linux-kernel - Re: [PATCH] nanosecond filesystem support???

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Message-Id: <1171356179.12771.50.camel@laptopd505.fenrus.org>
Date:	Tue, 13 Feb 2007 09:42:59 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Jeff Chua <jeff.chua.linux@...il.com>
Cc:	Andi Kleen <ak@...e.de>, lkml <linux-kernel@...r.kernel.org>,
	Miquel van Smoorenburg <miquels@...tron.nl>,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [PATCH] nanosecond filesystem support???

On Tue, 2007-02-13 at 16:38 +0800, Jeff Chua wrote:
> On 2/12/07, Andi Kleen <ak@...e.de> wrote:
> 
> > The bigger problem is getting a file system that support it.
> 
> 
> Andi,
> 
> It seems that the part that's not returning nanosecond is in the code 
> below. I've modified it, and now stat() is returning st_mtim.tv_nsec 
> correctly.
> 
> I've tested it on ext2 and reiserfs, and both seems to be working.
> 
> 
> I don't know why "t.tv_nsec = 0;" was set in the code. Any idea?

it was there to avoid the following situation:

on disk it's still in seconds
kernel has the inode in memory, with a recently updated times
user asks for it, gets nanoseconds data
kernel evicts inode to disk
user asks again,
kernel reads from disk (in whole seconds only on disk)
kernel reports a DIFFERENT time than it did before
user program gets confused

this actually happens, make is one of those cases that get confused for
example..

-- 
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