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Full Discussion: C++ Code to Access Linux Hard Disk Sectors (with a LoopBack Virtual Hard Disk)
Operating Systems Linux C++ Code to Access Linux Hard Disk Sectors (with a LoopBack Virtual Hard Disk) Post 302491431 by Corona688 on Thursday 27th of January 2011 12:13:11 PM
Old 01-27-2011
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:

Code:
$ hexdump -C 8gflash-2011-01-27.vfat | head
00000000  eb 58 90 29 5e 76 56 4b  49 48 43 00 02 08 90 08  |.X.)^vVKIHC.....|
00000010  02 00 00 00 00 f8 00 00  20 00 10 00 80 1f 00 00  |........ .......|
00000020  80 40 ef 00 b8 3b 00 00  00 00 00 00 02 00 00 00  |.@...;..........|
00000030  01 00 08 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000040  00 00 29 53 6a af d5 20  20 20 20 20 20 20 20 20  |..)Sj..         |
00000050  20 20 46 41 54 33 32 20  20 20 fa 33 c9 8e d1 bc  |  FAT32   .3....|
00000060  f8 7b 8e c1 bd 78 00 c5  76 00 1e 56 16 55 bf 22  |.{...x..v..V.U."|
00000070  05 89 7e 00 89 4e 02 b1  0b fc f3 a4 8e d9 bd 00  |..~..N..........|
00000080  7c c6 45 fe 0f 8b 46 18  88 45 f9 38 4e 40 7d 25  ||.E...F..E.8N@}%|
00000090  8b c1 99 bb 00 07 e8 97  00 72 1a 83 eb 3a 66 a1  |.........r...:f.|

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.

These links are good starting points on FAT and ext2.
Last edited by Corona688; 01-27-2011 at 01:30 PM.. Reason: collosal thinko
 

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LEARN ABOUT REDHAT

mkfs

MKFS(8) 						      System Manager's Manual							   MKFS(8)

NAME

       mkfs - build a Linux file system

SYNOPSIS

       mkfs [ -V ] [ -t fstype ] [ fs-options ] filesys [ blocks ]

DESCRIPTION

       mkfs  is used to build a Linux file system on a device, usually a hard disk partition.  filesys is either the device name (e.g.	/dev/hda1,
       /dev/sdb2) or the mount point (e.g.  /, /usr, /home) for the file system.  blocks is the number of blocks to be used for the file system.

       The exit code returned by mkfs is 0 on success and 1 on failure.

       In actuality, mkfs is simply a front-end for the various file system builders (mkfs.fstype) available under Linux.   The  file  system-spe-
       cific  builder  is  searched  for  in  a number of directories like perhaps /sbin, /sbin/fs, /sbin/fs.d, /etc/fs, /etc (the precise list is
       defined at compile time but at least contains /sbin and /sbin/fs), and finally in the directories listed in the PATH  enviroment  variable.
       Please see the file system-specific builder manual pages for further details.

OPTIONS

       -V     Produce  verbose	output,  including  all  file  system-specific	commands that are executed.  Specifying this option more than once
	      inhibits execution of any file system-specific commands.	This is really only useful for testing.

       -t fstype
	      Specifies the type of file system to be built.  If not specified, the default file system type (currently ext2) is used.

       fs-options
	      File system-specific options to be passed to the real file system builder.  Although not guaranteed, the following options are  sup-
	      ported by most file system builders.

       -c     Check the device for bad blocks before building the file system.

       -l filename
	      Read the bad blocks list from filename

       -v     Produce verbose output.

BUGS

       All  generic options must precede and not be combined with file system-specific options.  Some file system-specific programs do not support
       the -v (verbose) option, nor return meaningful exit codes.  Also, some file system-specific programs do not automatically detect the device
       size and require the blocks parameter to be specified.

AUTHORS

       David Engel (david@ods.com)
       Fred N. van Kempen (waltje@uwalt.nl.mugnet.org)
       Ron Sommeling (sommel@sci.kun.nl)
       The manual page was shamelessly adapted from Remy Card's version for the ext2 file system.

SEE ALSO

       fs(5),  badblocks(8),  fsck(8), mkdosfs(8), mke2fs(8), mkfs.bfs(8), mkfs.ext2(8), mkfs.ext3(8), mkfs.minix(8), mkfs.msdos(8), mkfs.vfat(8),
       mkfs.xfs(8), mkfs.xiafs(8)

Version 1.9							     Jun 1995								   MKFS(8)
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