linux-kernel - Re: [PATCH v2] netfilter: Clean up tests if NULL returned on failure

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Date:   Wed, 29 Mar 2017 14:19:31 +0530
From:   SIMRAN SINGHAL <singhalsimran0@...il.com>
To:     Jan Engelhardt <jengelh@...i.de>
Cc:     wensong@...ux-vs.org, Simon Horman <horms@...ge.net.au>,
        Julian Anastasov <ja@....bg>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        lvs-devel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, linux-kernel@...r.kernel.org,
        outreachy-kernel <outreachy-kernel@...glegroups.com>
Subject: Re: [PATCH v2] netfilter: Clean up tests if NULL returned on failure

On Wed, Mar 29, 2017 at 12:25 PM, Jan Engelhardt <jengelh@...i.de> wrote:
>
> On Tuesday 2017-03-28 18:23, SIMRAN SINGHAL wrote:
>>On Tue, Mar 28, 2017 at 7:24 PM, Jan Engelhardt <jengelh@...i.de> wrote:
>>> On Tuesday 2017-03-28 15:13, simran singhal wrote:
>>>
>>>>Some functions like kmalloc/kzalloc return NULL on failure. When NULL
>>>>represents failure, !x is commonly used.
>>>>
>>>>@@ -910,7 +910,7 @@ ip_vs_new_dest(struct ip_vs_service *svc, struct ip_vs_dest_user_kern *udest,
>>>>       }
>>>>
>>>>       dest = kzalloc(sizeof(struct ip_vs_dest), GFP_KERNEL);
>>>>-      if (dest == NULL)
>>>>+      if (!dest)
>>>>               return -ENOMEM;
>>>
>>> This kind of transformation however is not cleanup anymore, it's really
>>> bikeshedding and should be avoided. There are pro and cons for both
>>> variants, and there is not really an overwhelming number of arguments
>>> for either variant to justify the change.
>>
>>Sorry, but I didn't get what you are trying to convey. And particularly pros and
>>cons of both variants.
>
> The ==NULL/!=NULL part sort of ensures that the left side is a pointer, which
> is lost when just using the variable and have it implicitly convert to bool.

Thanks for the explaination!!!!

But, according to me we should prefer != NULL over ==NULL according to
coding style.