[9fans] dos boot record manglin'

[9fans] dos boot record manglin'

[Sam]

My laptop has three partitions:  fat16, plan9, fat32.
I recently copied a tarfile from /n/ftp to
/n/c: to do some Windows work.  I then halted
kfs and powered down.  I may have unmounted /n/c: --
I can't be certain.  It was later in the evening before
I came back to actually do said work.

Next boot, Windows didn't.  Mounting the partition
in plan 9 fails with "unknown format."

It appears that something stepped on the dos boot record
for both the fat16 and fat32 partitions.  eg, fat16:

term% dd -if /dev/sdC0/dos -bs 512 -count 1 | xd -c
1+0 records in
1+0 records out
0000000  13 00 00 00  d ff ff 18    00 00 06 00  9  P  2
0000010   0  0  0 00 00 f8 ff 00  ? 00 f0 00  ? 00 00 00
0000020  c1 c0  > 00 80 00  )  I  k 05 a0 00  O     N  A
0000030   M  E 00           F  A  T  1  6           3 c9
<snip!> (everything after this looks OK)

Note the peculiarly placed 9P2000 at byte 13.

I'm trying to come up to speed on the fat filesystem
format so I can re-establish the dos boot record fields
that have been stamped on.  Can anyone offer some
help in this regard?

For completeness, the dos boot record on the fat32
partition looks like:

term% dd -if /dev/sdC0/dos1 -bs 512 -count 1 | xd -c
1+0 records in
1+0 records out
0000000  13 00 00 00  d ff ff 18    00 00 06 00  9  P  2
0000010   0  0  0 00 00 f8 00 00  ? 00 f0 00  ? 00 00 00
0000020  f1  2  ~ 00 dc  > 00 00 00 00 00 00 02 00 00 00
0000030  01 00 06 00 f6 f6 f6 f6 f6 f6 f6 f6 f6 f6 f6 f6
0000040  80 00  ) \t  x c2  =
0000050         F  A  T  3  2          f6 f6 f6 f6 f6 f6
<snip!>

Cheers,

Sam

Re: [9fans] dos boot record manglin'

[Martin Harriss]

 From the horses mouth:

http://www.microsoft.com/hwdev/download/hardware/fatgen103.pdf

Martin


Sam wrote:
> My laptop has three partitions:  fat16, plan9, fat32.
> I recently copied a tarfile from /n/ftp to
> /n/c: to do some Windows work.  I then halted
> kfs and powered down.  I may have unmounted /n/c: --
> I can't be certain.  It was later in the evening before
> I came back to actually do said work.
>
> Next boot, Windows didn't.  Mounting the partition
> in plan 9 fails with "unknown format."
>
> It appears that something stepped on the dos boot record
> for both the fat16 and fat32 partitions.  eg, fat16:
>
> term% dd -if /dev/sdC0/dos -bs 512 -count 1 | xd -c
> 1+0 records in
> 1+0 records out
> 0000000  13 00 00 00  d ff ff 18    00 00 06 00  9  P  2
> 0000010   0  0  0 00 00 f8 ff 00  ? 00 f0 00  ? 00 00 00
> 0000020  c1 c0  > 00 80 00  )  I  k 05 a0 00  O     N  A
> 0000030   M  E 00           F  A  T  1  6           3 c9
> <snip!> (everything after this looks OK)
>
> Note the peculiarly placed 9P2000 at byte 13.
>
> I'm trying to come up to speed on the fat filesystem
> format so I can re-establish the dos boot record fields
> that have been stamped on.  Can anyone offer some
> help in this regard?
>
> For completeness, the dos boot record on the fat32
> partition looks like:
>
> term% dd -if /dev/sdC0/dos1 -bs 512 -count 1 | xd -c
> 1+0 records in
> 1+0 records out
> 0000000  13 00 00 00  d ff ff 18    00 00 06 00  9  P  2
> 0000010   0  0  0 00 00 f8 00 00  ? 00 f0 00  ? 00 00 00
> 0000020  f1  2  ~ 00 dc  > 00 00 00 00 00 00 02 00 00 00
> 0000030  01 00 06 00 f6 f6 f6 f6 f6 f6 f6 f6 f6 f6 f6 f6
> 0000040  80 00  ) \t  x c2  =
> 0000050         F  A  T  3  2          f6 f6 f6 f6 f6 f6
> <snip!>
>
> Cheers,
>
> Sam
>
>