Subject: Re: [PATCH v2 08/24] midx: respect 'core.multiPackIndex' when writing

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Fri, 25 Jun 2021 01:43:05 +0200

On Mon, Jun 21 2021, Taylor Blau wrote:

> When writing a new multi-pack index, write_midx_internal() attempts to
> load any existing one to fill in some pieces of information. But it uses
> load_multi_pack_index(), which ignores the configuration
> "core.multiPackIndex", which indicates whether or not Git is allowed to
> read an existing multi-pack-index.
>
> Replace this with a routine that does respect that setting, to avoid
> reading multi-pack-index files when told not to.
>
> This avoids a problem that would arise in subsequent patches due to the
> combination of 'git repack' reopening the object store in-process and
> the multi-pack index code not checking whether a pack already exists in
> the object store when calling add_pack_to_midx().
>
> This would ultimately lead to a cycle being created along the
> 'packed_git' struct's '->next' pointer. That is obviously bad, but it
> has hard-to-debug downstream effects like saying a bitmap can't be
> loaded for a pack because one already exists (for the same pack).
>
> Signed-off-by: Taylor Blau <[email-masked]>
> ---
>  midx.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/midx.c b/midx.c
> index 40eb7974ba..759007d5a8 100644
> --- a/midx.c
> +++ b/midx.c
> @@ -908,8 +908,18 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
>  
>  	if (m)
>  		ctx.m = m;
> -	else
> -		ctx.m = load_multi_pack_index(object_dir, 1);
> +	else {

Style nit: leaves the initial "if" braceless now that the "else" gained
braces.