Re: Git gc removes all packs

From: Michael Haggerty <mhagger@alum.mit.edu>
Date: Feb 17, 2015, 22:19 UTC
Message-ID: <54E3BE8B.2040403@alum.mit.edu>
In-Reply-To: <xmqq7fvg19se.fsf@gitster.dls.corp.google.com>

On 02/17/2015 10:57 PM, Junio C Hamano wrote:

Show 24 quoted lines

> Michael Haggerty <mhagger@alum.mit.edu> writes:
> 
>> On 02/17/2015 05:55 PM, Jeff King wrote:
>>> On Tue, Feb 17, 2015 at 05:39:27PM +0100, Michael Haggerty wrote:
>>>
>>>> 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.
>>> ...
>> 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?
> 
> Do you mean that we would end up reading refs/heads/hold if the user
> did this:
> 
>     git rev-parse --verify HEAD -- >precious
>     ln -s ../../../precious .git/refs/heads/hold
> 
> because that symbolic link does not begin with "refs/",

Correct, you can do exactly that. The "hold" reference is resolvable and listable using "for-each-ref". But if I try to update it, the contents of the "precious" file are overwritten. On the other hand, if I run "pack-refs", then the current value of the "hold" reference is moved to "packed-refs" and the symlink is removed. This behavior is not sane.

> and is an
> accident waiting to happen so we should forbid it in the longer
> term and warning when we see it would be the first step?

Yes, I am proposing that approach, though if somebody can suggest a use case I'm willing to be convinced otherwise. The only thing I can imagine symlinks being useful for might be to temporarily create a fake repo, run one or two specific known-safe commands, then delete the repo again.

Michael

-- 
Michael Haggerty
mhagger@alum.mit.edu