Re: [PATCH] fetch-pack: support negotiation tip whitelist

[Junio C Hamano <gitster@pobox.com>]

Jonathan Tan <jonathantanmy@google.com> writes:

> During negotiation, fetch-pack eventually reports as "have" lines all
> commits reachable from all refs. Allow the user to restrict the commits
> sent in this way by providing a whitelist of tips; only the tips
> themselves and their ancestors will be sent.
>
> This feature is only supported for protocols that support connect or
> stateless-connect (such as HTTP with protocol v2).
>
> This will speed up negotiation when the repository has multiple
> relatively independent branches (for example, when a repository
> interacts with multiple repositories, such as with linux-next [1] and
> torvalds/linux [2]), and the user knows which local branch is likely to
> have commits in common with the upstream branch they are fetching.
>
> [1] https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next/
> [2] https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux/
>
> Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
> ---
> This is based on jt/fetch-pack-negotiator, but if that branch is
> undesirable for whatever reason, I can port this to master.
> ---
>  builtin/fetch.c    | 21 ++++++++++++++++++
>  fetch-pack.c       | 19 ++++++++++++++--
>  fetch-pack.h       |  7 ++++++
>  t/t5510-fetch.sh   | 55 ++++++++++++++++++++++++++++++++++++++++++++++
>  transport-helper.c |  3 +++
>  transport.c        |  1 +
>  transport.h        | 10 +++++++++
>  7 files changed, 114 insertions(+), 2 deletions(-)

What's the plan to expose this "feature" to end-users?  There is no
end-user facing documentation added by this patch, and in-code
comments only talk about what (mechanical) effect the option has,
but not when a user may want to use the feature, or how the user
would best decide the set of commits to pass to this new option.

Would something like this

    git fetch $(git for-each-ref \
	--format=--nego-tip="%(objectname)" \
	refs/remotes/linux-next/) \
	linux-next

be an expected typical way to pull from one remote, exposing only
the tips of refs we got from that remote and not the ones we
obtained from other places?