vfs, fatfs: fix support for two FATFS instances (SD and flash)

- fix null pointer dereference in VFS when VFS implementations are added
  and removed in different order

- vfs_fat_sdmmc, vfs_fat_spiflash: pass correct drive to mkfs
  (previously it would always do mkfs in the first drive)

- add test case

components/fatfs/src/vfs_fat_sdmmc.c

@@ -80,6 +80,7 @@ esp_err_t esp_vfs_fat_sdmmc_mount(const char* base_path,
 
     ff_diskio_register_sdmmc(pdrv, s_card);
     s_pdrv = pdrv;
+    ESP_LOGD(TAG, "using pdrv=%i", pdrv);
     char drv[3] = {(char)('0' + pdrv), ':', 0};
 
     // connect FATFS to VFS
@@ -109,7 +110,7 @@ esp_err_t esp_vfs_fat_sdmmc_mount(const char* base_path,
             goto fail;
         }
         ESP_LOGW(TAG, "formatting card");
-        res = f_mkfs("", FM_ANY, s_card->csd.sector_size, workbuf, workbuf_size);
+        res = f_mkfs(drv, FM_ANY, s_card->csd.sector_size, workbuf, workbuf_size);
         if (res != FR_OK) {
             err = ESP_FAIL;
             ESP_LOGD(TAG, "f_mkfs failed (%d)", res);

components/fatfs/src/vfs_fat_spiflash.c

@@ -45,12 +45,11 @@ esp_err_t esp_vfs_fat_spiflash_mount(const char* base_path,
     }
     // connect driver to FATFS
     BYTE pdrv = 0xFF;
-    if (ff_diskio_get_drive(&pdrv) != ESP_OK || pdrv == 0xFF) {
+    if (ff_diskio_get_drive(&pdrv) != ESP_OK) {
         ESP_LOGD(TAG, "the maximum count of volumes is already mounted");
         return ESP_ERR_NO_MEM;
     }
-    ESP_LOGD(TAG, "pdrv=%i\n", pdrv);
-
+    ESP_LOGD(TAG, "using pdrv=%i", pdrv);
     char drv[3] = {(char)('0' + pdrv), ':', 0};
 
     result = ff_diskio_register_wl_partition(pdrv, *wl_handle);
@@ -77,7 +76,7 @@ esp_err_t esp_vfs_fat_spiflash_mount(const char* base_path,
         }
         workbuf = malloc(workbuf_size);
         ESP_LOGI(TAG, "Formatting FATFS partition");
-        fresult = f_mkfs("", FM_ANY | FM_SFD, workbuf_size, workbuf, workbuf_size);
+        fresult = f_mkfs(drv, FM_ANY | FM_SFD, workbuf_size, workbuf, workbuf_size);
         if (fresult != FR_OK) {
             result = ESP_FAIL;
             ESP_LOGE(TAG, "f_mkfs failed (%d)", fresult);
@@ -103,11 +102,14 @@ fail:
 
 esp_err_t esp_vfs_fat_spiflash_unmount(const char *base_path, wl_handle_t wl_handle)
 {
-    BYTE s_pdrv = ff_diskio_get_pdrv_wl(wl_handle);
-    char drv[3] = {(char)('0' + s_pdrv), ':', 0};
+    BYTE pdrv = ff_diskio_get_pdrv_wl(wl_handle);
+    if (pdrv == 0xff) {
+        return ESP_ERR_INVALID_STATE;
+    }
+    char drv[3] = {(char)('0' + pdrv), ':', 0};
 
     f_mount(0, drv, 0);
-    ff_diskio_unregister(s_pdrv);
+    ff_diskio_unregister(pdrv);
     // release partition driver
     esp_err_t err_drv = wl_unmount(wl_handle);
     esp_err_t err = esp_vfs_fat_unregister_path(base_path);

components/fatfs/test/test_fatfs_sdmmc.c

@@ -187,3 +187,47 @@ static void speed_test(void* buf, size_t buf_size, size_t file_size, bool write)
     TEST_ESP_OK(esp_vfs_fat_sdmmc_unmount());
 }
 
+TEST_CASE("(SD) mount two FAT partitions, SDMMC and WL, at the same time", "[fatfs][sdcard][ignore]")
+{
+    esp_vfs_fat_sdmmc_mount_config_t mount_config = {
+        .format_if_mount_failed = true,
+        .max_files = 5
+    };
+
+    const char* filename_sd = "/sdcard/sd.txt";
+    const char* filename_wl = "/spiflash/wl.txt";
+    const char* str_sd = "this is sd\n";
+    const char* str_wl = "this is spiflash\n";
+
+    /* Mount FATFS in SD can WL at the same time. Create a file on each FS */
+    wl_handle_t wl_handle = WL_INVALID_HANDLE;
+    test_setup();
+    TEST_ESP_OK(esp_vfs_fat_spiflash_mount("/spiflash", NULL, &mount_config, &wl_handle));
+    unlink(filename_sd);
+    unlink(filename_wl);
+    test_fatfs_create_file_with_text(filename_sd, str_sd);
+    test_fatfs_create_file_with_text(filename_wl, str_wl);
+    TEST_ESP_OK(esp_vfs_fat_spiflash_unmount("/spiflash", wl_handle));
+    test_teardown();
+
+    /* Check that the file "sd.txt" was created on FS in SD, and has the right data */
+    test_setup();
+    TEST_ASSERT_NULL(fopen(filename_wl, "r"));
+    FILE* f = fopen(filename_sd, "r");
+    TEST_ASSERT_NOT_NULL(f);
+    char buf[64];
+    TEST_ASSERT_NOT_NULL(fgets(buf, sizeof(buf) - 1, f));
+    TEST_ASSERT_EQUAL(0, strcmp(buf, str_sd));
+    fclose(f);
+    test_teardown();
+
+    /* Check that the file "wl.txt" was created on FS in WL, and has the right data */
+    TEST_ESP_OK(esp_vfs_fat_spiflash_mount("/spiflash", NULL, &mount_config, &wl_handle));
+    TEST_ASSERT_NULL(fopen(filename_sd, "r"));
+    f = fopen(filename_wl, "r");
+    TEST_ASSERT_NOT_NULL(f);
+    TEST_ASSERT_NOT_NULL(fgets(buf, sizeof(buf) - 1, f));
+    TEST_ASSERT_EQUAL(0, strcmp(buf, str_wl));
+    fclose(f);
+    TEST_ESP_OK(esp_vfs_fat_spiflash_unmount("/spiflash", wl_handle));
+}

components/vfs/vfs.c

@@ -125,6 +125,9 @@ static const vfs_entry_t* get_vfs_for_path(const char* path)
     size_t len = strlen(path);
     for (size_t i = 0; i < s_vfs_count; ++i) {
         const vfs_entry_t* vfs = s_vfs[i];
+        if (!vfs) {
+            continue;
+        }
         if (len < vfs->path_prefix_len + 1) {   // +1 is for the trailing slash after base path
             continue;
         }