fs: enable fstab devicetree integration for fatfs

dts/bindings/fs/zephyr,fstab,fatfs.yaml

@@ -0,0 +1,9 @@
+# Copyright (C) 2025 Endress+Hauser AG
+# SPDX-License-Identifier: Apache-2.0
+
+description: |
+    Description of pre-defined fatfs file systems.
+
+compatible: "zephyr,fstab,fatfs"
+
+include: zephyr,fstab-common.yaml

dts/bindings/fs/zephyr,fstab,littlefs.yaml

@@ -11,6 +11,12 @@ include: "zephyr,fstab-common.yaml"
 properties:
   # num-files and num-dirs are not filesystem-specific.
 
+  partition:
+    type: phandle
+    required: true
+    description: |
+      A reference to the file system's partition.
+
   read-size:
     type: int
     required: true

dts/bindings/fs/zephyr,fstab-common.yaml

@@ -12,12 +12,6 @@ properties:
     description: |
       The absolute path used as the file system mount point.
 
-  partition:
-    type: phandle
-    required: true
-    description: |
-      A reference to the file system's partition.
-
   automount:
     type: boolean
     description: |

samples/subsys/fs/fatfs_fstab/CMakeLists.txt

@@ -0,0 +1,9 @@
+# Copyright (c) 2025 Endress+Hauser AG
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(fatfs_fstab_sample)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

samples/subsys/fs/fatfs_fstab/README.rst

@@ -0,0 +1,36 @@
+.. zephyr:code-sample:: fatfs-fstab
+   :name: Fatfs filesystem fstab
+   :relevant-api: file_system_api
+
+   Define fatfs filesystems in the devicetree.
+
+Overview
+***********
+
+This sample shows how to define a fatfs fstab entry in the devicetree.
+This scenario uses a fatfs on a RAM disk. The sample is run on the
+``native_sim`` board.
+
+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/fatfs_fstab
+   :host-os: unix
+   :board: native_sim
+   :gen-args: -DDTC_OVERLAY_FILE=fatfs_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/fatfs_fstab/fatfs_fstab.overlay

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2025 Endress+Hauser AG
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	fstab {
+		compatible = "zephyr,fstab";
+		ffs1: ffs1 {
+			compatible = "zephyr,fstab,fatfs";
+			automount;
+			disk-access;
+			mount-point = "/RAM";
+		};
+	};
+
+	ramdisk0 {
+		compatible = "zephyr,ram-disk";
+		disk-name = "RAM";
+		sector-size = <512>;
+		sector-count = <128>;
+	};
+};

samples/subsys/fs/fatfs_fstab/prj.conf

@@ -0,0 +1,9 @@
+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_FAT_FILESYSTEM_ELM=y

samples/subsys/fs/fatfs_fstab/sample.yaml

@@ -0,0 +1,14 @@
+sample:
+  name: fatfs fstab sample
+tests:
+  sample.filesystem.fat_fs.fstab:
+    platform_allow:
+      - native_sim
+    extra_args:
+      - EXTRA_DTC_OVERLAY_FILE="fatfs_fstab.overlay"
+    tags: filesystem
+    harness: console
+    harness_config:
+      type: one_line
+      regex:
+        - "I: Filesystem access successful"

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

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2025 Endress+Hauser AG
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <ff.h>
+#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);
+
+int main(void)
+{
+	struct fs_file_t file;
+	int rc;
+	static const char data[] = "Hello";
+
+	fs_file_t_init(&file);
+	rc = fs_open(&file, "/RAM:/hello.txt", 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;
+	}
+
+	LOG_INF("Filesystem access successful");
+	return 0;
+}

subsys/fs/fat_fs.c

@@ -557,10 +557,54 @@ static const struct fs_file_system_t fatfs_fs = {
 #endif
 };
 
+#define DT_DRV_COMPAT zephyr_fstab_fatfs
+
+#define DEFINE_FS(inst)                                                                            \
+	BUILD_ASSERT(DT_INST_PROP(inst, disk_access), "FATFS needs disk-access");                  \
+	BUILD_ASSERT(!DT_INST_PROP(inst, read_only),                                               \
+		     "READ_ONLY not supported for individual instances see FS_FATFS_READ_ONLY");   \
+	BUILD_ASSERT(!DT_INST_PROP(inst, no_format),                                               \
+		     "NO_FORMAT not supported for individual instanzes FS_FATFS_MKFS");            \
+	FATFS fs_data_##inst;                                                                      \
+	struct fs_mount_t FS_FSTAB_ENTRY(DT_DRV_INST(inst)) = {                                    \
+		.type = FS_FATFS,                                                                  \
+		.mnt_point = DT_INST_PROP(inst, mount_point) ":",                                  \
+		.fs_data = &fs_data_##inst,                                                        \
+		.storage_dev = NULL,                                                               \
+		.flags = FSTAB_ENTRY_DT_MOUNT_FLAGS(DT_DRV_INST(inst)),                            \
+	};
+
+DT_INST_FOREACH_STATUS_OKAY(DEFINE_FS);
+
+#define REFERENCE_MOUNT(inst) (&FS_FSTAB_ENTRY(DT_DRV_INST(inst)))
+
 static int fatfs_init(void)
 {
+	int rc = fs_register(FS_FATFS, &fatfs_fs);
+
+	if (rc == 0) {
+		static struct fs_mount_t *partitions[] = {
+			DT_INST_FOREACH_STATUS_OKAY(REFERENCE_MOUNT)};
+		int ret = 0;
+
+		for (size_t i = 0; i < ARRAY_SIZE(partitions); i++) {
+			struct fs_mount_t *mpi = partitions[i];
+
+			if ((mpi->flags & FS_MOUNT_FLAG_AUTOMOUNT) != 0) {
+				ret = fs_mount(mpi);
+				if (ret < 0) {
+					LOG_ERR("Error mounting filesystem: mount id %u at %s: %d",
+						(unsigned int)mpi->storage_dev, mpi->mnt_point,
+						ret);
+				} else {
+					LOG_DBG("FATFS Filesystem \"%s\" initialized",
+						mpi->mnt_point);
+				}
+			}
+		}
+	}
 
-	return fs_register(FS_FATFS, &fatfs_fs);
+	return rc;
 }
 
 SYS_INIT(fatfs_init, POST_KERNEL, CONFIG_FILE_SYSTEM_INIT_PRIORITY);