------------------------+
|                Entry state bitmap (32)                           |
+------------------------------------------------------------------+
|                       Entry 0 (32)                               |
+------------------------------------------------------------------+
|                       Entry 1 (32)                               |
+------------------------------------------------------------------+
/                                                                  /
/                                                                  /
+------------------------------------------------------------------+
|                       Entry 125 (32)                             |
+------------------------------------------------------------------+

头部和条目状态位图写入 flash 时不加密。如果启用了 ESP32 flash 加密功能,则条目写入 flash 时将会加密。

通过将 0 写入某些位可以定义页面状态值,表示状态改变。因此,如果需要变更页面状态,并不一定要擦除页面,除非要将其变更为擦除状态。

头部中的 version 字段反映了所用的 NVS 格式版本。为实现向后兼容,版本升级从 0xff 开始依次递减(例如,version-1 为 0xff,version-2 为 0xfe 等)。

头部中 CRC32 值是由不包含状态值的条目计算所得(4 到 28 字节)。当前未使用的条目用 0xff 字节填充。

条目结构和条目状态位图详细信息见下文描述。

条目和条目状态位图

每个条目可处于以下三种状态之一,每个状态在条目状态位图中用两位表示。位图中的最后四位 (256 - 2 * 126) 未使用。

空 (2’b11)
条目还未写入任何内容,处于未初始化状态(全部字节为 0xff)。
写入(2’b10)
一个键值对(或跨多个条目的键值对的部分内容)已写入条目中。
擦除(2’b00)
条目中的键值对已丢弃,条目内容不再解析。

条目结构

如果键值类型为基础类型,即 1 - 8 个字节长度的整数型,条目将保存一个键值对;如果键值类型为字符串或 BLOB 类型,条目将保存整个键值对的部分内容。另外,如果键值为字符串类型且跨多个条目,则键值所跨的所有条目均保存在同一页面。BLOB 则可以切分为多个块,实现跨多个页面。BLOB 索引是一个附加的固定长度元数据条目,用于追踪 BLOB 块。目前条目仍支持早期 BLOB 格式(可读取可修改),但这些 BLOB 一经修改,即以新格式储存至条目。

+--------+----------+----------+----------------+-----------+---------------+----------+
| NS (1) | Type (1) | Span (1) | ChunkIndex (1) | CRC32 (4) |    Key (16)   | Data (8) |
+--------+----------+----------+----------------+-----------+---------------+----------+

                                         Primitive  +--------------------------------+
                                        +-------->  |     Data (8)                   |
                                        | Types     +--------------------------------+
                   +-> Fixed length --
                   |                    |           +---------+--------------+---------------+-------+
                   |                    +-------->  | Size(4) | ChunkCount(1)| ChunkStart(1) | Rsv(2)|
    Data format ---+                    BLOB Index  +---------+--------------+---------------+-------+
                   |
                   |                             +----------+---------+-----------+
                   +->   Variable length   -->   | Size (2) | Rsv (2) | CRC32 (4) |
                        (Strings, BLOB Data)     +----------+---------+-----------+

条目结构中各个字段含义如下:

命名空间 (NS, NameSpace)
该条目的命名空间索引,详细信息见命名空间实现章节。
类型 (Type)
一个字节表示的值的数据类型,可能的类型见 nvs_types.hItemType 枚举。
跨度 (Span)
该键值对所用的条目数量。如果键值为整数型,条目数量即为 1。如果键值为字符串或 BLOB,则条目数量取决于值的长度。
块索引 (ChunkIndex)
用于存储 BLOB 类型数据块的索引。如果键值为其他数据类型,则此处索引应写入 0xff
CRC32
对条目下所有字节进行校验,所得的校验和(CRC32 字段不计算在内)。
键 (Key)
即以零结尾的 ASCII 字符串,字符串最长为 15 字节,不包含最后一个字节的 NULL (\0) 终止符。
数据 (Data)

如果键值类型为整数型,则数据字段仅包含键值。如果键值小于八个字节,使用 0xff 填充未使用的部分(右侧)。

如果键值类型为 BLOB 索引条目,则该字段的八个字节将保存以下数据块信息:

  • 块大小
    整个 BLOB 数据的大小(以字节为单位)。该字段仅用于 BLOB 索引类型条目。
  • ChunkCount
    存储过程中 BLOB 分成的数据块数量。该字段仅用于 BLOB 索引类型条目。
  • ChunkStart
    BLOB 第一个数据块的块索引,后续数据块索引依次递增,步长为 1。该字段仅用于 BLOB 索引类型条目。

如果键值类型为字符串或 BLOB 数据块,数据字段的这八个字节将保存该键值的一些附加信息,如下所示:

