Re: [Y2038] [RFC v2] vfs 64 bit time transition proposals

From	Arnd Bergmann <arnd@arndb.de>
Newsgroups	linux.kernel
Subject	Re: [Y2038] [RFC v2] vfs 64 bit time transition proposals
Date	2016-02-12 15:10 +0100
Message-ID	<r1mA2-847-7@gated-at.bofh.it> (permalink)
References	<r1id4-51c-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Friday 12 February 2016 01:21:59 Deepa Dinamani wrote:
> Introduction
> 
> This is a follow on to the series: https://lkml.org/lkml/2016/1/7/20 [1].
> This is aimed at reaching a consensus on how to transition the vfs
> timestamps to use 64 bit time. This demonstrates three ways (2a, 2b and
> 2c) of solving this problem.  Each of the proposals has its own cover
> letter that explains the individual approach.  Proposals 2b and 2c also
> outline variant approaches which are similar to the respective proposals.
> This drives the proposal count to 5.  All the changes have been discussed
> with Arnd Bergmann, who posted the original series:
> https://lkml.org/lkml/2014/5/30/669 [2]
> 
> The series has been simplified to include only the 64 bit timestamp
> changes as per Dave Chinner’s suggestion.
> 
> Motivation
> 
> The problem is how to change the vfs inode timestamps to use 64 bit
> times to overcome the 2038 problem.
> 
> Below table [3] gives an overview of the extent/ type of changes
> needed of changes needed.
> The series is aimed at obtaining small manageable patches for all
> the cases in [3].
> 

Hi Deepa,

Thanks a lot for posting this updated series, very nice work!

Regarding the three versions, I think all of them are doable
doable, and they all have their upsides and downsides but no
showstoppers.

Let me summarize what I see in the patches:

2a is the smallest set of changes in number of lines, as you indicated
   in the previous discussion (I was skeptical here initially, but
   you were right). The main downside is that each patch has to
   carefully consider what happens at the point when the type gets
   flipped, so that printk format strings are correct and assignments
   to local variables don't truncate the range. It also requires
   changing the types again after the VFS change, but that is
   something we can automate using coccinelle.

2b has the main advantage of not changing behavior with the flip, so
   we can convert all file systems to use vfs_time relatively easily
   and then later make them actually use 64-bit timestamps with
   a patch that each file system developer can do for themselves.
   One downside is that it leads to rather ugly code as discussed
   before, examples are in "[RFC v2b 5/5] fs: xfs: change inode
   times to use vfs_time data type" and "[RFC v2b 3/5] fs: btrfs:
   Use vfs_time accessors".

2c gets us the furthest along the way for the conversion, close
   to where we want to end up in the long run, so we could do that
   to file systems one by one. The behavior change is immediate,
   so there are fewer possible surprises than with 2a, but it
   also means the most upfront work.

