Subject: Re: [PATCH v2 06/14] commit-graph: implement git-commit-graph --read

From: SZEDER Gábor <[email-masked]>
Date: Fri, 2 Feb 2018 01:02:25 +0100

> Teach git-commit-graph to read commit graph files and summarize their contents.
> 
> Use the --read option to verify the contents of a commit graph file in the
> tests.
> 
> Signed-off-by: Derrick Stolee <[email-masked]>
> ---
>  Documentation/git-commit-graph.txt |   7 ++
>  builtin/commit-graph.c             |  55 +++++++++++++++
>  commit-graph.c                     | 138 ++++++++++++++++++++++++++++++++++++-
>  commit-graph.h                     |  25 +++++++
>  t/t5318-commit-graph.sh            |  28 ++++++--
>  5 files changed, 247 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
> index 3f3790d9a8..09aeaf6c82 100644
> --- a/Documentation/git-commit-graph.txt
> +++ b/Documentation/git-commit-graph.txt
> @@ -10,6 +10,7 @@ SYNOPSIS
>  --------
>  [verse]
>  'git commit-graph' --write <options> [--pack-dir <pack_dir>]
> +'git commit-graph' --read <options> [--pack-dir <pack_dir>]

Again, what does this option do?

>  EXAMPLES
>  --------
> @@ -20,6 +21,12 @@ EXAMPLES
>  $ git commit-graph --write
>  ------------------------------------------------
>  
> +* Read basic information from a graph file.
> ++
> +------------------------------------------------
> +$ git commit-graph --read --graph-hash=<hash>
> +------------------------------------------------
> +
>  GIT
>  ---
>  Part of the linkgit:git[1] suite
> diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
> index 7affd512f1..218740b1f8 100644
> --- a/builtin/commit-graph.c
> +++ b/builtin/commit-graph.c

> +int close_commit_graph(struct commit_graph *g)

static, perhaps?  I see it's declared as extern in the headeer file
below, but I don't see it called outside of this source file by the
end of the patch series.

> +{
> +	if (g->graph_fd < 0)
> +		return 0;
> +
> +	munmap((void *)g->data, g->data_len);
> +	g->data = 0;
> +
> +	close(g->graph_fd);
> +	g->graph_fd = -1;
> +
> +	return 1;
> +}
> +
> +static void free_commit_graph(struct commit_graph **g)
> +{
> +	if (!g || !*g)
> +		return;
> +
> +	close_commit_graph(*g);
> +
> +	free(*g);
> +	*g = NULL;
> +}
> +
> +struct commit_graph *load_commit_graph_one(const char *graph_file, const char *pack_dir)
> +{
> +	void *graph_map;
> +	const unsigned char *data;
> +	struct commit_graph_header *hdr;
> +	size_t graph_size;
> +	struct stat st;
> +	uint32_t i;
> +	struct commit_graph *graph;
> +	int fd = git_open(graph_file);
> +	uint64_t last_chunk_offset;
> +	uint32_t last_chunk_id;
> +
> +	if (fd < 0)
> +		return 0;
> +	if (fstat(fd, &st)) {
> +		close(fd);
> +		return 0;
> +	}
> +	graph_size = xsize_t(st.st_size);
> +
> +	if (graph_size < GRAPH_MIN_SIZE) {
> +		close(fd);
> +		die("graph file %s is too small", graph_file);
> +	}
> +	graph_map = xmmap(NULL, graph_size, PROT_READ, MAP_PRIVATE, fd, 0);
> +	data = (const unsigned char *)graph_map;
> +
> +	hdr = graph_map;
> +	if (ntohl(hdr->graph_signature) != GRAPH_SIGNATURE) {
> +		uint32_t signature = ntohl(hdr->graph_signature);
> +		munmap(graph_map, graph_size);
> +		close(fd);
> +		die("graph signature %X does not match signature %X",
> +			signature, GRAPH_SIGNATURE);
> +	}
> +	if (hdr->graph_version != GRAPH_VERSION) {
> +		unsigned char version = hdr->graph_version;
> +		munmap(graph_map, graph_size);
> +		close(fd);
> +		die("graph version %X does not match version %X",
> +			version, GRAPH_VERSION);
> +	}
> +
> +	graph = alloc_commit_graph(strlen(pack_dir) + 1);
> +
> +	graph->hdr = hdr;
> +	graph->graph_fd = fd;
> +	graph->data = graph_map;
> +	graph->data_len = graph_size;
> +
> +	last_chunk_id = 0;
> +	last_chunk_offset = (uint64_t)sizeof(*hdr);
> +	for (i = 0; i < hdr->num_chunks; i++) {
> +		uint32_t chunk_id = ntohl(*(uint32_t*)(data + sizeof(*hdr) + 12 * i));
> +		uint64_t chunk_offset1 = ntohl(*(uint32_t*)(data + sizeof(*hdr) + 12 * i + 4));
> +		uint32_t chunk_offset2 = ntohl(*(uint32_t*)(data + sizeof(*hdr) + 12 * i + 8));

