Date: Sat, 1 Feb 1997 21:24:30 +1100 From: Bruce Evans <bde@zeta.org.au> To: freebsd-hackers@FreeBSD.ORG, sja@tekla.fi Subject: Re: Error Message (mounting a DOS partition) Message-ID: <199702011024.VAA17625@godzilla.zeta.org.au>
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>I also have a DOS partition I can't mount (not that I really care...)
>There seems to be some sort of offset thingie going on that FreeBSD
>doesn't know about.
Actually, FreeBSD knows a lot about it.
>I have three slices:
>/dev/wd0s1 is DOS C: and can be mounted from FreeBSD.
>/dev/wd0s2 is FreeBSD.
>/dev/wd0s3 is DOS D: and can NOT be mounted from FreeBSD.
>
>/dev/wd0s3 (aka D:) has NULs at the beginning where mountmsdosfs()
>expects a boot sector. However, there seems to be a DOS fs at an
>offset of 0x7e00 bytes (go figure) from the beginning:
>
>hexdump -C /dev/wd0s3 | head -12
This is a good way to check that the slice contains what you think it
does.
>00000000 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 00 00 00 00 00 00 00 01 |................|
>000001c0 c1 9a 06 3f ff fd 3f 00 00 00 c1 26 06 00 00 00 |...?..?....&....|
^^^^^^^^^^^^ ^^^^^^^^^^^
offset of 1st size of
slice in 1st slice
logical drive (403137 decimal)
>000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>*
>00007e00 eb 3c 90 4d 53 44 4f 53 35 2e 30 00 02 08 01 00 |.<.MSDOS5.0.....|
^^^^^^^^ (offset 0x3f) * (sector size 0x200) = 0x7e00
>00007e10 02 00 02 00 00 f8 c5 00 3f 00 40 00 3f 00 00 00 |........?.@.?...|
>00007e20 c1 26 06 00 80 00 29 cf 1e 40 11 44 20 20 20 20 |.&....)..@.D |
>Here is fdisk output:
>
>******* Working on device /dev/rwd0 *******
>parameters extracted from in-core disklabel are:
>cylinders=1023 heads=64 sectors/track=63 (4032 blks/cyl)
>...
>The data for partition 2 is:
>sysid 5,(Extended DOS)
> start 3717504, size 403200 (196 Meg), flag 0
^^^^^^ used up by 1 logical drive of size 403200
containing 1 slice of size 403200-63 at
relative offset 63
> beg: cyl 922/ sector 1/ head 0;
> end: cyl 1021/ sector 63/ head 63
wd0s3 is an extended partition. It may contain almost any number of
logical drives, of which DOS officially supports up to 23 (D:-Z:)
provided there is only one DOS drive, and FreeBSD supports 26
(wd0s5-wd0s30) independently of other drives.
>dev/wd0s3 is DOS D: and can NOT be mounted from FreeBSD.
/dev/wd0s5 is DOS D: and CAN be mounted from FreeBSD.
DOS drive numbering is very illogical and isn't understood by FreeBSD.
E.g., if you add another drive and put a primary DOS partition partition
on it, then IIRC it will become D: and the old D: will become E:.
FreeBSD attempts to support multiple extended partitions and multiple
logical drives at every level, but you shouldn't use this. It isn't
standard and makes the numbering more confusing.
Bruce
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