pkg/fatfs: VFS: internally handle fatfs_mtd_devs

This makes FAT behave more like the other file systems supported by VFS.
The `fatfs_mtd_devs` array is populated internally so the application does
not have to handle this.

examples/filesystem/main.c

@@ -45,8 +45,8 @@ static mtd_sdcard_t mtd_sdcard_dev = {
     .sd_card = &sdcard_spi_devs[0],
     .params = &sdcard_spi_params[0],
 };
-static mtd_dev_t *mtd0 = (mtd_dev_t*)&mtd_sdcard_dev;
+static mtd_dev_t *mtd_sdcard = (mtd_dev_t*)&mtd_sdcard_dev;
-#define MTD_0 mtd0
+#define MTD_0 mtd_sdcard
 #endif
 
 /* Flash mount point */
@@ -111,9 +111,6 @@ static spiffs_desc_t fs_desc = {
  * this example focus on basic usage, i.e. entire memory used */
 static fatfs_desc_t fs_desc;
 
-/* provide mtd devices for use within diskio layer of fatfs */
-mtd_dev_t *fatfs_mtd_devs[FF_VOLUMES];
-
 /* fatfs driver will be used */
 #define FS_DRIVER fatfs_file_system
 #endif
@@ -311,12 +308,12 @@ static const shell_command_t shell_commands[] = {
 
 int main(void)
 {
-#if defined(MTD_0) && (defined(MODULE_SPIFFS) || defined(MODULE_LITTLEFS) || defined(MODULE_LITTLEFS2))
+#if defined(MTD_0) && \
+   (defined(MODULE_SPIFFS) || defined(MODULE_LITTLEFS) || \
+    defined(MODULE_LITTLEFS2) || defined(MODULE_FATFS_VFS))
     /* spiffs and littlefs need a mtd pointer
      * by default the whole memory is used */
     fs_desc.dev = MTD_0;
-#elif defined(MTD_0) && defined(MODULE_FATFS_VFS)
-    fatfs_mtd_devs[fs_desc.vol_idx] = MTD_0;
 #endif
     int res = vfs_mount(&const_mount);
     if (res < 0) {

pkg/fatfs/fatfs_vfs/fatfs_vfs.c

@@ -35,6 +35,8 @@
 static int fatfs_err_to_errno(int32_t err);
 static void _fatfs_time_to_timespec(WORD fdate, WORD ftime, time_t *time);
 
+mtd_dev_t *fatfs_mtd_devs[FF_VOLUMES];
+
 /**
  * @brief Concatenate drive number and path into the buffer provided by fs_desc
  *
@@ -46,6 +48,25 @@ static void _build_abs_path(fatfs_desc_t *fs_desc, const char *name)
              fs_desc->vol_idx, name);
 }
 
+static int _init(vfs_mount_t *mountp)
+{
+    fatfs_desc_t *fs_desc = mountp->private_data;
+
+    for (unsigned i = 0; i < ARRAY_SIZE(fatfs_mtd_devs); ++i) {
+        if (fatfs_mtd_devs[i] == fs_desc->dev) {
+            /* already initialized */
+            return 0;
+        }
+        if (fatfs_mtd_devs[i] == NULL) {
+            fatfs_mtd_devs[i] = fs_desc->dev;
+            fs_desc->vol_idx = i;
+            return 0;
+        }
+    }
+
+    return -1;
+}
+
 static int _mount(vfs_mount_t *mountp)
 {
     /* if one of the lines below fail to compile you probably need to adjust
@@ -57,6 +78,11 @@ static int _mount(vfs_mount_t *mountp)
 
     fatfs_desc_t *fs_desc = (fatfs_desc_t *)mountp->private_data;
 
+    if (_init(mountp)) {
+        DEBUG("can't find free slot in fatfs_mtd_devs\n");
+        return -ENOMEM;
+    }
+
     _build_abs_path(fs_desc, "");
 
     memset(&fs_desc->fat_fs, 0, sizeof(fs_desc->fat_fs));

sys/include/fs/fatfs.h

@@ -54,6 +54,7 @@ extern "C" {
  */
 typedef struct fatfs_desc {
     FATFS fat_fs;       /**< FatFs work area needed for each volume */
+    mtd_dev_t *dev;     /**< MTD device to use */
     uint8_t vol_idx;    /**< low level device that is used by FatFs */
 
     /** most FatFs file operations need an absolute path. This buffer provides

tests/pkg_fatfs_vfs/main.c

@@ -54,9 +54,7 @@ static const char test_txt[]  = "the test file content 123 abc";
 static const char test_txt2[] = "another text";
 static const char test_txt3[] = "hello world for vfs";
 
-static fatfs_desc_t fatfs = {
+static fatfs_desc_t fatfs;
-    .vol_idx = 0
-};
 
 static vfs_mount_t _test_vfs_mount = {
     .mount_point = MNT_PATH,
@@ -64,9 +62,6 @@ static vfs_mount_t _test_vfs_mount = {
     .private_data = (void *)&fatfs,
 };
 
-/* provide mtd devices for use within diskio layer of fatfs */
-mtd_dev_t *fatfs_mtd_devs[FF_VOLUMES];
-
 #if defined(MODULE_MTD_NATIVE) || defined(MODULE_MTD_MCI)
 /* mtd devices are provided in the board's board_init.c*/
 extern mtd_dev_t *mtd0;
@@ -402,17 +397,16 @@ int main(void)
         mtd_sdcard_devs[i].base.driver = &mtd_sdcard_driver;
         mtd_sdcard_devs[i].sd_card = &sdcard_spi_devs[i];
         mtd_sdcard_devs[i].params = &sdcard_spi_params[i];
-        fatfs_mtd_devs[i] = &mtd_sdcard_devs[i].base;
         mtd_init(&mtd_sdcard_devs[i].base);
     }
 #endif
 
 #if defined(MODULE_MTD_NATIVE) || defined(MODULE_MTD_MCI)
-    fatfs_mtd_devs[fatfs.vol_idx] = mtd0;
+    fatfs.dev = mtd0;
 #endif
 
 #if defined(MODULE_MTD_SDCARD)
-    fatfs_mtd_devs[fatfs.vol_idx] = mtd_sdcard;
+    fatfs.dev = mtd_sdcard;
 #endif
 
     printf("Tests for FatFs over VFS - test results will be printed "