#include "cache.h"
#include "mru.h"
#include "pack.h"
#include "dir.h"
#include "mergesort.h"
#include "packfile.h"

char *odb_pack_name(struct strbuf *buf,
                    const unsigned char *sha1,
                    const char *ext)
{
        strbuf_reset(buf);
        strbuf_addf(buf, "%s/pack/pack-%s.%s", get_object_directory(),
                    sha1_to_hex(sha1), ext);
        return buf->buf;
}

char *sha1_pack_name(const unsigned char *sha1)
{
        static struct strbuf buf = STRBUF_INIT;
        return odb_pack_name(&buf, sha1, "pack");
}

char *sha1_pack_index_name(const unsigned char *sha1)
{
        static struct strbuf buf = STRBUF_INIT;
        return odb_pack_name(&buf, sha1, "idx");
}

static unsigned int pack_used_ctr;
static unsigned int pack_mmap_calls;
static unsigned int peak_pack_open_windows;
static unsigned int pack_open_windows;
static unsigned int pack_open_fds;
static unsigned int pack_max_fds;
static size_t peak_pack_mapped;
static size_t pack_mapped;
struct packed_git *packed_git;

static struct mru packed_git_mru_storage;
struct mru *packed_git_mru = &packed_git_mru_storage;

#define SZ_FMT PRIuMAX
static inline uintmax_t sz_fmt(size_t s) { return s; }

void pack_report(void)
{
        fprintf(stderr,
                "pack_report: getpagesize()            = %10" SZ_FMT "\n"
                "pack_report: core.packedGitWindowSize = %10" SZ_FMT "\n"
                "pack_report: core.packedGitLimit      = %10" SZ_FMT "\n",
                sz_fmt(getpagesize()),
                sz_fmt(packed_git_window_size),
                sz_fmt(packed_git_limit));
        fprintf(stderr,
                "pack_report: pack_used_ctr            = %10u\n"
                "pack_report: pack_mmap_calls          = %10u\n"
                "pack_report: pack_open_windows        = %10u / %10u\n"
                "pack_report: pack_mapped              = "
                        "%10" SZ_FMT " / %10" SZ_FMT "\n",
                pack_used_ctr,
                pack_mmap_calls,
                pack_open_windows, peak_pack_open_windows,
                sz_fmt(pack_mapped), sz_fmt(peak_pack_mapped));
}

/*
 * Open and mmap the index file at path, perform a couple of
 * consistency checks, then record its information to p.  Return 0 on
 * success.
 */
static int check_packed_git_idx(const char *path, struct packed_git *p)
{
        void *idx_map;
        struct pack_idx_header *hdr;
        size_t idx_size;
        uint32_t version, nr, i, *index;
        int fd = git_open(path);
        struct stat st;

        if (fd < 0)
                return -1;
        if (fstat(fd, &st)) {
                close(fd);
                return -1;
        }
        idx_size = xsize_t(st.st_size);
        if (idx_size < 4 * 256 + 20 + 20) {
                close(fd);
                return error("index file %s is too small", path);
        }
        idx_map = xmmap(NULL, idx_size, PROT_READ, MAP_PRIVATE, fd, 0);
        close(fd);

        hdr = idx_map;
        if (hdr->idx_signature == htonl(PACK_IDX_SIGNATURE)) {
                version = ntohl(hdr->idx_version);
                if (version < 2 || version > 2) {
                        munmap(idx_map, idx_size);
                        return error("index file %s is version %"PRIu32
                                     " and is not supported by this binary"
                                     " (try upgrading GIT to a newer version)",
                                     path, version);
                }
        } else
                version = 1;

        nr = 0;
        index = idx_map;
        if (version > 1)
                index += 2;  /* skip index header */
        for (i = 0; i < 256; i++) {
                uint32_t n = ntohl(index[i]);
                if (n < nr) {
                        munmap(idx_map, idx_size);
                        return error("non-monotonic index %s", path);
                }
                nr = n;
        }

