Merge branch 'tb/enable-cruft-packs-by-default'

[git.git] / builtin / gc.c

/*
 * git gc builtin command
 *
 * Cleanup unreachable files and optimize the repository.
 *
 * Copyright (c) 2007 James Bowes
 *
 * Based on git-gc.sh, which is
 *
 * Copyright (c) 2006 Shawn O. Pearce
 */

#include "builtin.h"
#include "abspath.h"
#include "environment.h"
#include "hex.h"
#include "repository.h"
#include "config.h"
#include "tempfile.h"
#include "lockfile.h"
#include "parse-options.h"
#include "run-command.h"
#include "sigchain.h"
#include "strvec.h"
#include "commit.h"
#include "commit-graph.h"
#include "packfile.h"
#include "object-file.h"
#include "object-store.h"
#include "pack.h"
#include "pack-objects.h"
#include "blob.h"
#include "tree.h"
#include "promisor-remote.h"
#include "refs.h"
#include "remote.h"
#include "exec-cmd.h"
#include "gettext.h"
#include "hook.h"
#include "setup.h"
#include "trace2.h"
#include "wrapper.h"

#define FAILED_RUN "failed to run %s"

static const char * const builtin_gc_usage[] = {
        N_("git gc [<options>]"),
        NULL
};

static int pack_refs = 1;
static int prune_reflogs = 1;
static int cruft_packs = 1;
static int aggressive_depth = 50;
static int aggressive_window = 250;
static int gc_auto_threshold = 6700;
static int gc_auto_pack_limit = 50;
static int detach_auto = 1;
static timestamp_t gc_log_expire_time;
static const char *gc_log_expire = "1.day.ago";
static const char *prune_expire = "2.weeks.ago";
static const char *prune_worktrees_expire = "3.months.ago";
static unsigned long big_pack_threshold;
static unsigned long max_delta_cache_size = DEFAULT_DELTA_CACHE_SIZE;

static struct strvec reflog = STRVEC_INIT;
static struct strvec repack = STRVEC_INIT;
static struct strvec prune = STRVEC_INIT;
static struct strvec prune_worktrees = STRVEC_INIT;
static struct strvec rerere = STRVEC_INIT;

static struct tempfile *pidfile;
static struct lock_file log_lock;

static struct string_list pack_garbage = STRING_LIST_INIT_DUP;

static void clean_pack_garbage(void)
{
        int i;
        for (i = 0; i < pack_garbage.nr; i++)
                unlink_or_warn(pack_garbage.items[i].string);
        string_list_clear(&pack_garbage, 0);
}

static void report_pack_garbage(unsigned seen_bits, const char *path)
{
        if (seen_bits == PACKDIR_FILE_IDX)
                string_list_append(&pack_garbage, path);
}

static void process_log_file(void)
{
        struct stat st;
        if (fstat(get_lock_file_fd(&log_lock), &st)) {
                /*
                 * Perhaps there was an i/o error or another
                 * unlikely situation.  Try to make a note of
                 * this in gc.log along with any existing
                 * messages.
                 */
                int saved_errno = errno;
                fprintf(stderr, _("Failed to fstat %s: %s"),
                        get_lock_file_path(&log_lock),
                        strerror(saved_errno));
                fflush(stderr);
                commit_lock_file(&log_lock);
                errno = saved_errno;
        } else if (st.st_size) {
                /* There was some error recorded in the lock file */
                commit_lock_file(&log_lock);
        } else {
                /* No error, clean up any old gc.log */
                unlink(git_path("gc.log"));
                rollback_lock_file(&log_lock);
        }
}

static void process_log_file_at_exit(void)
{
        fflush(stderr);
        process_log_file();
}

static void process_log_file_on_signal(int signo)
{
        process_log_file();
        sigchain_pop(signo);
        raise(signo);
}

static int gc_config_is_timestamp_never(const char *var)
{
        const char *value;
        timestamp_t expire;

        if (!git_config_get_value(var, &value) && value) {
                if (parse_expiry_date(value, &expire))
                        die(_("failed to parse '%s' value '%s'"), var, value);
                return expire == 0;
        }
        return 0;
}

static void gc_config(void)
{
        const char *value;

        if (!git_config_get_value("gc.packrefs", &value)) {
                if (value && !strcmp(value, "notbare"))
                        pack_refs = -1;
                else
                        pack_refs = git_config_bool("gc.packrefs", value);
        }

        if (gc_config_is_timestamp_never("gc.reflogexpire") &&
            gc_config_is_timestamp_never("gc.reflogexpireunreachable"))
                prune_reflogs = 0;

        git_config_get_int("gc.aggressivewindow", &aggressive_window);
        git_config_get_int("gc.aggressivedepth", &aggressive_depth);
        git_config_get_int("gc.auto", &gc_auto_threshold);
        git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
        git_config_get_bool("gc.autodetach", &detach_auto);
        git_config_get_bool("gc.cruftpacks", &cruft_packs);
        git_config_get_expiry("gc.pruneexpire", &prune_expire);
        git_config_get_expiry("gc.worktreepruneexpire", &prune_worktrees_expire);
        git_config_get_expiry("gc.logexpiry", &gc_log_expire);

        git_config_get_ulong("gc.bigpackthreshold", &big_pack_threshold);
        git_config_get_ulong("pack.deltacachesize", &max_delta_cache_size);

        git_config(git_default_config, NULL);
}

struct maintenance_run_opts;
static int maintenance_task_pack_refs(MAYBE_UNUSED struct maintenance_run_opts *opts)
{
        struct child_process cmd = CHILD_PROCESS_INIT;

        cmd.git_cmd = 1;
        strvec_pushl(&cmd.args, "pack-refs", "--all", "--prune", NULL);
        return run_command(&cmd);
}

static int too_many_loose_objects(void)
{
        /*
         * Quickly check if a "gc" is needed, by estimating how
         * many loose objects there are.  Because SHA-1 is evenly
         * distributed, we can check only one and get a reasonable
         * estimate.
         */
        DIR *dir;
        struct dirent *ent;
        int auto_threshold;
        int num_loose = 0;
        int needed = 0;
        const unsigned hexsz_loose = the_hash_algo->hexsz - 2;

        dir = opendir(git_path("objects/17"));
        if (!dir)
                return 0;

        auto_threshold = DIV_ROUND_UP(gc_auto_threshold, 256);
        while ((ent = readdir(dir)) != NULL) {
                if (strspn(ent->d_name, "0123456789abcdef") != hexsz_loose ||
                    ent->d_name[hexsz_loose] != '\0')
                        continue;
                if (++num_loose > auto_threshold) {
                        needed = 1;
                        break;
                }
        }
        closedir(dir);
        return needed;
}

static struct packed_git *find_base_packs(struct string_list *packs,
                                          unsigned long limit)
{
        struct packed_git *p, *base = NULL;

        for (p = get_all_packs(the_repository); p; p = p->next) {
                if (!p->pack_local || p->is_cruft)
                        continue;
                if (limit) {
                        if (p->pack_size >= limit)
                                string_list_append(packs, p->pack_name);
                } else if (!base || base->pack_size < p->pack_size) {
                        base = p;
                }
        }

        if (base)
                string_list_append(packs, base->pack_name);

        return base;
}

static int too_many_packs(void)
{
        struct packed_git *p;
        int cnt;

        if (gc_auto_pack_limit <= 0)
                return 0;

        for (cnt = 0, p = get_all_packs(the_repository); p; p = p->next) {
                if (!p->pack_local)
                        continue;
                if (p->pack_keep)
                        continue;
                /*
                 * Perhaps check the size of the pack and count only
                 * very small ones here?
                 */
                cnt++;
        }
        return gc_auto_pack_limit < cnt;
}

static uint64_t total_ram(void)
{
#if defined(HAVE_SYSINFO)
        struct sysinfo si;

        if (!sysinfo(&si))
                return si.totalram;
#elif defined(HAVE_BSD_SYSCTL) && (defined(HW_MEMSIZE) || defined(HW_PHYSMEM))
        int64_t physical_memory;
        int mib[2];
        size_t length;

        mib[0] = CTL_HW;
# if defined(HW_MEMSIZE)
        mib[1] = HW_MEMSIZE;
# else
        mib[1] = HW_PHYSMEM;
# endif
        length = sizeof(int64_t);
        if (!sysctl(mib, 2, &physical_memory, &length, NULL, 0))
                return physical_memory;
#elif defined(GIT_WINDOWS_NATIVE)
        MEMORYSTATUSEX memInfo;

        memInfo.dwLength = sizeof(MEMORYSTATUSEX);
        if (GlobalMemoryStatusEx(&memInfo))
                return memInfo.ullTotalPhys;
#endif
        return 0;
}

static uint64_t estimate_repack_memory(struct packed_git *pack)
{
        unsigned long nr_objects = repo_approximate_object_count(the_repository);
        size_t os_cache, heap;

        if (!pack || !nr_objects)
                return 0;

        /*
         * First we have to scan through at least one pack.
         * Assume enough room in OS file cache to keep the entire pack
         * or we may accidentally evict data of other processes from
         * the cache.
         */
        os_cache = pack->pack_size + pack->index_size;
        /* then pack-objects needs lots more for book keeping */
        heap = sizeof(struct object_entry) * nr_objects;
        /*
         * internal rev-list --all --objects takes up some memory too,
         * let's say half of it is for blobs
         */
        heap += sizeof(struct blob) * nr_objects / 2;
        /*
         * and the other half is for trees (commits and tags are
         * usually insignificant)
         */
        heap += sizeof(struct tree) * nr_objects / 2;
        /* and then obj_hash[], underestimated in fact */
        heap += sizeof(struct object *) * nr_objects;
        /* revindex is used also */
        heap += (sizeof(off_t) + sizeof(uint32_t)) * nr_objects;
        /*
         * read_sha1_file() (either at delta calculation phase, or
         * writing phase) also fills up the delta base cache
         */
        heap += delta_base_cache_limit;
        /* and of course pack-objects has its own delta cache */
        heap += max_delta_cache_size;

        return os_cache + heap;
}

static int keep_one_pack(struct string_list_item *item, void *data UNUSED)
{
        strvec_pushf(&repack, "--keep-pack=%s", basename(item->string));
        return 0;
}

static void add_repack_all_option(struct string_list *keep_pack)
{
        if (prune_expire && !strcmp(prune_expire, "now"))
                strvec_push(&repack, "-a");
        else if (cruft_packs) {
                strvec_push(&repack, "--cruft");
                if (prune_expire)
                        strvec_pushf(&repack, "--cruft-expiration=%s", prune_expire);
        } else {
                strvec_push(&repack, "-A");
                if (prune_expire)
                        strvec_pushf(&repack, "--unpack-unreachable=%s", prune_expire);
        }

        if (keep_pack)
                for_each_string_list(keep_pack, keep_one_pack, NULL);
}

static void add_repack_incremental_option(void)
{
        strvec_push(&repack, "--no-write-bitmap-index");
}

static int need_to_gc(void)
{
        /*
         * Setting gc.auto to 0 or negative can disable the
         * automatic gc.
         */
        if (gc_auto_threshold <= 0)
                return 0;

