maintenance: add start/stop subcommands

The GIT_TEST_CRONTAB environment variable is not intended for users to
edit, but instead as a way to mock the 'crontab [-l]' command. This
variable is set in test-lib.sh to avoid a future test from accidentally
running anything with the cron integration from modifying the user's
schedule. We use GIT_TEST_CRONTAB='test-tool crontab <file>' in our
tests to check how the schedule is modified in 'git maintenance
(start|stop)' commands.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

Author: derrickstolee

Documentation/git-maintenance.txt

@@ -45,6 +45,17 @@ run::
 	config options are true. By default, only `maintenance.gc.enabled`
 	is true.
 
+start::
+	Start running maintenance on the current repository. This performs
+	the same config updates as the `register` subcommand, then updates
+	the background scheduler to run `git maintenance run --scheduled`
+	on an hourly basis.
+
+stop::
+	Halt the background maintenance schedule. The current repository
+	is not removed from the list of maintained repositories, in case
+	the background maintenance is restarted later.
+
 unregister::
 	Remove the current repository from background maintenance. This
 	only removes the repository from the configured list. It does not

Makefile

@@ -690,6 +690,7 @@ TEST_BUILTINS_OBJS += test-advise.o
 TEST_BUILTINS_OBJS += test-bloom.o
 TEST_BUILTINS_OBJS += test-chmtime.o
 TEST_BUILTINS_OBJS += test-config.o
+TEST_BUILTINS_OBJS += test-crontab.o
 TEST_BUILTINS_OBJS += test-ctype.o
 TEST_BUILTINS_OBJS += test-date.o
 TEST_BUILTINS_OBJS += test-delta.o

builtin/gc.c

@@ -1509,6 +1509,140 @@ static int maintenance_unregister(void)
 	return run_command(&config_unset);
 }
 
+#define BEGIN_LINE "# BEGIN GIT MAINTENANCE SCHEDULE"
+#define END_LINE "# END GIT MAINTENANCE SCHEDULE"
+
+static void populate_crontab_args(struct strvec *argv, const char *crontab)
+{
+	char *name_dup, *word_start, *iter;
+
+	if (!crontab) {
+		strvec_push(argv, "crontab");
+		return;
+	}
+
+	name_dup = xstrdup(crontab);
+	word_start = name_dup;
+	iter = name_dup;
+
+	while (*iter) {
+		int space = (*iter == ' ');
+		if (space)
+			*iter = 0;
+		iter++;
+		if (space || *iter == 0) {
+			strvec_push(argv, word_start);
+			word_start = iter;
+		}
+	}
+	free(name_dup);
+}
+
+static int update_background_schedule(int run_maintenance)
+{
+	int result = 0;
+	int in_old_region = 0;
+	struct child_process crontab_list = CHILD_PROCESS_INIT;
+	struct child_process crontab_edit = CHILD_PROCESS_INIT;
+	FILE *cron_list, *cron_in;
+	const char *get_test_crontab_name;
+	struct strbuf line = STRBUF_INIT;
+	struct lock_file lk;
+	char *lock_path = xstrfmt("%s/schedule", the_repository->objects->odb->path);
+
+	if (hold_lock_file_for_update(&lk, lock_path, LOCK_NO_DEREF) < 0)
+		return error(_("another process is scheduling background maintenance"));
+
+	get_test_crontab_name = getenv("GIT_TEST_CRONTAB");
+
+	populate_crontab_args(&crontab_list.args, get_test_crontab_name);
+	strvec_push(&crontab_list.args, "-l");
+	crontab_list.in = -1;
+	crontab_list.out = dup(lk.tempfile->fd);
+	crontab_list.git_cmd = 0;
+
+	if (start_command(&crontab_list)) {
+		result = error(_("failed to run 'crontab -l'; your system might not support 'cron'"));
+		goto cleanup;
+	}
+
+	if (finish_command(&crontab_list)) {
+		result = error(_("'crontab -l' died"));
+		goto cleanup;
+	}
+
+	/*
+	 * Read from the .lock file, filtering out the old
+	 * schedule while appending the new schedule.
+	 */
+	cron_list = fdopen(lk.tempfile->fd, "r");
+	rewind(cron_list);
+
+	populate_crontab_args(&crontab_edit.args, get_test_crontab_name);
+	crontab_edit.in = -1;
+	crontab_edit.git_cmd = 0;
+
+	if (start_command(&crontab_edit)) {
+		result = error(_("failed to run 'crontab'; your system might not support 'cron'"));
+		goto cleanup;
+	}
+
+	cron_in = fdopen(crontab_edit.in, "w");
+	if (!cron_in) {
+		result = error(_("failed to open stdin of 'crontab'"));
+		goto done_editing;
+	}
+
+	while (!strbuf_getline_lf(&line, cron_list)) {
+		if (!in_old_region && !strcmp(line.buf, BEGIN_LINE))
+			in_old_region = 1;
+		if (in_old_region)
+			continue;
+		fprintf(cron_in, "%s\n", line.buf);
+		if (in_old_region && !strcmp(line.buf, END_LINE))
+			in_old_region = 0;
+	}
+
+	if (run_maintenance) {
+		fprintf(cron_in, "\n%s\n", BEGIN_LINE);
+		fprintf(cron_in, "# The following schedule was created by Git\n");
+		fprintf(cron_in, "# Any edits made in this region might be\n");
+		fprintf(cron_in, "# replaced in the future by a Git command.\n\n");
+
+		fprintf(cron_in, "0 * * * * git for-each-repo --config=maintenance.repo maintenance run --scheduled\n");
+
+		fprintf(cron_in, "\n%s\n", END_LINE);
+	}
+
+	fflush(cron_in);
+	fclose(cron_in);
+	close(crontab_edit.in);
+
+done_editing:
+	if (finish_command(&crontab_edit)) {
+		result = error(_("'crontab' died"));
+		goto cleanup;
+	}
+	fclose(cron_list);
+
+cleanup:
+	rollback_lock_file(&lk);
+	return result;
+}
+
+static int maintenance_start(void)
+{
+	if (maintenance_register())
+		warning(_("failed to add repo to global config"));
+
+	return update_background_schedule(1);
+}
+
+static int maintenance_stop(void)
+{
+	return update_background_schedule(0);
+}
+
 int cmd_maintenance(int argc, const char **argv, const char *prefix)
 {
 	static struct option builtin_maintenance_options[] = {
@@ -1546,6 +1680,10 @@ int cmd_maintenance(int argc, const char **argv, const char *prefix)
 			return maintenance_register();
 		if (!strcmp(argv[0], "run"))
 			return maintenance_run();
+		if (!strcmp(argv[0], "start"))
+			return maintenance_start();
+		if (!strcmp(argv[0], "stop"))
+			return maintenance_stop();
 		if (!strcmp(argv[0], "unregister"))
 			return maintenance_unregister();
 	}

