linux-kernel - Re: [PATCH v4 8/8] iommu/vt-d: Misc macro clean up for SVM

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Date:   Mon, 02 Dec 2019 10:22:13 -0800
From:   Joe Perches <joe@...ches.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        Eric Auger <eric.auger@...hat.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>
Subject: Re: [PATCH v4 8/8] iommu/vt-d: Misc macro clean up for SVM

On Mon, 2019-12-02 at 10:15 -0800, Jacob Pan wrote:
> On Thu, 21 Nov 2019 13:37:10 -0800
> Joe Perches <joe@...ches.com> wrote:
> 
> > On Thu, 2019-11-21 at 13:26 -0800, Jacob Pan wrote:
> > > Use combined macros for_each_svm_dev() to simplify SVM device
> > > iteration and error checking.  
> > []
> > > diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c  
> > []
> > > +#define for_each_svm_dev(sdev, svm, d)			\
> > > +	list_for_each_entry((sdev), &(svm)->devs, list)	\
> > > +		if ((d) != (sdev)->dev) {} else
> > > +
> > >  int intel_svm_bind_mm(struct device *dev, int *pasid, int flags,
> > > struct svm_dev_ops *ops) {
> > >  	struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
> > > @@ -274,15 +278,13 @@ int intel_svm_bind_mm(struct device *dev, int
> > > *pasid, int flags, struct svm_dev_ goto out;
> > >  			}
> > >  
> > > -			list_for_each_entry(sdev, &svm->devs,
> > > list) {
> > > -				if (dev == sdev->dev) {
> > > -					if (sdev->ops != ops) {
> > > -						ret = -EBUSY;
> > > -						goto out;
> > > -					}
> > > -					sdev->users++;
> > > -					goto success;
> > > +			for_each_svm_dev(sdev, svm, dev) {
> > > +				if (sdev->ops != ops) {
> > > +					ret = -EBUSY;
> > > +					goto out;
> > >  				}
> > > +				sdev->users++;
> > > +				goto success;
> > >  			}  
> > 
> > I think this does not read better as this is now a
> > for_each loop that exits the loop on the first match.
> > 
> I think one of the benefits is reduced indentation. What do you
> recommend?

Making the code intelligible for a reader.

At least add a comment describing why there is only
a single possible match.

Given the for_each name, it's odd code that only the
first match has an action.