        /*
         * If there are too many loose objects, but not too many
         * packs, we run "repack -d -l".  If there are too many packs,
         * we run "repack -A -d -l".  Otherwise we tell the caller
         * there is no need.
         */
        if (too_many_packs()) {
                struct string_list keep_pack = STRING_LIST_INIT_NODUP;

                if (big_pack_threshold) {
                        find_base_packs(&keep_pack, big_pack_threshold);
                        if (keep_pack.nr >= gc_auto_pack_limit) {
                                big_pack_threshold = 0;
                                string_list_clear(&keep_pack, 0);
                                find_base_packs(&keep_pack, 0);
                        }
                } else {
                        struct packed_git *p = find_base_packs(&keep_pack, 0);
                        uint64_t mem_have, mem_want;

                        mem_have = total_ram();
                        mem_want = estimate_repack_memory(p);

                        /*
                         * Only allow 1/2 of memory for pack-objects, leave
                         * the rest for the OS and other processes in the
                         * system.
                         */
                        if (!mem_have || mem_want < mem_have / 2)
                                string_list_clear(&keep_pack, 0);
                }

                add_repack_all_option(&keep_pack);
                string_list_clear(&keep_pack, 0);
        } else if (too_many_loose_objects())
                add_repack_incremental_option();
        else
                return 0;

        if (run_hooks("pre-auto-gc"))
                return 0;
        return 1;
}

/* return NULL on success, else hostname running the gc */
static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
{
        struct lock_file lock = LOCK_INIT;
        char my_host[HOST_NAME_MAX + 1];
        struct strbuf sb = STRBUF_INIT;
        struct stat st;
        uintmax_t pid;
        FILE *fp;
        int fd;
        char *pidfile_path;

        if (is_tempfile_active(pidfile))
                /* already locked */
                return NULL;

        if (xgethostname(my_host, sizeof(my_host)))
                xsnprintf(my_host, sizeof(my_host), "unknown");

        pidfile_path = git_pathdup("gc.pid");
        fd = hold_lock_file_for_update(&lock, pidfile_path,
                                       LOCK_DIE_ON_ERROR);
        if (!force) {
                static char locking_host[HOST_NAME_MAX + 1];
                static char *scan_fmt;
                int should_exit;

                if (!scan_fmt)
                        scan_fmt = xstrfmt("%s %%%ds", "%"SCNuMAX, HOST_NAME_MAX);
                fp = fopen(pidfile_path, "r");
                memset(locking_host, 0, sizeof(locking_host));
                should_exit =
                        fp != NULL &&
                        !fstat(fileno(fp), &st) &&
                        /*
                         * 12 hour limit is very generous as gc should
                         * never take that long. On the other hand we
                         * don't really need a strict limit here,
                         * running gc --auto one day late is not a big
                         * problem. --force can be used in manual gc
                         * after the user verifies that no gc is
                         * running.
                         */
                        time(NULL) - st.st_mtime <= 12 * 3600 &&
                        fscanf(fp, scan_fmt, &pid, locking_host) == 2 &&
                        /* be gentle to concurrent "gc" on remote hosts */
                        (strcmp(locking_host, my_host) || !kill(pid, 0) || errno == EPERM);
                if (fp)
                        fclose(fp);
                if (should_exit) {
                        if (fd >= 0)
                                rollback_lock_file(&lock);
                        *ret_pid = pid;
                        free(pidfile_path);
                        return locking_host;
                }
        }

        strbuf_addf(&sb, "%"PRIuMAX" %s",
                    (uintmax_t) getpid(), my_host);
        write_in_full(fd, sb.buf, sb.len);
        strbuf_release(&sb);
        commit_lock_file(&lock);
        pidfile = register_tempfile(pidfile_path);
        free(pidfile_path);
        return NULL;
}

/*
 * Returns 0 if there was no previous error and gc can proceed, 1 if
 * gc should not proceed due to an error in the last run. Prints a
 * message and returns with a non-[01] status code if an error occurred
 * while reading gc.log
 */
static int report_last_gc_error(void)
{
        struct strbuf sb = STRBUF_INIT;
        int ret = 0;
        ssize_t len;
        struct stat st;
        char *gc_log_path = git_pathdup("gc.log");

        if (stat(gc_log_path, &st)) {
                if (errno == ENOENT)
                        goto done;

                ret = die_message_errno(_("cannot stat '%s'"), gc_log_path);
                goto done;
        }

        if (st.st_mtime < gc_log_expire_time)
                goto done;

        len = strbuf_read_file(&sb, gc_log_path, 0);
        if (len < 0)
                ret = die_message_errno(_("cannot read '%s'"), gc_log_path);
        else if (len > 0) {
                /*
                 * A previous gc failed.  Report the error, and don't
                 * bother with an automatic gc run since it is likely
                 * to fail in the same way.
                 */
                warning(_("The last gc run reported the following. "
                               "Please correct the root cause\n"
                               "and remove %s\n"
                               "Automatic cleanup will not be performed "
                               "until the file is removed.\n\n"
                               "%s"),
                            gc_log_path, sb.buf);
                ret = 1;
        }
        strbuf_release(&sb);
done:
        free(gc_log_path);
        return ret;
}

static void gc_before_repack(void)
{
        /*
         * We may be called twice, as both the pre- and
         * post-daemonized phases will call us, but running these
         * commands more than once is pointless and wasteful.
         */
        static int done = 0;
        if (done++)
                return;

        if (pack_refs && maintenance_task_pack_refs(NULL))
                die(FAILED_RUN, "pack-refs");

        if (prune_reflogs) {
                struct child_process cmd = CHILD_PROCESS_INIT;

                cmd.git_cmd = 1;
                strvec_pushv(&cmd.args, reflog.v);
                if (run_command(&cmd))
                        die(FAILED_RUN, reflog.v[0]);
        }
}

int cmd_gc(int argc, const char **argv, const char *prefix)
{
        int aggressive = 0;
        int auto_gc = 0;
        int quiet = 0;
        int force = 0;
        const char *name;
        pid_t pid;
        int daemonized = 0;
        int keep_largest_pack = -1;
        timestamp_t dummy;
        struct child_process rerere_cmd = CHILD_PROCESS_INIT;

        struct option builtin_gc_options[] = {
                OPT__QUIET(&quiet, N_("suppress progress reporting")),
                { OPTION_STRING, 0, "prune", &prune_expire, N_("date"),
                        N_("prune unreferenced objects"),
                        PARSE_OPT_OPTARG, NULL, (intptr_t)prune_expire },
                OPT_BOOL(0, "cruft", &cruft_packs, N_("pack unreferenced objects separately")),
                OPT_BOOL(0, "aggressive", &aggressive, N_("be more thorough (increased runtime)")),
                OPT_BOOL_F(0, "auto", &auto_gc, N_("enable auto-gc mode"),
                           PARSE_OPT_NOCOMPLETE),
                OPT_BOOL_F(0, "force", &force,
                           N_("force running gc even if there may be another gc running"),
                           PARSE_OPT_NOCOMPLETE),
                OPT_BOOL(0, "keep-largest-pack", &keep_largest_pack,
                         N_("repack all other packs except the largest pack")),
                OPT_END()
        };

        if (argc == 2 && !strcmp(argv[1], "-h"))
                usage_with_options(builtin_gc_usage, builtin_gc_options);

        strvec_pushl(&reflog, "reflog", "expire", "--all", NULL);
        strvec_pushl(&repack, "repack", "-d", "-l", NULL);
        strvec_pushl(&prune, "prune", "--expire", NULL);
        strvec_pushl(&prune_worktrees, "worktree", "prune", "--expire", NULL);
        strvec_pushl(&rerere, "rerere", "gc", NULL);

        /* default expiry time, overwritten in gc_config */
        gc_config();
        if (parse_expiry_date(gc_log_expire, &gc_log_expire_time))
                die(_("failed to parse gc.logExpiry value %s"), gc_log_expire);

        if (pack_refs < 0)
                pack_refs = !is_bare_repository();

        argc = parse_options(argc, argv, prefix, builtin_gc_options,
                             builtin_gc_usage, 0);
        if (argc > 0)
                usage_with_options(builtin_gc_usage, builtin_gc_options);

        if (prune_expire && parse_expiry_date(prune_expire, &dummy))
                die(_("failed to parse prune expiry value %s"), prune_expire);

        if (aggressive) {
                strvec_push(&repack, "-f");
                if (aggressive_depth > 0)
                        strvec_pushf(&repack, "--depth=%d", aggressive_depth);
                if (aggressive_window > 0)
                        strvec_pushf(&repack, "--window=%d", aggressive_window);
        }
        if (quiet)
                strvec_push(&repack, "-q");

        if (auto_gc) {
                /*
                 * Auto-gc should be least intrusive as possible.
                 */
                if (!need_to_gc())
                        return 0;
                if (!quiet) {
                        if (detach_auto)
                                fprintf(stderr, _("Auto packing the repository in background for optimum performance.\n"));
                        else
                                fprintf(stderr, _("Auto packing the repository for optimum performance.\n"));
                        fprintf(stderr, _("See \"git help gc\" for manual housekeeping.\n"));
                }
                if (detach_auto) {
                        int ret = report_last_gc_error();

