fix: statfs can't get f_bfree and f_bavail of a FAT12/FAT16 partition

FAT12/FAT16 partition has no FSINFO sector storing the free cluster number,
so scanning the FAT is necessary to get the free clusters nums.

Close #I3Q0VS

source/ff.c

@@ -4290,35 +4290,17 @@ FRESULT f_stat (
 }
 
 
-
-#if !FF_FS_READONLY
-/*-----------------------------------------------------------------------*/
-/* Get Number of Free Clusters                                           */
-/*-----------------------------------------------------------------------*/
-
-FRESULT f_getfree (
-	const TCHAR* path,	/* Logical drive number */
-	DWORD* nclst,		/* Pointer to a variable to return number of free clusters */
-	FATFS** fatfs		/* Pointer to return pointer to corresponding filesystem object */
+FRESULT fat_count_free_entries(
+	DWORD *nclst,	/* Pointer to a variable to return number of free clusters */
+	FATFS *fs	/* Pointer to corresponding filesystem object */
 )
 {
-	FRESULT res;
-	FATFS *fs;
 	DWORD nfree, clst, stat;
 	QWORD sect;
 	UINT i;
 	FFOBJID obj;
+	FRESULT res = FR_OK;
 
-
-	/* Get logical drive */
-	res = find_volume(&path, &fs, 0);
-	if (res == FR_OK) {
-		*fatfs = fs;				/* Return ptr to the fs object */
-		/* If free_clst is valid, return it without full FAT scan */
-		if (fs->free_clst <= fs->n_fatent - 2) {
-			*nclst = fs->free_clst;
-		} else {
-			/* Scan FAT to obtain number of free clusters */
 	nfree = 0;
 	if (fs->fs_type == FS_FAT12) {	/* FAT12: Scan bit field FAT entries */
 		clst = 2; obj.fs = fs;
@@ -4351,6 +4333,33 @@ FRESULT f_getfree (
 	*nclst = nfree;		/* Return the free clusters */
 	fs->free_clst = nfree;	/* Now free_clst is valid */
 	fs->fsi_flag |= 1;	/* FAT32: FSInfo is to be updated */
+	return res;
+}
+
+#if !FF_FS_READONLY
+/*-----------------------------------------------------------------------*/
+/* Get Number of Free Clusters                                           */
+/*-----------------------------------------------------------------------*/
+
+FRESULT f_getfree (
+	const TCHAR* path,	/* Logical drive number */
+	DWORD* nclst,		/* Pointer to a variable to return number of free clusters */
+	FATFS** fatfs		/* Pointer to return pointer to corresponding filesystem object */
+)
+{
+	FRESULT res;
+	FATFS *fs;
+
+	/* Get logical drive */
+	res = find_volume(&path, &fs, 0);
+	if (res == FR_OK) {
+		*fatfs = fs;				/* Return ptr to the fs object */
+		/* If free_clst is valid, return it without full FAT scan */
+		if (fs->free_clst <= fs->n_fatent - 2) {
+			*nclst = fs->free_clst;
+		} else {
+			/* Scan FAT to obtain number of free clusters */
+			res = fat_count_free_entries(nclst, fs);
 		}
 	}
 

source/ff.h

@@ -450,7 +450,8 @@ FRESULT f_getclustinfo (FIL* fp, DWORD* fclust, DWORD* fcount);	/* get the clust
 FRESULT f_checkopenlock(int index);
 FRESULT sync_fs (FATFS* fs);
 FRESULT sync_window(FATFS *fs);
-FRESULT move_window ( FATFS* fs, QWORD	sector);
+FRESULT move_window (FATFS* fs, QWORD sector);
+FRESULT fat_count_free_entries(DWORD *nclst, FATFS *fs);
 void get_fileinfo (DIR* dp, FILINFO* fno);
 DWORD get_fat (FFOBJID *obj, DWORD clst);
 FRESULT put_fat(FATFS *fs, DWORD clst, DWORD val);