        if (version == 1) {
                /*
                 * Total size:
                 *  - 256 index entries 4 bytes each
                 *  - 24-byte entries * nr (20-byte sha1 + 4-byte offset)
                 *  - 20-byte SHA1 of the packfile
                 *  - 20-byte SHA1 file checksum
                 */
                if (idx_size != 4*256 + nr * 24 + 20 + 20) {
                        munmap(idx_map, idx_size);
                        return error("wrong index v1 file size in %s", path);
                }
        } else if (version == 2) {
                /*
                 * Minimum size:
                 *  - 8 bytes of header
                 *  - 256 index entries 4 bytes each
                 *  - 20-byte sha1 entry * nr
                 *  - 4-byte crc entry * nr
                 *  - 4-byte offset entry * nr
                 *  - 20-byte SHA1 of the packfile
                 *  - 20-byte SHA1 file checksum
                 * And after the 4-byte offset table might be a
                 * variable sized table containing 8-byte entries
                 * for offsets larger than 2^31.
                 */
                unsigned long min_size = 8 + 4*256 + nr*(20 + 4 + 4) + 20 + 20;
                unsigned long max_size = min_size;
                if (nr)
                        max_size += (nr - 1)*8;
                if (idx_size < min_size || idx_size > max_size) {
                        munmap(idx_map, idx_size);
                        return error("wrong index v2 file size in %s", path);
                }
                if (idx_size != min_size &&
                    /*
                     * make sure we can deal with large pack offsets.
                     * 31-bit signed offset won't be enough, neither
                     * 32-bit unsigned one will be.
                     */
                    (sizeof(off_t) <= 4)) {
                        munmap(idx_map, idx_size);
                        return error("pack too large for current definition of off_t in %s", path);
                }
        }

        p->index_version = version;
        p->index_data = idx_map;
        p->index_size = idx_size;
        p->num_objects = nr;
        return 0;
}

int open_pack_index(struct packed_git *p)
{
        char *idx_name;
        size_t len;
        int ret;

        if (p->index_data)
                return 0;

        if (!strip_suffix(p->pack_name, ".pack", &len))
                die("BUG: pack_name does not end in .pack");
        idx_name = xstrfmt("%.*s.idx", (int)len, p->pack_name);
        ret = check_packed_git_idx(idx_name, p);
        free(idx_name);
        return ret;
}

static struct packed_git *alloc_packed_git(int extra)
{
        struct packed_git *p = xmalloc(st_add(sizeof(*p), extra));
        memset(p, 0, sizeof(*p));
        p->pack_fd = -1;
        return p;
}

struct packed_git *parse_pack_index(unsigned char *sha1, const char *idx_path)
{
        const char *path = sha1_pack_name(sha1);
        size_t alloc = st_add(strlen(path), 1);
        struct packed_git *p = alloc_packed_git(alloc);

        memcpy(p->pack_name, path, alloc); /* includes NUL */
        hashcpy(p->sha1, sha1);
        if (check_packed_git_idx(idx_path, p)) {
                free(p);
                return NULL;
        }

        return p;
}

static void scan_windows(struct packed_git *p,
        struct packed_git **lru_p,
        struct pack_window **lru_w,
        struct pack_window **lru_l)
{
        struct pack_window *w, *w_l;

        for (w_l = NULL, w = p->windows; w; w = w->next) {
                if (!w->inuse_cnt) {
                        if (!*lru_w || w->last_used < (*lru_w)->last_used) {
                                *lru_p = p;
                                *lru_w = w;
                                *lru_l = w_l;
                        }
                }
                w_l = w;
        }
}

static int unuse_one_window(struct packed_git *current)
{
        struct packed_git *p, *lru_p = NULL;
        struct pack_window *lru_w = NULL, *lru_l = NULL;

        if (current)
                scan_windows(current, &lru_p, &lru_w, &lru_l);
        for (p = packed_git; p; p = p->next)
                scan_windows(p, &lru_p, &lru_w, &lru_l);
        if (lru_p) {
                munmap(lru_w->base, lru_w->len);
                pack_mapped -= lru_w->len;
                if (lru_l)
                        lru_l->next = lru_w->next;
                else
                        lru_p->windows = lru_w->next;
                free(lru_w);
                pack_open_windows--;
                return 1;
        }
        return 0;
}