                        if (ret == 1)
                                /* Last gc --auto failed. Skip this one. */
                                return 0;
                        else if (ret)
                                /* an I/O error occurred, already reported */
                                return ret;

                        if (lock_repo_for_gc(force, &pid))
                                return 0;
                        gc_before_repack(); /* dies on failure */
                        delete_tempfile(&pidfile);

                        /*
                         * failure to daemonize is ok, we'll continue
                         * in foreground
                         */
                        daemonized = !daemonize();
                }
        } else {
                struct string_list keep_pack = STRING_LIST_INIT_NODUP;

                if (keep_largest_pack != -1) {
                        if (keep_largest_pack)
                                find_base_packs(&keep_pack, 0);
                } else if (big_pack_threshold) {
                        find_base_packs(&keep_pack, big_pack_threshold);
                }

                add_repack_all_option(&keep_pack);
                string_list_clear(&keep_pack, 0);
        }

        name = lock_repo_for_gc(force, &pid);
        if (name) {
                if (auto_gc)
                        return 0; /* be quiet on --auto */
                die(_("gc is already running on machine '%s' pid %"PRIuMAX" (use --force if not)"),
                    name, (uintmax_t)pid);
        }

        if (daemonized) {
                hold_lock_file_for_update(&log_lock,
                                          git_path("gc.log"),
                                          LOCK_DIE_ON_ERROR);
                dup2(get_lock_file_fd(&log_lock), 2);
                sigchain_push_common(process_log_file_on_signal);
                atexit(process_log_file_at_exit);
        }

        gc_before_repack();

        if (!repository_format_precious_objects) {
                struct child_process repack_cmd = CHILD_PROCESS_INIT;

                repack_cmd.git_cmd = 1;
                repack_cmd.close_object_store = 1;
                strvec_pushv(&repack_cmd.args, repack.v);
                if (run_command(&repack_cmd))
                        die(FAILED_RUN, repack.v[0]);

                if (prune_expire) {
                        struct child_process prune_cmd = CHILD_PROCESS_INIT;

                        /* run `git prune` even if using cruft packs */
                        strvec_push(&prune, prune_expire);
                        if (quiet)
                                strvec_push(&prune, "--no-progress");
                        if (repo_has_promisor_remote(the_repository))
                                strvec_push(&prune,
                                            "--exclude-promisor-objects");
                        prune_cmd.git_cmd = 1;
                        strvec_pushv(&prune_cmd.args, prune.v);
                        if (run_command(&prune_cmd))
                                die(FAILED_RUN, prune.v[0]);
                }
        }

        if (prune_worktrees_expire) {
                struct child_process prune_worktrees_cmd = CHILD_PROCESS_INIT;

                strvec_push(&prune_worktrees, prune_worktrees_expire);
                prune_worktrees_cmd.git_cmd = 1;
                strvec_pushv(&prune_worktrees_cmd.args, prune_worktrees.v);
                if (run_command(&prune_worktrees_cmd))
                        die(FAILED_RUN, prune_worktrees.v[0]);
        }

        rerere_cmd.git_cmd = 1;
        strvec_pushv(&rerere_cmd.args, rerere.v);
        if (run_command(&rerere_cmd))
                die(FAILED_RUN, rerere.v[0]);

        report_garbage = report_pack_garbage;
        reprepare_packed_git(the_repository);
        if (pack_garbage.nr > 0) {
                close_object_store(the_repository->objects);
                clean_pack_garbage();
        }

        if (the_repository->settings.gc_write_commit_graph == 1)
                write_commit_graph_reachable(the_repository->objects->odb,
                                             !quiet && !daemonized ? COMMIT_GRAPH_WRITE_PROGRESS : 0,
                                             NULL);

        if (auto_gc && too_many_loose_objects())
                warning(_("There are too many unreachable loose objects; "
                        "run 'git prune' to remove them."));

        if (!daemonized)
                unlink(git_path("gc.log"));

        return 0;
}

static const char *const builtin_maintenance_run_usage[] = {
        N_("git maintenance run [--auto] [--[no-]quiet] [--task=<task>] [--schedule]"),
        NULL
};

enum schedule_priority {
        SCHEDULE_NONE = 0,
        SCHEDULE_WEEKLY = 1,
        SCHEDULE_DAILY = 2,
        SCHEDULE_HOURLY = 3,
};

static enum schedule_priority parse_schedule(const char *value)
{
        if (!value)
                return SCHEDULE_NONE;
        if (!strcasecmp(value, "hourly"))
                return SCHEDULE_HOURLY;
        if (!strcasecmp(value, "daily"))
                return SCHEDULE_DAILY;
        if (!strcasecmp(value, "weekly"))
                return SCHEDULE_WEEKLY;
        return SCHEDULE_NONE;
}

static int maintenance_opt_schedule(const struct option *opt, const char *arg,
                                    int unset)
{
        enum schedule_priority *priority = opt->value;

        if (unset)
                die(_("--no-schedule is not allowed"));

        *priority = parse_schedule(arg);

        if (!*priority)
                die(_("unrecognized --schedule argument '%s'"), arg);

        return 0;
}

struct maintenance_run_opts {
        int auto_flag;
        int quiet;
        enum schedule_priority schedule;
};

/* Remember to update object flag allocation in object.h */
#define SEEN            (1u<<0)

struct cg_auto_data {
        int num_not_in_graph;
        int limit;
};

static int dfs_on_ref(const char *refname UNUSED,
                      const struct object_id *oid,
                      int flags UNUSED,
                      void *cb_data)
{
        struct cg_auto_data *data = (struct cg_auto_data *)cb_data;
        int result = 0;
        struct object_id peeled;
        struct commit_list *stack = NULL;
        struct commit *commit;

        if (!peel_iterated_oid(oid, &peeled))
                oid = &peeled;
        if (oid_object_info(the_repository, oid, NULL) != OBJ_COMMIT)
                return 0;

        commit = lookup_commit(the_repository, oid);
        if (!commit)
                return 0;
        if (repo_parse_commit(the_repository, commit) ||
            commit_graph_position(commit) != COMMIT_NOT_FROM_GRAPH)
                return 0;

        data->num_not_in_graph++;

        if (data->num_not_in_graph >= data->limit)
                return 1;

        commit_list_append(commit, &stack);

        while (!result && stack) {
                struct commit_list *parent;

                commit = pop_commit(&stack);

                for (parent = commit->parents; parent; parent = parent->next) {
                        if (repo_parse_commit(the_repository, parent->item) ||
                            commit_graph_position(parent->item) != COMMIT_NOT_FROM_GRAPH ||
                            parent->item->object.flags & SEEN)
                                continue;

                        parent->item->object.flags |= SEEN;
                        data->num_not_in_graph++;

                        if (data->num_not_in_graph >= data->limit) {
                                result = 1;
                                break;
                        }

                        commit_list_append(parent->item, &stack);
                }
        }

        free_commit_list(stack);
        return result;
}

static int should_write_commit_graph(void)
{
        int result;
        struct cg_auto_data data;

        data.num_not_in_graph = 0;
        data.limit = 100;
        git_config_get_int("maintenance.commit-graph.auto",
                           &data.limit);

        if (!data.limit)
                return 0;
        if (data.limit < 0)
                return 1;

        result = for_each_ref(dfs_on_ref, &data);

        repo_clear_commit_marks(the_repository, SEEN);

        return result;
}

static int run_write_commit_graph(struct maintenance_run_opts *opts)
{
        struct child_process child = CHILD_PROCESS_INIT;

        child.git_cmd = child.close_object_store = 1;
        strvec_pushl(&child.args, "commit-graph", "write",
                     "--split", "--reachable", NULL);

        if (opts->quiet)
                strvec_push(&child.args, "--no-progress");

        return !!run_command(&child);
}

static int maintenance_task_commit_graph(struct maintenance_run_opts *opts)
{
        prepare_repo_settings(the_repository);
        if (!the_repository->settings.core_commit_graph)
                return 0;

        if (run_write_commit_graph(opts)) {
                error(_("failed to write commit-graph"));
                return 1;
        }

        return 0;
}

static int fetch_remote(struct remote *remote, void *cbdata)
{
        struct maintenance_run_opts *opts = cbdata;
        struct child_process child = CHILD_PROCESS_INIT;

        if (remote->skip_default_update)
                return 0;

        child.git_cmd = 1;
        strvec_pushl(&child.args, "fetch", remote->name,
                     "--prefetch", "--prune", "--no-tags",
                     "--no-write-fetch-head", "--recurse-submodules=no",
                     NULL);

        if (opts->quiet)
                strvec_push(&child.args, "--quiet");

        return !!run_command(&child);
}

static int maintenance_task_prefetch(struct maintenance_run_opts *opts)
{
        if (for_each_remote(fetch_remote, opts)) {
                error(_("failed to prefetch remotes"));
                return 1;
        }

        return 0;
}

static int maintenance_task_gc(struct maintenance_run_opts *opts)
{
        struct child_process child = CHILD_PROCESS_INIT;

        child.git_cmd = child.close_object_store = 1;
        strvec_push(&child.args, "gc");

        if (opts->auto_flag)
                strvec_push(&child.args, "--auto");
        if (opts->quiet)
                strvec_push(&child.args, "--quiet");
        else
                strvec_push(&child.args, "--no-quiet");

        return run_command(&child);
}

static int prune_packed(struct maintenance_run_opts *opts)
{
        struct child_process child = CHILD_PROCESS_INIT;

        child.git_cmd = 1;
        strvec_push(&child.args, "prune-packed");

        if (opts->quiet)
                strvec_push(&child.args, "--quiet");

        return !!run_command(&child);
}

struct write_loose_object_data {
        FILE *in;
        int count;
        int batch_size;
};

static int loose_object_auto_limit = 100;

static int loose_object_count(const struct object_id *oid UNUSED,
                              const char *path UNUSED,
                              void *data)
{
        int *count = (int*)data;
        if (++(*count) >= loose_object_auto_limit)
                return 1;
        return 0;
}

static int loose_object_auto_condition(void)
{
        int count = 0;

        git_config_get_int("maintenance.loose-objects.auto",
                           &loose_object_auto_limit);

        if (!loose_object_auto_limit)
                return 0;
        if (loose_object_auto_limit < 0)
                return 1;

        return for_each_loose_file_in_objdir(the_repository->objects->odb->path,
                                             loose_object_count,
                                             NULL, NULL, &count);
}

static int bail_on_loose(const struct object_id *oid UNUSED,
                         const char *path UNUSED,
                         void *data UNUSED)
{
        return 1;
}

static int write_loose_object_to_stdin(const struct object_id *oid,
                                       const char *path UNUSED,
                                       void *data)
{
        struct write_loose_object_data *d = (struct write_loose_object_data *)data;

        fprintf(d->in, "%s\n", oid_to_hex(oid));

        return ++(d->count) > d->batch_size;
}

static int pack_loose(struct maintenance_run_opts *opts)
{
        struct repository *r = the_repository;
        int result = 0;
        struct write_loose_object_data data;
        struct child_process pack_proc = CHILD_PROCESS_INIT;

