mount_msdosfs anomaly

[hoe-waa at hawaii.rr.com]

----- Original Message -----
From: Mark Ovens <mark at ukug.uk.freebsd.org>
Date: Saturday, May 15, 2004 2:18 am
Subject: Re: mount_msdosfs anomaly

Aloha Mark and thanks for responding. I'm sorry I wasn't able to get back to you sooner. I was in Kawaihae paddling in and outrigger canoe race. Alas, we didn't do very well. But, there's always next week.

> Malcolm Kay wrote:
> 
> > On Saturday 15 May 2004 12:04, hoe-waa at hawaii.rr.com wrote:
> > 
> >> Here is the output of fdisk when ran from FBSD:
> >> frankie# fdisk
> >> ******* Working on device /dev/ad0 *******
> >> parameters extracted from in-core disklabel are:
> >> cylinders=155061 heads=16 sectors/track=63 (1008 blks/cyl)
> >>
> >> Figures below won't work with BIOS for partitions not in cyl 1
> >> parameters to be used for BIOS calculations are:
> >> cylinders=155061 heads=16 sectors/track=63 (1008 blks/cyl)
> >>
> >> Media sector size is 512
> >> Warning: BIOS sector numbering starts with sector 1
> >> Information from DOS bootblock is:
> >> The data for partition 1 is:
> >> sysid 11 (0x0b),(DOS or Windows 95 with 32 bit FAT)
> >>     start 63, size 10249407 (5004 Meg), flag 0
> >>         beg: cyl 0/ head 1/ sector 1;
> >>         end: cyl 637/ head 254/ sector 63
> >> The data for partition 2 is:
> >> sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
> >>     start 10249470, size 40949685 (19994 Meg), flag 80 (active)
> >>         beg: cyl 638/ head 0/ sector 1;
> >>         end: cyl 1023/ head 254/ sector 63
> >> The data for partition 3 is:
> >> sysid 12 (0x0c),(DOS or Windows 95 with 32 bit FAT (LBA))
> >>     start 51199155, size 5863725 (2863 Meg), flag 0
> >>         beg: cyl 1023/ head 254/ sector 63;
> >>         end: cyl 1023/ head 254/ sector 63
> >> The data for partition 4 is:
> >> sysid 5 (0x05),(Extended DOS)
> >>     start 57062880, size 99233505 (48453 Meg), flag 0
> >>         beg: cyl 1023/ head 254/ sector 63;
> >>         end: cyl 1023/ head 254/ sector 63
> >> frankie#
> >> As you can see, I still have 98SE on partition 1 and partition 3 
> shows as
> >> fat32. Slackware was re-installed and is working on P-8 with 
> linux-swap 0n
> >> P-9.
> >>
> >> Is this weird that I cannot mount ad0s3?
> >>
> > 
> > Does someone out there know the significance of "sysid 12" versus 
> "sysid 11"?
> > 
> 
> According to the fdisk output sysid 11 is
>      DOS or Windows 95 with 32 bit FAT
> and sysid 12 is
>      DOS or Windows 95 with 32 bit FAT (LBA)
> 
> The difference is LBA although I thought that if you needed to use 
> LBA 
> then the _whole disk_ was LBA but since slice 3 is visible in Win98 
> I 
> guess it's correct (probably just a case of FreeBSD reporting 
> _accurately_ what's on the disk).
> 
> It's a few years since I messed with FAT so I may not have 
> remembered 
> this correctly, but originally DOS could only support a single 
> _active_ 
> primary partition (which is why extended was invented). Somewhere 
> in the 
> Win9x line that changed; the OS still had to be on the first 
> primary 
> partition but other primary partitions were visible in the OS.
> 
> The OP says that Win98 can see /dev/ados3 and write to it but, if 
> you 
> look at the fdisk output only slice 1 is flagged 'active'.
> 
> The last time I had a machine with multiple OSes (Win98, W2K, and 
> FreeBSD) I used BootMagic that comes with PartitionMagic which had 
> a 
> config option to choose which partitions/slices each OS could see. 
> With 
> FreeBSD the default setting hid _all_ the FAT & NTFS slices (I got 
> the 
> same problem you have) so I had to change the settings. The first 
> one or 
> two bytes in each entry in the partition table determine whether 
> the 
> partition is 'active' (i.e. the one that is booted from) but also 
> whether the partition is visible or hidden. When you choose an OS 
> from 
> BM's menu it edits the PT "on the fly" (which will set the BIOS 
> boot 
> sector anit-virus alarm off if it's enabled) and then continues the 
> boot 
> process.
> 
> IIRC Win9x can see adso3 (in this case) by simply ignoring the 
> visible 
> flag, i.e. a kludge, in typical MS fashion.
> 
> As to how to resolve it, if you are really brave you can edit the 
> partition table flags directly but the changes may not hold (I have 
> a 
> feeling that Win98 may "fix" them next time you boot Win98) or 
> install a 
> boot manager like BM that allows you to set the visibility.
> 

I'm plenty brave as this is not a mission critical box!  :)

> If you run this
> 
> # dd if=/dev/ad0 of=/tmp/foo bs=512 count=1
> # hd /tmp/foo > /tmp/foo.hd
> 
> and post the last 6 lines of foo.hd it will help identify which 
> byte is 
> set wrong; I've a load of notes here about partition tables so I'll 
> dig 
> them out.

Here are the last few lines. I'm glad you know what we are looking at.

00000180  cd 13 73 0f 4d 74 09 31  c0 cd 13 61 eb f1 b4 40  |..s.Mt.1...a...@|
00000190  e9 46 ff 88 64 1f 8d 64  10 61 c3 c1 c0 04 e8 03  |.F..d..d.a......|
000001a0  00 c1 c0 04 24 0f 27 04  f0 14 40 60 bb 07 00 b4  |....$.'...@`....|
000001b0  0e cd 10 61 c3 00 00 00  b3 12 b0 3d cf c9 00 01  |...a.......=....|
000001c0  01 00 0b fe bf 7d 3f 00  00 00 bf 64 9c 00 80 00  |.....}?....d....|
000001d0  81 7e a5 fe ff ff fe 64  9c 00 b5 d7 70 02 00 fe  |.~.....d....p...|
000001e0  ff ff 0c fe ff ff b3 3c  0d 03 2d 79 59 00 00 fe  |.......<..-yY...|
000001f0  ff ff 05 fe ff ff e0 b5  66 03 e1 2e ea 05 55 aa  |........f.....U.|
00000200
frankie#

> 
> HTH
> 
> Regards,
> 
> Mark
> 
> 
> 

Thanks again for all your help.
Robert