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Subject: Re: [PATCH] LoongArch: Define __ARCH_WANT_NEW_STAT in unistd.h
To: Arnd Bergmann <arnd@arndb.de>, Huacai Chen <chenhuacai@loongson.cn>,
 Huacai Chen <chenhuacai@kernel.org>
Cc: loongarch@lists.linux.dev, Linux-Arch <linux-arch@vger.kernel.org>,
 Xuefeng Li <lixuefeng@loongson.cn>, guoren <guoren@kernel.org>,
 WANG Xuerui <kernel@xen0n.name>, Jiaxun Yang <jiaxun.yang@flygoat.com>,
 linux-kernel@vger.kernel.org, loongson-kernel@lists.loongnix.cn,
 stable@vger.kernel.org
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From: maobibo <maobibo@loongson.cn>
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Date: Thu, 16 May 2024 10:52:06 +0800
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On 2024/5/15 下午10:25, Arnd Bergmann wrote:
> On Wed, May 15, 2024, at 09:30, maobibo wrote:
>> On 2024/5/11 下午8:17, Arnd Bergmann wrote:
>>> On Sat, May 11, 2024, at 12:01, Huacai Chen wrote:
>>>
>>> Importantly, we can't just add fstatat64() on riscv32 because
>>> there is no time64 version for it other than statx(), and I don't
>>> want the architectures to diverge more than necessary.
>> yes, I agree. Normally there is newfstatat() on 64-bit architectures but
>> fstatat64() on 32-bit ones.
>>
>> I do not understand why fstatat64() can be added for riscv32 still.
>> 32bit timestamp seems works well for the present, it is valid until
>> (0x1UL << 32) / 365 / 24 / 3600 + 1970 == 2106 year. Year 2106 should
>> be enough for 32bit system.
> 
> There is a very small number of interfaces for which we ended up
> not using a 64-bit time_t replacement, but those are only for
> relative times, not epoch based offsets. The main problems
> here are:
> 
> - time_t is defined to be a signed value in posix, and we need
>    to handle file timestamps before 1970 in stat(), so changing
>    this one to be unsigned is not an option.
> 
> - A lot of products have already shipped that will have to
>    be supported past 2038 on existing 32-bit hardware. We
>    cannot regress on architectures that have already been
>    fixed to support this.
> 
> - file timestamps can also be set into the future, so applications
>    relying on this are broken before 2038.
I see. And thanks for detailed explanation.

Regards
Bibo Mao
> 
>        Arnd
>