        /*
         * Do not start pack-objects process
         * if there are no loose objects.
         */
        if (!for_each_loose_file_in_objdir(r->objects->odb->path,
                                           bail_on_loose,
                                           NULL, NULL, NULL))
                return 0;

        pack_proc.git_cmd = 1;

        strvec_push(&pack_proc.args, "pack-objects");
        if (opts->quiet)
                strvec_push(&pack_proc.args, "--quiet");
        strvec_pushf(&pack_proc.args, "%s/pack/loose", r->objects->odb->path);

        pack_proc.in = -1;

        if (start_command(&pack_proc)) {
                error(_("failed to start 'git pack-objects' process"));
                return 1;
        }

        data.in = xfdopen(pack_proc.in, "w");
        data.count = 0;
        data.batch_size = 50000;

        for_each_loose_file_in_objdir(r->objects->odb->path,
                                      write_loose_object_to_stdin,
                                      NULL,
                                      NULL,
                                      &data);

        fclose(data.in);

        if (finish_command(&pack_proc)) {
                error(_("failed to finish 'git pack-objects' process"));
                result = 1;
        }

        return result;
}

static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
{
        return prune_packed(opts) || pack_loose(opts);
}

static int incremental_repack_auto_condition(void)
{
        struct packed_git *p;
        int incremental_repack_auto_limit = 10;
        int count = 0;

        prepare_repo_settings(the_repository);
        if (!the_repository->settings.core_multi_pack_index)
                return 0;

        git_config_get_int("maintenance.incremental-repack.auto",
                           &incremental_repack_auto_limit);

        if (!incremental_repack_auto_limit)
                return 0;
        if (incremental_repack_auto_limit < 0)
                return 1;

        for (p = get_packed_git(the_repository);
             count < incremental_repack_auto_limit && p;
             p = p->next) {
                if (!p->multi_pack_index)
                        count++;
        }

        return count >= incremental_repack_auto_limit;
}

static int multi_pack_index_write(struct maintenance_run_opts *opts)
{
        struct child_process child = CHILD_PROCESS_INIT;

        child.git_cmd = 1;
        strvec_pushl(&child.args, "multi-pack-index", "write", NULL);

        if (opts->quiet)
                strvec_push(&child.args, "--no-progress");

        if (run_command(&child))
                return error(_("failed to write multi-pack-index"));

        return 0;
}

static int multi_pack_index_expire(struct maintenance_run_opts *opts)
{
        struct child_process child = CHILD_PROCESS_INIT;

        child.git_cmd = child.close_object_store = 1;
        strvec_pushl(&child.args, "multi-pack-index", "expire", NULL);

        if (opts->quiet)
                strvec_push(&child.args, "--no-progress");

        if (run_command(&child))
                return error(_("'git multi-pack-index expire' failed"));

        return 0;
}

#define TWO_GIGABYTES (INT32_MAX)

static off_t get_auto_pack_size(void)
{
        /*
         * The "auto" value is special: we optimize for
         * one large pack-file (i.e. from a clone) and
         * expect the rest to be small and they can be
         * repacked quickly.
         *
         * The strategy we select here is to select a
         * size that is one more than the second largest
         * pack-file. This ensures that we will repack
         * at least two packs if there are three or more
         * packs.
         */
        off_t max_size = 0;
        off_t second_largest_size = 0;
        off_t result_size;
        struct packed_git *p;
        struct repository *r = the_repository;

        reprepare_packed_git(r);
        for (p = get_all_packs(r); p; p = p->next) {
                if (p->pack_size > max_size) {
                        second_largest_size = max_size;
                        max_size = p->pack_size;
                } else if (p->pack_size > second_largest_size)
                        second_largest_size = p->pack_size;
        }

        result_size = second_largest_size + 1;

        /* But limit ourselves to a batch size of 2g */
        if (result_size > TWO_GIGABYTES)
                result_size = TWO_GIGABYTES;

        return result_size;
}

static int multi_pack_index_repack(struct maintenance_run_opts *opts)
{
        struct child_process child = CHILD_PROCESS_INIT;

        child.git_cmd = child.close_object_store = 1;
        strvec_pushl(&child.args, "multi-pack-index", "repack", NULL);

        if (opts->quiet)
                strvec_push(&child.args, "--no-progress");

        strvec_pushf(&child.args, "--batch-size=%"PRIuMAX,
                                  (uintmax_t)get_auto_pack_size());

        if (run_command(&child))
                return error(_("'git multi-pack-index repack' failed"));

        return 0;
}

static int maintenance_task_incremental_repack(struct maintenance_run_opts *opts)
{
        prepare_repo_settings(the_repository);
        if (!the_repository->settings.core_multi_pack_index) {
                warning(_("skipping incremental-repack task because core.multiPackIndex is disabled"));
                return 0;
        }

        if (multi_pack_index_write(opts))
                return 1;
        if (multi_pack_index_expire(opts))
                return 1;
        if (multi_pack_index_repack(opts))
                return 1;
        return 0;
}

typedef int maintenance_task_fn(struct maintenance_run_opts *opts);

/*
 * An auto condition function returns 1 if the task should run
 * and 0 if the task should NOT run. See needs_to_gc() for an
 * example.
 */
typedef int maintenance_auto_fn(void);

struct maintenance_task {
        const char *name;
        maintenance_task_fn *fn;
        maintenance_auto_fn *auto_condition;
        unsigned enabled:1;

        enum schedule_priority schedule;

        /* -1 if not selected. */
        int selected_order;
};

enum maintenance_task_label {
        TASK_PREFETCH,
        TASK_LOOSE_OBJECTS,
        TASK_INCREMENTAL_REPACK,
        TASK_GC,
        TASK_COMMIT_GRAPH,
        TASK_PACK_REFS,

        /* Leave as final value */
        TASK__COUNT
};

static struct maintenance_task tasks[] = {
        [TASK_PREFETCH] = {
                "prefetch",
                maintenance_task_prefetch,
        },
        [TASK_LOOSE_OBJECTS] = {
                "loose-objects",
                maintenance_task_loose_objects,
                loose_object_auto_condition,
        },
        [TASK_INCREMENTAL_REPACK] = {
                "incremental-repack",
                maintenance_task_incremental_repack,
                incremental_repack_auto_condition,
        },
        [TASK_GC] = {
                "gc",
                maintenance_task_gc,
                need_to_gc,
                1,
        },
        [TASK_COMMIT_GRAPH] = {
                "commit-graph",
                maintenance_task_commit_graph,
                should_write_commit_graph,
        },
        [TASK_PACK_REFS] = {
                "pack-refs",
                maintenance_task_pack_refs,
                NULL,
        },
};

static int compare_tasks_by_selection(const void *a_, const void *b_)
{
        const struct maintenance_task *a = a_;
        const struct maintenance_task *b = b_;

        return b->selected_order - a->selected_order;
}

static int maintenance_run_tasks(struct maintenance_run_opts *opts)
{
        int i, found_selected = 0;
        int result = 0;
        struct lock_file lk;
        struct repository *r = the_repository;
        char *lock_path = xstrfmt("%s/maintenance", r->objects->odb->path);

        if (hold_lock_file_for_update(&lk, lock_path, LOCK_NO_DEREF) < 0) {
                /*
                 * Another maintenance command is running.
                 *
                 * If --auto was provided, then it is likely due to a
                 * recursive process stack. Do not report an error in
                 * that case.
                 */
                if (!opts->auto_flag && !opts->quiet)
                        warning(_("lock file '%s' exists, skipping maintenance"),
                                lock_path);
                free(lock_path);
                return 0;
        }
        free(lock_path);

        for (i = 0; !found_selected && i < TASK__COUNT; i++)
                found_selected = tasks[i].selected_order >= 0;

        if (found_selected)
                QSORT(tasks, TASK__COUNT, compare_tasks_by_selection);

        for (i = 0; i < TASK__COUNT; i++) {
                if (found_selected && tasks[i].selected_order < 0)
                        continue;

                if (!found_selected && !tasks[i].enabled)
                        continue;

                if (opts->auto_flag &&
                    (!tasks[i].auto_condition ||
                     !tasks[i].auto_condition()))
                        continue;

                if (opts->schedule && tasks[i].schedule < opts->schedule)
                        continue;

                trace2_region_enter("maintenance", tasks[i].name, r);
                if (tasks[i].fn(opts)) {
                        error(_("task '%s' failed"), tasks[i].name);
                        result = 1;
                }
                trace2_region_leave("maintenance", tasks[i].name, r);
        }

        rollback_lock_file(&lk);
        return result;
}

static void initialize_maintenance_strategy(void)
{
        char *config_str;

        if (git_config_get_string("maintenance.strategy", &config_str))
                return;

        if (!strcasecmp(config_str, "incremental")) {
                tasks[TASK_GC].schedule = SCHEDULE_NONE;
                tasks[TASK_COMMIT_GRAPH].enabled = 1;
                tasks[TASK_COMMIT_GRAPH].schedule = SCHEDULE_HOURLY;
                tasks[TASK_PREFETCH].enabled = 1;
                tasks[TASK_PREFETCH].schedule = SCHEDULE_HOURLY;
                tasks[TASK_INCREMENTAL_REPACK].enabled = 1;
                tasks[TASK_INCREMENTAL_REPACK].schedule = SCHEDULE_DAILY;
                tasks[TASK_LOOSE_OBJECTS].enabled = 1;
                tasks[TASK_LOOSE_OBJECTS].schedule = SCHEDULE_DAILY;
                tasks[TASK_PACK_REFS].enabled = 1;
                tasks[TASK_PACK_REFS].schedule = SCHEDULE_WEEKLY;
        }
}

static void initialize_task_config(int schedule)
{
        int i;
        struct strbuf config_name = STRBUF_INIT;
        gc_config();

        if (schedule)
                initialize_maintenance_strategy();

        for (i = 0; i < TASK__COUNT; i++) {
                int config_value;
                char *config_str;

                strbuf_reset(&config_name);
                strbuf_addf(&config_name, "maintenance.%s.enabled",
                            tasks[i].name);

                if (!git_config_get_bool(config_name.buf, &config_value))
                        tasks[i].enabled = config_value;

                strbuf_reset(&config_name);
                strbuf_addf(&config_name, "maintenance.%s.schedule",
                            tasks[i].name);

                if (!git_config_get_string(config_name.buf, &config_str)) {
                        tasks[i].schedule = parse_schedule(config_str);
                        free(config_str);
                }
        }

        strbuf_release(&config_name);
}

static int task_option_parse(const struct option *opt,
                             const char *arg, int unset)
{
        int i, num_selected = 0;
        struct maintenance_task *task = NULL;

