Re: Git gc removes all packs

[Michael Haggerty <mhagger@alum.mit.edu>]

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