Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 4 Sep 2018 09:53:47 +0200
From:   Rogier Wolff <R.E.Wolff@BitWizard.nl>
To:     =?utf-8?B?54Sm5pmT5Yas?= <milestonejxd@gmail.com>
Cc:     jlayton@redhat.com, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: POSIX violation by writeback error
Message-ID: <20180904075347.GH11854@BitWizard.nl>
References: <CAJDTihz-rFb2SGaxZsQnXGnee_2qW_ynhPe=tZ4yzQBSV_KQ1g@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CAJDTihz-rFb2SGaxZsQnXGnee_2qW_ynhPe=tZ4yzQBSV_KQ1g@mail.gmail.com>
Organization: BitWizard B.V.
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Sep 04, 2018 at 02:32:28PM +0800, 焦晓冬 wrote:
> Hi,
> 
> After reading several writeback error handling articles from LWN, I
> begin to be upset about writeback error handling.
> 
> Jlayton's patch is simple but wonderful idea towards correct error
> reporting. It seems one crucial thing is still here to be fixed. Does
> anyone have some idea?
> 
> The crucial thing may be that a read() after a successful
> open()-write()-close() may return old data.
> 
> That may happen where an async writeback error occurs after close()
> and the inode/mapping get evicted before read().

Suppose I have 1Gb of RAM. Suppose I open a file, write 0.5Gb to it
and then close it. Then I repeat this 9 times. 

Now, when writing those files to storage fails, there is 5Gb of data
to remember and only 1Gb of RAM. 

I can choose any part of that 5Gb and try to read it. 

Please make a suggestion about where we should store that data?

In the easy case, where the data easily fits in RAM, you COULD write a
solution. But when the hardware fails, the SYSTEM will not be able to
follow the posix rules. 

	Roger. 

-- 
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
**    Delftechpark 26 2628 XH  Delft, The Netherlands. KVK: 27239233    **
*-- BitWizard writes Linux device drivers for any device you may have! --*
The plan was simple, like my brother-in-law Phil. But unlike
Phil, this plan just might work.