[PATCH 0/8] packfiles: track pack lists via the packfile store

[Patrick Steinhardt <ps@pks.im>]

Hi,

while the recently-introduced packfile store tracks the head of the pack
lists, the actual lists themselves are still stored in a globally linked
list via the `struct packed_git::next` pointer. This makes it quite hard
to split up that list into per-object-source lists, as the assumption is
embedded in many places that one packfile will identify all the others.

This patch series thus moves the ownership of the lists into the
packfile store. This prepares us for a subsequent change where we can
push the packfile store one level down, from the object database into
the object source. So this is the second-last series before I'm done
refactoring the packfile subsystem.

Note: I'd like to have some extra careful eyes on the last patch. This
patch merges the two packfile lists we currently have (MRU and
mtime-sorted). It is not needed to achieve my goal in this series, but
there was some discussion around whether we really need both lists. I
don't think we do, and in fact I think it causes confusion which of
these one should really use.

The default is to use the mtime-sorted list, which I think is the wrong
choice in many cases, but that is only by gut feeling. So I'm dropping
that list in favor of the MRU list, but there is one gotcha here: when
iterating through packfiles and then reading their respective objects,
we end up in an infinite loop because we end up moving the respective
packfile to the front of the list again. I'm fixing that with a new
field that skips the MRU update, but I'm not quite sure wheter I think
that this is too fragile or not.

The series is built on top of 419c72cb8a (Sync with Git 2.51.2,
2025-10-26) with ps/remove-packfile-store-get-packs at ecad863c12
(packfile: rename `packfile_store_get_all_packs()`, 2025-10-09) merged
into it.

Thanks!

Patrick

---
Patrick Steinhardt (8):
      packfile: use a `strmap` to store packs by name
      packfile: move the MRU list into the packfile store
      http: refactor subsystem to use `packfile_list`s
      packfile: fix approximation of object counts
      builtin/pack-objects: simplify logic to find kept or nonlocal objects
      packfile: move list of packs into the packfile store
      packfile: always add packfiles to MRU when adding a pack
      packfile: track packs via the MRU list exclusively

 builtin/fast-import.c  |   4 +-
 builtin/pack-objects.c |  35 ++++----
 http-push.c            |   6 +-
 http-walker.c          |  26 ++----
 http.c                 |  21 ++---
 http.h                 |   5 +-
 midx.c                 |   2 -
 packfile.c             | 224 +++++++++++++++++++++++++++++--------------------
 packfile.h             |  70 ++++++++++------
 9 files changed, 222 insertions(+), 171 deletions(-)


---
base-commit: cad6ef1d7514e7450c04c2fe624a55b28d99ac88
change-id: 20251010-pks-packfiles-store-drop-list-64ea0a4c9a3b