netdev - Re: [PATCH v2 net] nfp: cast sizeof() to int when comparing with error code

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Date:   Tue, 26 Jun 2018 10:48:19 +0800
From:   cgxu519 <cgxu519@....com>
To:     Joe Perches <joe@...ches.com>, jakub.kicinski@...ronome.com,
        davem@...emloft.net
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net] nfp: cast sizeof() to int when comparing with
 error code



On 06/26/2018 10:29 AM, Joe Perches wrote:
> On Tue, 2018-06-26 at 09:16 +0800, Chengguang Xu wrote:
>> sizeof() will return unsigned value so in the error check
>> negative error code will be always larger than sizeof().
> []
>> diff --git a/drivers/net/ethernet/netronome/nfp/nfpcore/nfp_nffw.c b/drivers/net/ethernet/netronome/nfp/nfpcore/nfp_nffw.c
> []
>> @@ -232,7 +232,7 @@ struct nfp_nffw_info *nfp_nffw_info_open(struct nfp_cpp *cpp)
>>   	err = nfp_cpp_read(cpp, nfp_resource_cpp_id(state->res),
>>   			   nfp_resource_address(state->res),
>>   			   fwinf, sizeof(*fwinf));
>> -	if (err < sizeof(*fwinf))
>> +	if (err < (int)sizeof(*fwinf))
>>   		goto err_release;
>>   
>>   	if (!nffw_res_flg_init_get(fwinf))
> The way this is done in several places in the kernel is
> to test first for < 0 and then test for < sizeof
>
> 	if (err < 0 || err < sizeof(etc...)
>
> see net/ceph/ceph_common.c etc...
If we need to distinguish the cases <0 and >0 && <sizeof() then that 
approach is better.
If not I think cast to int will be enough.

Thanks,
Chengguang.