  • 数据大小
    实际数据的大小(以字节为单位)。如果键值类型为字符串,此字段也应将零终止符包含在内。此字段仅用于字符串和 BLOB 类型条目。
  • CRC32
    数据所有字节的校验和,该字段仅用于字符串和 BLOB 类型条目。

可变长度值(字符串和 BLOB)写入后续条目,每个条目 32 字节。第一个条目的 span 字段将指明使用了多少条目。

命名空间

如上所述,每个键值对属于一个命名空间。命名空间标识符(字符串)也作为键值对的键,存储在索引为 0 的命名空间中。与这些键对应的值就是这些命名空间的索引。

+-------------------------------------------+
| NS=0 Type=uint8_t Key="wifi" Value=1      |   Entry describing namespace "wifi"
+-------------------------------------------+
| NS=1 Type=uint32_t Key="channel" Value=6  |   Key "channel" in namespace "wifi"
+-------------------------------------------+
| NS=0 Type=uint8_t Key="pwm" Value=2       |   Entry describing namespace "pwm"
+-------------------------------------------+
| NS=2 Type=uint16_t Key="channel" Value=20 |   Key "channel" in namespace "pwm"
+-------------------------------------------+

条目哈希列表

为了减少对 flash 执行的读操作次数,Page 类对象均设有一个列表,包含一对数据:条目索引和条目哈希值。该列表可大大提高检索速度,而无需迭代所有条目并逐个从 flash 中读取。Page::findItem 首先从哈希列表中检索条目哈希值,如果条目存在,则在页面内给出条目索引。由于哈希冲突,在哈希列表中检索条目哈希值可能会得到不同的条目,对 flash 中条目再次迭代可解决这一冲突。

哈希列表中每个节点均包含一个 24 位哈希值和 8 位条目索引。哈希值根据条目命名空间、键名和块索引由 CRC32 计算所得,计算结果保留 24 位。为减少将 32 位条目存储在链表中的开销,链表采用了数组的双向链表。每个数组占用 128 个字节,包含 29 个条目、两个链表指针和一个 32 位计数字段。因此,每页额外需要的 RAM 最少为 128 字节,最多为 640 字节。

NVS 加密

NVS 分区内存储的数据可使用 AES-XTS 进行加密,类似于 IEEE P1619 磁盘加密标准中提到的加密方式。为了实现加密,每个条目被均视为一个扇区,并将条目相对地址(相对于分区开头)传递给加密算法,用作扇区号。NVS 加密所需的密钥存储于其他分区,并进行了 flash 加密。因此,在使用 NVS 加密前应先启用 flash 加密

NVS 密钥分区

应用程序如果想使用 NVS 加密,则需要编译进一个类型为 data,子类型为 key 的密钥分区。该分区应标记为已加密,且最小为 4096 字节,具体结构见下表。如需了解更多详细信息,请参考 分区表

+-----------+--------------+-------------+----+
|              XTS encryption key(32)         |
+---------------------------------------------+
|              XTS tweak key (32)             |
+---------------------------------------------+
|                  CRC32(4)                   |
+---------------------------------------------+

使用 NVS 分区生成程序生成上述分区表,并烧录至设备。由于分区已标记为已加密,而且启用了 flash 加密,引导程序在首次启动时将使用 flash 加密对密钥分区进行加密。您也可以在设备启动后调用 nvs_flash.h 提供的 nvs_flash_generate_keys API 生成加密密钥,然后再将密钥以加密形式写入密钥分区。

应用程序可以使用不同的密钥对不同的 NVS 分区进行加密,这样就会需要多个加密密钥分区。应用程序应为加解密操作提供正确的密钥或密钥分区。

加密读取/写入

nvs_read_*nvs_write_* 等 NVS API 函数同样可以对 NVS 加密分区执行读写操作。但用于初始化 NVS 非加密分区和加密分区的 API 则有所不同:初始化 NVS 非加密分区可以使用 nvs_flash_initnvs_flash_init_partition,但初始化 NVS 加密分区则需调用 nvs_flash_secure_initnvs_flash_secure_init_partition。上述 API 函数所需的 nvs_sec_cfg_t 结构可使用 nvs_flash_generate_keys 或者 nvs_flash_read_security_cfg 进行填充。

应用程序如需在加密状态下执行 NVS 读写操作,应遵循以下步骤:

  1. 使用 esp_partition_find* API 查找密钥分区和 NVS 数据分区;
  2. 使用 nvs_flash_read_security_cfgnvs_flash_generate_keys API 填充 nvs_sec_cfg_t 结构;
  3. 使用 nvs_flash_secure_initnvs_flash_secure_init_partition API 初始化 NVS flash 分区;
  4. 使用 nvs_opennvs_open_from_part API 打开命名空间;
  5. 使用 nvs_read_*nvs_write_* API 执行 NVS 读取/写入操作;
  6. 使用 nvs_flash_deinit API 释放已初始化的 NVS 分区。

