I am (or was) attempting to reimplement the discid.c program that can be downloaded from freedb.org. I know I could use Inline, but want to see if I can do the full thing in perl. I got it to import some constants from some header files and I got it to read the toc header using ioctl. However, to read individual entries, I have to read information into a more complex structure using ioctl (the header was easy as it took the first two bytes from the returned scalar).

So, my question is, how do I read into a more complex structure. My C isn't as good as it could be but I have attempted to come up with a pack structure that mimics the struct but ioctl doesn't like it.

I have included the beginning of my script with some of the calling C code and the structs from linux/cdrom.h. Again, I know I could use Inline to do this and will do that if no answer works, but I would rather see if there is an answer for reading a complex structure via ioctl.

Note: it is the second ioctl call that fails. 

#!/usr/bin/perl -w

use strict;
use vars qw();
use Fatal qw(open close ioctl);

### try to load some cdrom constants
if( ! eval { require "linux/cdrom.ph" } ){
  my $error;
  if( $@ =~ /^(Can\'t locate .+? in \@INC)/ ){
    $error = $1 ."\n  You may need to run h2ph.\n";
  }else{
    $error = $@;
  }
  print $error;
  print "Continuing with hard coded constants...\n";

  ### copy from linux/cdrom.ph
  eval 'sub CDROMREADTOCHDR () {0x5305;}' unless defined(&CDROMREADTOC
+HDR);
  eval 'sub CDROMREADTOCENTRY () {0x5306;}' unless defined(&CDROMREADT
+OCENTRY);
  eval 'sub CDROM_MSF () {0x02;}' unless defined(&CDROM_MSF);
}

### open the cdrom device
print "Opening cd device...\n";
my $device = "/dev/hdc"; # not portable...yet
open(_DEV,"<$device");

### read the toc range
print "Reading toc header...\n";
my $str = '';
ioctl(_DEV, CDROMREADTOCHDR(), $str);
my $track0 = ord( substr($str,0,1) );
my $trackn = ord( substr($str,1,1) );
print "Track range: [$track0][$trackn]\n";

### read the entries
print "Reading toc entries...\n";
for(my $i = $track0; $i <= $trackn; $i ++){
  my $track  = $i;
  my $format = CDROM_MSF();
  my $struct = "CC4C4CCCCiC";
  my $str = pack($struct,$track,0,0,$format);
  ioctl(_DEV, CDROMREADTOCENTRY(), $str);
  my($_track,$adr,$ctrl,$_format,
     $min,$sec,$frame,
     $lba,
     $datamode) = unpack($struct,$str);
  print "$_track $adr $_format $min $sec $frame\n";
}
print "Done\n";

__END__
#  Sample calling code and structs
#   struct cdrom_tocentry tocentry;
#   tocentry.cdte_track = i;
#   tocentry.cdte_format = CDROM_MSF;
#   ioctl(drive, CDROMREADTOCENTRY, &tocentry);
#
#   struct cdrom_msf0
#   {
#       __u8    minute;
#       __u8    second;
#       __u8    frame;
#   };
#
#   /* Address in either MSF or logical format */
#   union cdrom_addr
#   {
#       struct cdrom_msf0       msf;
#       int                     lba;
#   };
#
#   struct cdrom_tocentry
#   {
#       __u8    cdte_track;
#       __u8    cdte_adr        :4;
#       __u8    cdte_ctrl       :4;
#       __u8    cdte_format;
#       union cdrom_addr cdte_addr;
#       __u8    cdte_datamode;
#   };

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In reply to ioctl into or from perl structs by Rhandom

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