Re: [Linux-usb-users] Re: Problems accessing USB Mass Storage

[Rogier Wolff]

On Tue, Sep 17, 2002 at 10:13:13PM +0100, Mark C wrote:
> On Tue, 2002-09-17 at 21:13, Thomas Dodd wrote:
> 
> > 
> > Give that a go Mark.
> > 
> > Try a few values like 25, 50, 75, and 100. with bs=1k and
> > unset (default 512 byte).
> 
> If I'm reading this correctly, I have been trying:
> 
> [root@stimpy mark]# dd if=/dev/sda of=tmp/tmp.img skip=50 \
> bs=1k                                                                                                         dd: reading `/dev/sda': Input/output error
> 0+0 records in
> 0+0 records out

Guys, 

When dd is told to skip a certain number of input blocks it doesn't
seek past them, but reads them and then discards them. Thus if you're
not supposed to read sectors 1-100 then this will not work. 

Try the following program: 

/* seek.c (C) [e-mail] */
/* 
	gcc -Wall -O2 seek.c -o seek 
*/

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>

#ifndef O_LARGEFILE
#define O_LARGEFILE     0100000
#endif
long long lseek64 (int fd, long long offset, int whence);

int main (int argc,char **argv)
{
  long long off;
  long long tt;

  if(argc < 2)
        exit(0);        /* don't seek at all */

  if (strncmp (argv[1],"0x",2) )
    sscanf (argv[1],"%Ld",&off);
  else
    sscanf (argv[1],"%Lx",&off);

  if (argc > 3) {
    if (strncmp (argv[3],"0x",2) )
      sscanf (argv[3],"%Ld",&tt);
    else
      sscanf (argv[3],"%Lx",&tt);
    if (argv[2][0] == '+')
      off += tt;
    else
      off -= tt;
  }
  
  errno = 0;
  if ((lseek64 (0,off,SEEK_CUR) < 0) &&
      (errno != 0))
    perror ("seek");
  exit (0);
}

with the command: 

	dd if=/dev/sda of=firstpart 

(Get the partition table)

	(seek 0x100000;dd of=secondpart) < /dev/sda 

Get everything beyond 1Mb. If this works, then we have to figure out
how low we can make the "0x100000" number to get all of the data.

Hypothesis: The partition table specifies that the data starts
on sector 200, and they didn't implement sectors 1-199.....
Cheap basterds. 

(My memory stick is just over 128 * 10^6 bytes, and not even
close to 128 * 2^20 bytes....)

			Roger. 

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