There are a lot of magic number in these three lines, but at least
they are all multiples of 4.

> +		uint64_t chunk_offset = (chunk_offset1 << 32) | chunk_offset2;
> +
> +		if (chunk_offset > graph_size - GIT_MAX_RAWSZ)
> +			die("improper chunk offset %08x%08x", (uint32_t)(chunk_offset >> 32),
> +			    (uint32_t)chunk_offset);
> +
> +		switch (chunk_id) {
> +			case GRAPH_CHUNKID_OIDFANOUT:
> +				graph->chunk_oid_fanout = data + chunk_offset;
> +				break;
> +
> +			case GRAPH_CHUNKID_OIDLOOKUP:
> +				graph->chunk_oid_lookup = data + chunk_offset;
> +				break;
> +
> +			case GRAPH_CHUNKID_DATA:
> +				graph->chunk_commit_data = data + chunk_offset;
> +				break;
> +
> +			case GRAPH_CHUNKID_LARGEEDGES:
> +				graph->chunk_large_edges = data + chunk_offset;
> +				break;
> +
> +			case 0:
> +				break;
> +
> +			default:
> +				free_commit_graph(&graph);
> +				die("unrecognized graph chunk id: %08x", chunk_id);
> +		}
> +
> +		if (last_chunk_id == GRAPH_CHUNKID_OIDLOOKUP)
> +		{
> +			graph->num_commits = (chunk_offset - last_chunk_offset)
> +					     / hdr->hash_len;
> +		}
> +
> +		last_chunk_id = chunk_id;
> +		last_chunk_offset = chunk_offset;
> +	}
> +
> +	strcpy(graph->pack_dir, pack_dir);
> +	return graph;
> +}
> +
>  static void write_graph_chunk_fanout(struct sha1file *f,
>  				     struct commit **commits,
>  				     int nr_commits)
> @@ -361,7 +497,7 @@ struct object_id *construct_commit_graph(const char *pack_dir)
>  	sha1close(f, final_hash, CSUM_CLOSE | CSUM_FSYNC);
>  
>  	f_hash = (struct object_id *)malloc(sizeof(struct object_id));
> -	memcpy(f_hash->hash, final_hash, GIT_MAX_RAWSZ);
> +	hashcpy(f_hash->hash, final_hash);

Oh, look, I told you it's hashcpy()! ;)