void release_pack_memory(size_t need)
{
        size_t cur = pack_mapped;
        while (need >= (cur - pack_mapped) && unuse_one_window(NULL))
                ; /* nothing */
}

void close_pack_windows(struct packed_git *p)
{
        while (p->windows) {
                struct pack_window *w = p->windows;

                if (w->inuse_cnt)
                        die("pack '%s' still has open windows to it",
                            p->pack_name);
                munmap(w->base, w->len);
                pack_mapped -= w->len;
                pack_open_windows--;
                p->windows = w->next;
                free(w);
        }
}

static int close_pack_fd(struct packed_git *p)
{
        if (p->pack_fd < 0)
                return 0;

        close(p->pack_fd);
        pack_open_fds--;
        p->pack_fd = -1;

        return 1;
}

void close_pack_index(struct packed_git *p)
{
        if (p->index_data) {
                munmap((void *)p->index_data, p->index_size);
                p->index_data = NULL;
        }
}

static void close_pack(struct packed_git *p)
{
        close_pack_windows(p);
        close_pack_fd(p);
        close_pack_index(p);
}

void close_all_packs(void)
{
        struct packed_git *p;

        for (p = packed_git; p; p = p->next)
                if (p->do_not_close)
                        die("BUG: want to close pack marked 'do-not-close'");
                else
                        close_pack(p);
}

/*
 * The LRU pack is the one with the oldest MRU window, preferring packs
 * with no used windows, or the oldest mtime if it has no windows allocated.
 */
static void find_lru_pack(struct packed_git *p, struct packed_git **lru_p, struct pack_window **mru_w, int *accept_windows_inuse)
{
        struct pack_window *w, *this_mru_w;
        int has_windows_inuse = 0;

        /*
         * Reject this pack if it has windows and the previously selected
         * one does not.  If this pack does not have windows, reject
         * it if the pack file is newer than the previously selected one.
         */
        if (*lru_p && !*mru_w && (p->windows || p->mtime > (*lru_p)->mtime))
                return;

        for (w = this_mru_w = p->windows; w; w = w->next) {
                /*
                 * Reject this pack if any of its windows are in use,
                 * but the previously selected pack did not have any
                 * inuse windows.  Otherwise, record that this pack
                 * has windows in use.
                 */
                if (w->inuse_cnt) {
                        if (*accept_windows_inuse)
                                has_windows_inuse = 1;
                        else
                                return;
                }

                if (w->last_used > this_mru_w->last_used)
                        this_mru_w = w;

                /*
                 * Reject this pack if it has windows that have been
                 * used more recently than the previously selected pack.
                 * If the previously selected pack had windows inuse and
                 * we have not encountered a window in this pack that is
                 * inuse, skip this check since we prefer a pack with no
                 * inuse windows to one that has inuse windows.
                 */
                if (*mru_w && *accept_windows_inuse == has_windows_inuse &&
                    this_mru_w->last_used > (*mru_w)->last_used)
                        return;
        }

        /*
         * Select this pack.
         */
        *mru_w = this_mru_w;
        *lru_p = p;
        *accept_windows_inuse = has_windows_inuse;
}

static int close_one_pack(void)
{
        struct packed_git *p, *lru_p = NULL;
        struct pack_window *mru_w = NULL;
        int accept_windows_inuse = 1;

        for (p = packed_git; p; p = p->next) {
                if (p->pack_fd == -1)
                        continue;
                find_lru_pack(p, &lru_p, &mru_w, &accept_windows_inuse);
        }

        if (lru_p)
                return close_pack_fd(lru_p);

        return 0;
}

static unsigned int get_max_fd_limit(void)
{
#ifdef RLIMIT_NOFILE
        {
                struct rlimit lim;

                if (!getrlimit(RLIMIT_NOFILE, &lim))
                        return lim.rlim_cur;
        }
#endif

