Re: [PATCH 1/4] sg: disable SET_FORCE_LOW_DMA

[Johannes Thumshirn <jthumshirn@xxxxxxx>]

On 02/03/2017 09:54 AM, Hannes Reinecke wrote:
> The ioctl SET_FORCE_LOW_DMA has never worked since the initial
> git check-in, and the respective setting is nowadays handled
> correctly.
> So disable it entirely.
>
> Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
> ---

[...]

>   	case SG_SET_FORCE_LOW_DMA:
> -		result = get_user(val, ip);
> -		if (result)
> -			return result;
> -		if (val) {
> -			sfp->low_dma = 1;
> -			if ((0 == sfp->low_dma) && (0 == sg_res_in_use(sfp))) {
> -				val = (int) sfp->reserve.bufflen;
> -				sg_remove_scat(sfp, &sfp->reserve);
> -				sg_build_reserve(sfp, val);
> -			}
> -		} else {
> -			if (atomic_read(&sdp->detaching))
> -				return -ENODEV;
> -			sfp->low_dma = sdp->device->host->unchecked_isa_dma;
> -		}
> -		return 0;
> +		return -EINVAL;

I'm not sure if returning a bogus '0' is better here to not break any 
existing application, which assumed it always worked.