Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1180570 > unrolled thread

Re: [RFC PATCH v2 1/4] y2038: add 64bit time_t support in timeval for 32bit architecture

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [RFC PATCH v2 1/4] y2038: add 64bit time_t support in timeval  for 32bit architecture Bamvor Zhang Jian <bamvor.zhangjian@linaro.org> - 2015-07-09 11:10 +0200
    Re: [RFC PATCH v2 1/4] y2038: add 64bit time_t support in timeval  for 32bit architecture Bamvor Zhang Jian <bamvor.zhangjian@linaro.org> - 2015-07-15 05:20 +0200
      Re: [RFC PATCH v2 1/4] y2038: add 64bit time_t support in timeval for 32bit architecture Arnd Bergmann <arnd@arndb.de> - 2015-07-15 11:40 +0200

#1180570 — Re: [RFC PATCH v2 1/4] y2038: add 64bit time_t support in timeval for 32bit architecture

Hi, John

On 07/09/2015 04:09 AM, John Stultz wrote:
> On Mon, Jun 29, 2015 at 7:23 AM, Bamvor Zhang Jian
> <bamvor.zhangjian@linaro.org> wrote:
>> +int get_timeval64(struct timeval64 *tv,
>> +                  const struct __kernel_timeval __user *utv)
>> +{
>> +       struct __kernel_timeval ktv;
>> +       int ret;
>> +
>> +       ret = copy_from_user(&ktv, utv, sizeof(ktv));
>> +       if (ret)
>> +               return -EFAULT;
>> +
>> +       tv->tv_sec = ktv.tv_sec;
>> +       if (!IS_ENABLED(CONFIG_64BIT)
>> +#ifdef CONFIG_COMPAT
>> +          || is_compat_task()
>> +#endif
>
> These sorts of ifdefs are to be avoided inside of functions.

> Instead, it seems is_compat_task() should be defined to 0 in the
> !CONFIG_COMPAT case, so you can avoid the ifdefs and the compiler can
> still optimize it out.
I add this ifdef because I got compile failure on arm platform. This
file do not include the <linux/compat.h> directly. And in arm64,
compat.h is included implicitily.
So, I am not sure what I should do here. Include <linux/compat.h> in
this file directly or add a this check at the beginning of this file?

#ifndef is_compat_task
#define is_compat_task() (0)
#endif

> Otherwise this looks similar to a patch Baolin (cc'ed) has been working on.
Yes.

regards

bamvor
>
> thanks
> -john
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1184239

Hi, Arnd

On 07/09/2015 06:26 PM, Arnd Bergmann wrote:
> On Thursday 09 July 2015 17:02:47 Bamvor Zhang Jian wrote:
>> On 07/09/2015 04:09 AM, John Stultz wrote:
>>> On Mon, Jun 29, 2015 at 7:23 AM, Bamvor Zhang Jian
>>> <bamvor.zhangjian@linaro.org> wrote:
>>>> +int get_timeval64(struct timeval64 *tv,
>>>> +                  const struct __kernel_timeval __user *utv)
>>>> +{
>>>> +       struct __kernel_timeval ktv;
>>>> +       int ret;
>>>> +
>>>> +       ret = copy_from_user(&ktv, utv, sizeof(ktv));
>>>> +       if (ret)
>>>> +               return -EFAULT;
>>>> +
>>>> +       tv->tv_sec = ktv.tv_sec;
>>>> +       if (!IS_ENABLED(CONFIG_64BIT)
>>>> +#ifdef CONFIG_COMPAT
>>>> +          || is_compat_task()
>>>> +#endif
>>>
>>> These sorts of ifdefs are to be avoided inside of functions.
>>
>>> Instead, it seems is_compat_task() should be defined to 0 in the
>>> !CONFIG_COMPAT case, so you can avoid the ifdefs and the compiler can
>>> still optimize it out.
>> I add this ifdef because I got compile failure on arm platform. This
>> file do not include the <linux/compat.h> directly. And in arm64,
>> compat.h is included implicitily.
>> So, I am not sure what I should do here. Include <linux/compat.h> in
>> this file directly or add a this check at the beginning of this file?
>>
>> #ifndef is_compat_task
>> #define is_compat_task() (0)
>> #endif
>>
>
> Actually I think we can completely skip this test here: Unlike
> timespec, timeval is defined in a way that always lets user space
> use a 64-bit type for the microsecond portion (suseconds_t tv_usec).
I do not familar with this type. I grep the suseconds_t in glibc, it
seems that suseconds_t(__SUSECONDS_T_TYPE) is defined as
__SYSCALL_SLONG_TYPE which is __SLONGWORD_TYPE(32bit on 32bit
architecture).
> I think we should simplify this case and just assume that user space
> does exactly that, and treat a tv_usec value with a nonzero upper
> half as an error.
>
> I would also keep this function local to the ppdev driver, in order
> to not proliferate this to generic kernel code, but that is something
> we can debate, based on what other drivers need. For core kernel
> code, we should not need a get_timeval64 function because all system
> calls that pass a timeval structure are obsolete and we don't need
> to provide 64-bit time_t variants of them.
Got it.

