reftable: pass opts as constant pointer

We sometimes pass the refatble write options as value and sometimes as a
pointer. This is quite confusing and makes the reader wonder whether the
options get modified sometimes.

In fact, `reftable_new_writer()` does cause the caller-provided options
to get updated when some values aren't set up. This is quite unexpected,
but didn't cause any harm until now.

Adapt the code so that we do not modify the caller-provided values
anymore. While at it, refactor the code to code to consistently pass the
options as a constant pointer to clarify that the caller-provided opts
will not ever get modified.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

7 files changed, 46 insertions, 38 deletions

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 010ef811b6..f8f930380d 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -129,7 +129,7 @@ static struct reftable_stack *stack_for(struct reftable_ref_store *store,
 				    store->base.repo->commondir, wtname_buf.buf);
 
 			store->err = reftable_new_stack(&stack, wt_dir.buf,
-							store->write_options);
+							&store->write_options);
 			assert(store->err != REFTABLE_API_ERROR);
 			strmap_put(&store->worktree_stacks, wtname_buf.buf, stack);
 		}
@@ -263,7 +263,7 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	}
 	strbuf_addstr(&path, "/reftable");
 	refs->err = reftable_new_stack(&refs->main_stack, path.buf,
-				       refs->write_options);
+				       &refs->write_options);
 	if (refs->err)
 		goto done;
 
@@ -280,7 +280,7 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 		strbuf_addf(&path, "%s/reftable", gitdir);
 
 		refs->err = reftable_new_stack(&refs->worktree_stack, path.buf,
-					       refs->write_options);
+					       &refs->write_options);
 		if (refs->err)
 			goto done;
 	}
diff --git a/reftable/dump.c b/reftable/dump.c
index 9c770a10cc..586f3eb288 100644
--- a/reftable/dump.c
+++ b/reftable/dump.c
@@ -29,7 +29,7 @@ static int compact_stack(const char *stackdir)
 	struct reftable_stack *stack = NULL;
 	struct reftable_write_options opts = { 0 };
 
-	int err = reftable_new_stack(&stack, stackdir, opts);
+	int err = reftable_new_stack(&stack, stackdir, &opts);
 	if (err < 0)
 		goto done;
 
diff --git a/reftable/reftable-stack.h b/reftable/reftable-stack.h
index 9c8e4eef49..c15632c401 100644
--- a/reftable/reftable-stack.h
+++ b/reftable/reftable-stack.h
@@ -29,7 +29,7 @@ struct reftable_stack;
  *  stored in 'dir'. Typically, this should be .git/reftables.
  */
 int reftable_new_stack(struct reftable_stack **dest, const char *dir,
-		       struct reftable_write_options opts);
+		       const struct reftable_write_options *opts);
 
 /* returns the update_index at which a next table should be written. */
 uint64_t reftable_stack_next_update_index(struct reftable_stack *st);
diff --git a/reftable/reftable-writer.h b/reftable/reftable-writer.h
index b601a69a40..03df3a4963 100644
--- a/reftable/reftable-writer.h
+++ b/reftable/reftable-writer.h
@@ -88,7 +88,7 @@ struct reftable_stats {
 struct reftable_writer *
 reftable_new_writer(ssize_t (*writer_func)(void *, const void *, size_t),
 		    int (*flush_func)(void *),
-		    void *writer_arg, struct reftable_write_options *opts);
+		    void *writer_arg, const struct reftable_write_options *opts);
 
 /* Set the range of update indices for the records we will add. When writing a
    table into a stack, the min should be at least
diff --git a/reftable/stack.c b/reftable/stack.c
index 54e7473f3a..d2e68be7e8 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -54,12 +54,15 @@ static int reftable_fd_flush(void *arg)
 }
 
 int reftable_new_stack(struct reftable_stack **dest, const char *dir,
-		       struct reftable_write_options opts)
+		       const struct reftable_write_options *_opts)
 {
 	struct reftable_stack *p = reftable_calloc(1, sizeof(*p));
 	struct strbuf list_file_name = STRBUF_INIT;
+	struct reftable_write_options opts = {0};
 	int err = 0;
 