t/helper/test-crontab.c

@@ -0,0 +1,35 @@
+#include "test-tool.h"
+#include "cache.h"
+
+/*
+ * Usage: test-tool cron <file> [-l]
+ *
+ * If -l is specified, then write the contents of <file> to stdou.
+ * Otherwise, write from stdin into <file>.
+ */
+int cmd__crontab(int argc, const char **argv)
+{
+	char a;
+	FILE *from, *to;
+
+	if (argc == 3 && !strcmp(argv[2], "-l")) {
+		from = fopen(argv[1], "r");
+		if (!from)
+			return 0;
+		to = stdout;
+	} else if (argc == 2) {
+		from = stdin;
+		to = fopen(argv[1], "w");
+	} else
+		return error("unknown arguments");
+
+	while ((a = fgetc(from)) != EOF)
+		fputc(a, to);
+
+	if (argc == 3)
+		fclose(from);
+	else
+		fclose(to);
+
+	return 0;
+}

t/helper/test-tool.c

@@ -18,6 +18,7 @@ static struct test_cmd cmds[] = {
 	{ "bloom", cmd__bloom },
 	{ "chmtime", cmd__chmtime },
 	{ "config", cmd__config },
+	{ "crontab", cmd__crontab },
 	{ "ctype", cmd__ctype },
 	{ "date", cmd__date },
 	{ "delta", cmd__delta },

t/helper/test-tool.h

@@ -8,6 +8,7 @@ int cmd__advise_if_enabled(int argc, const char **argv);
 int cmd__bloom(int argc, const char **argv);
 int cmd__chmtime(int argc, const char **argv);
 int cmd__config(int argc, const char **argv);
+int cmd__crontab(int argc, const char **argv);
 int cmd__ctype(int argc, const char **argv);
 int cmd__date(int argc, const char **argv);
 int cmd__delta(int argc, const char **argv);

t/t7900-maintenance.sh

@@ -270,4 +270,48 @@ test_expect_success 'register and unregister' '
 	test_cmp before actual
 '
 
+test_expect_success 'start from empty cron table' '
+	GIT_TEST_CRONTAB="test-tool crontab cron.txt" git maintenance start &&
+
+	# start registers the repo
+	git config --get --global maintenance.repo "$TRASH_DIRECTORY" &&
+
+	cat >scheduled <<-\EOF &&
+
+	# BEGIN GIT MAINTENANCE SCHEDULE
+	# The following schedule was created by Git
+	# Any edits made in this region might be
+	# replaced in the future by a Git command.
+
+	0 * * * * git for-each-repo --config=maintenance.repo maintenance run --scheduled
+
+	# END GIT MAINTENANCE SCHEDULE
+	EOF
+	test_cmp scheduled cron.txt
+'
+
+test_expect_success 'stop from existing schedule' '
+	GIT_TEST_CRONTAB="test-tool crontab cron.txt" git maintenance stop &&
+
+	# stop does not unregister the repo
+	git config --get --global maintenance.repo "$TRASH_DIRECTORY" &&
+
+	# The newline is preserved
+	echo >empty &&
+	test_cmp empty cron.txt &&
+
+	# Operation is idempotent
+	GIT_TEST_CRONTAB="test-tool crontab cron.txt" git maintenance stop &&
+	test_cmp empty cron.txt
+'
+
+test_expect_success 'start preserves existing schedule' '
+	echo "Important information!" >warning &&
+	cat warning >cron.txt &&
+	GIT_TEST_CRONTAB="test-tool crontab cron.txt" git maintenance start &&
+	cat warning >kept-warning &&
+	cat scheduled >>kept-warning &&
+	test_cmp kept-warning cron.txt
+'
+
 test_done

t/test-lib.sh

@@ -1692,3 +1692,9 @@ test_lazy_prereq SHA1 '
 test_lazy_prereq REBASE_P '
 	test -z "$GIT_TEST_SKIP_REBASE_P"
 '
+
+# Ensure that no test accidentally triggers a Git command
+# that runs 'crontab', affecting a user's cron schedule.
+# Tests that verify the cron integration must set this locally
+# to avoid errors.
+GIT_TEST_CRONTAB="exit 1"