#ifdef _SC_OPEN_MAX
        {
                long open_max = sysconf(_SC_OPEN_MAX);
                if (0 < open_max)
                        return open_max;
                /*
                 * Otherwise, we got -1 for one of the two
                 * reasons:
                 *
                 * (1) sysconf() did not understand _SC_OPEN_MAX
                 *     and signaled an error with -1; or
                 * (2) sysconf() said there is no limit.
                 *
                 * We _could_ clear errno before calling sysconf() to
                 * tell these two cases apart and return a huge number
                 * in the latter case to let the caller cap it to a
                 * value that is not so selfish, but letting the
                 * fallback OPEN_MAX codepath take care of these cases
                 * is a lot simpler.
                 */
        }
#endif

#ifdef OPEN_MAX
        return OPEN_MAX;
#else
        return 1; /* see the caller ;-) */
#endif
}

/*
 * Do not call this directly as this leaks p->pack_fd on error return;
 * call open_packed_git() instead.
 */
static int open_packed_git_1(struct packed_git *p)
{
        struct stat st;
        struct pack_header hdr;
        unsigned char sha1[20];
        unsigned char *idx_sha1;
        long fd_flag;

        if (!p->index_data && open_pack_index(p))
                return error("packfile %s index unavailable", p->pack_name);

        if (!pack_max_fds) {
                unsigned int max_fds = get_max_fd_limit();

                /* Save 3 for stdin/stdout/stderr, 22 for work */
                if (25 < max_fds)
                        pack_max_fds = max_fds - 25;
                else
                        pack_max_fds = 1;
        }

        while (pack_max_fds <= pack_open_fds && close_one_pack())
                ; /* nothing */

        p->pack_fd = git_open(p->pack_name);
        if (p->pack_fd < 0 || fstat(p->pack_fd, &st))
                return -1;
        pack_open_fds++;

        /* If we created the struct before we had the pack we lack size. */
        if (!p->pack_size) {
                if (!S_ISREG(st.st_mode))
                        return error("packfile %s not a regular file", p->pack_name);
                p->pack_size = st.st_size;
        } else if (p->pack_size != st.st_size)
                return error("packfile %s size changed", p->pack_name);

        /* We leave these file descriptors open with sliding mmap;
         * there is no point keeping them open across exec(), though.
         */
        fd_flag = fcntl(p->pack_fd, F_GETFD, 0);
        if (fd_flag < 0)
                return error("cannot determine file descriptor flags");
        fd_flag |= FD_CLOEXEC;
        if (fcntl(p->pack_fd, F_SETFD, fd_flag) == -1)
                return error("cannot set FD_CLOEXEC");

        /* Verify we recognize this pack file format. */
        if (read_in_full(p->pack_fd, &hdr, sizeof(hdr)) != sizeof(hdr))
                return error("file %s is far too short to be a packfile", p->pack_name);
        if (hdr.hdr_signature != htonl(PACK_SIGNATURE))
                return error("file %s is not a GIT packfile", p->pack_name);
        if (!pack_version_ok(hdr.hdr_version))
                return error("packfile %s is version %"PRIu32" and not"
                        " supported (try upgrading GIT to a newer version)",
                        p->pack_name, ntohl(hdr.hdr_version));

        /* Verify the pack matches its index. */
        if (p->num_objects != ntohl(hdr.hdr_entries))
                return error("packfile %s claims to have %"PRIu32" objects"
                             " while index indicates %"PRIu32" objects",
                             p->pack_name, ntohl(hdr.hdr_entries),
                             p->num_objects);
        if (lseek(p->pack_fd, p->pack_size - sizeof(sha1), SEEK_SET) == -1)
                return error("end of packfile %s is unavailable", p->pack_name);
        if (read_in_full(p->pack_fd, sha1, sizeof(sha1)) != sizeof(sha1))
                return error("packfile %s signature is unavailable", p->pack_name);
        idx_sha1 = ((unsigned char *)p->index_data) + p->index_size - 40;
        if (hashcmp(sha1, idx_sha1))
                return error("packfile %s does not match index", p->pack_name);
        return 0;
}

