linux-kernel - 回复： [PATCH linux-next] net/dccp/timer.c: use 'u64' instead of 's64' to avoid compiler's warning

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Date:	Thu, 22 May 2014 08:26:39 +0800 (CST)
From:	管雪涛 <gxt@....edu.cn>
To:	Chen Gang <gang.chen.5i5j@...il.com>
Cc:	gerrit@....abdn.ac.uk, Guan Xuetao <gxt@...c.pku.edu.cn>,
	David Miller <davem@...emloft.net>, dccp@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: 回复： [PATCH linux-next] net/dccp/timer.c: use 'u64' instead of 's64' to avoid compiler's warning


----- Chen Gang <gang.chen.5i5j@...il.com> 写道：
> 'dccp_timestamp_seed' is initialized once by ktime_get_real() in
> dccp_timestamping_init(). It is always less than ktime_get_real()
> in dccp_timestamp().
> 
> Then, ktime_us_delta() in dccp_timestamp() will always return positive
> number. So can use manual type cast to let compiler and do_div() know
> about it to avoid warning.
> 
> The related warning (with allmodconfig under unicore32):
> 
>     CC [M]  net/dccp/timer.o
>   net/dccp/timer.c: In function ‘dccp_timestamp’:
>   net/dccp/timer.c:285: warning: comparison of distinct pointer types lacks a cast
> 
> 
> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
> ---
>  net/dccp/timer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/dccp/timer.c b/net/dccp/timer.c
> index 16f0b22..1cd46a3 100644
> --- a/net/dccp/timer.c
> +++ b/net/dccp/timer.c
> @@ -280,7 +280,7 @@ static ktime_t dccp_timestamp_seed;
>   */
>  u32 dccp_timestamp(void)
>  {
> -	s64 delta = ktime_us_delta(ktime_get_real(), dccp_timestamp_seed);
> +	u64 delta = (u64)ktime_us_delta(ktime_get_real(), dccp_timestamp_seed);

Do you assume that delta should be very small?
Otherwise, return value will be different if data type is changed.

>  
>  	do_div(delta, 10);
>  	return delta;
> -- 
> 1.9.2.459.g68773ac
--
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