linux-kernel - Re: [Y2038] [PATCH 00/10] Remove CURRENT_TIME and CURRENT_TIME_SEC

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Message-ID: <4775421.bkqoN6rOXc@wuerfel>
Date:	Wed, 03 Feb 2016 22:30:44 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	y2038@...ts.linaro.org
Cc:	Deepa Dinamani <deepa.kernel@...il.com>,
	linux-fsdevel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	Dave Chinner <david@...morbit.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [Y2038] [PATCH 00/10] Remove CURRENT_TIME and CURRENT_TIME_SEC - PART 1

On Tuesday 02 February 2016 22:07:40 Deepa Dinamani wrote:
> This patch series is aimed at getting rid of CURRENT_TIME and CURRENT_TIME_SEC
> macros.
> 
> The idea for the series evolved from my discussions with Arnd Bergmann.
> 
> This was originally part of the RFC series[2]:
> https://lkml.org/lkml/2016/1/7/20 (under discussion).
> 
> Dave Chinner suggested moving bug fixes out of the feature series to keep the
> original series simple.
> 
> There are 354 occurrences of the the above macros in the kernel.
> The series will be divided into 4 or 5 parts to keep the parts manageable
> and so that each part could be reviewed and merged independently.
> This is part 1 of the series. 

Looks very nice to me.

> Motivation
> 
> The macros: CURRENT_TIME and CURRENT_TIME_SEC are primarily used for
> filesystem timestamps.
> But, they are not accurate as they do not perform clamping according to
> filesystem timestamps ranges, nor do they truncate the nanoseconds value
> to the granularity as required by the filesystem.
> 
> The series is also viewed as an ancillary to another upcoming series[2]
> that attempts to transition file system timestamps to use 64 bit time to
> make these y2038 safe.
> 
> There will also be another series[3] to add range checks and clamping to
> filesystem time functions that are meant to substitute the above macros.
> 
> Solution
> 
> CURRENT_TIME macro has an equivalent function:
> 
> struct timespec current_fs_time(struct super_block *sb)
> 
> These will be the changes to the above function:
> 1. Function will return the type y2038 safe timespec64 in [2].
> 2. Function will use y2038 safe 64 bit functions in [2].
> 3. Function will be extended to perform range checks in [3].

I guess [2] and [3] are really independent of one another
and can be done in either order, correct?

[2] will help to make 32-bit kernels work correctly on file systems
that already support 64-bit timestamps internally, while [3] helps
sanitize the behavior of file systems that cannot support that
and that otherwise behave in unexpected ways on both 32-bit and
64-bit architectures.

	Arnd