int open_packed_git(struct packed_git *p)
{
        if (!open_packed_git_1(p))
                return 0;
        close_pack_fd(p);
        return -1;
}

static int in_window(struct pack_window *win, off_t offset)
{
        /* We must promise at least 20 bytes (one hash) after the
         * offset is available from this window, otherwise the offset
         * is not actually in this window and a different window (which
         * has that one hash excess) must be used.  This is to support
         * the object header and delta base parsing routines below.
         */
        off_t win_off = win->offset;
        return win_off <= offset
                && (offset + 20) <= (win_off + win->len);
}

unsigned char *use_pack(struct packed_git *p,
                struct pack_window **w_cursor,
                off_t offset,
                unsigned long *left)
{
        struct pack_window *win = *w_cursor;

        /* Since packfiles end in a hash of their content and it's
         * pointless to ask for an offset into the middle of that
         * hash, and the in_window function above wouldn't match
         * don't allow an offset too close to the end of the file.
         */
        if (!p->pack_size && p->pack_fd == -1 && open_packed_git(p))
                die("packfile %s cannot be accessed", p->pack_name);
        if (offset > (p->pack_size - 20))
                die("offset beyond end of packfile (truncated pack?)");
        if (offset < 0)
                die(_("offset before end of packfile (broken .idx?)"));

        if (!win || !in_window(win, offset)) {
                if (win)
                        win->inuse_cnt--;
                for (win = p->windows; win; win = win->next) {
                        if (in_window(win, offset))
                                break;
                }
                if (!win) {
                        size_t window_align = packed_git_window_size / 2;
                        off_t len;

                        if (p->pack_fd == -1 && open_packed_git(p))
                                die("packfile %s cannot be accessed", p->pack_name);

                        win = xcalloc(1, sizeof(*win));
                        win->offset = (offset / window_align) * window_align;
                        len = p->pack_size - win->offset;
                        if (len > packed_git_window_size)
                                len = packed_git_window_size;
                        win->len = (size_t)len;
                        pack_mapped += win->len;
                        while (packed_git_limit < pack_mapped
                                && unuse_one_window(p))
                                ; /* nothing */
                        win->base = xmmap(NULL, win->len,
                                PROT_READ, MAP_PRIVATE,
                                p->pack_fd, win->offset);
                        if (win->base == MAP_FAILED)
                                die_errno("packfile %s cannot be mapped",
                                          p->pack_name);
                        if (!win->offset && win->len == p->pack_size
                                && !p->do_not_close)
                                close_pack_fd(p);
                        pack_mmap_calls++;
                        pack_open_windows++;
                        if (pack_mapped > peak_pack_mapped)
                                peak_pack_mapped = pack_mapped;
                        if (pack_open_windows > peak_pack_open_windows)
                                peak_pack_open_windows = pack_open_windows;
                        win->next = p->windows;
                        p->windows = win;
                }
        }
        if (win != *w_cursor) {
                win->last_used = pack_used_ctr++;
                win->inuse_cnt++;
                *w_cursor = win;
        }
        offset -= win->offset;
        if (left)
                *left = win->len - xsize_t(offset);
        return win->base + offset;
}

void unuse_pack(struct pack_window **w_cursor)
{
        struct pack_window *w = *w_cursor;
        if (w) {
                w->inuse_cnt--;
                *w_cursor = NULL;
        }
}

static void try_to_free_pack_memory(size_t size)
{
        release_pack_memory(size);
}

struct packed_git *add_packed_git(const char *path, size_t path_len, int local)
{
        static int have_set_try_to_free_routine;
        struct stat st;
        size_t alloc;
        struct packed_git *p;

        if (!have_set_try_to_free_routine) {
                have_set_try_to_free_routine = 1;
                set_try_to_free_routine(try_to_free_pack_memory);
        }

