Merge branch 'jn/eoie-ieot'

As the warning message shown by existing versions of Git for
unknown index extensions is a bit too alarming, two new extensions
are held back and not written by default for the upcoming release.

* jn/eoie-ieot:
  index: make index.threads=true enable ieot and eoie
  ieot: default to not writing IEOT section
  eoie: default to not writing EOIE section

Documentation/config/index.txt

@@ -1,3 +1,19 @@
+index.recordEndOfIndexEntries::
+	Specifies whether the index file should include an "End Of Index
+	Entry" section. This reduces index load time on multiprocessor
+	machines but produces a message "ignoring EOIE extension" when
+	reading the index using Git versions before 2.20. Defaults to
+	'true' if index.threads has been explicitly enabled, 'false'
+	otherwise.
+
+index.recordOffsetTable::
+	Specifies whether the index file should include an "Index Entry
+	Offset Table" section. This reduces index load time on
+	multiprocessor machines but produces a message "ignoring IEOT
+	extension" when reading the index using Git versions before 2.20.
+	Defaults to 'true' if index.threads has been explicitly enabled,
+	'false' otherwise.
+
 index.threads::
 	Specifies the number of threads to spawn when loading the index.
 	This is meant to reduce index load time on multiprocessor machines.

config.c

@@ -2294,22 +2294,25 @@ int git_config_get_fsmonitor(void)
 	return 0;
 }
 
-int git_config_get_index_threads(void)
+int git_config_get_index_threads(int *dest)
 {
-	int is_bool, val = 0;
+	int is_bool, val;
 
 	val = git_env_ulong("GIT_TEST_INDEX_THREADS", 0);
-	if (val)
+	if (val) {
-		return val;
+		*dest = val;
+		return 0;
+	}
 
 	if (!git_config_get_bool_or_int("index.threads", &is_bool, &val)) {
 		if (is_bool)
-			return val ? 0 : 1;
+			*dest = val ? 0 : 1;
 		else
-			return val;
+			*dest = val;
+		return 0;
 	}
 
-	return 0; /* auto */
+	return 1;
 }
 
 NORETURN

config.h

@@ -246,11 +246,11 @@ extern int git_config_get_bool(const char *key, int *dest);
 extern int git_config_get_bool_or_int(const char *key, int *is_bool, int *dest);
 extern int git_config_get_maybe_bool(const char *key, int *dest);
 extern int git_config_get_pathname(const char *key, const char **dest);
+extern int git_config_get_index_threads(int *dest);
 extern int git_config_get_untracked_cache(void);
 extern int git_config_get_split_index(void);
 extern int git_config_get_max_percent_split_change(void);
 extern int git_config_get_fsmonitor(void);
-extern int git_config_get_index_threads(void);
 
 /* This dies if the configured or default date is in the future */
 extern int git_config_get_expiry(const char *key, const char **output);

read-cache.c

@@ -2176,7 +2176,8 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 
 	src_offset = sizeof(*hdr);
 
-	nr_threads = git_config_get_index_threads();
+	if (git_config_get_index_threads(&nr_threads))
+		nr_threads = 1;
 
 	/* TODO: does creating more threads than cores help? */
 	if (!nr_threads) {
@@ -2689,6 +2690,36 @@ void update_index_if_able(struct index_state *istate, struct lock_file *lockfile
 		rollback_lock_file(lockfile);
 }
 
+static int record_eoie(void)
+{
+	int val;
+
+	if (!git_config_get_bool("index.recordendofindexentries", &val))
+		return val;
+
+	/*
+	 * As a convenience, the end of index entries extension
+	 * used for threading is written by default if the user
+	 * explicitly requested threaded index reads.
+	 */
+	return !git_config_get_index_threads(&val) && val != 1;
+}
+
+static int record_ieot(void)
+{
+	int val;
+
+	if (!git_config_get_bool("index.recordoffsettable", &val))
+		return val;
+
+	/*
+	 * As a convenience, the offset table used for threading is
+	 * written by default if the user explicitly requested
+	 * threaded index reads.
+	 */
+	return !git_config_get_index_threads(&val) && val != 1;
+}
+
 /*
  * On success, `tempfile` is closed. If it is the temporary file
  * of a `struct lock_file`, we will therefore effectively perform
@@ -2747,12 +2778,10 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	if (ce_write(&c, newfd, &hdr, sizeof(hdr)) < 0)
 		return -1;
 
-	if (HAVE_THREADS)
+	if (!HAVE_THREADS || git_config_get_index_threads(&nr_threads))
-		nr_threads = git_config_get_index_threads();
-	else
 		nr_threads = 1;
 
-	if (nr_threads != 1) {
+	if (nr_threads != 1 && record_ieot()) {
 		int ieot_blocks, cpus;
 
 		/*
@@ -2936,7 +2965,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	 * read.  Write it out regardless of the strip_extensions parameter as we need it
 	 * when loading the shared index.
 	 */
-	if (offset) {
+	if (offset && record_eoie()) {
 		struct strbuf sb = STRBUF_INIT;
 
 		write_eoie_extension(&sb, &eoie_c, offset);

t/t1700-split-index.sh

@@ -25,14 +25,17 @@ test_expect_success 'enable split index' '
 	git update-index --split-index &&
 	test-tool dump-split-index .git/index >actual &&
 	indexversion=$(test-tool index-version <.git/index) &&
+
+	# NEEDSWORK: Stop hard-coding checksums.
 	if test "$indexversion" = "4"
 	then
-		own=3527df833c6c100d3d1d921a9a782d62a8be4b58
+		own=432ef4b63f32193984f339431fd50ca796493569
-		base=746f7ab2ed44fb839efdfbffcf399d0b113fb4cb
+		base=508851a7f0dfa8691e9f69c7f055865389012491
 	else
-		own=5e9b60117ece18da410ddecc8b8d43766a0e4204
+		own=8299b0bcd1ac364e5f1d7768efb62fa2da79a339
-		base=4370042739b31cd17a5c5cd6043a77c9a00df113
+		base=39d890139ee5356c7ef572216cebcd27aa41f9df
 	fi &&
+
 	cat >expect <<-EOF &&
 	own $own
 	base $base