Re: [PATCH v3 0/7] Lazy fetch with subprocess

> 2:  00ad7dd875 = 2:  9f277f1631 fetch: allow refspecs specified through stdin
> 3:  8b4a522a13 ! 3:  fda9f834f6 fetch: avoid reading submodule config until needed
>     @@ Metadata
>       ## Commit message ##
>          fetch: avoid reading submodule config until needed
>      
>     -    Teach "git fetch" to avoid reading the submodule config until necessary.
>     -    This allows users to avoid the lazy-fetching of this potentially missing
>     -    config file by specifying the --recurse-submodules=no command line
>     -    option.
>     +    In "fetch", there are two parameters submodule_fetch_jobs_config and
>     +    recurse_submodules that can be set in a variety of ways: through
>     +    .gitmodules, through .git/config, and through the command line.
>     +    Currently "fetch" handles this by first reading .gitmodules, then
>     +    reading .git/config (allowing it to overwrite existing values), then
>     +    reading the command line (allowing it to overwrite existing values).
>     +
>     +    Notice that we can avoid reading .gitmodules if .git/config and/or the
>     +    command line already provides us with what we need. In addition, if
>     +    recurse_submodules is found to be "no", we do not need the value of
>     +    submodule_fetch_jobs_config.
>     +
>     +    Avoiding reading .gitmodules is especially important when we use "git
>     +    fetch" to perform lazy fetches in a partial clone because the
>     +    .gitmodules file itself might need to be lazy fetched (and otherwise
>     +    causing an infinite loop).
>     +
>     +    In light of all this, avoid reading .gitmodules until necessary. When
>     +    reading it, we may only need one of the two parameters it provides, so
>     +    teach fetch_config_from_gitmodules() to support NULL arguments. With
>     +    this patch, users (including Git itself when invoking "git fetch" to
>     +    lazy-fetch) will be able to guarantee avoiding reading .gitmodules by
>     +    passing --recurse-submodules=no.

> 4:  77bc83e7f2 ! 4:  a5554cd27f fetch: only populate existing_refs if needed
>     @@ Metadata
>       ## Commit message ##
>          fetch: only populate existing_refs if needed
>      
>     -    When fetching tags, Git only writes tags that do not already exist in
>     -    the client repository. This necessitates an iteration over all the refs,
>     -    but fetch performs this iteration even if no tags are fetched.
>     +    In "fetch", get_ref_map() iterates over all refs to populate
>     +    "existing_refs" in order to populate peer_ref->old_oid in the returned
>     +    refmap, even if the refmap has no peer_ref set - which is the case when
>     +    only literal hashes (i.e. no refs by name) are fetched.