samples: fs: Add EXT2 automount sample.

Add a simple sample that tests the functionality of the EXT2 automount
feature. The sample creates a ramdisk and writes some content and tries
to read it back after unmount and mount operation.

Signed-off-by: Bas van Loon <[email protected]>

Author: bas-archembedded

samples/subsys/fs/ext2_fstab/CMakeLists.txt

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+# Copyright (c) 2025 Arch-Embedded B.V.
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(ext2_fstab_sample)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

samples/subsys/fs/ext2_fstab/README.rst

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+.. zephyr:code-sample:: ext2-fstab
+   :name: EXT2 filesystem fstab
+   :relevant-api: file_system_api
+
+   Define ext2 filesystems in the devicetree.
+
+Overview
+***********
+
+This sample shows how to define an ext2 fstab entry in the devicetree.
+The sample is run on the ``native_sim`` board and RAM disk is used for ext2 storage.
+
+Building and running
+********************
+
+To run this sample, build it for the ``native_sim`` board
+and afterwards run the generated executable file within the build folder.
+
+The RAM disk sample for the ``native_sim`` board can be built as follows:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/subsys/fs/ext2_fstab
+   :host-os: unix
+   :board: native_sim
+   :gen-args: -DDTC_OVERLAY_FILE=ext2_fstab.overlay
+   :goals: build
+   :compact:
+
+Sample Output
+=============
+
+When the sample runs successfully you should see following message on the screen:
+.. code-block:: console
+
+  I: Filesystem access successful

samples/subsys/fs/ext2_fstab/ext2_fstab.overlay

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+/*
+ * Copyright (c) 2025 Arch-Embedded B.V.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	fstab {
+		compatible = "zephyr,fstab";
+		ext2fs1: ext2fs1 {
+			compatible = "zephyr,fstab,ext2";
+			automount;
+			disk-access;
+			disk-name = "RAM";
+			mount-point = "/ext2";
+		};
+	};
+
+	ramdisk0 {
+		compatible = "zephyr,ram-disk";
+		disk-name = "RAM";
+		sector-size = <512>;
+		sector-count = <128>;
+	};
+};

samples/subsys/fs/ext2_fstab/prj.conf

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+CONFIG_DISK_ACCESS=y
+CONFIG_DISK_DRIVERS=y
+
+CONFIG_LOG=y
+CONFIG_LOG_MODE_MINIMAL=y
+
+CONFIG_FILE_SYSTEM=y
+CONFIG_FILE_SYSTEM_MKFS=y
+CONFIG_FILE_SYSTEM_EXT2=y
+CONFIG_EXT2_FSTAB_AUTOMOUNT=y
+
+# Needed for MKFS
+CONFIG_ENTROPY_GENERATOR=y
+CONFIG_XOSHIRO_RANDOM_GENERATOR=y

samples/subsys/fs/ext2_fstab/sample.yaml

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+sample:
+  name: EXT2 fstab sample
+tests:
+  sample.filesystem.ext2.fstab:
+    platform_allow:
+      - native_sim
+    extra_args:
+      - EXTRA_DTC_OVERLAY_FILE="ext2_fstab.overlay"
+    tags: filesystem
+    harness: console
+    harness_config:
+      type: one_line
+      regex:
+        - "I: Filesystem access successful"

samples/subsys/fs/ext2_fstab/src/main.c

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+/*
+ * Copyright (c) 2025 Endress+Hauser AG
+ * Copyright (c) 2025 Arch-Embedded B.V.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/device.h>
+#include <zephyr/fs/fs.h>
+#include <zephyr/kernel.h>
+#include <zephyr/logging/log.h>
+#include <zephyr/storage/disk_access.h>
+
+LOG_MODULE_REGISTER(main, LOG_LEVEL_INF);
+
+#define AUTOMOUNT_NODE DT_NODELABEL(ext2fs1)
+#define MOUNT_POINT DT_PROP(AUTOMOUNT_NODE, mount_point)
+
+FS_FSTAB_DECLARE_ENTRY(AUTOMOUNT_NODE);
+
+#define FILE_PATH MOUNT_POINT "/hello.txt"
+
+int main(void)
+{
+	struct fs_file_t file;
+	int rc;
+	static const char data[] = "Hello";
+	/* You can get direct mount point to automounted node too */
+	struct fs_mount_t *auto_mount_point = &FS_FSTAB_ENTRY(AUTOMOUNT_NODE);
+	struct fs_dirent stat;
+
+	fs_file_t_init(&file);
+
+	rc = fs_open(&file, FILE_PATH, FS_O_CREATE | FS_O_WRITE);
+	if (rc != 0) {
+		LOG_ERR("Accessing filesystem failed");
+		return rc;
+	}
+
+	rc = fs_write(&file, data, strlen(data));
+	if (rc != strlen(data)) {
+		LOG_ERR("Writing filesystem failed");
+		return rc;
+	}
+
+	rc = fs_close(&file);
+	if (rc != 0) {
+		LOG_ERR("Closing file failed");
+		return rc;
+	}
+
+	/* You can unmount the automount node */
+	rc = fs_unmount(auto_mount_point);
+	if (rc != 0) {
+		LOG_ERR("Failed to do unmount");
+		return rc;
+	};
+
+	/* And mount it back */
+	rc = fs_mount(auto_mount_point);
+	if (rc != 0) {
+		LOG_ERR("Failed to remount the auto-mount node");
+		return rc;
+	}
+
+	/* Is the file still there? */
+	rc = fs_stat(FILE_PATH, &stat);
+	if (rc != 0) {
+		LOG_ERR("File status check failed %d", rc);
+		return rc;
+	}
+
+	LOG_INF("Filesystem access successful");
+
+	return 0;
+}