bitbake: fetch/git: add support for shallow mirror tarballs

This adds support to the git fetcher for fetching, using, and generating
mirror tarballs of shallow git repositories. The external git-make-shallow
script is used for shallow mirror tarball creation.

This implements support for shallow mirror tarballs, not shallow clones.
Supporting shallow clones directly is not really doable for us, as we'd need
to hardcode the depth between branch HEAD and the SRCREV, and that depth would
change as the branch is updated.

When BB_GIT_SHALLOW is enabled, we will always attempt to fetch a shallow
mirror tarball. If the shallow mirror tarball cannot be fetched, it will try
to fetch the full mirror tarball and use that. If a shallow tarball is to be
used, it will be unpacked directly at `do_unpack` time, rather than extracting
it to DL_DIR at `do_fetch` time and cloning from there, to keep things simple.
There's no value in keeping a shallow repository in DL_DIR, and dealing with
the state for when to convert the clonedir to/from shallow is not worthwhile.

To clarify when shallow is used vs a real repository, a current clone is
preferred to either tarball, a shallow tarball is preferred to an out of date
clone, and a missing clone will use either tarball (attempting the shallow one
first).

All referenced branches are truncated to SRCREV (that is, commits *after*
SRCREV but before HEAD are removed) to further shrink the repository. By
default, the shallow construction process removes all unused refs
(branches/tags) from the repository, other than those referenced by the URL.

Example usage:

    BB_GIT_SHALLOW ?= "1"

    # Keep only the top commit
    BB_GIT_SHALLOW_DEPTH ?= "1"

    # This defaults to enabled if both BB_GIT_SHALLOW and
    # BB_GENERATE_MIRROR_TARBALLS are enabled
    BB_GENERATE_SHALLOW_TARBALLS ?= "1"

(Bitbake rev: 5ed7d85fda7c671be10ec24d7981b87a7d0d3366)

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions