Accessing existing partitions on SDHC card using FatFs

Question

I've been trying to transfer all my code from the STM32 Arduino library to ST Hal library, but I've been running into a problem with the SD-card. I'm using a SDHC sd card that has two partitions (one for factory reset and the other for normal settings) They show up on my PC as drive D and E.

So when setting up FATFS for my STM32F1 chip everything worked fine when using SD Bus one bit mode. Using standard code I could write into the factory reset partition:

  FRESULT res = f_open(&SDFile, (const TCHAR *)"Test2.txt", FA_CREATE_ALWAYS | FA_WRITE);
  if(res == FR_OK){
    HAL_GPIO_WritePin(DASH_LED_1_GPIO_Port, DASH_LED_1_Pin, GPIO_PIN_SET);
    res = f_putc('S', &SDFile);
    if(res != -1){
      HAL_GPIO_WritePin(DASH_LED_2_GPIO_Port, DASH_LED_2_Pin, GPIO_PIN_SET);
    }
    res = f_write(&SDFile, (const void*)buffer, sizeof(buffer), &byteswritten );
    if(res == FR_OK){
      HAL_GPIO_WritePin(DASH_LED_3_GPIO_Port, DASH_LED_3_Pin, GPIO_PIN_SET);

    }
    f_close(&SDFile);
  }

When initializing the code and mounting a drive everything seemed fine, even when I wanted to mount the second partitions (i'm not really sure if thats what i'm doing with the code) the returns in my debugger were all FR_OK:

uint8_t retSD;    /* Return value for SD */
char SDPath[4];   /* SD logical drive path */
char OtherPath[4];
FATFS SDFatFS;    /* File system object for SD logical drive */
FIL SDFile;       /* File object for SD */

/* USER CODE BEGIN Variables */
PARTITION VolToPart[2] = {
  {0,0},
  {0,1}
};
/* USER CODE END Variables */    

void MX_FATFS_Init(void) 
{
  /*## FatFS: Link the SD driver ###########################*/
  retSD = FATFS_LinkDriver(&SD_Driver, SDPath);

  /* USER CODE BEGIN Init */
  FRESULT res = f_mount(&SDFatFS, SDPath, 0 );
  if(res != FR_OK){
    Error_Handler();
  }
  res = f_mount(&SDFatFS, OtherPath, 0);
  if(res != FR_OK){
    Error_Handler();
  }

  /* additional user code for init */     
  /* USER CODE END Init */
}

I will admit that even though I did my research I found the mounting and the subsequent VolToPart array that you apparently need to be a little bit vague.

After debugging the code while mounting twice (see code above), I tested the code using the drive identifiers (I turned on _FS_RPATH, which I don't think has an effect, but just to be sure) I could write Hello World to 0:Test2.txt but got an invalid drive error for 1:Test2.txt.

I want to be able to switch between drives, but I feel like I'm missing something that I need to initiliaze or do. At this moment I'm not sure if FatFs can see the SDCard partitions and I'm just not initializing it or if its a completely seperate drive that the SD card cannot see. I hope someone it able to help me with this, let me know if you need more info.

Edit: I found out some stuff after debugging for a while: SDPath is getting defined as "0:/"in link driver, so it makes sense for that this drive works. Other path does not get defined (as far as I can tell, and just gets the default value of "0:/", which means I'm doing the same mount twice. When I tried to add a seperate driver and intialize that one, it still ended up being an invalid disk error.

extern Diskio_drvTypeDef  SD_Driver;
extern Diskio_drvTypeDef  Other_Driver;

const Diskio_drvTypeDef  SD_Driver =
{
  SD_initialize,
  SD_status,
  SD_read, 
#if  _USE_WRITE == 1
  SD_write,
#endif /* _USE_WRITE == 1 */

#if  _USE_IOCTL == 1
  SD_ioctl,
#endif /* _USE_IOCTL == 1 */
};

const Diskio_drvTypeDef  Other_Driver =
{
  SD_initialize,
  SD_status,
  SD_read, 
#if  _USE_WRITE == 1
  SD_write,
#endif /* _USE_WRITE == 1 */

#if  _USE_IOCTL == 1
  SD_ioctl,
#endif /* _USE_IOCTL == 1 */
};

I then ran link driver twice and received a FR_INVALID_DRIVE message on the second mount. I tried this both with the same FATFS object and different ones.

uint8_t retSD;    /* Return value for SD */
char SDPath[4];   /* SD logical drive path */
char OtherPath[4];
FATFS SDFatFS;    /* File system object for SD logical drive */
FATFS OtherFatFS;
FIL SDFile;       /* File object for SD */

/* USER CODE BEGIN VolToPart */
/* Volume - Partition resolution table should be user defined in case of Multiple partition */
/* When multi-partition feature is enabled (1), each logical drive number is bound to arbitrary physical drive and partition
listed in the VolToPart[] */
PARTITION VolToPart[] = {
  {0,0},
  {1,0}
};
/* USER CODE END VolToPart */  

/* USER CODE BEGIN Variables */
/* USER CODE END Variables */    

void MX_FATFS_Init(void) 
{
  /*## FatFS: Link the SD driver ###########################*/
  retSD = FATFS_LinkDriver(&SD_Driver, SDPath);
  retSD = FATFS_LinkDriver(&Other_Driver, OtherPath);
  /* USER CODE BEGIN Init */
  FRESULT res = f_mount(&SDFatFS, SDPath, 1 );
  if(res != FR_OK){
    Error_Handler();
  }
  res = f_mount(&SDFatFS, OtherPath, 1);
  if(res != FR_OK){
    Error_Handler();
  }