Yes, that's what I mean, you have to understand how ext3 works to mess with it raw. With the bits of it you've overwritten now, it probably needs a reformat to be valid ext3 again.
Do you need to use ext3? If not, I'd reformat it with /sbin/fsck.msdos -F 16 filename/sbin/mkfs.msdos -F 16 filename as the MSDOS filesystem is far, far simpler: just a big table, instead of a tree.
You might find the hexdump utility handy to show you what data you should expect to find in what places. Here's part of a hex dump of a flash drive I had lying around:
If you want to use a proper Linux filesystem, try ext2 instead of ext3, it's pretty much the same as ext3 but with a lot of journalling fluff cut out.
Theselinks are good starting points on FAT and ext2.
Last edited by Corona688; 01-27-2011 at 01:30 PM..
Reason: collosal thinko
I think going with the MS-DOS filesystem (FAT-16) is a much better Idea. I formatted my current loop back device using the command you gave as follows :
But I get the following error.
Could you please verify how can I do this correctly ?. So I could format my loop back device with FAT-16 (for DOS file system) mode ?.
I found the following article through a Google search(while awaiting your reply) on creating a floppy drive with the loop back device and got it mounted.
Is the above approach correct ?.
Anyways now I'm back where I began as of how can I create files & folders inside the loop back device. Now with the MS-DOS FAT-16 file system. If you have any direct pointers to get me started on implementing this it would be a great help .
Floppies use the FAT12 filesystem, which is good at not wasting space, but very hard to use. Its FAT entries are, as the name suggests, twelve bits in size. That's one and a half bytes, like this:
You can't make an array of that. You'd have to tease the data out the hard way, figuring out where the entry starts, which whole bytes and which half bytes should be retrieved, etc, etc.
You don't need to use the loop device at all to make the DOS filesystem, just to mount it. mkfs.msdos will warn you a file's not a device but write to it anyway.
Be sure to run losetup -d /dev/loop0 when you're done with that tutorial, or you'll find the loop device still busy when you try to use it for something else.
The instructions I posted in the post before yours should work fine for creating a FAT16 filesystem on a file 500 megabytes or smaller. FAT16 entries fit nicely in an array of 16-bit integers.
You should start making data structures to hold information so you don't have to find absolutely everything by byte offsets all the time:
All that's gleaned from information on the wiki, and it appears to match the dump I posted above(the OEM name is indeed filled with garbage for some reason!)
Look if the values you get in that structure seem normal. Try to use the information in it to find other structures. See if you can find the information you need to piece the partition together. You have to understand what's going on in those structures before you can alter them properly.
I hope this gives you the idea as I don't have the time to do absolutely everything for you.
Last edited by Corona688; 01-27-2011 at 02:17 PM..
Thank you very very much for the immense support you've given me throughout this thread. I've learned a lot from you since I started this thread . I understand what I should do and how I should proceed. Thanks you very much sir.
I've tried the HexDump Command you gave me on my Virtual MS-DOS(FAT-16) Floppy Drive & as follows :
and following is the output I got :
I hope this information will also be useful as I proceed as you've mentioned earlier. Thanks again for all your help & time .
Thank you very very much for the immense support you've given me throughout this thread. I've learned a lot from you since I started this thread . I understand what I should do and how I should proceed. Thanks you very much sir.
I've tried the HexDump Command you gave me on my Virtual MS-DOS(FAT-16) Floppy Drive & as follows :
Your virtual floppy disk, like any floppy disk, is FAT12, not FAT16. Look closely at your dump:
To make a FAT16 partition you might want to use the instructions I gave you on a blank file of a couple megabytes in size.
You don't need to use the loop device for anything but mounting the partition (something you intend to avoid doing anyway). As far as mkfs.msdos, read(), and write() are concerned they act the same.
Last edited by Corona688; 01-27-2011 at 02:44 PM..
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