What does the letter »r« stand for in /dev/sr0?

[James Michael Fultz]

* Rashkae <ubuntu at tigershaunt.com> [2009-11-05 10:31 -0500]:
> Simply looking at the relative udev rules and comments thereof:
> 
> (These are from Gutsy, there may have been changes, I'm too lazy to verify)
> 
> # SCSI CD-ROM devices use /dev/scdN now
> SUBSYSTEMS=="scsi", KERNEL=="sr[0-9]*", NAME="scd%n"
> 
> # Raw block devices need to be /dev/raw/*
> SUBSYSTEM=="raw", KERNEL=="raw[0-9]*",  NAME="raw/%k"
> 
> # Compatibility symlinks for /dev/scd* devices
> SUBSYSTEMS=="scsi", KERNEL=="sr[0-9]*", SYMLINK+="%k"

Interesting.  It has changed at least as of Jaunty.

# cdrom
SUBSYSTEM=="block", KERNEL=="sr[0-9]*", SYMLINK+="scd%n", GROUP="cdrom"

Yes, according to '/usr/share/doc/udev/changelog.Debian.gz', the changed
occurred in Jaunty.

"
  * Merged our rules with Upstream default rules, this results in a number
    of minor changes but achieves consistency with other distributions:
[...]
    * /dev/srN are now the definitive names of SCSI CD-ROM devices, with
      /dev/scdN as deprecated symlinks to them; this is the exact opposite of
      how we had things before.
[...]
 -- Scott James Remnant <scott at ubuntu.com>  Wed, 07 Jan 2009 14:01:19 +0000
"

According to the Linux Device List[1], sr? should only be
a compatibility symlink to scd?.  Strange that the change reversed the
correct behavior at least according to the Linux Device List.

1. Linux Device List:
<http://www.lanana.org/docs/device-list/devices-2.6+.txt>