Re: [PATCH 1/1] sha1-file: split OBJECT_INFO_FOR_PREFETCH

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

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Derrick Stolee <dstolee@microsoft.com>
>
> The OBJECT_INFO_FOR_PREFETCH bitflag was added to sha1-file.c in 0f4a4fb1
> (sha1-file: support OBJECT_INFO_FOR_PREFETCH, 2019-03-29) and is used to
> prevent the fetch_objects() method when enabled.
>
> However, there is a problem with the current use. The definition of
> OBJECT_INFO_FOR_PREFETCH is given by adding 32 to OBJECT_INFO_QUICK. This is
> clearly stated above the definition (in a comment) that this is so
> OBJECT_INFO_FOR_PREFETCH implies OBJECT_INFO_QUICK. The problem is that using
> "flag & OBJECT_INFO_FOR_PREFETCH" means that OBJECT_INFO_QUICK also implies
> OBJECT_INFO_FOR_PREFETCH.

So the right test to see prefetch is in effect is not

	if (!!(flag & TWO_BITS))

but to use

	if ((flag & TWO_BITS) == TWO_BITS)

instead?

> Split out the single bit from OBJECT_INFO_FOR_PREFETCH into a new
> OBJECT_INFO_SKIP_FETCH_OBJECT as the single bit and keep
> OBJECT_INFO_FOR_PREFETCH as the union of two flags. This allows a clearer use
> of flag checking while also keeping the implication of OBJECT_INFO_QUICK.

OK, I guess that would work and with far less damage to the existing
code.

>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  object-store.h | 10 +++++++---
>  sha1-file.c    |  2 +-
>  2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/object-store.h b/object-store.h
> index dd3f9b75f0..c90628d839 100644
> --- a/object-store.h
> +++ b/object-store.h
> @@ -282,10 +282,14 @@ struct object_info {
>  #define OBJECT_INFO_IGNORE_LOOSE 16
>  /*
>   * Do not attempt to fetch the object if missing (even if fetch_is_missing is
> - * nonzero). This is meant for bulk prefetching of missing blobs in a partial
> - * clone. Implies OBJECT_INFO_QUICK.
> + * nonzero).
>   */
> -#define OBJECT_INFO_FOR_PREFETCH (32 + OBJECT_INFO_QUICK)
> +#define OBJECT_INFO_SKIP_FETCH_OBJECT 32
> +/*
> + * This is meant for bulk prefetching of missing blobs in a partial
> + * clone. Implies OBJECT_INFO_SKIP_FETCH_OBJECT and OBJECT_INFO_QUICK
> + */
> +#define OBJECT_INFO_FOR_PREFETCH (OBJECT_INFO_SKIP_FETCH_OBJECT | OBJECT_INFO_QUICK)
>  
>  int oid_object_info_extended(struct repository *r,
>  			     const struct object_id *,
> diff --git a/sha1-file.c b/sha1-file.c
> index ad02649124..0299fdd516 100644
> --- a/sha1-file.c
> +++ b/sha1-file.c
> @@ -1371,7 +1371,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
>  		/* Check if it is a missing object */
>  		if (fetch_if_missing && repository_format_partial_clone &&
>  		    !already_retried && r == the_repository &&
> -		    !(flags & OBJECT_INFO_FOR_PREFETCH)) {
> +		    !(flags & OBJECT_INFO_SKIP_FETCH_OBJECT)) {
>  			/*
>  			 * TODO Investigate having fetch_object() return
>  			 * TODO error/success and stopping the music here.