NVS 迭代器

迭代器允许根据指定的分区名称、命名空间和数据类型轮询 NVS 中存储的键值对。

您可以使用以下函数,执行相关操作:

  • nvs_entry_find:返回一个不透明句柄,用于后续调用 nvs_entry_nextnvs_entry_info 函数;
  • nvs_entry_next:返回指向下一个键值对的迭代器;
  • nvs_entry_info:返回每个键值对的信息。

如果未找到符合标准的键值对,nvs_entry_findnvs_entry_next 将返回 NULL,此时不必释放迭代器。若不再需要迭代器,可使用 nvs_release_iterator 释放迭代器。

NVS 分区生成程序

NVS 分区生成程序帮助生成 NVS 分区二进制文件,可使用烧录程序将二进制文件单独烧录至特定分区。烧录至分区上的键值对由 CSV 文件提供,详情请参考 NVS 分区生成程序

应用示例

ESP-IDF storage 目录下提供了两个代码示例:

storage/nvs_rw_value

演示如何读取及写入 NVS 单个整数值。

此示例中的值表示 ESP32 模组重启次数。NVS 中数据不会因为模组重启而丢失,因此只有将这一值存储于 NVS 中,才能起到重启次数计数器的作用。

该示例也演示了如何检测读取/写入操作是否成功,以及某个特定值是否在 NVS 中尚未初始化。诊断程序以纯文本形式提供,帮助您追踪程序流程,及时发现问题。

storage/nvs_rw_blob

演示如何读取及写入 NVS 单个整数值和 Blob(二进制大对象),并在 NVS 中存储这一数值,即便 ESP32 模组重启也不会消失。

  • value - 记录 ESP32 模组软重启次数和硬重启次数。
  • blob - 内含记录模组运行次数的表格。此表格将被从 NVS 读取至动态分配的 RAM 上。每次手动软重启后,表格内运行次数即增加一次,新加的运行次数被写入 NVS。下拉 GPIO0 即可手动软重启。

该示例也演示了如何执行诊断程序以检测读取/写入操作是否成功。

API 参考

Functions

esp_err_t nvs_flash_init(void)

Initialize the default NVS partition.

This API initialises the default NVS partition. The default NVS partition is the one that is labeled “nvs” in the partition table.

Return
  • ESP_OK if storage was successfully initialized.
  • ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages (which may happen if NVS partition was truncated)
  • ESP_ERR_NOT_FOUND if no partition with label “nvs” is found in the partition table
  • one of the error codes from the underlying flash storage driver

esp_err_t nvs_flash_init_partition(const char *partition_label)

Initialize NVS flash storage for the specified partition.

Return
  • ESP_OK if storage was successfully initialized.
  • ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages (which may happen if NVS partition was truncated)
  • ESP_ERR_NOT_FOUND if specified partition is not found in the partition table
  • one of the error codes from the underlying flash storage driver
Parameters
  • partition_label: Label of the partition. Note that internally a reference to passed value is kept and it should be accessible for future operations

esp_err_t nvs_flash_deinit(void)

Deinitialize NVS storage for the default NVS partition.

Default NVS partition is the partition with “nvs” label in the partition table.

Return
  • ESP_OK on success (storage was deinitialized)
  • ESP_ERR_NVS_NOT_INITIALIZED if the storage was not initialized prior to this call

esp_err_t nvs_flash_deinit_partition(const char *partition_label)

Deinitialize NVS storage for the given NVS partition.

Return
  • ESP_OK on success
  • ESP_ERR_NVS_NOT_INITIALIZED if the storage for given partition was not initialized prior to this call
Parameters
  • partition_label: Label of the partition

esp_err_t nvs_flash_erase(void)

Erase the default NVS partition.

This function erases all contents of the default NVS partition (one with label “nvs”)

Return
  • ESP_OK on success
  • ESP_ERR_NOT_FOUND if there is no NVS partition labeled “nvs” in the partition table

esp_err_t nvs_flash_erase_partition(const char *part_name)

Erase specified NVS partition.

This function erases all contents of specified NVS partition

Return
  • ESP_OK on success
  • ESP_ERR_NOT_FOUND if there is no NVS partition with the specified name in the partition table
Parameters
  • part_name: Name (label) of the partition to be erased

esp_err_t nvs_flash_secure_init(nvs_sec_cfg_t *cfg)

Initialize the default NVS partition.

This API initialises the default NVS partition. The default NVS partition is the one that is labeled “nvs” in the partition table.

Return
  • ESP_OK if storage was successfully initialized.
  • ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages (which may happen if NVS partition was truncated)
  • ESP_ERR_NOT_FOUND if no partition with label “nvs” is found in the partition table
  • one of the error codes from the underlying flash storage driver
Parameters
  • cfg: Security configuration (keys) to be used for NVS encryption/decryption. If cfg is NULL, no encryption is used.

esp_err_t nvs_flash_secure_init_partition(const char *partition_label, nvs_sec_cfg_t *cfg)

Initialize NVS flash storage for the specified partition.