+	if (_opts)
+		opts = *_opts;
 	if (opts.hash_id == 0)
 		opts.hash_id = GIT_SHA1_FORMAT_ID;
 
@@ -1438,7 +1441,7 @@ int reftable_stack_print_directory(const char *stackdir, uint32_t hash_id)
 	struct reftable_merged_table *merged = NULL;
 	struct reftable_table table = { NULL };
 
-	int err = reftable_new_stack(&stack, stackdir, opts);
+	int err = reftable_new_stack(&stack, stackdir, &opts);
 	if (err < 0)
 		goto done;
 
diff --git a/reftable/stack_test.c b/reftable/stack_test.c
index e17ad4dc62..d15f11d712 100644
--- a/reftable/stack_test.c
+++ b/reftable/stack_test.c
@@ -163,7 +163,7 @@ static void test_reftable_stack_add_one(void)
 	};
 	struct reftable_ref_record dest = { NULL };
 	struct stat stat_result = { 0 };
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, &write_test_ref, &ref);
@@ -232,10 +232,10 @@ static void test_reftable_stack_uptodate(void)
 	/* simulate multi-process access to the same stack
 	   by creating two stacks for the same directory.
 	 */
-	err = reftable_new_stack(&st1, dir, opts);
+	err = reftable_new_stack(&st1, dir, &opts);
 	EXPECT_ERR(err);
 
-	err = reftable_new_stack(&st2, dir, opts);
+	err = reftable_new_stack(&st2, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st1, &write_test_ref, &ref1);
@@ -270,7 +270,7 @@ static void test_reftable_stack_transaction_api(void)
 	};
 	struct reftable_ref_record dest = { NULL };
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	reftable_addition_destroy(add);
@@ -304,7 +304,7 @@ static void test_reftable_stack_transaction_api_performs_auto_compaction(void)
 	struct reftable_stack *st = NULL;
 	int i, n = 20, err;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i <= n; i++) {
@@ -365,7 +365,7 @@ static void test_reftable_stack_auto_compaction_fails_gracefully(void)
 	char *dir = get_tmp_dir(__LINE__);
 	int err;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, write_test_ref, &ref);
@@ -418,7 +418,7 @@ static void test_reftable_stack_update_index_check(void)
 		.value.symref = "master",
 	};
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, &write_test_ref, &ref1);
@@ -437,7 +437,7 @@ static void test_reftable_stack_lock_failure(void)
 	struct reftable_stack *st = NULL;
 	int err, i;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 	for (i = -1; i != REFTABLE_EMPTY_TABLE_ERROR; i--) {
 		err = reftable_stack_add(st, &write_error, &i);
@@ -465,7 +465,7 @@ static void test_reftable_stack_add(void)
 	struct stat stat_result;
 	int N = ARRAY_SIZE(refs);
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i < N; i++) {
@@ -575,7 +575,7 @@ static void test_reftable_stack_log_normalize(void)
 		.update_index = 1,
 	};
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	input.value.update.message = "one\ntwo";
@@ -617,7 +617,7 @@ static void test_reftable_stack_tombstone(void)
 	struct reftable_ref_record dest = { NULL };
 	struct reftable_log_record log_dest = { NULL };
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	/* even entries add the refs, odd entries delete them. */
@@ -701,18 +701,18 @@ static void test_reftable_stack_hash_id(void)
 	struct reftable_stack *st_default = NULL;
 	struct reftable_ref_record dest = { NULL };
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, &write_test_ref, &ref);
 	EXPECT_ERR(err);
 
 	/* can't read it with the wrong hash ID. */
-	err = reftable_new_stack(&st32, dir, opts32);
+	err = reftable_new_stack(&st32, dir, &opts32);
 	EXPECT(err == REFTABLE_FORMAT_ERROR);
 
 	/* check that we can read it back with default opts too. */
-	err = reftable_new_stack(&st_default, dir, opts_default);
+	err = reftable_new_stack(&st_default, dir, &opts_default);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_read_ref(st_default, "master", &dest);
@@ -756,7 +756,7 @@ static void test_reflog_expire(void)
 	};
 	struct reftable_log_record log = { NULL };
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 1; i <= N; i++) {
@@ -825,13 +825,13 @@ static void test_empty_add(void)
 	char *dir = get_tmp_dir(__LINE__);
 	struct reftable_stack *st2 = NULL;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_add(st, &write_nothing, NULL);
 	EXPECT_ERR(err);
 
