linux-kernel - Re: [PATCH 1/2] cgroup: cgroup

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Date:   Tue, 30 Nov 2021 00:33:41 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Wei Yang <richard.weiyang@...il.com>, lizefan.x@...edance.com,
        hannes@...xchg.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] cgroup: cgroup_subsys[ssid] is never NULL

On Mon, Nov 29, 2021 at 07:35:54AM -1000, Tejun Heo wrote:
>On Sat, Nov 27, 2021 at 02:59:18PM +0000, Wei Yang wrote:
>> When the check, (ssid) < CGROUP_SUBSYS_COUNT, passed, it means
>> cgroup_subsys[ssid] is defined to its proper value. It is not
>> necessary to use a true to enter the loop.
>...
>>  #define for_each_subsys(ss, ssid)					\
>>  	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&		\
>> -	     (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
>> +	     ((ss) = cgroup_subsys[ssid]); (ssid)++)
>
>So, now the compiler has to test whether ss is NULL or not before each
>iteration even though we know that it's never NULL. The whole point of that
>"|| true" is telling the compiler that the pointer is never NULL.
>

That's interesting. Thanks.

>Thanks.
>
>-- 
>tejun

-- 
Wei Yang
Help you, Help me