linux-kernel - Re: [PATCH 09/10] fs: ceph: Replace CURRENT_TIME by ktime_get_real

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Message-Id: <A70D88EB-6B14-4553-9C9D-88D54F7BA689@redhat.com>
Date:	Thu, 4 Feb 2016 10:00:19 +0800
From:	"Yan, Zheng" <zyan@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Deepa Dinamani <deepa.kernel@...il.com>,
	Zheng Yan <ukernel@...il.com>, linux-fsdevel@...r.kernel.org,
	y2038@...ts.linaro.org, Dave Chinner <david@...morbit.com>,
	"Theodore Ts'o" <tytso@....edu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sage Weil <sage@...hat.com>, Ilya Dryomov <idryomov@...il.com>,
	ceph-devel <ceph-devel@...r.kernel.org>
Subject: Re: [PATCH 09/10] fs: ceph: Replace CURRENT_TIME by ktime_get_real_ts()


> On Feb 4, 2016, at 05:27, Arnd Bergmann <arnd@...db.de> wrote:
> 
> On Wednesday 03 February 2016 08:17:23 Deepa Dinamani wrote:
>> On Wed, Feb 03, 2016 at 10:34:00PM +0800, Yan, Zheng wrote:
>>> On Wed, Feb 3, 2016 at 2:07 PM, Deepa Dinamani <deepa.kernel@...il.com> wrote:
>>>> --- a/fs/ceph/mds_client.c
>>>> +++ b/fs/ceph/mds_client.c
>>>> @@ -1721,7 +1721,7 @@ ceph_mdsc_create_request(struct ceph_mds_client *mdsc, int op, int mode)
>>>>        init_completion(&req->r_safe_completion);
>>>>        INIT_LIST_HEAD(&req->r_unsafe_item);
>>>> 
>>>> -       req->r_stamp = CURRENT_TIME;
>>>> +       ktime_get_real_ts(&req->r_stamp);
>>> 
>>> I think we should use current_fs_time() here. I have squash the change
>>> into another patch
>> 
>> Ok. I missed this commit b8e69066d8afa8d2670dc697252ff0e5907aafad
>> earlier which says that the r_stamp is used as ctime now.
>> I had assumed that this is a message timestamp.
>> 
>> I was not able to find any documentation on what the server does
>> with the message sent by the client. Where can I find that?
>> 
>> So, this should actually look like
>> 
>> req->r_stamp = current_fs_time(mdsc->fsc->sb);
>> 
>> Let me know if you want me to resend.

I have already squashed the change into patch 8

> 
> I see that the timestamp is sent using
> 
> 	ceph_encode_copy(&p, &req->r_stamp, sizeof(req->r_stamp));

this code is outdated, current code is:

{
          struct ceph_timespec ts;
          ceph_encode_timespec(&ts, &req->r_stamp);
          ceph_encode_copy(&p, &ts, sizeof(ts));
}
> 
> What happens with the timestamp across reboots if we change the
> type? I assume the data will not be used across reboots, if it
> does, we already have a problem on machines that can boot
> both big-endian and little-endian kernels, or that can boot
> both 32-bit and 64-bit kernels.
> 
> 	Arnd