-	err = reftable_new_stack(&st2, dir, opts);
+	err = reftable_new_stack(&st2, dir, &opts);
 	EXPECT_ERR(err);
 	clear_dir(dir);
 	reftable_stack_destroy(st);
@@ -858,7 +858,7 @@ static void test_reftable_stack_auto_compaction(void)
 	int err, i;
 	int N = 100;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i < N; i++) {
@@ -894,7 +894,7 @@ static void test_reftable_stack_add_performs_auto_compaction(void)
 	char *dir = get_tmp_dir(__LINE__);
 	int err, i, n = 20;
 
-	err = reftable_new_stack(&st, dir, opts);
+	err = reftable_new_stack(&st, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i <= n; i++) {
@@ -942,7 +942,7 @@ static void test_reftable_stack_compaction_concurrent(void)
 	int err, i;
 	int N = 3;
 
-	err = reftable_new_stack(&st1, dir, opts);
+	err = reftable_new_stack(&st1, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i < N; i++) {
@@ -959,7 +959,7 @@ static void test_reftable_stack_compaction_concurrent(void)
 		EXPECT_ERR(err);
 	}
 
-	err = reftable_new_stack(&st2, dir, opts);
+	err = reftable_new_stack(&st2, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_compact_all(st1, NULL);
@@ -991,7 +991,7 @@ static void test_reftable_stack_compaction_concurrent_clean(void)
 	int err, i;
 	int N = 3;
 
-	err = reftable_new_stack(&st1, dir, opts);
+	err = reftable_new_stack(&st1, dir, &opts);
 	EXPECT_ERR(err);
 
 	for (i = 0; i < N; i++) {
@@ -1008,7 +1008,7 @@ static void test_reftable_stack_compaction_concurrent_clean(void)
 		EXPECT_ERR(err);
 	}
 
-	err = reftable_new_stack(&st2, dir, opts);
+	err = reftable_new_stack(&st2, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_compact_all(st1, NULL);
@@ -1017,7 +1017,7 @@ static void test_reftable_stack_compaction_concurrent_clean(void)
 	unclean_stack_close(st1);
 	unclean_stack_close(st2);
 
-	err = reftable_new_stack(&st3, dir, opts);
+	err = reftable_new_stack(&st3, dir, &opts);
 	EXPECT_ERR(err);
 
 	err = reftable_stack_clean(st3);
diff --git a/reftable/writer.c b/reftable/writer.c
index 10eccaaa07..4cc6e2ebd8 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -122,20 +122,25 @@ static struct strbuf reftable_empty_strbuf = STRBUF_INIT;
 struct reftable_writer *
 reftable_new_writer(ssize_t (*writer_func)(void *, const void *, size_t),
 		    int (*flush_func)(void *),
-		    void *writer_arg, struct reftable_write_options *opts)
+		    void *writer_arg, const struct reftable_write_options *_opts)
 {
 	struct reftable_writer *wp = reftable_calloc(1, sizeof(*wp));
-	strbuf_init(&wp->block_writer_data.last_key, 0);
-	options_set_defaults(opts);
-	if (opts->block_size >= (1 << 24)) {
+	struct reftable_write_options opts = {0};
+
+	if (_opts)
+		opts = *_opts;
+	options_set_defaults(&opts);
+	if (opts.block_size >= (1 << 24)) {
 		/* TODO - error return? */
 		abort();
 	}
+
+	strbuf_init(&wp->block_writer_data.last_key, 0);
 	wp->last_key = reftable_empty_strbuf;
-	REFTABLE_CALLOC_ARRAY(wp->block, opts->block_size);
+	REFTABLE_CALLOC_ARRAY(wp->block, opts.block_size);
 	wp->write = writer_func;
 	wp->write_arg = writer_arg;
-	wp->opts = *opts;
+	wp->opts = opts;
 	wp->flush = flush_func;
 	writer_reinit_block_writer(wp, BLOCK_TYPE_REF);