Can not send SCSI command to the cdrom device.

[fangxiaozhi 00110321 <huananhu@huawei.com>]

Dear all:
 
  I have a CDROM device, and after I plug it into the Linux system, the Linux system will generate three device files in the directory of /dev/, such as:
  scd1: block special (11/0)
  sr1:  link to scd1
  sg1: character special(21/1)
 
  And I write a c program to send the SCSI command of SPACE to my CDROM device. Such as :
 
   fd = open("/dev/sg1", 0_RDWR);
   ioctl(fd, SCSI_IOCTL_SEND_COMMAND, cmdbuff);
 
  And I found that I can send the SPACE command to my CDROM device, if I open the file of /dev/sg1.
  But if I open the file of /dev/scd1, then I can not send the SPACE command to my CDROM device.
 
   Why I can not send SCSI command through /dev/scd1 ?
 
   What difference between /dev/sg1 and /dev/scd1 ?
 
   And how can I send send the command through /dev/scd1?
 
   Wait for the help, thanks.
 
Best Regards,
 
Franko Fang
2009-1-17


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