From 26ceedb5f89a22d49c45ff9b175e251fd14db926 Mon Sep 17 00:00:00 2001
From: Martin Vychodil <martin.vychodil@espressif.com>
Date: Tue, 7 Apr 2026 12:08:49 +0200
Subject: [PATCH] fix(fatfs): Fixed uninitialized FATFS pointer for already
 mounted path

---
 components/fatfs/host_test/main/test_fatfs_vfs.cpp | 2 +-
 components/fatfs/vfs/esp_vfs_fat.h                 | 4 +++-
 components/fatfs/vfs/vfs_fat.c                     | 9 +++++++--
 components/fatfs/vfs/vfs_fat_bdl.c                 | 2 +-
 components/fatfs/vfs/vfs_fat_spiflash.c            | 4 ++--
 5 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/components/fatfs/host_test/main/test_fatfs_vfs.cpp b/components/fatfs/host_test/main/test_fatfs_vfs.cpp
index 33e018906d..7a71878220 100644
--- a/components/fatfs/host_test/main/test_fatfs_vfs.cpp
+++ b/components/fatfs/host_test/main/test_fatfs_vfs.cpp
@@ -26,7 +26,7 @@ static char drv[3];
 
 static void test_setup(void)
 {
-    FATFS *fs;
+    FATFS *fs = nullptr;
     esp_err_t ret = ESP_OK;
     FRESULT fr_result;
 
diff --git a/components/fatfs/vfs/esp_vfs_fat.h b/components/fatfs/vfs/esp_vfs_fat.h
index 76df5ff2be..c65196016d 100644
--- a/components/fatfs/vfs/esp_vfs_fat.h
+++ b/components/fatfs/vfs/esp_vfs_fat.h
@@ -66,7 +66,9 @@ typedef struct {
  * @param[out] out_fs  pointer to FATFS structure which can be used for FATFS f_mount call is returned via this argument.
  * @return
  *      - ESP_OK on success
- *      - ESP_ERR_INVALID_STATE if esp_vfs_fat_register was already called
+ *      - ESP_ERR_INVALID_STATE if a filesystem is already registered at this base path.
+ *        If @p out_fs is not NULL, @p *out_fs is set to the existing FATFS object so callers
+ *        can run f_mount (e.g. remount the same path).
  *      - ESP_ERR_NO_MEM if not enough memory or too many VFSes already registered
  */
 esp_err_t esp_vfs_fat_register(const esp_vfs_fat_conf_t* conf, FATFS** out_fs);
diff --git a/components/fatfs/vfs/vfs_fat.c b/components/fatfs/vfs/vfs_fat.c
index 25229cf0b1..b19f8c10d0 100644
--- a/components/fatfs/vfs/vfs_fat.c
+++ b/components/fatfs/vfs/vfs_fat.c
@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2015-2025 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2015-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -179,6 +179,9 @@ esp_err_t esp_vfs_fat_register(const esp_vfs_fat_conf_t* conf, FATFS** out_fs)
 {
     size_t ctx = find_context_index_by_path(conf->base_path);
     if (ctx < FF_VOLUMES) {
+        if (out_fs) {
+            *out_fs = &s_fat_ctxs[ctx]->fs;
+        }
         return ESP_ERR_INVALID_STATE;
     }
 
@@ -221,7 +224,9 @@ esp_err_t esp_vfs_fat_register(const esp_vfs_fat_conf_t* conf, FATFS** out_fs)
     //compatibility
     s_fat_ctx = fat_ctx;
 
-    *out_fs = &fat_ctx->fs;
+    if (out_fs) {
+        *out_fs = &fat_ctx->fs;
+    }
 
     return ESP_OK;
 }
diff --git a/components/fatfs/vfs/vfs_fat_bdl.c b/components/fatfs/vfs/vfs_fat_bdl.c
index e3adb837bf..ec60d671db 100644
--- a/components/fatfs/vfs/vfs_fat_bdl.c
+++ b/components/fatfs/vfs/vfs_fat_bdl.c
@@ -116,7 +116,7 @@ esp_err_t esp_vfs_fat_bdl_mount(const char *base_path,
     ESP_GOTO_ON_ERROR(ff_diskio_register_bdl(pdrv, bdl_handle), fail, TAG,
                       "ff_diskio_register_bdl failed pdrv=%i, error - 0x(%x)", pdrv, ret);
 
-    FATFS *fs;
+    FATFS *fs = NULL;
     esp_vfs_fat_conf_t conf = {
         .base_path = base_path,
         .fat_drive = drv,
diff --git a/components/fatfs/vfs/vfs_fat_spiflash.c b/components/fatfs/vfs/vfs_fat_spiflash.c
index b1764a049a..8c8cf099af 100644
--- a/components/fatfs/vfs/vfs_fat_spiflash.c
+++ b/components/fatfs/vfs/vfs_fat_spiflash.c
@@ -171,7 +171,7 @@ esp_err_t esp_vfs_fat_spiflash_mount_rw_wl(const char* base_path,
     char drv[3] = {(char)('0' + pdrv), ':', 0};
     ESP_GOTO_ON_ERROR(ff_diskio_register_wl_partition(pdrv, *wl_handle), fail, TAG, "ff_diskio_register_wl_partition failed pdrv=%i, error - 0x(%x)", pdrv, ret);
 
-    FATFS *fs;
+    FATFS *fs = NULL;
     esp_vfs_fat_conf_t conf = {
         .base_path = base_path,
         .fat_drive = drv,
@@ -366,7 +366,7 @@ esp_err_t esp_vfs_fat_spiflash_mount_ro(const char* base_path,
     char drv[3] = {(char)('0' + pdrv), ':', 0};
     ESP_GOTO_ON_ERROR(ff_diskio_register_raw_partition(pdrv, data_partition), fail, TAG, "ff_diskio_register_raw_partition failed pdrv=%i, error - 0x(%x)", pdrv, ret);
 
-    FATFS *fs;
+    FATFS *fs = NULL;
     esp_vfs_fat_conf_t conf = {
         .base_path = base_path,
         .fat_drive = drv,