Return
  • ESP_OK if storage was successfully initialized.
  • ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages (which may happen if NVS partition was truncated)
  • ESP_ERR_NOT_FOUND if specified partition is not found in the partition table
  • one of the error codes from the underlying flash storage driver
Parameters
  • partition_label: Label of the partition. Note that internally a reference to passed value is kept and it should be accessible for future operations
  • cfg: Security configuration (keys) to be used for NVS encryption/decryption. If cfg is null, no encryption/decryption is used.

esp_err_t nvs_flash_generate_keys(const esp_partition_t *partition, nvs_sec_cfg_t *cfg)

Generate and store NVS keys in the provided esp partition.

Return
-ESP_OK, if cfg was read successfully; -or error codes from esp_partition_write/erase APIs.
Parameters
  • partition: Pointer to partition structure obtained using esp_partition_find_first or esp_partition_get. Must be non-NULL.
  • cfg: Pointer to nvs security configuration structure. Pointer must be non-NULL. Generated keys will be populated in this structure.

esp_err_t nvs_flash_read_security_cfg(const esp_partition_t *partition, nvs_sec_cfg_t *cfg)

Read NVS security configuration from a partition.

Note
Provided parition is assumed to be marked ‘encrypted’.
Return
-ESP_OK, if cfg was read successfully; -ESP_ERR_NVS_KEYS_NOT_INITIALIZED, if the partition is not yet written with keys. -ESP_ERR_NVS_CORRUPT_KEY_PART, if the partition containing keys is found to be corrupt -or error codes from esp_partition_read API.
Parameters
  • partition: Pointer to partition structure obtained using esp_partition_find_first or esp_partition_get. Must be non-NULL.
  • cfg: Pointer to nvs security configuration structure. Pointer must be non-NULL.

Structures

struct nvs_sec_cfg_t

Key for encryption and decryption.

Public Members

uint8_t eky[NVS_KEY_SIZE]

XTS encryption and decryption key

uint8_t tky[NVS_KEY_SIZE]

XTS tweak key

Macros

NVS_KEY_SIZE

Functions

esp_err_t nvs_set_i8(nvs_handle_t handle, const char *key, int8_t value)

set value for given key

This family of functions set value for the key, given its name. Note that actual storage will not be updated until nvs_commit function is called.

Return
  • ESP_OK if value was set successfully
  • ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
  • ESP_ERR_NVS_READ_ONLY if storage handle was opened as read only
  • ESP_ERR_NVS_INVALID_NAME if key name doesn’t satisfy constraints
  • ESP_ERR_NVS_NOT_ENOUGH_SPACE if there is not enough space in the underlying storage to save the value
  • ESP_ERR_NVS_REMOVE_FAILED if the value wasn’t updated because flash write operation has failed. The value was written however, and update will be finished after re-initialization of nvs, provided that flash operation doesn’t fail again.
  • ESP_ERR_NVS_VALUE_TOO_LONG if the string value is too long
Parameters
  • handle: Handle obtained from nvs_open function. Handles that were opened read only cannot be used.
  • key: Key name. Maximal length is determined by the underlying implementation, but is guaranteed to be at least 15 characters. Shouldn’t be empty.
  • value: The value to set. For strings, the maximum length (including null character) is 4000 bytes.

esp_err_t nvs_set_u8(nvs_handle_t handle, const char *key, uint8_t value)
esp_err_t nvs_set_i16(nvs_handle_t handle, const char *key, int16_t value)
esp_err_t nvs_set_u16(nvs_handle_t handle, const char *key, uint16_t value)
esp_err_t nvs_set_i32(nvs_handle_t handle, const char *key, int32_t value)
esp_err_t nvs_set_u32(nvs_handle_t handle, const char *key, uint32_t value)
esp_err_t nvs_set_i64(nvs_handle_t handle, const char *key, int64_t value)
esp_err_t nvs_set_u64(nvs_handle_t handle, const char *key, uint64_t value)
esp_err_t nvs_set_str(nvs_handle_t handle, const char *key, const char *value)
esp_err_t nvs_get_i8(nvs_handle_t handle, const char *key, int8_t *out_value)

get value for given key

These functions retrieve value for the key, given its name. If key does not exist, or the requested variable type doesn’t match the type which was used when setting a value, an error is returned.

In case of any error, out_value is not modified.

All functions expect out_value to be a pointer to an already allocated variable of the given type.

// Example of using nvs_get_i32:
int32_t max_buffer_size = 4096; // default value
esp_err_t err = nvs_get_i32(my_handle, "max_buffer_size", &max_buffer_size);
assert(err == ESP_OK || err == ESP_ERR_NVS_NOT_FOUND);
// if ESP_ERR_NVS_NOT_FOUND was returned, max_buffer_size will still
// have its default value.

