Re: [PATCH v3 4/4] packfile: recover when a multi-pack-index names a removed pack

>
> On 8/29/2026 3:00 AM, Elijah Newren via GitGitGadget wrote:
> > From: Elijah Newren <newren@gmail.com>
>
> I'm late in reviewing this patch, so forgive me responding inline as
> I discover how it works.
>
> tl;dr: Good patch. LGTM.

> > +     /*
> > +      * Recovery for a concurrent-repack race: a stale MIDX may still name a
> > +      * vanished owning pack even though the object survives in another pack
> > +      * the same MIDX covers.  The regular fallback above skips MIDX-covered
> > +      * packs, and repreparing the on-disk pack set does not reload the
> > +      * borrowed, cached MIDX, so scan its packs directly for the survivor.
> > +      *
> > +      * Do this only on the second read, by which point repreparing packs has
> > +      * already had a chance to find an object merely relocated into a new,
> > +      * uncovered pack; only a genuine hidden duplicate reaches here.
> > +      */
>
> This comment does a lot of important context-setting to show
> that we are in a very narrow case: the stale MIDX has multiple
> packs that contain the requested object, but the "newer" one
> was deleted without creating a new packfile, so we need to
> look at each contained pack for the object from its pack-index.

> > +     if (midx_result == MIDX_FILL_OWNER_UNAVAILABLE &&
> > +         (flags & OBJECT_INFO_SECOND_READ)) {
> > +             struct multi_pack_index *m = store->midx;
> > +             uint32_t i;
> > +
> > +             for (i = 0; i < m->num_packs + m->num_packs_in_base; i++) {
> > +                     struct packed_git *p;
> > +
> > +                     if (prepare_midx_pack(m, i))
> > +                             continue;
> > +                     p = nth_midxed_pack(m, i);
> > +                     if (p && packfile_fill_entry(p, oid, e, bad_pack))
> > +                             return 1;
> > +             }
> > +     }
> > +
>
> This is hopefully a very rare case, but it's good to have
> this "fall back to O(num packs)" situation.