On Tue, Oct 26 2004, Jeff Garzik wrote:

When I added ioctl handling, I returned EOPNOTSUPP for the "I didn't
recognize that ioctl you wanted to execute" return code.

The block layer will execute certain ioctl operations IFF the low-level
driver returns ENOTTY, signalling to the block layer that that driver
does not support the specified ioctl.

The net effect of libata returning EOPNOTSUPP was such that it
__broke__ BLSFLSBUF ioctl, simply by implementing ->ioctl.

So, we return the proper return code, and ioctls we don't handle
start to work again.  Overall, though, this is a fragile way to do
things in the block layer, IMHO.

Well, it's pretty much the universally accepted way of signalling this
information, I'm not sure I agree. The crappy part is that EINVAL is so
wide spread as well.

And EOPNOTSUPP just shows you are a networking whore as well :-)

-- 
Jens Axboe