packfile: carve out a new packfile store

Hi,

information about a object database's packfiles is currently distributed across two different structures:

• struct packed_git contains the next pointer as well as the mru_head, both of which serve to store the list of packfiles.

• struct object_database contains several fields that relate to the packfiles.

So we don't really have a central data structure that tracks our packfiles, and consequently responsibilities aren't always clear cut. A consequence for the upcoming pluggable object databases is that this makes it very hard to move management of packfiles from the object database level down into the object database source.

This patch series introduces a new struct packfile_store, which is about to become the single source of truth for managing packfiles, and carves out the packfile store subsystem.

This is the first step to make packfiles work with pluggable object databases. Next steps will be to:

• Move the struct packed_git::next and struct packed::mru_head pointers into the packfile store so that struct packed_git only tracks a single packfile.

• Push the struct packfile_store down one level so that it's not hosted by the object database anymore, but instead by the object database source.

Thanks!

Patrick

To: git@vger.kernel.org

--- b4-submit-tracking ---

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{ "series": { "revision": 1, "change-id": "20250806-b4-pks-packfiles-store-a44a608ca396", "prefixes": [] } }

Part of Move packfile-related state out of `struct obje... (#547). Implements Compartmentalize packfile store (#599 - closed).