Subject: Re: [PATCH] commit-graph: fix buggy --expire-time option

From: SZEDER Gábor <[email-masked]>
Date: Wed, 1 Apr 2020 21:47:06 +0200

On Wed, Apr 01, 2020 at 06:11:35PM +0000, Derrick Stolee via GitGitGadget wrote:
> From: Derrick Stolee <[email-masked]>
> 
> The commit-graph builtin has an --expire-time option that takes a
> datetime using OPT_EXPIRY_DATE(). However, the implementation inside
> expire_commit_graphs() was treating a non-zero value as a number of
> seconds to subtract from "now".
> 
> Update t5323-split-commit-graph.sh to demonstrate the correct value
> of the --expire-time option by actually creating a crud .graph file
> with mtime earlier than the expire time. Instead of using a super-
> early time (1980) we need to use a recent time or else the old
> logic actually passes by accident. This test will start passing
> again on the old logic in 40 years or so.
> 
> I noticed this when inspecting some Scalar repos that had an excess
> number of commit-graph files. In Scalar, we were using this second
> interpretation by using "--expire-time=3600" to mean "delete graphs
> older than one hour ago" to avoid deleting a commit-graph that a
> foreground process may be trying to load.
> 
> Also I noticed that the help text was copied from the --max-commits
> option. Fix that help text.
> 
> Signed-off-by: Derrick Stolee <[email-masked]>
> ---
>     commit-graph: fix buggy --expire-time option
>     
>     This is embarassing. I should have noticed this when writing it the
>     first time, or when integrating the feature into Scalar and VFS for Git.
>     Sorry!
>     
>     Thanks, -Stolee
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-596%2Fderrickstolee%2Fcommit-graph-expire-fix-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-596/derrickstolee/commit-graph-expire-fix-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/596
> 
>  builtin/commit-graph.c        | 2 +-
>  commit-graph.c                | 2 +-
>  t/t5324-split-commit-graph.sh | 4 +++-
>  3 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
> index 4a70b33fb5f..8000ff0d2ee 100644
> --- a/builtin/commit-graph.c
> +++ b/builtin/commit-graph.c
> @@ -140,7 +140,7 @@ static int graph_write(int argc, const char **argv)
>  		OPT_INTEGER(0, "size-multiple", &split_opts.size_multiple,
>  			N_("maximum ratio between two levels of a split commit-graph")),
>  		OPT_EXPIRY_DATE(0, "expire-time", &split_opts.expire_time,
> -			N_("maximum number of commits in a non-base split commit-graph")),
> +			N_("do not expire files newer than a number of seconds before now")),
>  		OPT_END(),
>  	};
>  
> diff --git a/commit-graph.c b/commit-graph.c
> index f013a84e294..0d0d37787a0 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -1707,7 +1707,7 @@ static void expire_commit_graphs(struct write_commit_graph_context *ctx)
>  	timestamp_t expire_time = time(NULL);
>  
>  	if (ctx->split_opts && ctx->split_opts->expire_time)
> -		expire_time -= ctx->split_opts->expire_time;
> +		expire_time = ctx->split_opts->expire_time;
>  	if (!ctx->split) {
>  		char *chain_file_name = get_chain_filename(ctx->odb);
>  		unlink(chain_file_name);
> diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
> index 53b2e6b4555..4e4efcaff22 100755
> --- a/t/t5324-split-commit-graph.sh
> +++ b/t/t5324-split-commit-graph.sh
> @@ -210,8 +210,10 @@ test_expect_success 'test merge stragety constants' '
>  		git config core.commitGraph true &&
>  		test_line_count = 2 $graphdir/commit-graph-chain &&
>  		test_commit 15 &&
> -		git commit-graph write --reachable --split --size-multiple=10 --expire-time=1980-01-01 &&
> +		touch -m -t 201801010000.00 $graphdir/extra.graph &&

You can set a mtime relative to the current time with:

  test-tool chmtime =-3600 $graphdir/extra.graph

> +		git commit-graph write --reachable --split --size-multiple=10 --expire-time=2019-01-01 &&
>  		test_line_count = 1 $graphdir/commit-graph-chain &&
> +		test_path_is_missing $graphdir/extra.graph &&
>  		ls $graphdir/graph-*.graph >graph-files &&
>  		test_line_count = 3 graph-files
>  	) &&
> 
> base-commit: 274b9cc25322d9ee79aa8e6d4e86f0ffe5ced925
> -- 
> gitgitgadget