        /*
         * Make sure a corresponding .pack file exists and that
         * the index looks sane.
         */
        if (!strip_suffix_mem(path, &path_len, ".idx"))
                return NULL;

        /*
         * ".pack" is long enough to hold any suffix we're adding (and
         * the use xsnprintf double-checks that)
         */
        alloc = st_add3(path_len, strlen(".pack"), 1);
        p = alloc_packed_git(alloc);
        memcpy(p->pack_name, path, path_len);

        xsnprintf(p->pack_name + path_len, alloc - path_len, ".keep");
        if (!access(p->pack_name, F_OK))
                p->pack_keep = 1;

        xsnprintf(p->pack_name + path_len, alloc - path_len, ".pack");
        if (stat(p->pack_name, &st) || !S_ISREG(st.st_mode)) {
                free(p);
                return NULL;
        }

        /* ok, it looks sane as far as we can check without
         * actually mapping the pack file.
         */
        p->pack_size = st.st_size;
        p->pack_local = local;
        p->mtime = st.st_mtime;
        if (path_len < 40 || get_sha1_hex(path + path_len - 40, p->sha1))
                hashclr(p->sha1);
        return p;
}

void install_packed_git(struct packed_git *pack)
{
        if (pack->pack_fd != -1)
                pack_open_fds++;

        pack->next = packed_git;
        packed_git = pack;
}

void (*report_garbage)(unsigned seen_bits, const char *path);

static void report_helper(const struct string_list *list,
                          int seen_bits, int first, int last)
{
        if (seen_bits == (PACKDIR_FILE_PACK|PACKDIR_FILE_IDX))
                return;

        for (; first < last; first++)
                report_garbage(seen_bits, list->items[first].string);
}

static void report_pack_garbage(struct string_list *list)
{
        int i, baselen = -1, first = 0, seen_bits = 0;

        if (!report_garbage)
                return;

        string_list_sort(list);

        for (i = 0; i < list->nr; i++) {
                const char *path = list->items[i].string;
                if (baselen != -1 &&
                    strncmp(path, list->items[first].string, baselen)) {
                        report_helper(list, seen_bits, first, i);
                        baselen = -1;
                        seen_bits = 0;
                }
                if (baselen == -1) {
                        const char *dot = strrchr(path, '.');
                        if (!dot) {
                                report_garbage(PACKDIR_FILE_GARBAGE, path);
                                continue;
                        }
                        baselen = dot - path + 1;
                        first = i;
                }
                if (!strcmp(path + baselen, "pack"))
                        seen_bits |= 1;
                else if (!strcmp(path + baselen, "idx"))
                        seen_bits |= 2;
        }
        report_helper(list, seen_bits, first, list->nr);
}

static void prepare_packed_git_one(char *objdir, int local)
{
        struct strbuf path = STRBUF_INIT;
        size_t dirnamelen;
        DIR *dir;
        struct dirent *de;
        struct string_list garbage = STRING_LIST_INIT_DUP;

        strbuf_addstr(&path, objdir);
        strbuf_addstr(&path, "/pack");
        dir = opendir(path.buf);
        if (!dir) {
                if (errno != ENOENT)
                        error_errno("unable to open object pack directory: %s",
                                    path.buf);
                strbuf_release(&path);
                return;
        }
        strbuf_addch(&path, '/');
        dirnamelen = path.len;
        while ((de = readdir(dir)) != NULL) {
                struct packed_git *p;
                size_t base_len;

                if (is_dot_or_dotdot(de->d_name))
                        continue;

                strbuf_setlen(&path, dirnamelen);
                strbuf_addstr(&path, de->d_name);

                base_len = path.len;
                if (strip_suffix_mem(path.buf, &base_len, ".idx")) {
                        /* Don't reopen a pack we already have. */
                        for (p = packed_git; p; p = p->next) {
                                size_t len;
                                if (strip_suffix(p->pack_name, ".pack", &len) &&
                                    len == base_len &&
                                    !memcmp(p->pack_name, path.buf, len))
                                        break;
                        }
                        if (p == NULL &&
                            /*
                             * See if it really is a valid .idx file with
                             * corresponding .pack file that we can map.
                             */
                            (p = add_packed_git(path.buf, path.len, local)) != NULL)
                                install_packed_git(p);
                }

