On 3/25/2022 10:25 AM, Ævar Arnfjörð Bjarmason wrote:

In the preceding [1] (pack-objects: move revs out of
get_object_list(), 2022-03-22) the "repo_init_revisions()" was moved
to cmd_pack_objects() so that it unconditionally took place for all
invocations of "git pack-objects".

We'd thus start leaking memory, which is easily reproduced in
e.g. git.git by feeding e83c5163316 (Initial revision of "git", the
information manager from hell, 2005-04-07) to "git pack-objects";

    $ echo e83c5163316f89bfbde7d9ab23ca2e25604af290 | ./git pack-objects initial
    [...]
	==19130==ERROR: LeakSanitizer: detected memory leaks

	Direct leak of 7120 byte(s) in 1 object(s) allocated from:
	    #0 0x455308 in __interceptor_malloc (/home/avar/g/git/git+0x455308)
	    #1 0x75b399 in do_xmalloc /home/avar/g/git/wrapper.c:41:8
	    #2 0x75b356 in xmalloc /home/avar/g/git/wrapper.c:62:9
	    #3 0x5d7609 in prep_parse_options /home/avar/g/git/diff.c:5647:2
	    #4 0x5d415a in repo_diff_setup /home/avar/g/git/diff.c:4621:2
	    #5 0x6dffbb in repo_init_revisions /home/avar/g/git/revision.c:1853:2
	    #6 0x4f599d in cmd_pack_objects /home/avar/g/git/builtin/pack-objects.c:3980:2
	    #7 0x4592ca in run_builtin /home/avar/g/git/git.c:465:11
	    #8 0x457d81 in handle_builtin /home/avar/g/git/git.c:718:3
	    #9 0x458ca5 in run_argv /home/avar/g/git/git.c:785:4
	    #10 0x457b40 in cmd_main /home/avar/g/git/git.c:916:19
	    #11 0x562259 in main /home/avar/g/git/common-main.c:56:11
	    #12 0x7fce792ac7ec in __libc_start_main csu/../csu/libc-start.c:332:16
	    #13 0x4300f9 in _start (/home/avar/g/git/git+0x4300f9)

	SUMMARY: LeakSanitizer: 7120 byte(s) leaked in 1 allocation(s).
	Aborted

Narrowly fixing that commit would have been easy, just add call
repo_init_revisions() right before get_object_list(), which is
effectively what was done before that commit.

But an unstated constraint when setting it up early is that it was
needed for the subsequent [2] (pack-objects: parse --filter directly
into revs.filter, 2022-03-22), i.e. we might have a --filter
command-line option, and need to either have the "struct rev_info"
setup when we encounter that option, or later.

Let's just change the control flow so that we'll instead set up the
"struct rev_info" only when we need it. Doing so leads to a bit more
verbosity, but it's a lot clearer what we're doing and why.

This makes sense.

We could furthermore combine the two get_object_list() invocations
here by having repo_init_revisions() invoked on &pfd.revs, but I think
clearly separating the two makes the flow clearer. Likewise
redundantly but explicitly (i.e. redundant v.s. a "{ 0 }") "0" to
"have_revs" early in cmd_pack_objects().

I disagree, especially when you later want to make sure we free
the data from revs using your release_revisions().

This does add the future constraint to opt_parse_list_objects_filter()
that we'll need to adjust this wrapper code if it looks at any other
value of the "struct option" than the "value" member.

So we are coupling ourselves to the implementation of this method.

But that regression should be relatively easy to spot. I'm
intentionally not initializing the "struct wrap" with e.g. "{ 0 }" so
that various memory sanity checkers would spot that, we just
initialize the "value" in po_filter_cb(). By doing this e.g. we'll die
on e.g. this test if we were to use another member of "opt" in
opt_parse_list_objects_filter()>

So you are using uninitialized memory as a way to discover any
necessary changes to that coupling. I'm not sure this is super-safe
because we don't necessarily run memory checkers during CI builds.

I'd rather have a consistently initialized chunk of data that would
behave predictably (and hopefully we'd discover it is behaving
incorrectly with that predictable behavior).

The coupling here is unfortunate, but unavoidable. The future-proof
way to do it would be to modify opt->value and pass the rest of its
members as-is, but it's marked const so that's not an option.

One way to help make this coupling more obvious would be to move
this method into list-filter-options.c so we can have their
implementations adjacent and even refer to them.

Here is a potential version that looks like that:

--- >8 ---

diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index f02d8df142..55c7131814 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c

@@ -281,6 +281,10 @@ void parse_list_objects_filter(
 		die("%s", errbuf.buf);
 }
 
+/*
+ * If you change this to use any member in 'opt' other than 'value',
+ * then be sure to update opt_parse_list_objects_filter_in_revs().
+ */
 int opt_parse_list_objects_filter(const struct option *opt,
 				  const char *arg, int unset)
 {

@@ -293,6 +297,18 @@ int opt_parse_list_objects_filter(const struct option *opt,
 	return 0;
 }
 
+int opt_parse_list_objects_filter_in_revs(const struct option *opt,
+					  const char *arg, int unset)
+{
+	struct rev_info_maybe_empty *ri = opt->value;
+	struct option wrap = { .value = &ri->revs.filter };
+
+	repo_init_revisions(the_repository, &ri->revs, NULL);
+	ri->has_revs = 1;
+
+	return opt_parse_list_objects_filter(&wrap, arg, unset);
+}
+
 const char *list_objects_filter_spec(struct list_objects_filter_options *filter)
 {
 	if (!filter->filter_spec.nr)

diff --git a/list-objects-filter-options.h b/list-objects-filter-options.h
index 90e4bc9625..cf8b710a76 100644
--- a/list-objects-filter-options.h
+++ b/list-objects-filter-options.h

@@ -106,6 +106,8 @@ void parse_list_objects_filter(
 
 int opt_parse_list_objects_filter(const struct option *opt,
 				  const char *arg, int unset);
+int opt_parse_list_objects_filter_in_revs(const struct option *opt,
+					  const char *arg, int unset);
 
 #define OPT_PARSE_LIST_OBJECTS_FILTER(fo) \
 	OPT_CALLBACK(0, "filter", fo, N_("args"), \

diff --git a/revision.h b/revision.h
index 5bc59c7bfe..95aa3ee891 100644
--- a/revision.h
+++ b/revision.h

@@ -329,6 +329,11 @@ struct rev_info {
 	struct tmp_objdir *remerge_objdir;
 };
 
+struct rev_info_maybe_empty {
+	int has_revs;
+	struct rev_info revs;
+};
+
 int ref_excluded(struct string_list *, const char *path);
 void clear_ref_exclusion(struct string_list **);
 void add_ref_exclusion(struct string_list **, const char *exclude);

--- >8 ---

+	} else if (pfd.have_revs) {
+		get_object_list(&pfd.revs, rp.nr, rp.v);
 	} else {
+		struct rev_info revs;
+
+		repo_init_revisions(the_repository, &revs, NULL);
 		get_object_list(&revs, rp.nr, rp.v);
 	}

Here, I think it would be better to have

	else {
		if (!pfd.have_revs) {
			repo_init_revisions(the_repository, &pfd.revs, NULL);
			pfd.have_revs = 1;
		}
		get_object_list(&pfd.revs, rp.nr, rp.v);
	}

and then later you can add

	if (pfd.have_revs)
		release_revisions(&pfd.revs);

to clear the memory in exactly one place.

Thanks,
-Stolee