Return
  • ESP_OK if the value was retrieved successfully
  • ESP_ERR_NVS_NOT_FOUND if the requested key doesn’t exist
  • ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
  • ESP_ERR_NVS_INVALID_NAME if key name doesn’t satisfy constraints
  • ESP_ERR_NVS_INVALID_LENGTH if length is not sufficient to store data
Parameters
  • handle: Handle obtained from nvs_open function.
  • key: Key name. Maximal length is determined by the underlying implementation, but is guaranteed to be at least 15 characters. Shouldn’t be empty.
  • out_value: Pointer to the output value. May be NULL for nvs_get_str and nvs_get_blob, in this case required length will be returned in length argument.

esp_err_t nvs_get_u8(nvs_handle_t handle, const char *key, uint8_t *out_value)
esp_err_t nvs_get_i16(nvs_handle_t handle, const char *key, int16_t *out_value)
esp_err_t nvs_get_u16(nvs_handle_t handle, const char *key, uint16_t *out_value)
esp_err_t nvs_get_i32(nvs_handle_t handle, const char *key, int32_t *out_value)
esp_err_t nvs_get_u32(nvs_handle_t handle, const char *key, uint32_t *out_value)
esp_err_t nvs_get_i64(nvs_handle_t handle, const char *key, int64_t *out_value)
esp_err_t nvs_get_u64(nvs_handle_t handle, const char *key, uint64_t *out_value)
esp_err_t nvs_get_str(nvs_handle_t handle, const char *key, char *out_value, size_t *length)

get value for given key

These functions retrieve value for the key, given its name. If key does not exist, or the requested variable type doesn’t match the type which was used when setting a value, an error is returned.

In case of any error, out_value is not modified.

All functions expect out_value to be a pointer to an already allocated variable of the given type.

nvs_get_str and nvs_get_blob functions support WinAPI-style length queries. To get the size necessary to store the value, call nvs_get_str or nvs_get_blob with zero out_value and non-zero pointer to length. Variable pointed to by length argument will be set to the required length. For nvs_get_str, this length includes the zero terminator. When calling nvs_get_str and nvs_get_blob with non-zero out_value, length has to be non-zero and has to point to the length available in out_value. It is suggested that nvs_get/set_str is used for zero-terminated C strings, and nvs_get/set_blob used for arbitrary data structures.

// Example (without error checking) of using nvs_get_str to get a string into dynamic array:
size_t required_size;
nvs_get_str(my_handle, "server_name", NULL, &required_size);
char* server_name = malloc(required_size);
nvs_get_str(my_handle, "server_name", server_name, &required_size);

// Example (without error checking) of using nvs_get_blob to get a binary data
into a static array:
uint8_t mac_addr[6];
size_t size = sizeof(mac_addr);
nvs_get_blob(my_handle, "dst_mac_addr", mac_addr, &size);

Return
  • ESP_OK if the value was retrieved successfully
  • ESP_ERR_NVS_NOT_FOUND if the requested key doesn’t exist
  • ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
  • ESP_ERR_NVS_INVALID_NAME if key name doesn’t satisfy constraints
  • ESP_ERR_NVS_INVALID_LENGTH if length is not sufficient to store data
Parameters
  • handle: Handle obtained from nvs_open function.
  • key: Key name. Maximal length is determined by the underlying implementation, but is guaranteed to be at least 15 characters. Shouldn’t be empty.
  • out_value: Pointer to the output value. May be NULL for nvs_get_str and nvs_get_blob, in this case required length will be returned in length argument.
  • length: A non-zero pointer to the variable holding the length of out_value. In case out_value a zero, will be set to the length required to hold the value. In case out_value is not zero, will be set to the actual length of the value written. For nvs_get_str this includes zero terminator.

esp_err_t nvs_get_blob(nvs_handle_t handle, const char *key, void *out_value, size_t *length)
esp_err_t nvs_open(const char *name, nvs_open_mode_t open_mode, nvs_handle_t *out_handle)

Open non-volatile storage with a given namespace from the default NVS partition.

Multiple internal ESP-IDF and third party application modules can store their key-value pairs in the NVS module. In order to reduce possible conflicts on key names, each module can use its own namespace. The default NVS partition is the one that is labelled “nvs” in the partition table.

