Offset into block file for mounting?

Hi...

I recently got a "floppy drive emulator" that uses an USB thumb drive to emulate floppy images to be used as a floppy drive. In trying out the software (it is a bit cryptic), I found that this model stores the floppy images consecutively on said thumb drive (with some padding to make the drives on 1.5 Mbyte borders on the thumb drive. When plugging in the thumb drive, the 'vfat' module just mounts the first image (as I expect). What I would like to do is mount some of the other images that exist (I dumped out the raw thumb drive). I believe that a simple way to do this is to add an offset to the vfat mount, so that the accesses begin at (as in my example) 0x180000 (and multiples thereof) from the start of the physical drive.

Is there any way to add such an offset?
Would it be useful in any other file systems?

Sorry, but there is no partition map in the way this device formats the thumb drive. I suspect that this is due to the way it was designed, and it makes the task much simpler to do it that way (and I have no way of changing the hardware simply).

My reason for doing this is that I want to use this device in my Data I/O programmer, which has ONLY a floppy interface, and I am a bit tired of playing the shuffle game for the programmers disks. I also want to transfer data as well, and having the ability to do the offset where one finds the disk image makes this useful.

Thanks for any assistance. Please copy me on replies, as I don't currently subscribe.

p.s. A similar item is on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290507795223 (I tried to make the URL as short as possible!)

Tom Watson <[email protected]>
I'm at home now

Probably the easist way to solve this is to use devicemapper. You can use dmsetup[1] to create a device mapper volume that starts and ends at the appropriate offsets. You can then mount the device mapper volume using anyu file system without having to hack in a offset mount option.

[1] See the dmsetup man page for more details.

- Ted

Hi Tom,

mount diskimage /dir -t vfat -o loop,offset=xxx,sizelimit=yyy

mount will then forward the offset and sizelimit options to losetup which sets up a loop device before mounting.

Have a look at the man-pages for mount and losetup. :-)

Hope that helps.

Martin