	Arnd

Thread

[RFC v2] vfs 64 bit time transition proposals Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:30 +0100
  [RFC v2a 12/12] fs: xfs: change inode times to use vfs_time data type Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
  [RFC v2a 10/12] fs: ceph: Replace timespec data type with vfs_time Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
  [RFC v2a 06/12] fs: btrfs: Change btrfs_inode.i_otime to use vfs_time data type Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
  [RFC v2a 02/12] fs: cifs: Change cifs_fscache_inode_auxdata to use vfs_time data type Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
  [RFC v2a 09/12] fs: ceph: Change encode and decode functions to use vfs_time Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
  [RFC v2a 04/12] fs: cifs: Make cnvrtDosUnixTm() y2038 safe Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
  [RFC v2a 05/12] fs: cifs: Use vfs_time_get_real_* time functions Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
  [RFC v2a 00/12] vfs 64 bit time transition proposal Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
    [RFC v2a 11/12] net: ceph: use vfs_time data type instead of timespec Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
      Re: [RFC v2a 11/12] net: ceph: use vfs_time data type instead of  timespec Dave Chinner <david@fromorbit.com> - 2016-02-13 23:10 +0100
        Re: [RFC v2a 11/12] net: ceph: use vfs_time data type instead of timespec Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-14 02:50 +0100
          Re: [RFC v2a 11/12] net: ceph: use vfs_time data type instead of timespec Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-14 03:10 +0100
          Re: [RFC v2a 11/12] net: ceph: use vfs_time data type instead of  timespec Dave Chinner <david@fromorbit.com> - 2016-02-14 22:10 +0100
            Re: [RFC v2a 11/12] net: ceph: use vfs_time data type instead of timespec Arnd Bergmann <arnd@arndb.de> - 2016-02-17 10:40 +0100
    [RFC v2a 07/12] fs: btrfs: Use vfs_time data type for btrfs_update_time() Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
    [RFC v2a 08/12] fs: btrfs: Change timespec data types to use vfs_time Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:40 +0100
    [RFC v2a 03/12] fs: cifs: Change cifs_fattr timestamps data type to vfs_time Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:50 +0100
    [RFC v2a 01/12] vfs: Add vfs_time abstractions Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:50 +0100
  [RFC v2b 4/5] fs: ceph: Use vfs timestamp accessors Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:50 +0100
  [RFC v2b 2/5] fs: cifs: Use vfs_time accessors Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:50 +0100
  [RFC v2b 3/5] fs: btrfs: Use vfs_time accessors Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:50 +0100
    Re: [RFC v2b 3/5] fs: btrfs: Use vfs_time accessors Arnd Bergmann <arnd@arndb.de> - 2016-02-12 15:00 +0100
      Re: [RFC v2b 3/5] fs: btrfs: Use vfs_time accessors Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-13 08:10 +0100
  [RFC v2b 0/5] vfs 64 bit time transition proposal Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:50 +0100
    [RFC v2b 1/5] vfs: Add vfs_time accessors Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 10:50 +0100
    [RFC v2b 5/5] fs: xfs: change inode times to use vfs_time data type Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
      Re: [RFC v2b 5/5] fs: xfs: change inode times to use vfs_time data  type Dave Chinner <david@fromorbit.com> - 2016-02-13 03:20 +0100
        Re: [Y2038] [RFC v2b 5/5] fs: xfs: change inode times to use vfs_time data type Arnd Bergmann <arnd@arndb.de> - 2016-02-13 16:00 +0100
          Re: [Y2038] [RFC v2b 5/5] fs: xfs: change inode times to use vfs_time  data type "David F." <df7729@gmail.com> - 2016-02-13 17:00 +0100
  [RFC v2c 8/8] fs: xfs: change inode times to use vfs_time data type Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
  [RFC v2c 2/8] fs: cifs: Change auxdata to struct timespec64 data type Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
  [RFC v2c 1/8] vfs: Add vfs_time abstractions Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
  [RFC v2c 4/8] fs: cifs: Make cnvrtDosUnixTm() y2038 safe Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
  [RFC v2c 6/8] fs: btrfs: Use vfs timestamp abstraction helper Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
  [RFC v2c 5/8] fs: btrfs: Change btrfs_inode.i_otime to vfs_time data type Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
  [RFC v2c 3/8] fs: cifs: Change cifs_fattr timestamps data type to timespec64 Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
  [RFC v2c 0/8] vfs 64 bit time transition proposal Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
    [RFC v2c 7/8] fs: ceph: Use vfs timestamp abstraction helpers Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-12 11:00 +0100
  Re: [Y2038] [RFC v2] vfs 64 bit time transition proposals Arnd Bergmann <arnd@arndb.de> - 2016-02-12 15:10 +0100
    Re: [Y2038] [RFC v2] vfs 64 bit time transition proposals Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-13 08:00 +0100
      [RFC v2] vfs 64 bit time transition proposals Deepa Dinamani <deepa.kernel@gmail.com> - 2016-02-13 13:00 +0100

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