Return
  • ESP_OK if storage handle was opened successfully
  • ESP_ERR_NVS_NOT_INITIALIZED if the storage driver is not initialized
  • ESP_ERR_NVS_PART_NOT_FOUND if the partition with label “nvs” is not found
  • ESP_ERR_NVS_NOT_FOUND id namespace doesn’t exist yet and mode is NVS_READONLY
  • ESP_ERR_NVS_INVALID_NAME if namespace name doesn’t satisfy constraints
  • other error codes from the underlying storage driver
Parameters
  • name: Namespace name. Maximal length is determined by the underlying implementation, but is guaranteed to be at least 15 characters. Shouldn’t be empty.
  • open_mode: NVS_READWRITE or NVS_READONLY. If NVS_READONLY, will open a handle for reading only. All write requests will be rejected for this handle.
  • out_handle: If successful (return code is zero), handle will be returned in this argument.

esp_err_t nvs_open_from_partition(const char *part_name, const char *name, nvs_open_mode_t open_mode, nvs_handle_t *out_handle)

Open non-volatile storage with a given namespace from specified partition.

The behaviour is same as nvs_open() API. However this API can operate on a specified NVS partition instead of default NVS partition. Note that the specified partition must be registered with NVS using nvs_flash_init_partition() API.

Return
  • ESP_OK if storage handle was opened successfully
  • ESP_ERR_NVS_NOT_INITIALIZED if the storage driver is not initialized
  • ESP_ERR_NVS_PART_NOT_FOUND if the partition with specified name is not found
  • ESP_ERR_NVS_NOT_FOUND id namespace doesn’t exist yet and mode is NVS_READONLY
  • ESP_ERR_NVS_INVALID_NAME if namespace name doesn’t satisfy constraints
  • other error codes from the underlying storage driver
Parameters
  • part_name: Label (name) of the partition of interest for object read/write/erase
  • name: Namespace name. Maximal length is determined by the underlying implementation, but is guaranteed to be at least 15 characters. Shouldn’t be empty.
  • open_mode: NVS_READWRITE or NVS_READONLY. If NVS_READONLY, will open a handle for reading only. All write requests will be rejected for this handle.
  • out_handle: If successful (return code is zero), handle will be returned in this argument.

esp_err_t nvs_set_blob(nvs_handle_t handle, const char *key, const void *value, size_t length)

set variable length binary value for given key

This family of functions set value for the key, given its name. Note that actual storage will not be updated until nvs_commit function is called.

Return
  • ESP_OK if value was set successfully
  • ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
  • ESP_ERR_NVS_READ_ONLY if storage handle was opened as read only
  • ESP_ERR_NVS_INVALID_NAME if key name doesn’t satisfy constraints
  • ESP_ERR_NVS_NOT_ENOUGH_SPACE if there is not enough space in the underlying storage to save the value
  • ESP_ERR_NVS_REMOVE_FAILED if the value wasn’t updated because flash write operation has failed. The value was written however, and update will be finished after re-initialization of nvs, provided that flash operation doesn’t fail again.
  • ESP_ERR_NVS_VALUE_TOO_LONG if the value is too long
Parameters
  • handle: Handle obtained from nvs_open function. Handles that were opened read only cannot be used.
  • key: Key name. Maximal length is 15 characters. Shouldn’t be empty.
  • value: The value to set.
  • length: length of binary value to set, in bytes; Maximum length is 508000 bytes or (97.6% of the partition size - 4000) bytes whichever is lower.

esp_err_t nvs_erase_key(nvs_handle_t handle, const char *key)

Erase key-value pair with given key name.

Note that actual storage may not be updated until nvs_commit function is called.

Return
  • ESP_OK if erase operation was successful
  • ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
  • ESP_ERR_NVS_READ_ONLY if handle was opened as read only
  • ESP_ERR_NVS_NOT_FOUND if the requested key doesn’t exist
  • other error codes from the underlying storage driver
Parameters
  • handle: Storage handle obtained with nvs_open. Handles that were opened read only cannot be used.
  • key: Key name. Maximal length is determined by the underlying implementation, but is guaranteed to be at least 15 characters. Shouldn’t be empty.

esp_err_t nvs_erase_all(nvs_handle_t handle)

Erase all key-value pairs in a namespace.

Note that actual storage may not be updated until nvs_commit function is called.

Return
  • ESP_OK if erase operation was successful
  • ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
  • ESP_ERR_NVS_READ_ONLY if handle was opened as read only
  • other error codes from the underlying storage driver
Parameters
  • handle: Storage handle obtained with nvs_open. Handles that were opened read only cannot be used.

esp_err_t nvs_commit(nvs_handle_t handle)

Write any pending changes to non-volatile storage.

After setting any values, nvs_commit() must be called to ensure changes are written to non-volatile storage. Individual implementations may write to storage at other times, but this is not guaranteed.

Return
  • ESP_OK if the changes have been written successfully
  • ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL
  • other error codes from the underlying storage driver
Parameters
  • handle: Storage handle obtained with nvs_open. Handles that were opened read only cannot be used.

void nvs_close(nvs_handle_t handle)

Close the storage handle and free any allocated resources.

