linux-kernel - Re: [PATCH][next] net: hinic: fix comparison of a uint16

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Message-Id: <20170824.143230.1441873385968459116.davem@davemloft.net>
Date:   Thu, 24 Aug 2017 14:32:30 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     colin.king@...onical.com
Cc:     aviad.krawczyk@...wei.com, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] net: hinic: fix comparison of a uint16_t type
 with -1

From: Colin King <colin.king@...onical.com>
Date: Wed, 23 Aug 2017 16:39:36 +0100

> From: Colin Ian King <colin.king@...onical.com>
> 
> The comparison of hw_ioctxt.rx_buf_sz_idx == -1 is always false because
> rx_buf_sz_idx is a uint16_t. Fix this by explicitly casting -1 to uint16_t.
> 
> Detected by CoverityScan, CID#1454559 ("Operands don't affect result")
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c b/drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c
> index 09dec6de8dd5..71e26070fb7f 100644
> --- a/drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c
> +++ b/drivers/net/ethernet/huawei/hinic/hinic_hw_dev.c
> @@ -352,7 +352,7 @@ static int set_hw_ioctxt(struct hinic_hwdev *hwdev, unsigned int rq_depth,
>  		}
>  	}
>  
> -	if (hw_ioctxt.rx_buf_sz_idx == -1)
> +	if (hw_ioctxt.rx_buf_sz_idx == (uint16_t)-1)
>  		return -EINVAL;
>  
>  	hw_ioctxt.sq_depth  = ilog2(sq_depth);

This is really silly.

The code in question is trying to convert a size (HINIC_RX_BUF_SZ)
into a table index, using a loop.

It should just compute this at compile time and do away with this
overly confusing code.

Even a switch statement would be much better and the compiler
would optimize the whole away into a single assignment in
the generated code.