Re: [PATCH v2 0/7] odb: track multi-pack-indices via their object sources

> Hi,
> 
> multi-pack-indices are tracked via `struct multi_pack_index`. This data
> structure is stored inside `struct object_database`, which is the global
> database that spans across all of the object sources
> 
> This layout causes two problems:
> 
>   - Multi-pack indices aren't global to an object database, but instead
>     there can be one multi-pack index per object source. This creates a
>     mismatch between the on-disk layout and how things are organized in
>     the object database subsystems and makes some parts, like figuring
>     out whether an object source has an MIDX, quite awkward.
> 
>   - Multi-pack indices are an implementation detail of how efficient
>     access for packfiles work. As such, they are neither relevant in the
>     context of loose objects, nor in a potential future where we have
>     pluggable backends.
> 
> This patch series thus refactors the codebase to stop tracking MIDX's
> globally. Instead, they are being pushed down one level so that every
> `struct odb_source` has an optional MIDX itself. This simplifies some of
> our code and will make it easier in a future iteration to move the data
> into a packfile-specific object source backend.
> 
> Changes in v2:
>   - Changed the base of this series. It is now built on top of
>     a30f80fde92 (The eighth batch, 2025-07-08) with "ps/object-store" at
>     841a03b4046 (odb: rename `read_object_with_reference()`, 2025-07-01)
>     and "tb/midx-avoid-cruft-packs" at 5ee86c273bf (repack: exclude
>     cruft pack(s) from the MIDX where possible, 2025-06-23) merged into
>     it.
>   - Re-explain the split between object databases and object sources
>     to help readers out a bit, given that this is a rather recent
>     change.
>   - Rename `struct odb_source::multi_pack_index` to `struct
>     odb_source::midx`.
>   - Fix some overly long lines when looping through the individual
>     sources.
>   - Drop the patch that guards re-loading MIDXs, as we already have the
>     guard via `packed_git_initialized`.
>   - Remove some while-at-it changes to make the diffs easier to read.
>   - Link to v1: https://lore.kernel.org/r/20250709-b4-pks-midx-via-odb-alternate-v1-0-f31150d21331@pks.im