This function should be called for each handle opened with nvs_open once the handle is not in use any more. Closing the handle may not automatically write the changes to nonvolatile storage. This has to be done explicitly using nvs_commit function. Once this function is called on a handle, the handle should no longer be used.

Parameters
  • handle: Storage handle to close

esp_err_t nvs_get_stats(const char *part_name, nvs_stats_t *nvs_stats)

Fill structure nvs_stats_t. It provides info about used memory the partition.

This function calculates to runtime the number of used entries, free entries, total entries, and amount namespace in partition.

// Example of nvs_get_stats() to get the number of used entries and free entries:
nvs_stats_t nvs_stats;
nvs_get_stats(NULL, &nvs_stats);
printf("Count: UsedEntries = (%d), FreeEntries = (%d), AllEntries = (%d)\n",
       nvs_stats.used_entries, nvs_stats.free_entries, nvs_stats.total_entries);

Return
  • ESP_OK if the changes have been written successfully. Return param nvs_stats will be filled.
  • ESP_ERR_NVS_PART_NOT_FOUND if the partition with label “name” is not found. Return param nvs_stats will be filled 0.
  • ESP_ERR_NVS_NOT_INITIALIZED if the storage driver is not initialized. Return param nvs_stats will be filled 0.
  • ESP_ERR_INVALID_ARG if nvs_stats equal to NULL.
  • ESP_ERR_INVALID_STATE if there is page with the status of INVALID. Return param nvs_stats will be filled not with correct values because not all pages will be counted. Counting will be interrupted at the first INVALID page.
Parameters
  • part_name: Partition name NVS in the partition table. If pass a NULL than will use NVS_DEFAULT_PART_NAME (“nvs”).
  • nvs_stats: Returns filled structure nvs_states_t. It provides info about used memory the partition.

esp_err_t nvs_get_used_entry_count(nvs_handle_t handle, size_t *used_entries)

Calculate all entries in a namespace.

Note that to find out the total number of records occupied by the namespace, add one to the returned value used_entries (if err is equal to ESP_OK). Because the name space entry takes one entry.

// Example of nvs_get_used_entry_count() to get amount of all key-value pairs in one namespace:
nvs_handle_t handle;
nvs_open("namespace1", NVS_READWRITE, &handle);
...
size_t used_entries;
size_t total_entries_namespace;
if(nvs_get_used_entry_count(handle, &used_entries) == ESP_OK){
    // the total number of records occupied by the namespace
    total_entries_namespace = used_entries + 1;
}

Return
  • ESP_OK if the changes have been written successfully. Return param used_entries will be filled valid value.
  • ESP_ERR_NVS_NOT_INITIALIZED if the storage driver is not initialized. Return param used_entries will be filled 0.
  • ESP_ERR_NVS_INVALID_HANDLE if handle has been closed or is NULL. Return param used_entries will be filled 0.
  • ESP_ERR_INVALID_ARG if nvs_stats equal to NULL.
  • Other error codes from the underlying storage driver. Return param used_entries will be filled 0.
Parameters
  • handle: Handle obtained from nvs_open function.
  • used_entries: Returns amount of used entries from a namespace.

nvs_iterator_t nvs_entry_find(const char *part_name, const char *namespace_name, nvs_type_t type)

Create an iterator to enumerate NVS entries based on one or more parameters.

// Example of listing all the key-value pairs of any type under specified partition and namespace
nvs_iterator_t it = nvs_entry_find(partition, namespace, NVS_TYPE_ANY);
while (it != NULL) {
        nvs_entry_info_t info;
        nvs_entry_info(it, &info);
        it = nvs_entry_next(it);
        printf("key '%s', type '%d' \n", info.key, info.type);
};
// Note: no need to release iterator obtained from nvs_entry_find function when
//       nvs_entry_find or nvs_entry_next function return NULL, indicating no other
//       element for specified criteria was found.
}

Return
Iterator used to enumerate all the entries found, or NULL if no entry satisfying criteria was found. Iterator obtained through this function has to be released using nvs_release_iterator when not used any more.
Parameters
  • part_name: Partition name
  • namespace_name: Set this value if looking for entries with a specific namespace. Pass NULL otherwise.
  • type: One of nvs_type_t values.

nvs_iterator_t nvs_entry_next(nvs_iterator_t iterator)

Returns next item matching the iterator criteria, NULL if no such item exists.

Note that any copies of the iterator will be invalid after this call.

Return
NULL if no entry was found, valid nvs_iterator_t otherwise.
Parameters
  • iterator: Iterator obtained from nvs_entry_find function. Must be non-NULL.

void nvs_entry_info(nvs_iterator_t iterator, nvs_entry_info_t *out_info)

Fills nvs_entry_info_t structure with information about entry pointed to by the iterator.

Parameters
  • iterator: Iterator obtained from nvs_entry_find or nvs_entry_next function. Must be non-NULL.
  • out_info: Structure to which entry information is copied.

void nvs_release_iterator(nvs_iterator_t iterator)

Release iterator.

