Solved Random seek on CD-ROM drive

[Bill Evans at Mariposa]

I wish to exercise my CD-ROM drive, to keep the dust off the lens. On Linux I run (as root) a C program I wrote which seeks back and forth, reading a single block each time as it goes. On FreeBSD this program doesn't get too far. I can open the device and seek to (say) block 1. But when I try to read the block, I get error 22 (EINVAL). It fails on the first read, at block 1, whether or not the device is mounted (-t cd9660). How do I proceed?

  lo_fd=Open(ar_argv[1],
             O_RDONLY,
             0
            );

  lo_high_bit=1;

  while(lo_high_bit>0)
  {
    if(lseek(lo_fd,
             lo_high_bit,
             SEEK_SET
            )
       ==
       (off_t)-1
      )
    {
      lo_high_bit>>=1;

      break;
    }

    if(read(lo_fd,
            lo_buffer,
            1
           )
       !=
       1
      )
    {
      lo_high_bit>>=1;

      break;
    }

    lo_high_bit<<=1;
  }

 

[Juha Nurmela]

Maybe you didn't

#include <unistd.h>

and the seek went off limits. off_t argument needs the prototype.

Juha

 

[Bill Evans at Mariposa]

No, sorry. I hadn't included the full source file. The full source file is here, and the #include statement is on line 31.

 

[Bill Evans at Mariposa]

SOLVED: it turns out there were two problems: I was seeking to byte 1 (not sector 1), and reading just one byte.

fstat(1) on that device yields a block size of 4096.

If I seek to 4096 and read 4096 bytes, it works.

If I seek to 2048 and read 2048 bytes, it works.

If I seek to 2048 and read 1024 bytes, I get EINVAL on the read().

If I seek to 1024 and read 2048 bytes, I get EINVAL on the read().