On 04/07/2016 03:02 PM, David Turner wrote: > We now have quite a large number of patches before we even get into > the meat of the pluggable refs backend series. So it's worth breaking > those out and getting them in before we get into the main series > (which Michael Haggerty swants to redesign a bit anyway). > > This set of patches should be applied on top of > jk/check-repository-format. > > Michael Haggerty has reviewed those of my patches which are in here > except maybe: > refs: on symref reflog expire, lock symref not referrent > This was the one from later in the series that was straightforward to > move to before the vtable; the other two were going to be harder to > move and can wait until after the vtable.
This last patch deserves a little bit of discussion. Currently, when the reflog of a symref is expired, the pointed-to ref is locked rather than the symref. This patch changes the code to lock the symref instead. This is clearly the right thing to do, and I consider this change a bug fix. However, it introduces an incompatibility. An old version of `git reflog expire` and a new version wouldn't agree on the locking protocol, and could potentially try to overwrite the same reflog at the same time. I think this risk is acceptable nevertheless, because expiring reflogs is an uncommon operation and unlikely to be done from two processes at the same time; moreover, the integrity of reflogs is not a matter of life or death. A far more likely conflict would be between a reflog expiration and a symref update (e.g., `git checkout otherbranch`). This use case is currently *broken* because `git checkout` locks HEAD. It would be fixed by this patch. If somebody is really upset about the risk of a race between an old and new version of `git reflog expire`, the way to increase the safety would be to lock *both* the symref and the referent while changing the symref's reflog. I think that would be overkill. This whole series is Reviewed-by: Michael Haggerty <mhag...@alum.mit.edu> David mentioned that I want to redesign the vtable patches somewhat. Anybody who is curious can look at the work in progress branch on my GitHub fork [1], branch wip/ref-storage. Michael [1] https://github.com/mhagger/git -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