Parameters
  • iterator: Release iterator obtained from nvs_entry_find function. NULL argument is allowed.

Structures

struct nvs_entry_info_t

information about entry obtained from nvs_entry_info function

Public Members

char namespace_name[16]

Namespace to which key-value belong

char key[16]

Key of stored key-value pair

nvs_type_t type

Type of stored key-value pair

struct nvs_stats_t

Note
Info about storage space NVS.

Public Members

size_t used_entries

Amount of used entries.

size_t free_entries

Amount of free entries.

size_t total_entries

Amount all available entries.

size_t namespace_count

Amount name space.

Macros

ESP_ERR_NVS_BASE

Starting number of error codes

ESP_ERR_NVS_NOT_INITIALIZED

The storage driver is not initialized

ESP_ERR_NVS_NOT_FOUND

Id namespace doesn’t exist yet and mode is NVS_READONLY

ESP_ERR_NVS_TYPE_MISMATCH

The type of set or get operation doesn’t match the type of value stored in NVS

ESP_ERR_NVS_READ_ONLY

Storage handle was opened as read only

ESP_ERR_NVS_NOT_ENOUGH_SPACE

There is not enough space in the underlying storage to save the value

ESP_ERR_NVS_INVALID_NAME

Namespace name doesn’t satisfy constraints

ESP_ERR_NVS_INVALID_HANDLE

Handle has been closed or is NULL

ESP_ERR_NVS_REMOVE_FAILED

The value wasn’t updated because flash write operation has failed. The value was written however, and update will be finished after re-initialization of nvs, provided that flash operation doesn’t fail again.

ESP_ERR_NVS_KEY_TOO_LONG

Key name is too long

ESP_ERR_NVS_PAGE_FULL

Internal error; never returned by nvs API functions

ESP_ERR_NVS_INVALID_STATE

NVS is in an inconsistent state due to a previous error. Call nvs_flash_init and nvs_open again, then retry.

ESP_ERR_NVS_INVALID_LENGTH

String or blob length is not sufficient to store data

ESP_ERR_NVS_NO_FREE_PAGES

NVS partition doesn’t contain any empty pages. This may happen if NVS partition was truncated. Erase the whole partition and call nvs_flash_init again.

ESP_ERR_NVS_VALUE_TOO_LONG

String or blob length is longer than supported by the implementation

ESP_ERR_NVS_PART_NOT_FOUND

Partition with specified name is not found in the partition table

ESP_ERR_NVS_NEW_VERSION_FOUND

NVS partition contains data in new format and cannot be recognized by this version of code

ESP_ERR_NVS_XTS_ENCR_FAILED

XTS encryption failed while writing NVS entry

ESP_ERR_NVS_XTS_DECR_FAILED

XTS decryption failed while reading NVS entry

ESP_ERR_NVS_XTS_CFG_FAILED

XTS configuration setting failed

ESP_ERR_NVS_XTS_CFG_NOT_FOUND

XTS configuration not found

ESP_ERR_NVS_ENCR_NOT_SUPPORTED

NVS encryption is not supported in this version

ESP_ERR_NVS_KEYS_NOT_INITIALIZED

NVS key partition is uninitialized

ESP_ERR_NVS_CORRUPT_KEY_PART

NVS key partition is corrupt

ESP_ERR_NVS_CONTENT_DIFFERS

Internal error; never returned by nvs API functions. NVS key is different in comparison

NVS_DEFAULT_PART_NAME

Default partition name of the NVS partition in the partition table

Type Definitions

typedef uint32_t nvs_handle_t

Opaque pointer type representing non-volatile storage handle

typedef nvs_handle_t nvs_handle
typedef nvs_open_mode_t nvs_open_mode
typedef struct nvs_opaque_iterator_t *nvs_iterator_t

Opaque pointer type representing iterator to nvs entries

Enumerations

enum nvs_open_mode_t

Mode of opening the non-volatile storage.

Values:

NVS_READONLY

Read only

NVS_READWRITE

Read and write

enum nvs_type_t

Types of variables.

Values:

NVS_TYPE_U8 = 0x01

Type uint8_t

NVS_TYPE_I8 = 0x11

Type int8_t

NVS_TYPE_U16 = 0x02

Type uint16_t

NVS_TYPE_I16 = 0x12

Type int16_t

NVS_TYPE_U32 = 0x04

Type uint32_t

NVS_TYPE_I32 = 0x14

Type int32_t

NVS_TYPE_U64 = 0x08

Type uint64_t

NVS_TYPE_I64 = 0x18

Type int64_t

NVS_TYPE_STR = 0x21

Type string

NVS_TYPE_BLOB = 0x42

Type blob

NVS_TYPE_ANY = 0xff

Must be last