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sbin/fsck_msdosfs does not handle media with 2K blocks (fwd)

Last night I sent the post below to 
Greg Troxel <> kindly suggested I also send it here to
(which I am also subscribed to, BTW, but happy to receive CC anyway)

Hopefully BSDs can share a solution :-)

Archives of any subsequent follow up:


Forwarded from: "Julian Stacey" <>

------- Forwarded Message

Message-Id: <>
Subject: sbin/fsck_msdosfs does not handle media with 2K blocks
Date: Fri, 01 Mar 2013 01:45:03 +0100
List-Archive: <>

cc: gdt@NetBSD,  (< grep @ 
cc:                      (< man newfs_msdos)
cc: Tom Rhodes <>  (< man 5 msdosfs>

sbin/fsck_msdosfs (FreeBSD 9.1-RELEASE) fails on 2K block media,
media in this case, an mp3 player:

sysctl kern.geom.debugflags=16
        kern.geom.debugflags: 16 -> 16

/sbin/fsck_msdosfs /dev/da0s1
                ** /dev/da0s1
        could not read boot block (Invalid argument)

        "vendor" "0x066f"; "product" "0x8000"; "devclass" "0x00";
        "devsubclass" "0x00"; "intclass" "0x08"; "intsubclass"
        "0x06"; "intprotocol" "0x50" ; "release" "0x1001";

/sys/dev/usb/usbdevs: vendor SIGMATEL         0x066f  Sigmatel

dd if=/dev/da0   bs=2k of=da0   # 242304+0 records      496238592 bytes
dd if=/dev/da0s1 bs=2k of=da0s1 # 242256+0 records      496140288 bytes
echo "2048 242304 * p" | dc     #                       496238592
echo "2048 242256 * p" | dc     #                       496140288

fdisk /dev/da0
        cylinders=118 heads=64 sectors/track=32 (2048 blks/cyl)
        Media sector size is 2048
        Warning: BIOS sector numbering starts with sector 1
        Information from DOS bootblock is:
        The data for partition 1 is:
        sysid 6 (0x06),(Primary DOS, 16 bit FAT (>= 32MB))
            start 48, size 242256 (473 Meg), flag 80 (active)
                beg: cyl 0/ head 1/ sector 1;
                end: cyl 630/ head 7/ sector 48

( I think this unit's FS got corrupted. Possibly as part of media error ?
  This unit (when not USB connected, but powered on battery as a
  player, flashed its LCD display on & off, (ame warning as to also
  indicate a low battery) whereas other units of same type with
  same battery powered up OK, & battery is OK, so player is probably
  also seeing a bad FS. )

I tried this:
        sysctl kern.geom.debugflags=16
        dd if=/dev/da0s1 bs=2k of=image
        mdconfig -a -t vnode -f image
        /sbin/fsck_msdosfs -y /dev/md2
                ** /dev/md2
                ** Phase 1 - Read and Compare FATs
                ** Phase 2 - Check Cluster Chains
                ** Phase 3 - Checking Directories
                /audio has entries after end of directory
                Extend? yes
                /audio has entries after end of directory
                Extend? yes
                long filename record cluster start != 0
                Invalid long filename entry for volume label
                Remove? yes
                ** Phase 4 - Checking for Lost Files
                139 files, 60280 free (7535 clusters)
                ***** FILE SYSTEM WAS MODIFIED *****
        ... Repeating fsck above, shows the same errors above ...
        newfs_msdos -F 16 -S 2048 /dev/md2
                newfs_msdos: Cannot get number of sectors per track,
                        Operation not supported
                newfs_msdos: Cannot get number of heads,
                        Operation not supported
                newfs_msdos: trim 21 sectors to adjust to a multiple of 63
                /dev/md2: 242192 sectors in 15137 FAT16 clusters
                         (32768 bytes/cluster)
                BytesPerSec=2048 SecPerClust=16 ResSectors=1 FATs=2
                        RootDirEnts=512 Media=0xf0 FATsecs=15 SecPerTrack=63
                        Heads=16 HiddenSecs=0 HugeSectors=242235
        /sbin/fsck_msdosfs -y /dev/md2
                ** /dev/md2
                ** Phase 1 - Read and Compare FATs
                ** Phase 2 - Check Cluster Chains
                ** Phase 3 - Checking Directories
                ** Phase 4 - Checking for Lost Files
                1 files, 484384 free (15137 clusters)
        mount -t msdosfs /dev/md2 /mnt
        cp SETTINGS.DAT /mnt
        umount /mnt
        mdconfig -d -u 2
        dd if=image bs=2k of=/dev/da0s1
                dd: /dev/da0s1: Input/output error
                80+0 records in 79+0 records out
                161792 bytes transferred in 32.715037 secs (4945 bytes/sec)
        ... Remove & Reinsert & waited for devd & unmounted after auto-mount...
        Repeated dd & same error.
        ... Remove & Reinsert & wait for devd automount
        ls /usb/sigmatel        ... it has the new empty FS with SETTINGS.DAT
        ... but still the LCD flashes
        fdisk -B /dev/da0
                fdisk: /boot/mbr: length must be a multiple of sector size
        cat /boot/mbr /boot/mbr /boot/mbr /boot/mbr > /boot/mbr2k
        fdisk -B -b /boot/mbr2k /dev/da0
                Should we write new partition table? [n] y
        ... still the LCD flashes
        fdisk -i /dev/da0
        fdisk -u /dev/da0
        ( Not Tried: newfs_msdos with -s 512 to see if the Sigmatel chipset
                will play it, but not much point as fdisk says 2K ... )

So it seems this particular unit has a problem (that other units
of same manufacture here do not have). I can't think what else to try ?

It seems I discovered a limitation in FreeBSD (while doing the above):
        We should hack various sources to [also?] allow R/W of 2K
        media blocks , eg inc. here:
                #define DOSBOOTBLOCKSIZE 512
                readboot(int dosfs, struct bootblock *boot)
                u_char block[DOSBOOTBLOCKSIZE];
                if (read(dosfs, block, sizeof block) != sizeof block) {
                        perror("could not read boot block");
        Who might best hack those sources ?
        Maybe someone since 1997 Wolfgang Solfrank & 1995 Martin Husemann 
        be interested?

- -- 
Julian Stacey, BSD Unix Linux C Sys Eng Consultant, Munich
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