linux-kernel - Re: POSIX violation by writeback error

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Message-ID: <20180904075347.GH11854@BitWizard.nl>
Date:   Tue, 4 Sep 2018 09:53:47 +0200
From:   Rogier Wolff <R.E.Wolff@...Wizard.nl>
To:     焦晓冬 <milestonejxd@...il.com>
Cc:     jlayton@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: POSIX violation by writeback error

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. 

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