[PATCH 06/10] dasd: implement ->set_read_only to hook into BLKROSET processing

[Christoph Hellwig]

On Thu, Nov 05, 2020 at 09:56:47PM +0100, Stefan Haberland wrote:
> > +	/* do not manipulate hardware state for partitions */
> >  	if (bdev_is_partition(bdev))
> > -		// ro setting is not allowed for partitions
> > -		return -EINVAL;
> > -	if (get_user(intval, (int __user *)argp))
> > -		return -EFAULT;
> > +		return 0;
> > +
> >  	base = dasd_device_from_gendisk(bdev->bd_disk);
> >  	if (!base)
> >  		return -ENODEV;
> > -	if (!intval && test_bit(DASD_FLAG_DEVICE_RO, &base->flags)) {
> > -		dasd_put_device(base);
> > -		return -EROFS;
> > -	}
> > -	set_disk_ro(bdev->bd_disk, intval);
> 
> 
> While testing this patch I just noticed that when I set a device readonly this is
> not going to be passed on to the partitions on this device any longer.
> 
> This is caused by the removed call to set_disk_ro().
> 
> Is this intentional or was this removed by accident?

It was unintentionally intentional :)

The generic code used already by almost all drivers in mainline only
calls set_device_ro from blkdev_roset, that is it only sets the main
device read-only.  dasd was the outlier here, and I didn't notice it
actually called set_disk_ro instead of set_device_ro.   That being
said I think setting all the partitions read-only as well when the
full device is set read-only makes perfect sense.  I'm just a little
worried it could cause regressions.  Let me prepare a follow on patch
on top of the series that switches to that behavior.