[PATCH 00/16] odb: introduce "inmemory" source

[Patrick Steinhardt <ps@pks.im>]

Hi,

this patch series introduces the second object database source type,
which is the "inmemory" source.

This source may seem somewhat odd at first: it always starts out empty,
and any object written into it will only exist in memory until the
process exits. But the source already serves a purpose in our codebase,
where some commands, for example git-blame(1), write an in-memory
worktree commit.

Furthermore, I think that going forward it can serve more purposes as we
now have an easy way to write and read objects that will not get
persisted. I could see that this may be useful when for example
re-merging diffs. But eventually, once we have the object storage format
extension wired up, callers might even want to manually set up an
in-memory database as the primary ODB for write operations so that no
data will be persisted in an arbitrary write.

Last but not least, this patch series also serves the purpose of
eventually getting rid of the `struct object_info::whence` member.
Instead, we'll simply yield the ODB source a specific object has been
read from, together with some backend-specific data, which gives
strictly more information compared to the status quo.

The series is based on cf2139f8e1 (The 24th batch, 2026-04-01) with
ps/odb-cleanup at 109bcb7d1d (odb: drop unneeded headers and forward
decls, 2026-04-01) merged into it.

Thanks!

Patrick

---
Patrick Steinhardt (16):
      odb: introduce "inmemory" source
      odb/source-inmemory: implement `free()` callback
      odb: fix unnecessary call to `find_cached_object()`
      odb/source-inmemory: implement `read_object_info()` callback
      odb/source-inmemory: implement `read_object_stream()` callback
      odb/source-inmemory: implement `write_object()` callback
      odb/source-inmemory: implement `write_object_stream()` callback
      cbtree: allow using arbitrary wrapper structures for nodes
      oidtree: add ability to store data
      odb/source-inmemory: convert to use oidtree
      odb/source-inmemory: implement `for_each_object()` callback
      odb/source-inmemory: implement `find_abbrev_len()` callback
      odb/source-inmemory: implement `count_objects()` callback
      odb/source-inmemory: implement `freshen_object()` callback
      odb/source-inmemory: stub out remaining functions
      odb: generic inmemory source

 Makefile                 |   1 +
 cbtree.c                 |  25 +++-
 cbtree.h                 |  11 +-
 loose.c                  |   2 +-
 meson.build              |   1 +
 object-file.c            |   3 +-
 odb.c                    |  82 ++---------
 odb.h                    |   4 +-
 odb/source-inmemory.c    | 375 +++++++++++++++++++++++++++++++++++++++++++++++
 odb/source-inmemory.h    |  33 +++++
 odb/source.h             |   3 +
 oidtree.c                |  66 ++++++---
 oidtree.h                |  12 +-
 t/unit-tests/u-oidtree.c |  26 +++-
 14 files changed, 529 insertions(+), 115 deletions(-)


---
base-commit: 3d05c3e2906489caa9f12f0af18dc233a6b8032c
change-id: 20260401-b4-pks-odb-source-inmemory-7b17c83d9e43