        BUG_ON_OPT_NEG(unset);

        for (i = 0; i < TASK__COUNT; i++) {
                if (tasks[i].selected_order >= 0)
                        num_selected++;
                if (!strcasecmp(tasks[i].name, arg)) {
                        task = &tasks[i];
                }
        }

        if (!task) {
                error(_("'%s' is not a valid task"), arg);
                return 1;
        }

        if (task->selected_order >= 0) {
                error(_("task '%s' cannot be selected multiple times"), arg);
                return 1;
        }

        task->selected_order = num_selected + 1;

        return 0;
}

static int maintenance_run(int argc, const char **argv, const char *prefix)
{
        int i;
        struct maintenance_run_opts opts;
        struct option builtin_maintenance_run_options[] = {
                OPT_BOOL(0, "auto", &opts.auto_flag,
                         N_("run tasks based on the state of the repository")),
                OPT_CALLBACK(0, "schedule", &opts.schedule, N_("frequency"),
                             N_("run tasks based on frequency"),
                             maintenance_opt_schedule),
                OPT_BOOL(0, "quiet", &opts.quiet,
                         N_("do not report progress or other information over stderr")),
                OPT_CALLBACK_F(0, "task", NULL, N_("task"),
                        N_("run a specific task"),
                        PARSE_OPT_NONEG, task_option_parse),
                OPT_END()
        };
        memset(&opts, 0, sizeof(opts));

        opts.quiet = !isatty(2);

        for (i = 0; i < TASK__COUNT; i++)
                tasks[i].selected_order = -1;

        argc = parse_options(argc, argv, prefix,
                             builtin_maintenance_run_options,
                             builtin_maintenance_run_usage,
                             PARSE_OPT_STOP_AT_NON_OPTION);

        if (opts.auto_flag && opts.schedule)
                die(_("use at most one of --auto and --schedule=<frequency>"));

        initialize_task_config(opts.schedule);

        if (argc != 0)
                usage_with_options(builtin_maintenance_run_usage,
                                   builtin_maintenance_run_options);
        return maintenance_run_tasks(&opts);
}

static char *get_maintpath(void)
{
        struct strbuf sb = STRBUF_INIT;
        const char *p = the_repository->worktree ?
                the_repository->worktree : the_repository->gitdir;

        strbuf_realpath(&sb, p, 1);
        return strbuf_detach(&sb, NULL);
}

static char const * const builtin_maintenance_register_usage[] = {
        "git maintenance register [--config-file <path>]",
        NULL
};

static int maintenance_register(int argc, const char **argv, const char *prefix)
{
        char *config_file = NULL;
        struct option options[] = {
                OPT_STRING(0, "config-file", &config_file, N_("file"), N_("use given config file")),
                OPT_END(),
        };
        int found = 0;
        const char *key = "maintenance.repo";
        char *maintpath = get_maintpath();
        struct string_list_item *item;
        const struct string_list *list;

        argc = parse_options(argc, argv, prefix, options,
                             builtin_maintenance_register_usage, 0);
        if (argc)
                usage_with_options(builtin_maintenance_register_usage,
                                   options);

        /* Disable foreground maintenance */
        git_config_set("maintenance.auto", "false");

        /* Set maintenance strategy, if unset */
        if (git_config_get("maintenance.strategy"))
                git_config_set("maintenance.strategy", "incremental");

        if (!git_config_get_string_multi(key, &list)) {
                for_each_string_list_item(item, list) {
                        if (!strcmp(maintpath, item->string)) {
                                found = 1;
                                break;
                        }
                }
        }

        if (!found) {
                int rc;
                char *user_config = NULL, *xdg_config = NULL;

                if (!config_file) {
                        git_global_config(&user_config, &xdg_config);
                        config_file = user_config;
                        if (!user_config)
                                die(_("$HOME not set"));
                }
                rc = git_config_set_multivar_in_file_gently(
                        config_file, "maintenance.repo", maintpath,
                        CONFIG_REGEX_NONE, 0);
                free(user_config);
                free(xdg_config);

                if (rc)
                        die(_("unable to add '%s' value of '%s'"),
                            key, maintpath);
        }

        free(maintpath);
        return 0;
}

static char const * const builtin_maintenance_unregister_usage[] = {
        "git maintenance unregister [--config-file <path>] [--force]",
        NULL
};

static int maintenance_unregister(int argc, const char **argv, const char *prefix)
{
        int force = 0;
        char *config_file = NULL;
        struct option options[] = {
                OPT_STRING(0, "config-file", &config_file, N_("file"), N_("use given config file")),
                OPT__FORCE(&force,
                           N_("return success even if repository was not registered"),
                           PARSE_OPT_NOCOMPLETE),
                OPT_END(),
        };
        const char *key = "maintenance.repo";
        char *maintpath = get_maintpath();
        int found = 0;
        struct string_list_item *item;
        const struct string_list *list;
        struct config_set cs = { { 0 } };

        argc = parse_options(argc, argv, prefix, options,
                             builtin_maintenance_unregister_usage, 0);
        if (argc)
                usage_with_options(builtin_maintenance_unregister_usage,
                                   options);

        if (config_file) {
                git_configset_init(&cs);
                git_configset_add_file(&cs, config_file);
        }
        if (!(config_file
              ? git_configset_get_string_multi(&cs, key, &list)
              : git_config_get_string_multi(key, &list))) {
                for_each_string_list_item(item, list) {
                        if (!strcmp(maintpath, item->string)) {
                                found = 1;
                                break;
                        }
                }
        }

        if (found) {
                int rc;
                char *user_config = NULL, *xdg_config = NULL;
                if (!config_file) {
                        git_global_config(&user_config, &xdg_config);
                        config_file = user_config;
                        if (!user_config)
                                die(_("$HOME not set"));
                }
                rc = git_config_set_multivar_in_file_gently(
                        config_file, key, NULL, maintpath,
                        CONFIG_FLAGS_MULTI_REPLACE | CONFIG_FLAGS_FIXED_VALUE);
                free(user_config);
                free(xdg_config);

                if (rc &&
                    (!force || rc == CONFIG_NOTHING_SET))
                        die(_("unable to unset '%s' value of '%s'"),
                            key, maintpath);
        } else if (!force) {
                die(_("repository '%s' is not registered"), maintpath);
        }

        git_configset_clear(&cs);
        free(maintpath);
        return 0;
}

static const char *get_frequency(enum schedule_priority schedule)
{
        switch (schedule) {
        case SCHEDULE_HOURLY:
                return "hourly";
        case SCHEDULE_DAILY:
                return "daily";
        case SCHEDULE_WEEKLY:
                return "weekly";
        default:
                BUG("invalid schedule %d", schedule);
        }
}

/*
 * get_schedule_cmd` reads the GIT_TEST_MAINT_SCHEDULER environment variable
 * to mock the schedulers that `git maintenance start` rely on.
 *
 * For test purpose, GIT_TEST_MAINT_SCHEDULER can be set to a comma-separated
 * list of colon-separated key/value pairs where each pair contains a scheduler
 * and its corresponding mock.
 *
 * * If $GIT_TEST_MAINT_SCHEDULER is not set, return false and leave the
 *   arguments unmodified.
 *
 * * If $GIT_TEST_MAINT_SCHEDULER is set, return true.
 *   In this case, the *cmd value is read as input.
 *
 *   * if the input value *cmd is the key of one of the comma-separated list
 *     item, then *is_available is set to true and *cmd is modified and becomes
 *     the mock command.
 *
 *   * if the input value *cmd isn’t the key of any of the comma-separated list
 *     item, then *is_available is set to false.
 *
 * Ex.:
 *   GIT_TEST_MAINT_SCHEDULER not set
 *     +-------+-------------------------------------------------+
 *     | Input |                     Output                      |
 *     | *cmd  | return code |       *cmd        | *is_available |
 *     +-------+-------------+-------------------+---------------+
 *     | "foo" |    false    | "foo" (unchanged) |  (unchanged)  |
 *     +-------+-------------+-------------------+---------------+
 *
 *   GIT_TEST_MAINT_SCHEDULER set to “foo:./mock_foo.sh,bar:./mock_bar.sh”
 *     +-------+-------------------------------------------------+
 *     | Input |                     Output                      |
 *     | *cmd  | return code |       *cmd        | *is_available |
 *     +-------+-------------+-------------------+---------------+
 *     | "foo" |    true     |  "./mock.foo.sh"  |     true      |
 *     | "qux" |    true     | "qux" (unchanged) |     false     |
 *     +-------+-------------+-------------------+---------------+
 */
static int get_schedule_cmd(const char **cmd, int *is_available)
{
        char *testing = xstrdup_or_null(getenv("GIT_TEST_MAINT_SCHEDULER"));
        struct string_list_item *item;
        struct string_list list = STRING_LIST_INIT_NODUP;

        if (!testing)
                return 0;

        if (is_available)
                *is_available = 0;

        string_list_split_in_place(&list, testing, ',', -1);
        for_each_string_list_item(item, &list) {
                struct string_list pair = STRING_LIST_INIT_NODUP;

                if (string_list_split_in_place(&pair, item->string, ':', 2) != 2)
                        continue;

                if (!strcmp(*cmd, pair.items[0].string)) {
                        *cmd = pair.items[1].string;
                        if (is_available)
                                *is_available = 1;
                        string_list_clear(&list, 0);
                        UNLEAK(testing);
                        return 1;
                }
        }

        string_list_clear(&list, 0);
        free(testing);
        return 1;
}

static int is_launchctl_available(void)
{
        const char *cmd = "launchctl";
        int is_available;
        if (get_schedule_cmd(&cmd, &is_available))
                return is_available;

