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[xfs-masters] Re: potential xfs_repair bug

To: xfs-masters@xxxxxxxxxxx
Subject: [xfs-masters] Re: potential xfs_repair bug
From: Nathan Scott <nathans@xxxxxxx>
Date: Fri, 3 Sep 2004 10:52:38 +1000
Cc: Junfeng Yang <yjf@xxxxxxxxxxxx>
In-reply-to: <41378D8F.4020708@xxxxxxx>
References: <Pine.GSO.4.44.0409021340120.15188-100000@xxxxxxxxxxxxxxxxxxxxx> <41378D8F.4020708@xxxxxxx>
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Hi guys,

On Thu, Sep 02, 2004 at 04:15:59PM -0500, Steve Lord wrote:
> Junfeng Yang wrote:
> > 
> >>>I suspect what you are doing with this change is making repair fail
> >>>in the middle of creating the lost+found dir, repair always does that.
> >>>
> > 
> > 
> > you mean xfs_repair creates lost+found everytime it runs?  I'm not sure if

Thats correct.

> > the crash happens in the middling of creating lost+found, as our checker

For a clean filesystem, I think the only writes will be the log
zeroing and the creation of lost+found.

> > only sees block writes with little file system knowledge.  We caught this
> > warning automatically (w/o chaing the xfs_repair code).
> > 
> > so is it true that in the rare case that xfs_repair fails in the middle of
> > creating lost+found, '/.' can be wiped off?  do you guys consider this as
> > a bug?
> Well, I don't work on xfs anymore really, I just watch from the sidelines.
> It is a pretty small window in reality, but it probably says that while
> repair is running the filesystem is vulnerable to machine outages.
> Getting repair out of that hole would be a big job I suspect. It would

Yep.

> need to implement a journal and do all its work that way. Hmm, I cannot
> remember if it actually does that for the most part to be honest.

Nope, not even in libsim on IRIX. Only some of the xfs_log_*
routines exist there, mainly the ones needed for xfs_logprint,
the rest are stubbed out.

Even if it implemented the log, we'd then have to start doing all
writes O_SYNC (ouch), and other little things like that I suspect
(a pinnable buffer cache in userspace, etc?).  Hmmm.

cheers.

-- 
Nathan

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