regards

bamvor
>
> 	Arnd
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1184527 — Re: [RFC PATCH v2 1/4] y2038: add 64bit time_t support in timeval for 32bit architecture

On Wednesday 15 July 2015 11:18:31 Bamvor Zhang Jian wrote:
> Hi, Arnd
> 
> On 07/09/2015 06:26 PM, Arnd Bergmann wrote:
> > On Thursday 09 July 2015 17:02:47 Bamvor Zhang Jian wrote:
> >> On 07/09/2015 04:09 AM, John Stultz wrote:
> >>> On Mon, Jun 29, 2015 at 7:23 AM, Bamvor Zhang Jian
> >>> <bamvor.zhangjian@linaro.org> wrote:
> >>>> +int get_timeval64(struct timeval64 *tv,
> >>>> +                  const struct __kernel_timeval __user *utv)
> >>>> +{
> >>>> +       struct __kernel_timeval ktv;
> >>>> +       int ret;
> >>>> +
> >>>> +       ret = copy_from_user(&ktv, utv, sizeof(ktv));
> >>>> +       if (ret)
> >>>> +               return -EFAULT;
> >>>> +
> >>>> +       tv->tv_sec = ktv.tv_sec;
> >>>> +       if (!IS_ENABLED(CONFIG_64BIT)
> >>>> +#ifdef CONFIG_COMPAT
> >>>> +          || is_compat_task()
> >>>> +#endif
> >>>
> >>> These sorts of ifdefs are to be avoided inside of functions.
> >>
> >>> Instead, it seems is_compat_task() should be defined to 0 in the
> >>> !CONFIG_COMPAT case, so you can avoid the ifdefs and the compiler can
> >>> still optimize it out.
> >> I add this ifdef because I got compile failure on arm platform. This
> >> file do not include the <linux/compat.h> directly. And in arm64,
> >> compat.h is included implicitily.
> >> So, I am not sure what I should do here. Include <linux/compat.h> in
> >> this file directly or add a this check at the beginning of this file?
> >>
> >> #ifndef is_compat_task
> >> #define is_compat_task() (0)
> >> #endif
> >>
> >
> > Actually I think we can completely skip this test here: Unlike
> > timespec, timeval is defined in a way that always lets user space
> > use a 64-bit type for the microsecond portion (suseconds_t tv_usec).
>
> I do not familar with this type. I grep the suseconds_t in glibc, it
> seems that suseconds_t(__SUSECONDS_T_TYPE) is defined as
> __SYSCALL_SLONG_TYPE which is __SLONGWORD_TYPE(32bit on 32bit
> architecture).

Correct, but POSIX allows it to be redefined along with time_t, so
timeval can be a pair of 64-bit values. In contrast, timespec is
required by POSIX (and C11) to be a time_t and a 'long', which is
why we need a hack to check the size of the second word of the
timespec structure.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web