#ifdef __APPLE__
        return 1;
#else
        return 0;
#endif
}

static char *launchctl_service_name(const char *frequency)
{
        struct strbuf label = STRBUF_INIT;
        strbuf_addf(&label, "org.git-scm.git.%s", frequency);
        return strbuf_detach(&label, NULL);
}

static char *launchctl_service_filename(const char *name)
{
        char *expanded;
        struct strbuf filename = STRBUF_INIT;
        strbuf_addf(&filename, "~/Library/LaunchAgents/%s.plist", name);

        expanded = interpolate_path(filename.buf, 1);
        if (!expanded)
                die(_("failed to expand path '%s'"), filename.buf);

        strbuf_release(&filename);
        return expanded;
}

static char *launchctl_get_uid(void)
{
        return xstrfmt("gui/%d", getuid());
}

static int launchctl_boot_plist(int enable, const char *filename)
{
        const char *cmd = "launchctl";
        int result;
        struct child_process child = CHILD_PROCESS_INIT;
        char *uid = launchctl_get_uid();

        get_schedule_cmd(&cmd, NULL);
        strvec_split(&child.args, cmd);
        strvec_pushl(&child.args, enable ? "bootstrap" : "bootout", uid,
                     filename, NULL);

        child.no_stderr = 1;
        child.no_stdout = 1;

        if (start_command(&child))
                die(_("failed to start launchctl"));

        result = finish_command(&child);

        free(uid);
        return result;
}

static int launchctl_remove_plist(enum schedule_priority schedule)
{
        const char *frequency = get_frequency(schedule);
        char *name = launchctl_service_name(frequency);
        char *filename = launchctl_service_filename(name);
        int result = launchctl_boot_plist(0, filename);
        unlink(filename);
        free(filename);
        free(name);
        return result;
}

static int launchctl_remove_plists(void)
{
        return launchctl_remove_plist(SCHEDULE_HOURLY) ||
               launchctl_remove_plist(SCHEDULE_DAILY) ||
               launchctl_remove_plist(SCHEDULE_WEEKLY);
}

static int launchctl_list_contains_plist(const char *name, const char *cmd)
{
        struct child_process child = CHILD_PROCESS_INIT;

        strvec_split(&child.args, cmd);
        strvec_pushl(&child.args, "list", name, NULL);

        child.no_stderr = 1;
        child.no_stdout = 1;

        if (start_command(&child))
                die(_("failed to start launchctl"));

        /* Returns failure if 'name' doesn't exist. */
        return !finish_command(&child);
}

static int launchctl_schedule_plist(const char *exec_path, enum schedule_priority schedule)
{
        int i, fd;
        const char *preamble, *repeat;
        const char *frequency = get_frequency(schedule);
        char *name = launchctl_service_name(frequency);
        char *filename = launchctl_service_filename(name);
        struct lock_file lk = LOCK_INIT;
        static unsigned long lock_file_timeout_ms = ULONG_MAX;
        struct strbuf plist = STRBUF_INIT, plist2 = STRBUF_INIT;
        struct stat st;
        const char *cmd = "launchctl";

        get_schedule_cmd(&cmd, NULL);
        preamble = "<?xml version=\"1.0\"?>\n"
                   "<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" \"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">\n"
                   "<plist version=\"1.0\">"
                   "<dict>\n"
                   "<key>Label</key><string>%s</string>\n"
                   "<key>ProgramArguments</key>\n"
                   "<array>\n"
                   "<string>%s/git</string>\n"
                   "<string>--exec-path=%s</string>\n"
                   "<string>for-each-repo</string>\n"
                   "<string>--config=maintenance.repo</string>\n"
                   "<string>maintenance</string>\n"
                   "<string>run</string>\n"
                   "<string>--schedule=%s</string>\n"
                   "</array>\n"
                   "<key>StartCalendarInterval</key>\n"
                   "<array>\n";
        strbuf_addf(&plist, preamble, name, exec_path, exec_path, frequency);

        switch (schedule) {
        case SCHEDULE_HOURLY:
                repeat = "<dict>\n"
                         "<key>Hour</key><integer>%d</integer>\n"
                         "<key>Minute</key><integer>0</integer>\n"
                         "</dict>\n";
                for (i = 1; i <= 23; i++)
                        strbuf_addf(&plist, repeat, i);
                break;

        case SCHEDULE_DAILY:
                repeat = "<dict>\n"
                         "<key>Day</key><integer>%d</integer>\n"
                         "<key>Hour</key><integer>0</integer>\n"
                         "<key>Minute</key><integer>0</integer>\n"
                         "</dict>\n";
                for (i = 1; i <= 6; i++)
                        strbuf_addf(&plist, repeat, i);
                break;

        case SCHEDULE_WEEKLY:
                strbuf_addstr(&plist,
                              "<dict>\n"
                              "<key>Day</key><integer>0</integer>\n"
                              "<key>Hour</key><integer>0</integer>\n"
                              "<key>Minute</key><integer>0</integer>\n"
                              "</dict>\n");
                break;

        default:
                /* unreachable */
                break;
        }
        strbuf_addstr(&plist, "</array>\n</dict>\n</plist>\n");

        if (safe_create_leading_directories(filename))
                die(_("failed to create directories for '%s'"), filename);

        if ((long)lock_file_timeout_ms < 0 &&
            git_config_get_ulong("gc.launchctlplistlocktimeoutms",
                                 &lock_file_timeout_ms))
                lock_file_timeout_ms = 150;

        fd = hold_lock_file_for_update_timeout(&lk, filename, LOCK_DIE_ON_ERROR,
                                               lock_file_timeout_ms);

        /*
         * Does this file already exist? With the intended contents? Is it
         * registered already? Then it does not need to be re-registered.
         */
        if (!stat(filename, &st) && st.st_size == plist.len &&
            strbuf_read_file(&plist2, filename, plist.len) == plist.len &&
            !strbuf_cmp(&plist, &plist2) &&
            launchctl_list_contains_plist(name, cmd))
                rollback_lock_file(&lk);
        else {
                if (write_in_full(fd, plist.buf, plist.len) < 0 ||
                    commit_lock_file(&lk))
                        die_errno(_("could not write '%s'"), filename);

                /* bootout might fail if not already running, so ignore */
                launchctl_boot_plist(0, filename);
                if (launchctl_boot_plist(1, filename))
                        die(_("failed to bootstrap service %s"), filename);
        }

        free(filename);
        free(name);
        strbuf_release(&plist);
        strbuf_release(&plist2);
        return 0;
}

static int launchctl_add_plists(void)
{
        const char *exec_path = git_exec_path();

        return launchctl_schedule_plist(exec_path, SCHEDULE_HOURLY) ||
               launchctl_schedule_plist(exec_path, SCHEDULE_DAILY) ||
               launchctl_schedule_plist(exec_path, SCHEDULE_WEEKLY);
}

static int launchctl_update_schedule(int run_maintenance, int fd)
{
        if (run_maintenance)
                return launchctl_add_plists();
        else
                return launchctl_remove_plists();
}

static int is_schtasks_available(void)
{
        const char *cmd = "schtasks";
        int is_available;
        if (get_schedule_cmd(&cmd, &is_available))
                return is_available;

#ifdef GIT_WINDOWS_NATIVE
        return 1;
#else
        return 0;
#endif
}

static char *schtasks_task_name(const char *frequency)
{
        struct strbuf label = STRBUF_INIT;
        strbuf_addf(&label, "Git Maintenance (%s)", frequency);
        return strbuf_detach(&label, NULL);
}

static int schtasks_remove_task(enum schedule_priority schedule)
{
        const char *cmd = "schtasks";
        struct child_process child = CHILD_PROCESS_INIT;
        const char *frequency = get_frequency(schedule);
        char *name = schtasks_task_name(frequency);

        get_schedule_cmd(&cmd, NULL);
        strvec_split(&child.args, cmd);
        strvec_pushl(&child.args, "/delete", "/tn", name, "/f", NULL);
        free(name);

        return run_command(&child);
}

static int schtasks_remove_tasks(void)
{
        return schtasks_remove_task(SCHEDULE_HOURLY) ||
               schtasks_remove_task(SCHEDULE_DAILY) ||
               schtasks_remove_task(SCHEDULE_WEEKLY);
}

static int schtasks_schedule_task(const char *exec_path, enum schedule_priority schedule)
{
        const char *cmd = "schtasks";
        int result;
        struct child_process child = CHILD_PROCESS_INIT;
        const char *xml;
        struct tempfile *tfile;
        const char *frequency = get_frequency(schedule);
        char *name = schtasks_task_name(frequency);
        struct strbuf tfilename = STRBUF_INIT;

        get_schedule_cmd(&cmd, NULL);

        strbuf_addf(&tfilename, "%s/schedule_%s_XXXXXX",
                    get_git_common_dir(), frequency);
        tfile = xmks_tempfile(tfilename.buf);
        strbuf_release(&tfilename);

        if (!fdopen_tempfile(tfile, "w"))
                die(_("failed to create temp xml file"));

        xml = "<?xml version=\"1.0\" ?>\n"
              "<Task version=\"1.4\" xmlns=\"http://schemas.microsoft.com/windows/2004/02/mit/task\">\n"
              "<Triggers>\n"
              "<CalendarTrigger>\n";
        fputs(xml, tfile->fp);

