+++ This bug was initially created as a clone of Bug #1931821 +++ Description of problem: This is a bug in dosfstools which happened between dosfstools-4.1-12.fc33 and dosfstools-4.2-1.fc34. The following command: mkfs -t vfat -I -n TEST /dev/sda previously would create a filesystem directly on /dev/sda. Now it creates some kind of corrupted MBR partition table. If you look at the difference between good (-) and bad (+) you can see the extra partition table at offset 0x1b0-0x1cf in the image: --- test1.img.hex 2021-02-23 12:29:49.815043947 +0000 +++ test1-bad.img.hex 2021-02-23 12:30:00.197159306 +0000 @@ -1,6 +1,6 @@ 00000000 eb 3c 90 6d 6b 66 73 2e 66 61 74 00 02 04 04 00 |.<.mkfs.fat.....| 00000010 02 00 02 00 50 f8 14 00 14 00 01 00 00 00 00 00 |....P...........| -00000020 00 00 00 00 80 00 29 c1 0d 23 51 54 45 53 54 20 |......)..#QTEST | +00000020 00 00 00 00 80 00 29 65 e1 e3 4f 54 45 53 54 20 |......)e..OTEST | 00000030 20 20 20 20 20 20 46 41 54 31 36 20 20 20 0e 1f | FAT16 ..| 00000040 be 5b 7c ac 22 c0 74 0b 56 b4 0e bb 07 00 cd 10 |.[|.".t.V.......| 00000050 5e eb f0 32 e4 cd 16 cd 19 eb fe 54 68 69 73 20 |^..2.......This | @@ -12,6 +12,10 @@ 000000b0 72 79 20 61 67 61 69 6e 20 2e 2e 2e 20 0d 0a 00 |ry again ... ...| 000000c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * +000001b0 00 00 00 00 00 00 00 00 e4 e4 e3 4f 00 00 80 00 |...........O....| +000001c0 01 00 04 fe ff ff 00 00 00 00 00 50 00 00 00 00 |...........P....| +000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| +* 000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.| 00000200 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * @@ -21,8 +25,8 @@ 00003000 f8 ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00003010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * -00005800 54 45 53 54 20 20 20 20 20 20 20 08 00 00 a3 63 |TEST ....c| -00005810 57 52 57 52 00 00 a3 63 57 52 00 00 00 00 00 00 |WRWR...cWR......| +00005800 54 45 53 54 20 20 20 20 20 20 20 08 00 00 97 63 |TEST ....c| +00005810 57 52 57 52 00 00 97 63 57 52 00 00 00 00 00 00 |WRWR...cWR......| 00005820 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00a00000 This only happens when mkfs is used to create a filesystem on a block device like /dev/sda, not when you do it on a local file.
Closing, because it's upstream intended behaviour controlled by the --mbr option.