Correct VFAT partition is not recognised

[paaguti]

I have an ebook reader unbricking image which I transfer to a microSD card.
Using GPARTED I can grow the DOS FAT32 partition to take up all the free space.
Once grown I'm not able to read the partition's information

 paag@840g5  ~/tmp/kobo  sudo fdisk -l /dev/sda
Disk /dev/sda: 7,4 GiB, 7948206080 bytes, 15523840 sectors
Disk model: SD/MMC          
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x66e8b073

Device     Boot   Start      End  Sectors  Size Id Type
/dev/sda1         19456   543744   524289  256M 83 Linux
/dev/sda2        543745  1068033   524289  256M 83 Linux
/dev/sda3       1068034 15523839 14455806  6,9G  b W95 FAT32

paag@840g5  ~/tmp/kobo  sudo fatresize -i /dev/sda3
fatresize 1.1.0 (20201114)
.Error: /dev/sda3 is not valid FAT16/FAT32 partition.

sudo fsck.vfat /dev/sda3             
fsck.fat 4.2 (2021-01-31)
There are differences between boot sector and its backup.
This is mostly harmless. Differences: (offset:original/backup)
  65:00/01
1) Copy original to backup
2) Copy backup to original
3) No action
[123?q]? 1

*** Filesystem was changed ***
The changes have not yet been written, you can still choose to leave the
filesystem unmodified:
1) Write changes
2) Leave filesystem unchanged
[12?q]? 1
/dev/sda3: 84 files, 1444/1803444 clusters

[paaguti]

I added the partition name to the error message and this is what I get:

 paag@840g5  ~/Devel/fatresize   master ±  sudo ./fatresize --info /dev/sda3
fatresize 1.0.3 (20240330)
Error: /dev/sda3 is not valid FAT16/FAT32 partition. (ext4)

However, fdisk tells me that /dev/sda3 is a W95 FAT32 partition.

 ✘ paag@840g5  ~/Devel/fatresize   master ±  sudo fdisk /dev/sda

Welcome to fdisk (util-linux 2.37.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/sda: 3,69 GiB, 3965190144 bytes, 7744512 sectors
Disk model: SD/MMC          
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x6834f926

Device     Boot   Start     End Sectors  Size Id Type
/dev/sda1         19456  543744  524289  256M 83 Linux
/dev/sda2        543745 1068033  524289  256M 83 Linux
/dev/sda3       1068034 7743487 6675454  3,2G  b W95 FAT32

Command (m for help): quit

[paaguti]

Problem seems to be in getpartnum()

201	  probe_device(&peddev, devname);
(gdb) n
211	    opts.pnum = get_partnum(devname);
(gdb) n
213	  ped_device_destroy(peddev);
(gdb) print opts
$5 = {fullpath = 0x55555555bbf0 "/dev/sda3", device = 0x0, pnum = 1, size = 0, 
  verbose = 0, progress = 0, info = 1, force_yes = 0}

more precisely, in the way get_partnum is called!

Breakpoint 1, get_partnum (dev=0x55555555bc10 "/dev/sda") at fatresize.c:154

There is no partition number to get there!

[paaguti]

A quick fix to allow at least -n <PARTNUM> <dev> attached...
0001-Allow-n-N-DEV.zip

[paaguti]

A PoC for alternative way of splitting the cmd line arguments could be:

#!/usr/bin/tcc -run

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

int main(int argc, char **argv)
{
		char *dev = "/dev/sda3";
		char *p = &dev[strlen(dev) - 1];
		int pnum = -1;

		while (*p && isdigit(*p)) {
				p--;
		}
		p++;
		printf("dev = %s\n",dev);
		printf("p   = %s\n",p);
		printf("strlen(p) = %d\n",strlen(p));
		if ((strlen(p) > 0) && (pnum == -1)) {
				pnum = atoi(p);
				printf("pnum = %d\n",pnum);
		} else if ((strlen(p) > 0) && (pnum != -1)) {
				printf("Don\'t use -n!\n");
		}
		char *realdev = strndup(dev,p-dev);
		printf("realdev = %s\n", realdev);
}

I use tinycc to avoid compiling micro prototypes ;-)

[paaguti]

Implemented in pull request 38.