IDE vs. SCSI CDROM last block handling

Larry M. Augustin (lma@varesearch.com)
Mon, 29 Dec 1997 13:48:49 -0800

In kernel 2.0.32 the IDE and SCSI CDROM drivers behave differently at
the end of data on a CDROM. The IDE driver returns an I/O error. The
SCSI driver returns the end of file.

For example, on IDE this fails with an I/O error:

10:18:33 [3] ~ root-l29$ md5sum /dev/hda
md5sum: /dev/hda: I/O error

While it will complete normally on SCSI:

[root@cray /root]# md5sum /dev/scd0
f474d26e7bac5b755b4ac261947bd89c /dev/scd0

[root@cray /root]# dd if=/dev/scd0 | md5sum
1275728+0 records in
1275728+0 records out
f474d26e7bac5b755b4ac261947bd89c -

Of course, it's easy enough to buffer programs from the I/O error on
IDE devices using dd:

11:01:38 [5] ~ root-l29$ dd if=/dev/hda | md5sum
dd: /dev/hda: I/O error
1275724+0 records in
1275724+0 records out
0aa766e51134fe1cc1750380e45ae32d -

Also, note that the number of records read is slightly different. The
SCSI driver successfully reads 318932 2K blocks and the IDE driver
reads 318931 2K blocks (the I/O error presumably coming on block
318932).

Shouldn't the SCSI and IDE drivers be consistent in handling this?

Larry