                if (!report_garbage)
                        continue;

                if (ends_with(de->d_name, ".idx") ||
                    ends_with(de->d_name, ".pack") ||
                    ends_with(de->d_name, ".bitmap") ||
                    ends_with(de->d_name, ".keep"))
                        string_list_append(&garbage, path.buf);
                else
                        report_garbage(PACKDIR_FILE_GARBAGE, path.buf);
        }
        closedir(dir);
        report_pack_garbage(&garbage);
        string_list_clear(&garbage, 0);
        strbuf_release(&path);
}

static int approximate_object_count_valid;

/*
 * Give a fast, rough count of the number of objects in the repository. This
 * ignores loose objects completely. If you have a lot of them, then either
 * you should repack because your performance will be awful, or they are
 * all unreachable objects about to be pruned, in which case they're not really
 * interesting as a measure of repo size in the first place.
 */
unsigned long approximate_object_count(void)
{
        static unsigned long count;
        if (!approximate_object_count_valid) {
                struct packed_git *p;

                prepare_packed_git();
                count = 0;
                for (p = packed_git; p; p = p->next) {
                        if (open_pack_index(p))
                                continue;
                        count += p->num_objects;
                }
        }
        return count;
}

static void *get_next_packed_git(const void *p)
{
        return ((const struct packed_git *)p)->next;
}

static void set_next_packed_git(void *p, void *next)
{
        ((struct packed_git *)p)->next = next;
}

static int sort_pack(const void *a_, const void *b_)
{
        const struct packed_git *a = a_;
        const struct packed_git *b = b_;
        int st;

        /*
         * Local packs tend to contain objects specific to our
         * variant of the project than remote ones.  In addition,
         * remote ones could be on a network mounted filesystem.
         * Favor local ones for these reasons.
         */
        st = a->pack_local - b->pack_local;
        if (st)
                return -st;

        /*
         * Younger packs tend to contain more recent objects,
         * and more recent objects tend to get accessed more
         * often.
         */
        if (a->mtime < b->mtime)
                return 1;
        else if (a->mtime == b->mtime)
                return 0;
        return -1;
}

static void rearrange_packed_git(void)
{
        packed_git = llist_mergesort(packed_git, get_next_packed_git,
                                     set_next_packed_git, sort_pack);
}

static void prepare_packed_git_mru(void)
{
        struct packed_git *p;

        mru_clear(packed_git_mru);
        for (p = packed_git; p; p = p->next)
                mru_append(packed_git_mru, p);
}

static int prepare_packed_git_run_once = 0;
void prepare_packed_git(void)
{
        struct alternate_object_database *alt;

        if (prepare_packed_git_run_once)
                return;
        prepare_packed_git_one(get_object_directory(), 1);
        prepare_alt_odb();
        for (alt = alt_odb_list; alt; alt = alt->next)
                prepare_packed_git_one(alt->path, 0);
        rearrange_packed_git();
        prepare_packed_git_mru();
        prepare_packed_git_run_once = 1;
}

void reprepare_packed_git(void)
{
        approximate_object_count_valid = 0;
        prepare_packed_git_run_once = 0;
        prepare_packed_git();
}

unsigned long unpack_object_header_buffer(const unsigned char *buf,
                unsigned long len, enum object_type *type, unsigned long *sizep)
{
        unsigned shift;
        unsigned long size, c;
        unsigned long used = 0;

        c = buf[used++];
        *type = (c >> 4) & 7;
        size = c & 15;
        shift = 4;
        while (c & 0x80) {
                if (len <= used || bitsizeof(long) <= shift) {
                        error("bad object header");
                        size = used = 0;
                        break;
                }
                c = buf[used++];
                size += (c & 0x7f) << shift;
                shift += 7;
        }
        *sizep = size;
        return used;
}