linux-kernel - Re: POSIX violation by writeback error

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Message-ID: <20180905124646.GR17123@BitWizard.nl>
Date:   Wed, 5 Sep 2018 14:46:46 +0200
From:   Rogier Wolff <R.E.Wolff@...Wizard.nl>
To:     "Austin S. Hemmelgarn" <ahferroin7@...il.com>
Cc:     焦晓冬 <milestonejxd@...il.com>,
        martin@...htvoll.de, jlayton@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: POSIX violation by writeback error

On Wed, Sep 05, 2018 at 08:07:25AM -0400, Austin S. Hemmelgarn wrote:
> On 2018-09-05 04:37, 焦晓冬 wrote:

> >At this point, the /bin/sh may be partially old and partially new. Execute
> >this corrupted bin is also dangerous though.

> But the system may still be usable in that state, while returning an
> error there guarantees it isn't.  This is, in general, not the best
> example though, because no sane package manager directly overwrites
> _anything_, they all do some variation on replace-by-rename and call
> fsync _before_ renaming, so this situation is not realistically
> going to happen on any real system.

Again, the "returning an error guarantees it isn't" is what's
important here. A lot of scenarios exist where it is a slightly less
important file than "/bin/sh" that would trigger such a comiplete
system failure. But there are a whole lot of files that can be pretty
critical for a system where "old value" is better than "all programs
get an error now". So when you propose "reads should now return error", 
you really need to think things through. 

It is not enough to say: But I encountered a situation where returning
an error was preferable, you need to think through the counter-cases
that others might run into that would make the "new" situation worse
than before.

	Roger. 

-- 
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