[svlug] mounting a partition in the middle of a device dumped to a file

[Marc MERLIN]

On Tue, Aug 13, 2002 at 02:56:31PM -0700, Tim wrote:
> > So, I have a disk that is dded to a file:
> > Disk ./wholedisk: 0 heads, 0 sectors, 0 cylinders
> > Units = cylinders of 1 * 512 bytes
> > 
> >       Device Boot    Start       End    Blocks   Id  System
> > ./wholedisk1   *        64   8391600   4195768+   b  Win95 FAT32
> 
> You can specify an offset into the file using losetup, but I don't know
> if it will work properly.
 
Oh, I so forgot about that. Waay back when loop devices were introduced, you
were forced to use losetup before you could mount a file. Soon after mount
introduced -o loop and I haven't used losetup since then. It's been more
than 6 or 7 years now :-)

Thanks for the pointer.
> Anyway, to mount the first partition, if this offset (64*512) is right,
> you can do this:
> 
> losetup -o 32768 /dev/loop0 ./wholedisk
> mount /dev/loop0 /mnt/mnt

Unfortunately, I was having problems finding the offset, until, I popped up
my trusty mc, and opened the file in hexa mode (F3 + hexa)
(it helps to have the "signature" of what you're looking for)
00007E00 EB 58 90 4D ? 53 57 49 4E ? 34 2E 31 00 ? 02 04 20 00 ?X.MSWIN4.1... .
00007E10 02 00 00 00 ? 00 F8 00 00 ? 3F 00 F0 00 ? 3F 00 00 00 .....?..?.?.?...

moremagic:~# bc
(...)
obase=10
ibase=16
7E00
32256

I guess the first cylinder is 1, and not 0, which means that cylinder 64 is
an offset of 63*512=32256

gargamel:/net/gargamel/auto/dshelf2/backup/disk# mount -t vfat /dev/loop0 /mnt/mnt
gargamel:/net/gargamel/auto/dshelf2/backup/disk# ls /mnt/mnt
Documents and Settings  boot.ini      comused.dbg   io.sys        pcdrdos
Dos                     bootlog.prv   config.sys    lotuslnk      support
Install                 bootlog.txt   discover      msdos.sys     syslevel.ibm
Program Files           bootsect.dos  hiberfil.sys  ntdetect.com  thinkpad
Recycled                cfgsafe       ibmtools      ntldr         winnt
autoexec.bat            comreads.dbg  icons         pagefile.sys

Thanks much for the help
Marc

PS: BTW, if you're curious, I have the disk image because I dded a drive that
was dying and dded chunks out of it until I got a copy minus a few blocks.
-- 
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                                      .... what McDonalds is to gourmet cooking
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