oofatfs: enable use of random volume IDs

This may help address #7409 if the underlying cause is the deterministic
volume ID. However, not all boards have working urandom (samd21
at least does not) so a couple of fallbacks are attempted when it fails.

I verified that on a pico_w, each `storage.erase_filesystem()` gives
a distinct 32-bit volume ID (pico_w's urandom can never fail)

lib/oofatfs/ff.c

@@ -257,6 +257,11 @@
 #define GET_FATTIME()   get_fattime()
 #endif
 
+#if FF_FS_MAKE_VOLID == 1
+#define MAKE_VOLID(x) (make_volid())
+#else
+#define MAKE_VOLID(x) (GET_FATTIME())
+#endif
 
 /* File lock controls */
 #if FF_FS_LOCK != 0
@@ -5421,6 +5426,7 @@ FRESULT f_mkfs (
     DWORD tbl[3];
 #endif
 
+    DWORD volid = MAKE_VOLID();
 
     /* Check mounted drive and clear work area */
     fs->fs_type = 0;    /* Clear mounted volume */
@@ -5622,7 +5628,7 @@ FRESULT f_mkfs (
             st_dword(buf + BPB_DataOfsEx, b_data - b_vol);          /* Data offset [sector] */
             st_dword(buf + BPB_NumClusEx, n_clst);                  /* Number of clusters */
             st_dword(buf + BPB_RootClusEx, 2 + tbl[0] + tbl[1]);    /* Root dir cluster # */
-            st_dword(buf + BPB_VolIDEx, GET_FATTIME());             /* VSN */
+            st_dword(buf + BPB_VolIDEx, volid);             /* VSN */
             st_word(buf + BPB_FSVerEx, 0x100);                      /* Filesystem version (1.00) */
             for (buf[BPB_BytsPerSecEx] = 0, i = ss; i >>= 1; buf[BPB_BytsPerSecEx]++) ; /* Log2 of sector size [byte] */
             for (buf[BPB_SecPerClusEx] = 0, i = au; i >>= 1; buf[BPB_SecPerClusEx]++) ; /* Log2 of cluster size [sector] */
@@ -5758,7 +5764,7 @@ FRESULT f_mkfs (
         st_dword(buf + BPB_HiddSec, b_vol);             /* Volume offset in the physical drive [sector] */
 #if FF_MKFS_FAT32
         if (fmt == FS_FAT32) {
-            st_dword(buf + BS_VolID32, GET_FATTIME());  /* VSN */
+            st_dword(buf + BS_VolID32, volid);  /* VSN */
             st_dword(buf + BPB_FATSz32, sz_fat);        /* FAT size [sector] */
             st_dword(buf + BPB_RootClus32, 2);          /* Root directory cluster # (2) */
             st_word(buf + BPB_FSInfo32, 1);             /* Offset of FSINFO sector (VBR + 1) */
@@ -5769,7 +5775,7 @@ FRESULT f_mkfs (
         } else
 #endif
         {
-            st_dword(buf + BS_VolID, GET_FATTIME());    /* VSN */
+            st_dword(buf + BS_VolID, volid);    /* VSN */
             st_word(buf + BPB_FATSz16, (WORD)sz_fat);   /* FAT size [sector] */
             buf[BS_DrvNum] = 0x80;                      /* Drive number (for int13) */
             buf[BS_BootSig] = 0x29;                     /* Extended boot signature */

lib/oofatfs/ff.h

@@ -334,6 +334,10 @@ FRESULT f_setcp (WORD cp);                                          /* Set curre
 DWORD get_fattime (void);
 #endif
 
+#if FF_FS_MAKE_VOLID
+DWORD make_volid (void);
+#endif
+
 /* LFN support functions */
 #if FF_USE_LFN >= 1                     /* Code conversion (defined in unicode.c) */
 WCHAR ff_oem2uni (WCHAR oem, WORD cp);  /* OEM code to Unicode conversion */

lib/oofatfs/ffconf.h

@@ -373,6 +373,10 @@
 /  SemaphoreHandle_t and etc. A header file for O/S definitions needs to be
 /  included somewhere in the scope of ff.h. */
 
-
+#ifndef FF_FS_MAKE_VOLID
+#define FF_FS_MAKE_VOLID (0)
+#endif
+/* The option FF_FS_MAKE_VOLID enables the use of a function to return a 32-bit volume identifier.
+/  If it is disabled, a Volume ID based on the current time is used. */
 
 /*--- End of configuration options ---*/

py/circuitpy_mpconfig.h

@@ -594,6 +594,7 @@ void supervisor_run_background_tasks_if_tick(void);
 #define CIRCUITPY_DIGITALIO_HAVE_INVALID_DRIVE_MODE (0)
 #endif
 
+#define FF_FS_MAKE_VOLID (1)
 
 #define MICROPY_PY_OPTIMIZE_PROPERTY_FLASH_SIZE (CIRCUITPY_OPTIMIZE_PROPERTY_FLASH_SIZE)
 

supervisor/shared/fatfs.c

@@ -28,9 +28,11 @@
 
 #include "py/runtime.h"
 #include "lib/oofatfs/ff.h"
-#include "shared/timeutils/timeutils.h"
+#include "shared-bindings/microcontroller/Processor.h"
+#include "shared-bindings/os/__init__.h"
 #include "shared-bindings/rtc/RTC.h"
 #include "shared-bindings/time/__init__.h"
+#include "shared/timeutils/timeutils.h"
 
 DWORD _time_override = 0;
 DWORD get_fattime(void) {
@@ -50,3 +52,17 @@ DWORD get_fattime(void) {
 void override_fattime(DWORD time) {
     _time_override = time;
 }
+
+DWORD make_volid(void) {
+    DWORD result;
+    if (!common_hal_os_urandom((uint8_t *)&result, sizeof(result))) {
+        #if CIRCUITPY_MICROCONTROLLER && COMMON_HAL_MCU_PROCESSOR_UID_LENGTH >= 4
+        uint8_t raw_id[COMMON_HAL_MCU_PROCESSOR_UID_LENGTH];
+        common_hal_mcu_processor_get_uid(raw_id);
+        memcpy(&result, raw_id, sizeof(result));
+        #else
+        result = (DWORD)common_hal_time_monotonic_ns();
+        #endif
+    }
+    return result;
+}