[PATCHv9 0/4] ref namespaces

This series adds support for dividing the refs of a single repository into multiple namespaces, each of which can have its own branches, tags, and HEAD. Git can expose each namespace as an independent repository to pull from and push to, while sharing the object store, and exposing all the refs to operations such as git-gc.

Storing multiple repositories as namespaces of a single repository avoids storing duplicate copies of the same objects, such as when storing multiple branches of the same source. The alternates mechanism provides similar support for avoiding duplicates, but alternates do not prevent duplication between new objects added to the repositories without ongoing maintenance, while namespaces do.

The first patch improves the prefix handling in the ref iteration functions, making it possible for us to implement for_each_namespaced_ref later. The next two patches implement and then use infrastructure for tracking the current namespace and iterating over the refs in that namespace. The last patch adds general documentation for namespaces, and specific references from the documentation on receive-pack, upload-pack, http-backend, and git.

v9: Fix a regression in alternatives handling, introduced in patch 3: the ref filtering also filtered out the ".have" refs added by receive-pack to announce refs provided by alternates. In the process of fixing this, also announce any refs outside the current namespace as ".have" refs, to allow the client to use those for minimal transfer as well. Also, remove patch attribution in commit messages as requested by Junio C Hamano. Finally, attempt to change the commit message style to more closely match Git's preferred style; further feedback welcome on any other desired changes to the commit message style.

Josh Triplett (4):
  Fix prefix handling in ref iteration functions
  ref namespaces: infrastructure
  ref namespaces: Support remote repositories via upload-pack and
    receive-pack
  ref namespaces: documentation

 Documentation/Makefile                 |    2 +-
 Documentation/git-http-backend.txt     |    8 +++
 Documentation/git-receive-pack.txt     |    2 +-
 Documentation/git-upload-pack.txt      |    4 ++
 Documentation/git.txt                  |   13 +++++-
 Documentation/gitnamespaces.txt        |   75 ++++++++++++++++++++++++++++++++
 builtin/receive-pack.c                 |   37 +++++++++++++---
 cache.h                                |    3 +
 contrib/completion/git-completion.bash |    3 +-
 environment.c                          |   41 +++++++++++++++++
 git.c                                  |   18 +++++++-
 refs.c                                 |   33 ++++++++++++--
 refs.h                                 |    3 +
 upload-pack.c                          |   15 +++---
 14 files changed, 233 insertions(+), 24 deletions(-)
 create mode 100644 Documentation/gitnamespaces.txt