Re: [PATCH v4 05/10] commit-graph: always load commit-graph information

> Derrick Stolee <dstolee@microsoft.com> writes:
>
>> Most code paths load commits using lookup_commit() and then
>> parse_commit().
> And this automatically loads commit graph if needed, thanks to changes
> in parse_commit_gently(), which parse_commit() uses.
>
>>                  In some cases, including some branch lookups, the commit
>> is parsed using parse_object_buffer() which side-steps parse_commit() in
>> favor of parse_commit_buffer().
> I guess the problem is that we cannot just add parse_commit_in_graph()
> like we did in parse_commit_gently(), for some reason?  Like for example
> that parse_commit_gently() uses parse_commit_buffer() - which could have
> been handled by moving parse_commit_in_graph() down the call chain from
> parse_commit_gently() to parse_commit_buffer()... if not the fact that
> check_commit() also uses parse_commit_buffer(), but it does not want to
> load commit graph.  Am I right?

>
>> With generation numbers in the commit-graph, we need to ensure that any
>> commit that exists in the commit-graph file has its generation number
>> loaded.
> Is it generation number, or generation number and position in commit
> graph?

>
>> Create new load_commit_graph_info() method to fill in the information
>> for a commit that exists only in the commit-graph file. Call it from
>> parse_commit_buffer() after loading the other commit information from
>> the given buffer. Only fill this information when specified by the
>> 'check_graph' parameter.
> I think this commit would be easier to review if it was split into pure
> refactoring part (extracting fill_commit_graph_info() and
> find_commit_in_graph()).  On the other hand the refactoring was needed
> to reduce code duplication betweem existing parse_commit_in_graph() and
> new load_commit_graph_info() functions.
>
> I guess that the difference between parse_commit_in_graph() and
> load_commit_graph_info() is that the former cares only about having just
> enough information that is needed for parse_commit_gently() - and does
> not load graph data if commit is parsed, while the latter is about
> loading commit-graph data like generation numbers.
>
>> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
>> ---
>>   commit-graph.c | 45 ++++++++++++++++++++++++++++++---------------
>>   commit-graph.h |  8 ++++++++
>>   commit.c       |  7 +++++--
>>   commit.h       |  2 +-
>>   object.c       |  2 +-
>>   sha1_file.c    |  2 +-
>>   6 files changed, 46 insertions(+), 20 deletions(-)
> I wonder if it would be possible to add tests for this feature, for
> example that commit-graph is read when it should (including those branch
> lookups), and is not read when the feature should be disabled.
>
> But the only way to test it I can think of is a stupid one: create
> invalid commit graph, and check that git fails as expected (trying to
> read said malformed file), and does not fail if commit graph feature is
> disabled.
>
> Let me reorder files (BTW, is there a way for Git to put *.h files
> before *.c files in diff?) for easier review:
>
>> diff --git a/commit-graph.h b/commit-graph.h
>> index 260a468e73..96cccb10f3 100644
>> --- a/commit-graph.h
>> +++ b/commit-graph.h
>> @@ -17,6 +17,14 @@ char *get_commit_graph_filename(const char *obj_dir);
>>    */
>>   int parse_commit_in_graph(struct commit *item);
>>   
>> +/*
>> + * It is possible that we loaded commit contents from the commit buffer,
>> + * but we also want to ensure the commit-graph content is correctly
>> + * checked and filled. Fill the graph_pos and generation members of
>> + * the given commit.
>> + */
>> +void load_commit_graph_info(struct commit *item);
>> +
>>   struct tree *get_commit_tree_in_graph(const struct commit *c);
>>   
>>   struct commit_graph {
>> diff --git a/commit-graph.c b/commit-graph.c
>> index 047fa9fca5..aebd242def 100644
>> --- a/commit-graph.c
>> +++ b/commit-graph.c
>> @@ -245,6 +245,12 @@ static struct commit_list **insert_parent_or_die(struct commit_graph *g,
>>   	return &commit_list_insert(c, pptr)->next;
>>   }
>>   
>> +static void fill_commit_graph_info(struct commit *item, struct commit_graph *g, uint32_t pos)
>> +{
>> +	const unsigned char *commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * pos;
>> +	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
>> +}
> The comment in the header file commit-graph.h talks about filling
> graph_pos and generation members of the given commit, but I don't see
> filling graph_pos member here.

