feat(spiffs): Add SPIFFS base example

examples/storage/spiffs/CMakeLists.txt

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+# The following lines of boilerplate have to be in your project's CMakeLists
+# in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(spiffs)

examples/storage/spiffs/Makefile

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+#
+# This is a project Makefile. It is assumed the directory this Makefile resides in is a
+# project subdirectory.
+#
+
+PROJECT_NAME := spiffs
+
+include $(IDF_PATH)/make/project.mk
+

examples/storage/spiffs/README.md

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+# SPIFFS example
+
+This example demonstrates how to use SPIFFS at this software platform. Example does the following steps:
+
+1. Enable SPIFFS at "menuconfig"
+2. Use an "all-in-one" `esp_vfs_spiffs_register` function to:
+    - initialize SPIFFS,
+    - mount SPIFFS filesystem using SPIFFS library (and format, if the filesystem can not be mounted),
+    - register SPIFFS filesystem in VFS, enabling C standard library and POSIX functions to be used.
+3. Create a file using `fopen` and write to it using `fprintf`.
+4. Rename the file. Before renaming, check if destination file already exists using `stat` function, and remove it using `unlink` function.
+5. Open renamed file for reading, read back the line, and print it to the terminal.
+
+SPIFFS partition size is set in partitions_example.csv file. See `docs/en/api-guides/partition-tables.rst` documentation for more information.
+
+## How to use example
+
+### Hardware required
+
+This example does not require any special hardware, and can be run on any common development board.
+
+### Configure the project
+
+If using Make based build system, run `make menuconfig` and set serial port under Serial Flasher Options.
+
+If using CMake based build system, no configuration is required.
+
+### Build and flash
+
+Build the project and flash it to the board, then run monitor tool to view serial output:
+
+```
+make -j4 flash monitor
+```
+
+Or, for CMake based build system (replace PORT with serial port name):
+
+```
+idf.py -p PORT flash monitor
+```
+
+(To exit the serial monitor, type ``Ctrl-]``.)
+
+See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
+
+## Example output
+
+Here is an example console output. In this case `format_if_mount_failed` parameter was set to `true` in the source code. SPIFFS was unformatted, so the initial mount has failed. SPIFFS was then formatted, and mounted again.
+
+```
+I (324) example: Initializing SPIFFS
+W (324) SPIFFS: mount failed, -10025. formatting...
+I (19414) example: Partition size: total: 896321, used: 0
+I (19414) example: Opening file
+I (19504) example: File written
+I (19544) example: Renaming file
+I (19584) example: Reading file
+I (19584) example: Read from file: 'Hello World!'
+I (19584) example: SPIFFS unmounted
+```
+
+To erase the contents of SPIFFS partition, run `make erase_flash` command (or `idf.py erase_flash`, if using CMake build system). Then upload the example again as described above.

examples/storage/spiffs/main/CMakeLists.txt

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+set(COMPONENT_SRCS "spiffs_example_main.c")
+set(COMPONENT_ADD_INCLUDEDIRS ".")
+
+register_component()

examples/storage/spiffs/main/component.mk

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+#
+# "main" pseudo-component makefile.
+#
+# (Uses default behaviour of compiling all source files in directory, adding 'include' to include path.)

examples/storage/spiffs/main/spiffs_example_main.c

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+/* SPIFFS filesystem example.
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+
+#include <stdio.h>
+#include <string.h>
+#include <sys/unistd.h>
+#include <sys/stat.h>
+#include "esp_err.h"
+#include "esp_log.h"
+#include "esp_spiffs.h"
+
+static const char *TAG = "example";
+
+void app_main(void)
+{
+    ESP_LOGI(TAG, "Initializing SPIFFS");
+    
+    esp_vfs_spiffs_conf_t conf = {
+      .base_path = "/spiffs",
+      .partition_label = NULL,
+      .max_files = 5,
+      .format_if_mount_failed = true
+    };
+    
+    // Use settings defined above to initialize and mount SPIFFS filesystem.
+    // Note: esp_vfs_spiffs_register is an all-in-one convenience function.
+    esp_err_t ret = esp_vfs_spiffs_register(&conf);
+
+    if (ret != ESP_OK) {
+        if (ret == ESP_FAIL) {
+            ESP_LOGE(TAG, "Failed to mount or format filesystem");
+        } else if (ret == ESP_ERR_NOT_FOUND) {
+            ESP_LOGE(TAG, "Failed to find SPIFFS partition");
+        } else {
+            ESP_LOGE(TAG, "Failed to initialize SPIFFS (%s)", esp_err_to_name(ret));
+        }
+        return;
+    }
+    
+    size_t total = 0, used = 0;
+    ret = esp_spiffs_info(NULL, &total, &used);
+    if (ret != ESP_OK) {
+        ESP_LOGE(TAG, "Failed to get SPIFFS partition information (%s)", esp_err_to_name(ret));
+    } else {
+        ESP_LOGI(TAG, "Partition size: total: %d, used: %d", total, used);
+    }
+
+    // Use POSIX and C standard library functions to work with files.
+    // First create a file.
+    ESP_LOGI(TAG, "Opening file");
+    FILE* f = fopen("/spiffs/hello.txt", "w");
+    if (f == NULL) {
+        ESP_LOGE(TAG, "Failed to open file for writing");
+        return;
+    }
+    fprintf(f, "Hello World!\n");
+    fclose(f);
+    ESP_LOGI(TAG, "File written");
+
+    // Check if destination file exists before renaming
+    struct stat st;
+    if (stat("/spiffs/foo.txt", &st) == 0) {
+        // Delete it if it exists
+        unlink("/spiffs/foo.txt");
+    }
+
+    // Rename original file
+    ESP_LOGI(TAG, "Renaming file");
+    if (rename("/spiffs/hello.txt", "/spiffs/foo.txt") != 0) {
+        ESP_LOGE(TAG, "Rename failed");
+        return;
+    }
+
+    // Open renamed file for reading
+    ESP_LOGI(TAG, "Reading file");
+    f = fopen("/spiffs/foo.txt", "r");
+    if (f == NULL) {
+        ESP_LOGE(TAG, "Failed to open file for reading");
+        return;
+    }
+    char line[64];
+    fgets(line, sizeof(line), f);
+    fclose(f);
+    // strip newline
+    char* pos = strchr(line, '\n');
+    if (pos) {
+        *pos = '\0';
+    }
+    ESP_LOGI(TAG, "Read from file: '%s'", line);
+
+    // All done, unmount partition and disable SPIFFS
+    esp_vfs_spiffs_unregister(NULL);
+    ESP_LOGI(TAG, "SPIFFS unmounted");
+}

examples/storage/spiffs/partitions_example.csv

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+# Name,   Type, SubType, Offset,  Size, Flags
+# Note: if you change the phy_init or app partition offset, make sure to change the offset in Kconfig.projbuild
+nvs,      data, nvs,     0x9000,  0x6000,
+phy_init, data, phy,     0xf000,  0x1000,
+factory,  app,  factory, 0x10000, 512K,
+storage,  data, spiffs,  ,        448K, 

examples/storage/spiffs/sdkconfig.defaults

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+CONFIG_PARTITION_TABLE_CUSTOM=y
+CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="partitions_example.csv"
+CONFIG_PARTITION_TABLE_FILENAME="partitions_example.csv"
+
+CONFIG_USING_SPIFFS=y