        switch (schedule) {
        case SCHEDULE_HOURLY:
                fprintf(tfile->fp,
                        "<StartBoundary>2020-01-01T01:00:00</StartBoundary>\n"
                        "<Enabled>true</Enabled>\n"
                        "<ScheduleByDay>\n"
                        "<DaysInterval>1</DaysInterval>\n"
                        "</ScheduleByDay>\n"
                        "<Repetition>\n"
                        "<Interval>PT1H</Interval>\n"
                        "<Duration>PT23H</Duration>\n"
                        "<StopAtDurationEnd>false</StopAtDurationEnd>\n"
                        "</Repetition>\n");
                break;

        case SCHEDULE_DAILY:
                fprintf(tfile->fp,
                        "<StartBoundary>2020-01-01T00:00:00</StartBoundary>\n"
                        "<Enabled>true</Enabled>\n"
                        "<ScheduleByWeek>\n"
                        "<DaysOfWeek>\n"
                        "<Monday />\n"
                        "<Tuesday />\n"
                        "<Wednesday />\n"
                        "<Thursday />\n"
                        "<Friday />\n"
                        "<Saturday />\n"
                        "</DaysOfWeek>\n"
                        "<WeeksInterval>1</WeeksInterval>\n"
                        "</ScheduleByWeek>\n");
                break;

        case SCHEDULE_WEEKLY:
                fprintf(tfile->fp,
                        "<StartBoundary>2020-01-01T00:00:00</StartBoundary>\n"
                        "<Enabled>true</Enabled>\n"
                        "<ScheduleByWeek>\n"
                        "<DaysOfWeek>\n"
                        "<Sunday />\n"
                        "</DaysOfWeek>\n"
                        "<WeeksInterval>1</WeeksInterval>\n"
                        "</ScheduleByWeek>\n");
                break;

        default:
                break;
        }

        xml = "</CalendarTrigger>\n"
              "</Triggers>\n"
              "<Principals>\n"
              "<Principal id=\"Author\">\n"
              "<LogonType>InteractiveToken</LogonType>\n"
              "<RunLevel>LeastPrivilege</RunLevel>\n"
              "</Principal>\n"
              "</Principals>\n"
              "<Settings>\n"
              "<MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>\n"
              "<Enabled>true</Enabled>\n"
              "<Hidden>true</Hidden>\n"
              "<UseUnifiedSchedulingEngine>true</UseUnifiedSchedulingEngine>\n"
              "<WakeToRun>false</WakeToRun>\n"
              "<ExecutionTimeLimit>PT72H</ExecutionTimeLimit>\n"
              "<Priority>7</Priority>\n"
              "</Settings>\n"
              "<Actions Context=\"Author\">\n"
              "<Exec>\n"
              "<Command>\"%s\\git.exe\"</Command>\n"
              "<Arguments>--exec-path=\"%s\" for-each-repo --config=maintenance.repo maintenance run --schedule=%s</Arguments>\n"
              "</Exec>\n"
              "</Actions>\n"
              "</Task>\n";
        fprintf(tfile->fp, xml, exec_path, exec_path, frequency);
        strvec_split(&child.args, cmd);
        strvec_pushl(&child.args, "/create", "/tn", name, "/f", "/xml",
                                  get_tempfile_path(tfile), NULL);
        close_tempfile_gently(tfile);

        child.no_stdout = 1;
        child.no_stderr = 1;

        if (start_command(&child))
                die(_("failed to start schtasks"));
        result = finish_command(&child);

        delete_tempfile(&tfile);
        free(name);
        return result;
}

static int schtasks_schedule_tasks(void)
{
        const char *exec_path = git_exec_path();

        return schtasks_schedule_task(exec_path, SCHEDULE_HOURLY) ||
               schtasks_schedule_task(exec_path, SCHEDULE_DAILY) ||
               schtasks_schedule_task(exec_path, SCHEDULE_WEEKLY);
}

static int schtasks_update_schedule(int run_maintenance, int fd)
{
        if (run_maintenance)
                return schtasks_schedule_tasks();
        else
                return schtasks_remove_tasks();
}

MAYBE_UNUSED
static int check_crontab_process(const char *cmd)
{
        struct child_process child = CHILD_PROCESS_INIT;

        strvec_split(&child.args, cmd);
        strvec_push(&child.args, "-l");
        child.no_stdin = 1;
        child.no_stdout = 1;
        child.no_stderr = 1;
        child.silent_exec_failure = 1;

        if (start_command(&child))
                return 0;
        /* Ignore exit code, as an empty crontab will return error. */
        finish_command(&child);
        return 1;
}

static int is_crontab_available(void)
{
        const char *cmd = "crontab";
        int is_available;

        if (get_schedule_cmd(&cmd, &is_available))
                return is_available;

#ifdef __APPLE__
        /*
         * macOS has cron, but it requires special permissions and will
         * create a UI alert when attempting to run this command.
         */
        return 0;
#else
        return check_crontab_process(cmd);
#endif
}

#define BEGIN_LINE "# BEGIN GIT MAINTENANCE SCHEDULE"
#define END_LINE "# END GIT MAINTENANCE SCHEDULE"

static int crontab_update_schedule(int run_maintenance, int fd)
{
        const char *cmd = "crontab";
        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;
        struct strbuf line = STRBUF_INIT;
        struct tempfile *tmpedit = NULL;

        get_schedule_cmd(&cmd, NULL);
        strvec_split(&crontab_list.args, cmd);
        strvec_push(&crontab_list.args, "-l");
        crontab_list.in = -1;
        crontab_list.out = dup(fd);
        crontab_list.git_cmd = 0;

        if (start_command(&crontab_list))
                return error(_("failed to run 'crontab -l'; your system might not support 'cron'"));

        /* Ignore exit code, as an empty crontab will return error. */
        finish_command(&crontab_list);

        tmpedit = mks_tempfile_t(".git_cron_edit_tmpXXXXXX");
        if (!tmpedit) {
                result = error(_("failed to create crontab temporary file"));
                goto out;
        }
        cron_in = fdopen_tempfile(tmpedit, "w");
        if (!cron_in) {
                result = error(_("failed to open temporary file"));
                goto out;
        }

        /*
         * Read from the .lock file, filtering out the old
         * schedule while appending the new schedule.
         */
        cron_list = fdopen(fd, "r");
        rewind(cron_list);

        while (!strbuf_getline_lf(&line, cron_list)) {
                if (!in_old_region && !strcmp(line.buf, BEGIN_LINE))
                        in_old_region = 1;
                else if (in_old_region && !strcmp(line.buf, END_LINE))
                        in_old_region = 0;
                else if (!in_old_region)
                        fprintf(cron_in, "%s\n", line.buf);
        }
        strbuf_release(&line);

        if (run_maintenance) {
                struct strbuf line_format = STRBUF_INIT;
                const char *exec_path = git_exec_path();

                fprintf(cron_in, "%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");

                strbuf_addf(&line_format,
                            "%%s %%s * * %%s \"%s/git\" --exec-path=\"%s\" for-each-repo --config=maintenance.repo maintenance run --schedule=%%s\n",
                            exec_path, exec_path);
                fprintf(cron_in, line_format.buf, "0", "1-23", "*", "hourly");
                fprintf(cron_in, line_format.buf, "0", "0", "1-6", "daily");
                fprintf(cron_in, line_format.buf, "0", "0", "0", "weekly");
                strbuf_release(&line_format);

                fprintf(cron_in, "\n%s\n", END_LINE);
        }

        fflush(cron_in);

        strvec_split(&crontab_edit.args, cmd);
        strvec_push(&crontab_edit.args, get_tempfile_path(tmpedit));
        crontab_edit.git_cmd = 0;

        if (start_command(&crontab_edit)) {
                result = error(_("failed to run 'crontab'; your system might not support 'cron'"));
                goto out;
        }

        if (finish_command(&crontab_edit))
                result = error(_("'crontab' died"));
        else
                fclose(cron_list);
out:
        delete_tempfile(&tmpedit);
        return result;
}

static int real_is_systemd_timer_available(void)
{
        struct child_process child = CHILD_PROCESS_INIT;

        strvec_pushl(&child.args, "systemctl", "--user", "list-timers", NULL);
        child.no_stdin = 1;
        child.no_stdout = 1;
        child.no_stderr = 1;
        child.silent_exec_failure = 1;

        if (start_command(&child))
                return 0;
        if (finish_command(&child))
                return 0;
        return 1;
}

static int is_systemd_timer_available(void)
{
        const char *cmd = "systemctl";
        int is_available;

        if (get_schedule_cmd(&cmd, &is_available))
                return is_available;

        return real_is_systemd_timer_available();
}

static char *xdg_config_home_systemd(const char *filename)
{
        return xdg_config_home_for("systemd/user", filename);
}

static int systemd_timer_enable_unit(int enable,
                                     enum schedule_priority schedule)
{
        const char *cmd = "systemctl";
        struct child_process child = CHILD_PROCESS_INIT;
        const char *frequency = get_frequency(schedule);

