linux-kernel - Re: [PATCH v4 01/11] iommu/vt-d: debugfs: Remove device_domain

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Date:   Thu, 7 Jul 2022 17:18:04 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Ethan Zhao <haifeng.zhao@...ux.intel.com>,
        iommu@...ts.linux-foundation.org, iommu@...ts.linux.dev
Cc:     baolu.lu@...ux.intel.com, Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 01/11] iommu/vt-d: debugfs: Remove device_domain_lock
 usage

On 2022/7/7 16:30, Ethan Zhao wrote:
>> -static int show_device_domain_translation(struct device *dev, void *data)
>> +static int __show_device_domain_translation(struct device *dev, void *data)
>>   {
>> -	struct device_domain_info *info = dev_iommu_priv_get(dev);
>> -	struct dmar_domain *domain = info->domain;
>> +	struct dmar_domain *domain;
>>   	struct seq_file *m = data;
>>   	u64 path[6] = { 0 };
>>   
>> +	domain = to_dmar_domain(iommu_get_domain_for_dev(dev));
>>   	if (!domain)
>>   		return 0;
>>   
>> @@ -359,20 +359,39 @@ static int show_device_domain_translation(struct device *dev, void *data)
>>   	pgtable_walk_level(m, domain->pgd, domain->agaw + 2, 0, path);
>>   	seq_putc(m, '\n');
>>   
>> -	return 0;
>> +	/* Don't iterate */
>> +	return 1;
>>   }
> 
> Using this return value trick to change the caller behaviour, seems not 
> saving
> 
> anything, but really cost me a few seconds more to know the 
> *incantation* --
> 
> 'Don't iterate' :) .

This is defined by iommu_group_for_each_dev(). Return value 0 means
continuing to next one, while non-zero means stopping iteration.

Best regards,
baolu