From: Junio C Hamano <gitster@pobox.com>
Date: Wed, 19 Aug 2026 18:21:03 GMT
Subject: Re: [PATCH 2/2] packfile: recover when a multi-pack-index names a removed pack
Message-ID: <xmqqbjayug34.fsf@gitster.g>
In-Reply-To: <5792c08f4ee0f9627ab1432d91299fe676e0a2f5.1787092446.git.gitgitgadget@gmail.com>

"Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> @@ -31,6 +31,35 @@ static int find_pack_entry(struct odb_source_packed *store,
>  		}
>  	}
>  
> +	/*
> +	 * Recovery for a concurrent-repack race: a MIDX can name an owning
> +	 * pack for an object that a simultaneous repack has since deleted,
> +	 * even though the object still exists in another pack the same MIDX
> +	 * covers (e.g. a kept base pack that geometric repack did not rewrite).
> +	 * If the object is present in a MIDX yet none of the paths above could
> +	 * serve it, its recorded owning pack has become unavailable.  The
> +	 * regular fallback above deliberately skips MIDX-covered packs, so
> +	 * scan this MIDX's packs directly to find the surviving copy.  The
> +	 * bsearch gate keeps genuine misses (objects absent from the MIDX) on
> +	 * the fast path.
> +	 */
> +	if (store->midx) {
> +		struct multi_pack_index *m = store->midx;
> +		uint32_t midx_pos, i;
> +
> +		if (bsearch_midx(oid, m, &midx_pos)) {
> +			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))
> +					return 1;
> +			}
> +		}
> +	}
> +
>  	return 0;
>  }

I'll prepare an evil-merge to rewrite this line to

			if (p && packfile_fill_entry(p, oid, e, bad_pack))

to adjust to the API change another topic in-flight brings in when
merging these patches to 'seen'.

This is strictly FYI.  You do not need to rebase on top of the other
topic, until I and/or the author of the other topic ask you.

Thanks.