>
>> +
>>   static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t pos)
>>   {
>>   	uint32_t edge_value;
>> @@ -292,31 +298,40 @@ static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uin
>>   	return 1;
>>   }
>>   
>> +static int find_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t *pos)
>> +{
>> +	if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
>> +		*pos = item->graph_pos;
>> +		return 1;
>> +	} else {
>> +		return bsearch_graph(g, &(item->object.oid), pos);
>> +	}
>> +}
> Nice refactoring here.
>
>> +
>>   int parse_commit_in_graph(struct commit *item)
>>   {
>> +	uint32_t pos;
>> +
>>   	if (!core_commit_graph)
>>   		return 0;
>>   	if (item->object.parsed)
>>   		return 1;
>> -
>>   	prepare_commit_graph();
>> -	if (commit_graph) {
>> -		uint32_t pos;
>> -		int found;
>> -		if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
>> -			pos = item->graph_pos;
>> -			found = 1;
>> -		} else {
>> -			found = bsearch_graph(commit_graph, &(item->object.oid), &pos);
>> -		}
>> -
>> -		if (found)
>> -			return fill_commit_in_graph(item, commit_graph, pos);
>> -	}
>> -
>> +	if (commit_graph && find_commit_in_graph(item, commit_graph, &pos))
>> +		return fill_commit_in_graph(item, commit_graph, pos);
>>   	return 0;
>>   }
>>   
>> +void load_commit_graph_info(struct commit *item)
>> +{
>> +	uint32_t pos;
>> +	if (!core_commit_graph)
>> +		return;
>> +	prepare_commit_graph();
>> +	if (commit_graph && find_commit_in_graph(item, commit_graph, &pos))
>> +		fill_commit_graph_info(item, commit_graph, pos);
>> +}
> Similar functions, different goals (as the names imply).
>
>> +
>>   static struct tree *load_tree_for_commit(struct commit_graph *g, struct commit *c)
>>   {
>>   	struct object_id oid;
>> diff --git a/commit.c b/commit.c
>> index 4d00b0a1d6..39a3749abd 100644
>> --- a/commit.c
>> +++ b/commit.c
>> @@ -331,7 +331,7 @@ const void *detach_commit_buffer(struct commit *commit, unsigned long *sizep)
>>   	return ret;
>>   }
>>   
>> -int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size)
>> +int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size, int check_graph)
>>   {
>>   	const char *tail = buffer;
>>   	const char *bufptr = buffer;
>> @@ -386,6 +386,9 @@ int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long s
>>   	}
>>   	item->date = parse_commit_date(bufptr, tail);
>>   
>> +	if (check_graph)
>> +		load_commit_graph_info(item);
>> +
> All right, read commit-graph specific data after parsing commit itself.
> It is at the end because commit object needs to be parsed sequentially,
> and it includes more info that is contained in commit-graph CDAT+EDGE
> data.
>
>>   	return 0;
>>   }
>>   
>> @@ -412,7 +415,7 @@ int parse_commit_gently(struct commit *item, int quiet_on_missing)
>>   		return error("Object %s not a commit",
>>   			     oid_to_hex(&item->object.oid));
>>   	}
>> -	ret = parse_commit_buffer(item, buffer, size);
>> +	ret = parse_commit_buffer(item, buffer, size, 0);
> The parse_commit_gently() contract is that it provides only bare minimum
> of information, from commit-graph if possible, and does read object from
> disk and parses it only when it could not avoid it.  If it needs to
> parse it, it doesn't need to fill commit-graph specific data again.
>
> All right.
>
>>   	if (save_commit_buffer && !ret) {
>>   		set_commit_buffer(item, buffer, size);
>>   		return 0;
>> diff --git a/commit.h b/commit.h
>> index 64436ff44e..b5afde1ae9 100644
>> --- a/commit.h
>> +++ b/commit.h
>> @@ -72,7 +72,7 @@ struct commit *lookup_commit_reference_by_name(const char *name);
>>    */
>>   struct commit *lookup_commit_or_die(const struct object_id *oid, const char *ref_name);
>>   
>> -int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size);
>> +int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size, int check_graph);
>>   int parse_commit_gently(struct commit *item, int quiet_on_missing);
>>   static inline int parse_commit(struct commit *item)
>>   {
>> diff --git a/object.c b/object.c
>> index e6ad3f61f0..efe4871325 100644
>> --- a/object.c
>> +++ b/object.c
>> @@ -207,7 +207,7 @@ struct object *parse_object_buffer(const struct object_id *oid, enum object_type
>>   	} else if (type == OBJ_COMMIT) {
>>   		struct commit *commit = lookup_commit(oid);
>>   		if (commit) {
>> -			if (parse_commit_buffer(commit, buffer, size))
>> +			if (parse_commit_buffer(commit, buffer, size, 1))
> All that rigamarole was needed because of
>
> DS>                 In some cases, including some branch lookups, the commit
> DS> is parsed using parse_object_buffer() which side-steps parse_commit() in
> DS> favor of parse_commit_buffer().
>
> Here we want parse_object_buffer() to get also commit-graph specific
> data, if available.  All right.
>
>>   				return NULL;
>>   			if (!get_cached_commit_buffer(commit, NULL)) {
>>   				set_commit_buffer(commit, buffer, size);
>> diff --git a/sha1_file.c b/sha1_file.c
>> index 1b94f39c4c..0fd4f0b8b6 100644
>> --- a/sha1_file.c
>> +++ b/sha1_file.c
>> @@ -1755,7 +1755,7 @@ static void check_commit(const void *buf, size_t size)
>>   {
>>   	struct commit c;
>>   	memset(&c, 0, sizeof(c));
>> -	if (parse_commit_buffer(&c, buf, size))
>> +	if (parse_commit_buffer(&c, buf, size, 0))
> For check we don't need commit graph data.  Looks all right.
>
>>   		die("corrupt commit");
>>   }
> Best,