>  	fname = get_commit_graph_filename_hash(pack_dir, f_hash);
>  
>  	if (rename(graph_name, fname))
> diff --git a/commit-graph.h b/commit-graph.h
> index 7b3469a7df..e046ae575c 100644
> --- a/commit-graph.h
> +++ b/commit-graph.h
> @@ -15,6 +15,31 @@ struct commit_graph_header {
>  	unsigned char num_chunks;
>  };
>  
> +extern struct commit_graph {
> +	int graph_fd;
> +
> +	const unsigned char *data;
> +	size_t data_len;
> +
> +	const struct commit_graph_header *hdr;
> +
> +	struct object_id oid;
> +
> +	uint32_t num_commits;
> +
> +	const unsigned char *chunk_oid_fanout;
> +	const unsigned char *chunk_oid_lookup;
> +	const unsigned char *chunk_commit_data;
> +	const unsigned char *chunk_large_edges;
> +
> +	/* something like ".git/objects/pack" */
> +	char pack_dir[FLEX_ARRAY]; /* more */
> +} *commit_graph;
> +
> +extern int close_commit_graph(struct commit_graph *g);
> +
> +extern struct commit_graph *load_commit_graph_one(const char *graph_file, const char *pack_dir);
> +
>  extern struct object_id *construct_commit_graph(const char *pack_dir);
>  
>  #endif
> diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
> index 6bcd1cc264..da565624e3 100755
> --- a/t/t5318-commit-graph.sh
> +++ b/t/t5318-commit-graph.sh
> @@ -25,11 +25,23 @@ test_expect_success 'create commits and repack' \
>       done &&
>       git repack'
>  
> +_graph_read_expect() {
> +    cat >expect <<- EOF
> +header: 43475048 01 01 14 04
> +num_commits: $1
> +chunks: oid_fanout oid_lookup commit_metadata large_edges
> +pack_dir: $2
> +EOF
> +}

Style nit: since you are already using the '<<-' operator for the
here-doc, you could indent it with tabs.

> +
>  test_expect_success 'write graph' \
>      'graph1=$(git commit-graph --write) &&
> -     test_path_is_file ${packdir}/graph-${graph1}.graph'
> +     test_path_is_file ${packdir}/graph-${graph1}.graph &&
> +     git commit-graph --read --graph-hash=${graph1} >output &&
> +     _graph_read_expect "5" "${packdir}" &&
> +     cmp expect output'

Please use the 'test_cmp' helper throughout the tests instead.
If the two files don't match, 'cmp' will only tell you where they
start to differ, whereas 'test_cmp' will actually show the difference.

> -t_expect_success 'Add more commits' \
> +test_expect_success 'Add more commits' \

This should be squashed into the earlier commit.

>      'git reset --hard commits/3 &&
>       for i in $(test_seq 6 10)
>       do
> @@ -79,7 +91,10 @@ t_expect_success 'Add more commits' \
>  
>  test_expect_success 'write graph with merges' \
>      'graph2=$(git commit-graph --write) &&
> -     test_path_is_file ${packdir}/graph-${graph2}.graph'
> +     test_path_is_file ${packdir}/graph-${graph2}.graph &&
> +     git commit-graph --read --graph-hash=${graph2} >output &&
> +     _graph_read_expect "18" "${packdir}" &&
> +     cmp expect output'
>  
>  test_expect_success 'setup bare repo' \
>      'cd .. &&
> @@ -87,10 +102,13 @@ test_expect_success 'setup bare repo' \
>       cd bare &&
>       git config core.graph true &&
>       git config pack.threads 1 &&
> -     baredir="objects/pack"'
> +     baredir="./objects/pack"'

Is this change really necessary?  If it is, then perhaps it should
have been written this way upon its introduction.

>  test_expect_success 'write graph in bare repo' \
>      'graphbare=$(git commit-graph --write) &&
> -     test_path_is_file ${baredir}/graph-${graphbare}.graph'
> +     test_path_is_file ${baredir}/graph-${graphbare}.graph &&
> +     git commit-graph --read --graph-hash=${graphbare} >output &&
> +     _graph_read_expect "18" "${baredir}" &&
> +     cmp expect output'
>  
>  test_done
> -- 
> 2.16.0.15.g9c3cf44.dirty