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From: Michael Haggerty <mhagger@alum.mit.edu>
To: Jeff King <peff@peff.net>
Cc: Dmitry Neverov <dmitry.neverov@gmail.com>, git@vger.kernel.org
Subject: Re: Git gc removes all packs
Date: Tue, 17 Feb 2015 21:37:41 +0100	[thread overview]
Message-ID: <54E3A695.1050708@alum.mit.edu> (raw)
In-Reply-To: <20150217165514.GA12176@peff.net>

On 02/17/2015 05:55 PM, Jeff King wrote:
> On Tue, Feb 17, 2015 at 05:39:27PM +0100, Michael Haggerty wrote:
> 
>>> You can't symlink refs like this. The loose refs in the filesystem may
>>> be migrated into the "packed-refs" file, at which point your symlink
>>> will be broken. That is a likely reason why git would not find any refs.
>>>
>>> So your setup will not ever work reliably.  But IMHO, it is a bug that
>>> git does not notice the broken symlink and abort an operation which is
>>> computing reachability in order to drop objects. As you noticed, it
>>> means a misconfiguration or filesystem error results in data loss.
>>
>> There's a bunch of code in refs.c that is there explicitly for reading
>> loose references that are symlinks. If the link contents literally start
>> with "refs/", then they are read and treated as a symbolic ref.
>> Otherwise, the symlink is just followed.
> 
> Right, but we should be able to notice that:
> 
>   1. We found a symlink.
> 
>   2. We couldn't read it its ref value (because it's a broken link).
> 
> I think we _do_ notice that at the lowest level, and set REF_ISBROKEN.
> But the problem is that the reachability code in prune and in
> pack-objects (triggered by "repack -ad") uses for_each_ref, and not
> for_each_rawref. So they ignore "broken" refs rather than complaining,
> even though failing to read a ref may mean we could drop objects which
> were only mentioned by that ref.

Yes, this makes sense too. But my point was that sticking symlinks to
random files in your refs hierarchy is pretty questionable even *before*
the symlink gets broken. If we would warn the user as soon as we saw
such a thing, then the user's problem would never have advanced as far
as it did. Do you think that emitting warnings on *intact* symlinks is
too draconian?

> [...]

Michael

-- 
Michael Haggerty
mhagger@alum.mit.edu

  reply	other threads:[~2015-02-17 20:37 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-05 15:13 Git gc removes all packs Dmitry Neverov
2015-02-05 20:03 ` Jeff King
2015-02-17 16:39   ` Michael Haggerty
2015-02-17 16:55     ` Jeff King
2015-02-17 20:37       ` Michael Haggerty [this message]
2015-02-17 21:57         ` Junio C Hamano
2015-02-17 22:19           ` Michael Haggerty
2015-02-18  7:13             ` Junio C Hamano
2015-02-27 10:16   ` Dmitry Neverov
2015-02-27 13:14     ` Jeff King

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