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Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts()

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On Fri, Jun 2, 2017 at 2:18 PM, Yan, Zheng <ukernel@gmail.com> wrote:
> On Fri, Jun 2, 2017 at 7:33 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Fri, Jun 2, 2017 at 1:18 PM, Yan, Zheng <ukernel@gmail.com> wrote:
>> What I meant is another related problem in ceph_mkdir() where the
>> i_ctime field of the parent inode is different between the persistent
>> representation in the mds and the in-memory representation.
>>
>
> I don't see any problem in mkdir case. Parent inode's i_ctime in mds is set to
> r_stamp. When client receives request reply, it set its in-memory inode's ctime
> to the same time stamp.

Ok, I see it now, thanks for the clarification. Most other file systems do this
the other way round and update all fields in the in-memory inode structure
first and then write that to persistent storage, so I was getting confused about
the order of events here.

If I understand it all right, we have three different behaviors in ceph now,
though the differences are very minor and probably don't ever matter:

- in setattr(), we update ctime in the in-memory inode first and then send
  the same time to the mds, and expect to set it again when the reply comes.

- in ceph_write_iter write() and mmap/page_mkwrite(), we call
  file_update_time() to set i_mtime and i_ctime to the same
  timestamp first once a write is observed by the fs and then take
  two other timestamps that we send to the mds, and update the
  in-memory inode a second time when the reply comes. ctime
  is never older than mtime here, as far as I can tell, but it may
  be newer when the timer interrupt happens between taking the
  two stamps.

- in all other calls, we only update the inode (and/or parent inode)
  after the reply arrives.

       Arnd

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Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() "Yan, Zheng" <ukernel@gmail.com> - 2017-06-01 12:00 +0200
  Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() Arnd Bergmann <arnd@arndb.de> - 2017-06-01 12:30 +0200
    Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() "Yan, Zheng" <ukernel@gmail.com> - 2017-06-02 02:30 +0200
      Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() John Stultz <john.stultz@linaro.org> - 2017-06-02 02:40 +0200
        Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() Deepa Dinamani <deepa.kernel@gmail.com> - 2017-06-02 03:00 +0200
          Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() "Yan, Zheng" <ukernel@gmail.com> - 2017-06-02 04:20 +0200
            Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() Arnd Bergmann <arnd@arndb.de> - 2017-06-02 11:50 +0200
              Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() "Yan, Zheng" <ukernel@gmail.com> - 2017-06-02 12:20 +0200
                Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() Arnd Bergmann <arnd@arndb.de> - 2017-06-02 13:00 +0200
                Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() "Yan, Zheng" <ukernel@gmail.com> - 2017-06-02 13:20 +0200
                Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() Arnd Bergmann <arnd@arndb.de> - 2017-06-02 13:40 +0200
                Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() "Yan, Zheng" <ukernel@gmail.com> - 2017-06-02 14:20 +0200
                Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() Arnd Bergmann <arnd@arndb.de> - 2017-06-02 16:20 +0200
                Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() "Yan, Zheng" <ukernel@gmail.com> - 2017-06-04 10:00 +0200
    Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() "Yan, Zheng" <ukernel@gmail.com> - 2017-06-02 02:40 +0200

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