linux-kernel - RE: [PATCH v3 1/6] vfio/type1: Introduce iova list and add iommu aperture validity check

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Date:   Tue, 20 Feb 2018 09:05:30 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     Alex Williamson <alex.williamson@...hat.com>
CC:     "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "pmorel@...ux.vnet.ibm.com" <pmorel@...ux.vnet.ibm.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>,
        John Garry <john.garry@...wei.com>,
        "xuwei (O)" <xuwei5@...wei.com>
Subject: RE: [PATCH v3 1/6] vfio/type1: Introduce iova list and add iommu
 aperture validity check



> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@...hat.com]
> Sent: Monday, February 19, 2018 7:51 PM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
> Cc: eric.auger@...hat.com; pmorel@...ux.vnet.ibm.com;
> kvm@...r.kernel.org; linux-kernel@...r.kernel.org; Linuxarm
> <linuxarm@...wei.com>; John Garry <john.garry@...wei.com>; xuwei (O)
> <xuwei5@...wei.com>
> Subject: Re: [PATCH v3 1/6] vfio/type1: Introduce iova list and add iommu
> aperture validity check
> 
> On Mon, 19 Feb 2018 09:50:24 +0000
> Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com> wrote:
> > > -----Original Message-----
> > > From: Alex Williamson [mailto:alex.williamson@...hat.com]
> > > Sent: Friday, February 16, 2018 8:49 PM
> > > On Thu, 15 Feb 2018 09:44:59 +0000
> > > Shameer Kolothum <shameerali.kolothum.thodi@...wei.com> wrote:
> > > > +			node->end = end;
> > > > +			continue;
> > > > +		}
> > > > +		/* Delete nodes after new end */
> > > > +		list_del(&node->list);
> > > > +		kfree(node);
> > > > +	}
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +static int vfio_iommu_get_iova_copy(struct vfio_iommu *iommu,
> > > > +				struct list_head *iova_copy)
> > > > +{
> > > > +
> > > > +	struct list_head *iova = &iommu->iova_list;
> > > > +	struct vfio_iova *n;
> > > > +
> > > > +	list_for_each_entry(n, iova, list) {
> > > > +		int ret;
> > > > +
> > > > +		ret = vfio_insert_iova(n->start, n->end, iova_copy);
> > > > +		if (ret)
> > > > +			return ret;
> > >
> > > Let's delete and free any entries added to the copy here too.
> >
> > Ok. My original thought was caller will free up in case of error.
> 
> This comes down to Rusty's suggestions of how to make an API hard to
> misuse rather than simply easy to use to me.  Placing the onus on the
> caller to cleanup a list sounds simple, but the caller passed an empty
> list and the function failed, why should the caller bother to check if
> the function left any cruft on the list in the course of failing?  This
> is not a hard to misuse interface, in fact it's very easy to forget
> that cleanup.  Thanks,

Ok. I understand the concerns. I will sent out a revised one soon.

Thanks,
Shameer