Re: [PATCH 2/7] xen-gntdev: Change page limit to be global instead of per-open

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Jan 11, 2011 at 01:18:09PM -0500, Daniel De Graaf wrote:
> On 01/11/2011 12:51 PM, Konrad Rzeszutek Wilk wrote:
> > On Tue, Jan 11, 2011 at 07:45:34AM -0500, Daniel De Graaf wrote:
> >> On 01/10/2011 04:52 PM, Konrad Rzeszutek Wilk wrote:
> >>>>  static long gntdev_ioctl(struct file *flip,
> >>>>  			 unsigned int cmd, unsigned long arg)
> >>>>  {
> >>>> @@ -555,9 +538,6 @@ static long gntdev_ioctl(struct file *flip,
> >>>>  	case IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR:
> >>>>  		return gntdev_ioctl_get_offset_for_vaddr(priv, ptr);
> >>>>  
> >>>> -	case IOCTL_GNTDEV_SET_MAX_GRANTS:
> >>>> -		return gntdev_ioctl_set_max_grants(priv, ptr);
> >>>
> >>> Would it make sense to return -EPNOTSUPPORTED? Or does it not really
> >>> matter as nobody has been using this ioctl call?
> >>
> >> Does this produce a clearer error message than the default -ENOIOCTLCMD?
> >> It's possible that some people use it, since it was exposed as an API.
> > 
> > Looking at the Xen tools the user of this is:
> > xc_gnttab_set_max_grants which would end up returning whatever the
> > error is. I don't see any users of this in the Xen tools, thought there might
> > be some in the XCP code. Lets stay with your ENOIOCTLCMD.
> > 
> > However, I was wondering if you are going to submit a patch to the Xen
> > tool stack so that it can utlize the SysFS interface to set the limits
> > for that API call?
> > 
> 
> No, because the semantics of what the limit is covering have changed. The
> new limit is per-domain, and if there was any existing code that set the
> limit, it would have been a per-open value and probably too low. I think
> it was suggested that the call be removed from the Xen API; I can submit
> a patch to do that, if you want.

Please do. Thank you.
> 
> The new value is probably best set in modprobe.conf if gntdev is a module;
> the sysfs interface is useful for runtime adjustment or if it is builtin.
> 
> -- 
> Daniel De Graaf
> National Security Agency