linux-kernel - Re: [PATCH v2 1/3] blk-cgroup: check for pd_(alloc|free)_fn in blkcg_activate

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Message-ID: <ab8f117b-0e0a-4157-b261-471328f6b4e3@acm.org>
Date: Fri, 19 Jul 2024 09:25:07 -0700
From: Bart Van Assche <bvanassche@....org>
To: Christoph Hellwig <hch@...radead.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: jack@...e.cz, tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk,
 cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, yukuai3@...wei.com, yi.zhang@...wei.com,
 yangerkun@...wei.com
Subject: Re: [PATCH v2 1/3] blk-cgroup: check for pd_(alloc|free)_fn in
 blkcg_activate_policy()

On 7/18/24 10:29 PM, Christoph Hellwig wrote:
> On Fri, Jul 19, 2024 at 10:34:29AM +0800, Yu Kuai wrote:
>> +	/*
>> +	 * Make sure cpd/pd_alloc_fn and cpd/pd_free_fn in pairs, and policy
>> +	 * without pd_alloc_fn/pd_free_fn can't be activated.
>> +	 */
>>   	if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
>>   		(!pol->pd_alloc_fn ^ !pol->pd_free_fn))
>>   		goto err_unlock;
>> -- 
> 
> I know this is existing code, but can you fix up the incorrect
> indentation while you touch this:
> 
>   	if ((!pol->cpd_alloc_fn ^ !pol->cpd_free_fn) ||
>   	    (!pol->pd_alloc_fn ^ !pol->pd_free_fn))

Using xor (^) for booleans seems weird to me. Is there any preference in
Linux kernel code whether to use ^ or != to check whether to booleans
are different?

Thanks,

Bart.