Herbert,
in the USB  case, I think simply stalling the pipe on a WRITE_10 or
WRITE_12 command is enough to indicate that the device is read-only.
As for the linux side of things, you should be able to add 'ro' to
your mount options. That should be enough for read-only.
>From what I understand, though, your device works at the ATA level,
not the USB level, and I don't know anything about that, sorry.
- Marcel

>  Nothing in my device is "writable", so I'm not concerned about the OS
>  attempting to write stuff and it mucking up my hardware. The issue is
>  because I don't have anything writable the OS gets confused when it
>  writes something but then notices the copy on my "drive" doesn't match
>  (I get dropped write page errors in dmesg). The most common occurance is
>  updating the root directory entries with access times. So far it doesn't
>  appear that these errors are an issue, things seem to work fine, but I
>  am concerned that with the right software/hardware combination it will
>  pop up as a problem.
>
>  How does a hard drive tell an OS it's write protected? Is it even
>  possible?
>
>  Thanks, TTYL
>
>
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