modules: fs: Add reentrant zephyr support

This commit enables zephyr to configure the FatFs FF_FS_REENTRANT
option and support fs actions from multiple threads.
CONFIG_FS_FATFS_REENTRANT enables the option and provides zephyr
mutex wrappers.

Signed-off-by: Nicola Ochsenbein <Nicola.Ochsenbein@husqvarnagroup.com>

modules/fatfs/CMakeLists.txt

@@ -18,9 +18,12 @@ if(CONFIG_FAT_FILESYSTEM_ELM)
 
   zephyr_library_sources_ifdef(CONFIG_FS_FATFS_LFN
     ${ZEPHYR_FATFS_MODULE_DIR}/option/ffunicode.c
-    ${ZEPHYR_FATFS_MODULE_DIR}/option/ffsystem.c
   )
 
+  if(DEFINED CONFIG_FS_FATFS_LFN OR DEFINED CONFIG_FS_FATFS_REENTRANT)
+    zephyr_library_sources(zfs_ffsystem.c)
+  endif()
+
   zephyr_library_link_libraries(ELMFAT)
   target_link_libraries(ELMFAT INTERFACE zephyr_interface)
 endif()

modules/fatfs/zephyr_fatfs_config.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2022 Nordic Semiconductor ASA
+ * Copyright (c) 2023 Husqvarna AB
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -62,6 +63,14 @@
 #define FF_FS_EXFAT		CONFIG_FS_FATFS_EXFAT
 #endif /* defined(CONFIG_FS_FATFS_EXFAT) */
 
+#if defined(CONFIG_FS_FATFS_REENTRANT)
+#undef FF_FS_REENTRANT
+#undef FF_FS_TIMEOUT
+#include <zephyr/kernel.h>
+#define FF_FS_REENTRANT		CONFIG_FS_FATFS_REENTRANT
+#define FF_FS_TIMEOUT		K_FOREVER
+#endif /* defined(CONFIG_FS_FATFS_REENTRANT) */
+
 /*
  * These options are override from default values, but have no Kconfig
  * options.

modules/fatfs/zfs_ffsystem.c

@@ -0,0 +1,69 @@
+/*
+ * OS Dependent Functions for FatFs
+ *
+ * Copyright (c) 2023 Husqvarna AB
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+/* The file is based on template file by (C)ChaN, 2022, as
+ * available from FAT FS module source:
+ * https://github.com/zephyrproject-rtos/fatfs/blob/master/option/ffsystem.c
+ */
+
+#include <ff.h>
+
+#if FF_USE_LFN == 3	/* Dynamic memory allocation */
+/* Allocate a memory block */
+void *ff_memalloc(UINT msize)
+{
+	return k_malloc(msize);
+}
+
+/* Free a memory block */
+void ff_memfree(void *mblock)
+{
+	k_free(mblock);
+}
+#endif /* FF_USE_LFN == 3 */
+
+#if FF_FS_REENTRANT	/* Mutual exclusion */
+/* Table of Zephyr mutex. One for each volume and an extra one for the ff system.
+ * See also the template file used as reference. Link is available in the header of this file.
+ */
+static struct k_mutex fs_reentrant_mutex[FF_VOLUMES + 1];
+
+/* Create a Mutex
+ * Mutex ID vol: Volume mutex (0 to FF_VOLUMES - 1) or system mutex (FF_VOLUMES)
+ * Returns 1: Succeeded or 0: Could not create the mutex
+ */
+int ff_mutex_create(int vol)
+{
+	return (int)(k_mutex_init(&fs_reentrant_mutex[vol]) == 0);
+}
+
+/* Delete a Mutex
+ * Mutex ID vol: Volume mutex (0 to FF_VOLUMES - 1) or system mutex (FF_VOLUMES)
+ */
+void ff_mutex_delete(int vol)
+{
+	/* (nothing to do) */
+	(void)vol;
+}
+
+/* Request Grant to Access the Volume
+ * Mutex ID vol: Volume mutex (0 to FF_VOLUMES - 1) or system mutex (FF_VOLUMES)
+ * Returns 1: Succeeded or 0: Timeout
+ */
+int ff_mutex_take(int vol)
+{
+	return (int)(k_mutex_lock(&fs_reentrant_mutex[vol], FF_FS_TIMEOUT) == 0);
+}
+
+/* Release Grant to Access the Volume
+ * Mutex ID vol: Volume mutex (0 to FF_VOLUMES - 1) or system mutex (FF_VOLUMES)
+ */
+void ff_mutex_give(int vol)
+{
+	k_mutex_unlock(&fs_reentrant_mutex[vol]);
+}
+#endif /* FF_FS_REENTRANT */

subsys/fs/Kconfig.fatfs

@@ -1,5 +1,6 @@
 # Copyright (c) 2016 Intel Corporation
 # Copyright (c) 2020 Nordic Semiconductor ASA
+# Copyright (c) 2023 Husqvarna AB
 # SPDX-License-Identifier: Apache-2.0
 
 config FAT_FILESYSTEM_ELM
@@ -220,6 +221,14 @@ config FS_FATFS_WINDOW_ALIGNMENT
 	  that, in worst scenario, value provided here may cause FATFS
 	  structure to have size of twice the value.
 
+config FS_FATFS_REENTRANT
+	bool "FatFs reentrant"
+	depends on !FS_FATFS_LFN_MODE_BSS
+	help
+	  Enable the FatFs re-entrancy (thread safe) option for file/directory
+	  access for each volume. Will create a zephyr mutex object for each
+	  FatFs volume and a FatFs system mutex.
+
 endmenu
 
 endif # FAT_FILESYSTEM_ELM