----- Chen Gang <gang.chen.5i5j@xxxxxxxxx> 写道：
> On 05/22/2014 08:26 AM, 管雪涛 wrote:
> >
> > ----- Chen Gang <gang.chen.5i5j@xxxxxxxxx> 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@xxxxxxxxx>
> >> ---
> >> 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.
> >
>
> 'u64' is a very very large number. after calculation, if it is based on
> nano second (although I am not quite sure whether it is based on it).
>
> a hour, 3,600,000,000,000ns
> a day, 90,000,000,000,000ns
> a year, 50,000,000,000,000,000ns
> 10 years, 500,000,000,000,000,000ns
> 100 years, 5,000,000,000,000,000,000ns
> 4G * 4G = 16,000,000,000,000,000,000ns
>
> So we can assume it will never overflow for 'u64'.
However, return value of dccp_timestamp function is u32.
>
>
> Thanks.
> --
> Chen Gang
>
> Open, share, and attitude like air, water, and life which God blessed
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