linux-kernel - Re: [PATCH 18/21] fs: nfs: Make nfs boot time y2038 safe

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Message-ID: <CABeXuvoLr7amTYBs5AbMv15Vqx2CQib9F8Qr4GzX9RoZZ9ZnpQ@mail.gmail.com>
Date:	Thu, 9 Jun 2016 14:10:35 -0700
From:	Deepa Dinamani <deepa.kernel@...il.com>
To:	Trond Myklebust <trondmy@...marydata.com>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"y2038@...ts.linaro.org" <y2038@...ts.linaro.org>,
	Anna Schumaker <anna.schumaker@...app.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH 18/21] fs: nfs: Make nfs boot time y2038 safe

>>boot_time is represented as a struct timespec.
>>struct timespec and CURRENT_TIME are not y2038 safe.
>>Overall, the plan is to use timespec64 for all internal
>>kernel representation of timestamps.
>>CURRENT_TIME will also be removed.
>>Use struct timespec64 to represent boot_time.
>>And, ktime_get_real_ts64() for the boot_time value.
>>
>>boot_time is used to construct the nfs client boot verifier.
>>This will now wrap in 2106 instead of 2038 on 32-bit systems.
>>The server only relies on the value being persistent until
>>reboot so the wrapping should be fine.
>
> We really do not give a damn about wraparound here, since the boot time is
> only ever compared for an exact match, and the odds of two reboots occurring
> exactly 2^32 * 10^9 nanoseconds apart are cosmically small...
> If struct timespec is going away, can we just convert this into a ktime_t?

timespec64 is the same as timespec already on 64 bit machines.
But, yes, we can use ktime_t here.

Did you mean the internal storage value or the wire boo_time used for verifier?
In case you don't want to change the wire value, then we will have a division
operation, every time the verifier needs to be sent.

-Deepa

-Deepa