        /*
         * Disabling the systemd unit while it is already disabled makes
         * systemctl print an error.
         * Let's ignore it since it means we already are in the expected state:
         * the unit is disabled.
         *
         * On the other hand, enabling a systemd unit which is already enabled
         * produces no error.
         */
        if (!enable)
                child.no_stderr = 1;

        get_schedule_cmd(&cmd, NULL);
        strvec_split(&child.args, cmd);
        strvec_pushl(&child.args, "--user", enable ? "enable" : "disable",
                     "--now", NULL);
        strvec_pushf(&child.args, "git-maintenance@%s.timer", frequency);

        if (start_command(&child))
                return error(_("failed to start systemctl"));
        if (finish_command(&child))
                /*
                 * Disabling an already disabled systemd unit makes
                 * systemctl fail.
                 * Let's ignore this failure.
                 *
                 * Enabling an enabled systemd unit doesn't fail.
                 */
                if (enable)
                        return error(_("failed to run systemctl"));
        return 0;
}

static int systemd_timer_delete_unit_templates(void)
{
        int ret = 0;
        char *filename = xdg_config_home_systemd("git-maintenance@.timer");
        if (unlink(filename) && !is_missing_file_error(errno))
                ret = error_errno(_("failed to delete '%s'"), filename);
        FREE_AND_NULL(filename);

        filename = xdg_config_home_systemd("git-maintenance@.service");
        if (unlink(filename) && !is_missing_file_error(errno))
                ret = error_errno(_("failed to delete '%s'"), filename);

        free(filename);
        return ret;
}

static int systemd_timer_delete_units(void)
{
        return systemd_timer_enable_unit(0, SCHEDULE_HOURLY) ||
               systemd_timer_enable_unit(0, SCHEDULE_DAILY) ||
               systemd_timer_enable_unit(0, SCHEDULE_WEEKLY) ||
               systemd_timer_delete_unit_templates();
}

static int systemd_timer_write_unit_templates(const char *exec_path)
{
        char *filename;
        FILE *file;
        const char *unit;

        filename = xdg_config_home_systemd("git-maintenance@.timer");
        if (safe_create_leading_directories(filename)) {
                error(_("failed to create directories for '%s'"), filename);
                goto error;
        }
        file = fopen_or_warn(filename, "w");
        if (!file)
                goto error;

        unit = "# This file was created and is maintained by Git.\n"
               "# Any edits made in this file might be replaced in the future\n"
               "# by a Git command.\n"
               "\n"
               "[Unit]\n"
               "Description=Optimize Git repositories data\n"
               "\n"
               "[Timer]\n"
               "OnCalendar=%i\n"
               "Persistent=true\n"
               "\n"
               "[Install]\n"
               "WantedBy=timers.target\n";
        if (fputs(unit, file) == EOF) {
                error(_("failed to write to '%s'"), filename);
                fclose(file);
                goto error;
        }
        if (fclose(file) == EOF) {
                error_errno(_("failed to flush '%s'"), filename);
                goto error;
        }
        free(filename);

        filename = xdg_config_home_systemd("git-maintenance@.service");
        file = fopen_or_warn(filename, "w");
        if (!file)
                goto error;

        unit = "# This file was created and is maintained by Git.\n"
               "# Any edits made in this file might be replaced in the future\n"
               "# by a Git command.\n"
               "\n"
               "[Unit]\n"
               "Description=Optimize Git repositories data\n"
               "\n"
               "[Service]\n"
               "Type=oneshot\n"
               "ExecStart=\"%s/git\" --exec-path=\"%s\" for-each-repo --config=maintenance.repo maintenance run --schedule=%%i\n"
               "LockPersonality=yes\n"
               "MemoryDenyWriteExecute=yes\n"
               "NoNewPrivileges=yes\n"
               "RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6\n"
               "RestrictNamespaces=yes\n"
               "RestrictRealtime=yes\n"
               "RestrictSUIDSGID=yes\n"
               "SystemCallArchitectures=native\n"
               "SystemCallFilter=@system-service\n";
        if (fprintf(file, unit, exec_path, exec_path) < 0) {
                error(_("failed to write to '%s'"), filename);
                fclose(file);
                goto error;
        }
        if (fclose(file) == EOF) {
                error_errno(_("failed to flush '%s'"), filename);
                goto error;
        }
        free(filename);
        return 0;

error:
        free(filename);
        systemd_timer_delete_unit_templates();
        return -1;
}

static int systemd_timer_setup_units(void)
{
        const char *exec_path = git_exec_path();

        int ret = systemd_timer_write_unit_templates(exec_path) ||
                  systemd_timer_enable_unit(1, SCHEDULE_HOURLY) ||
                  systemd_timer_enable_unit(1, SCHEDULE_DAILY) ||
                  systemd_timer_enable_unit(1, SCHEDULE_WEEKLY);
        if (ret)
                systemd_timer_delete_units();
        return ret;
}

static int systemd_timer_update_schedule(int run_maintenance, int fd)
{
        if (run_maintenance)
                return systemd_timer_setup_units();
        else
                return systemd_timer_delete_units();
}

enum scheduler {
        SCHEDULER_INVALID = -1,
        SCHEDULER_AUTO,
        SCHEDULER_CRON,
        SCHEDULER_SYSTEMD,
        SCHEDULER_LAUNCHCTL,
        SCHEDULER_SCHTASKS,
};

static const struct {
        const char *name;
        int (*is_available)(void);
        int (*update_schedule)(int run_maintenance, int fd);
} scheduler_fn[] = {
        [SCHEDULER_CRON] = {
                .name = "crontab",
                .is_available = is_crontab_available,
                .update_schedule = crontab_update_schedule,
        },
        [SCHEDULER_SYSTEMD] = {
                .name = "systemctl",
                .is_available = is_systemd_timer_available,
                .update_schedule = systemd_timer_update_schedule,
        },
        [SCHEDULER_LAUNCHCTL] = {
                .name = "launchctl",
                .is_available = is_launchctl_available,
                .update_schedule = launchctl_update_schedule,
        },
        [SCHEDULER_SCHTASKS] = {
                .name = "schtasks",
                .is_available = is_schtasks_available,
                .update_schedule = schtasks_update_schedule,
        },
};

static enum scheduler parse_scheduler(const char *value)
{
        if (!value)
                return SCHEDULER_INVALID;
        else if (!strcasecmp(value, "auto"))
                return SCHEDULER_AUTO;
        else if (!strcasecmp(value, "cron") || !strcasecmp(value, "crontab"))
                return SCHEDULER_CRON;
        else if (!strcasecmp(value, "systemd") ||
                 !strcasecmp(value, "systemd-timer"))
                return SCHEDULER_SYSTEMD;
        else if (!strcasecmp(value, "launchctl"))
                return SCHEDULER_LAUNCHCTL;
        else if (!strcasecmp(value, "schtasks"))
                return SCHEDULER_SCHTASKS;
        else
                return SCHEDULER_INVALID;
}

static int maintenance_opt_scheduler(const struct option *opt, const char *arg,
                                     int unset)
{
        enum scheduler *scheduler = opt->value;

        BUG_ON_OPT_NEG(unset);

        *scheduler = parse_scheduler(arg);
        if (*scheduler == SCHEDULER_INVALID)
                return error(_("unrecognized --scheduler argument '%s'"), arg);
        return 0;
}

struct maintenance_start_opts {
        enum scheduler scheduler;
};

static enum scheduler resolve_scheduler(enum scheduler scheduler)
{
        if (scheduler != SCHEDULER_AUTO)
                return scheduler;

#if defined(__APPLE__)
        return SCHEDULER_LAUNCHCTL;

#elif defined(GIT_WINDOWS_NATIVE)
        return SCHEDULER_SCHTASKS;

#elif defined(__linux__)
        if (is_systemd_timer_available())
                return SCHEDULER_SYSTEMD;
        else if (is_crontab_available())
                return SCHEDULER_CRON;
        else
                die(_("neither systemd timers nor crontab are available"));

#else
        return SCHEDULER_CRON;
#endif
}

static void validate_scheduler(enum scheduler scheduler)
{
        if (scheduler == SCHEDULER_INVALID)
                BUG("invalid scheduler");
        if (scheduler == SCHEDULER_AUTO)
                BUG("resolve_scheduler should have been called before");

        if (!scheduler_fn[scheduler].is_available())
                die(_("%s scheduler is not available"),
                    scheduler_fn[scheduler].name);
}

static int update_background_schedule(const struct maintenance_start_opts *opts,
                                      int enable)
{
        unsigned int i;
        int result = 0;
        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) {
                free(lock_path);
                return error(_("another process is scheduling background maintenance"));
        }

        for (i = 1; i < ARRAY_SIZE(scheduler_fn); i++) {
                if (enable && opts->scheduler == i)
                        continue;
                if (!scheduler_fn[i].is_available())
                        continue;
                scheduler_fn[i].update_schedule(0, get_lock_file_fd(&lk));
        }

        if (enable)
                result = scheduler_fn[opts->scheduler].update_schedule(
                        1, get_lock_file_fd(&lk));

        rollback_lock_file(&lk);

        free(lock_path);
        return result;
}

static const char *const builtin_maintenance_start_usage[] = {
        N_("git maintenance start [--scheduler=<scheduler>]"),
        NULL
};

static int maintenance_start(int argc, const char **argv, const char *prefix)
{
        struct maintenance_start_opts opts = { 0 };
        struct option options[] = {
                OPT_CALLBACK_F(
                        0, "scheduler", &opts.scheduler, N_("scheduler"),
                        N_("scheduler to trigger git maintenance run"),
                        PARSE_OPT_NONEG, maintenance_opt_scheduler),
                OPT_END()
        };
        const char *register_args[] = { "register", NULL };

        argc = parse_options(argc, argv, prefix, options,
                             builtin_maintenance_start_usage, 0);
        if (argc)
                usage_with_options(builtin_maintenance_start_usage, options);

        opts.scheduler = resolve_scheduler(opts.scheduler);
        validate_scheduler(opts.scheduler);

        if (maintenance_register(ARRAY_SIZE(register_args)-1, register_args, NULL))
                warning(_("failed to add repo to global config"));
        return update_background_schedule(&opts, 1);
}

static const char *const builtin_maintenance_stop_usage[] = {
        "git maintenance stop",
        NULL
};

static int maintenance_stop(int argc, const char **argv, const char *prefix)
{
        struct option options[] = {
                OPT_END()
        };
        argc = parse_options(argc, argv, prefix, options,
                             builtin_maintenance_stop_usage, 0);
        if (argc)
                usage_with_options(builtin_maintenance_stop_usage, options);
        return update_background_schedule(NULL, 0);
}

static const char * const builtin_maintenance_usage[] = {
        N_("git maintenance <subcommand> [<options>]"),
        NULL,
};

int cmd_maintenance(int argc, const char **argv, const char *prefix)
{
        parse_opt_subcommand_fn *fn = NULL;
        struct option builtin_maintenance_options[] = {
                OPT_SUBCOMMAND("run", &fn, maintenance_run),
                OPT_SUBCOMMAND("start", &fn, maintenance_start),
                OPT_SUBCOMMAND("stop", &fn, maintenance_stop),
                OPT_SUBCOMMAND("register", &fn, maintenance_register),
                OPT_SUBCOMMAND("unregister", &fn, maintenance_unregister),
                OPT_END(),
        };

        argc = parse_options(argc, argv, prefix, builtin_maintenance_options,
                             builtin_maintenance_usage, 0);
        return fn(argc, argv, prefix);
}