git-compat-util: move alloc macros to git-compat-util.h

[thirdparty/git.git] / builtin / index-pack.c

#include "builtin.h"
#include "config.h"
#include "delta.h"
#include "environment.h"
#include "gettext.h"
#include "hex.h"
#include "pack.h"
#include "csum-file.h"
#include "blob.h"
#include "commit.h"
#include "tag.h"
#include "tree.h"
#include "progress.h"
#include "fsck.h"
#include "exec-cmd.h"
#include "strbuf.h"
#include "streaming.h"
#include "thread-utils.h"
#include "packfile.h"
#include "pack-revindex.h"
#include "object-file.h"
#include "object-store-ll.h"
#include "oid-array.h"
#include "replace-object.h"
#include "promisor-remote.h"
#include "setup.h"

static const char index_pack_usage[] =
"git index-pack [-v] [-o <index-file>] [--keep | --keep=<msg>] [--[no-]rev-index] [--verify] [--strict] (<pack-file> | --stdin [--fix-thin] [<pack-file>])";

struct object_entry {
        struct pack_idx_entry idx;
        unsigned long size;
        unsigned char hdr_size;
        signed char type;
        signed char real_type;
};

struct object_stat {
        unsigned delta_depth;
        int base_object_no;
};

struct base_data {
        /* Initialized by make_base(). */
        struct base_data *base;
        struct object_entry *obj;
        int ref_first, ref_last;
        int ofs_first, ofs_last;
        /*
         * Threads should increment retain_data if they are about to call
         * patch_delta() using this struct's data as a base, and decrement this
         * when they are done. While retain_data is nonzero, this struct's data
         * will not be freed even if the delta base cache limit is exceeded.
         */
        int retain_data;
        /*
         * The number of direct children that have not been fully processed
         * (entered work_head, entered done_head, left done_head). When this
         * number reaches zero, this struct base_data can be freed.
         */
        int children_remaining;

        /* Not initialized by make_base(). */
        struct list_head list;
        void *data;
        unsigned long size;
};

/*
 * Stack of struct base_data that have unprocessed children.
 * threaded_second_pass() uses this as a source of work (the other being the
 * objects array).
 *
 * Guarded by work_mutex.
 */
static LIST_HEAD(work_head);

/*
 * Stack of struct base_data that have children, all of whom have been
 * processed or are being processed, and at least one child is being processed.
 * These struct base_data must be kept around until the last child is
 * processed.
 *
 * Guarded by work_mutex.
 */
static LIST_HEAD(done_head);

/*
 * All threads share one delta base cache.
 *
 * base_cache_used is guarded by work_mutex, and base_cache_limit is read-only
 * in a thread.
 */
static size_t base_cache_used;
static size_t base_cache_limit;

struct thread_local {
        pthread_t thread;
        int pack_fd;
};

/* Remember to update object flag allocation in object.h */
#define FLAG_LINK (1u<<20)
#define FLAG_CHECKED (1u<<21)

struct ofs_delta_entry {
        off_t offset;
        int obj_no;
};

struct ref_delta_entry {
        struct object_id oid;
        int obj_no;
};

static struct object_entry *objects;
static struct object_stat *obj_stat;
static struct ofs_delta_entry *ofs_deltas;
static struct ref_delta_entry *ref_deltas;
static struct thread_local nothread_data;
static int nr_objects;
static int nr_ofs_deltas;
static int nr_ref_deltas;
static int ref_deltas_alloc;
static int nr_resolved_deltas;
static int nr_threads;

static int from_stdin;
static int strict;
static int do_fsck_object;
static struct fsck_options fsck_options = FSCK_OPTIONS_MISSING_GITMODULES;
static int verbose;
static const char *progress_title;
static int show_resolving_progress;
static int show_stat;
static int check_self_contained_and_connected;

static struct progress *progress;

/* We always read in 4kB chunks. */
static unsigned char input_buffer[4096];
static unsigned int input_offset, input_len;
static off_t consumed_bytes;
static off_t max_input_size;
static unsigned deepest_delta;
static git_hash_ctx input_ctx;
static uint32_t input_crc32;
static int input_fd, output_fd;
static const char *curr_pack;

static struct thread_local *thread_data;
static int nr_dispatched;
static int threads_active;

static pthread_mutex_t read_mutex;
#define read_lock()             lock_mutex(&read_mutex)
#define read_unlock()           unlock_mutex(&read_mutex)

static pthread_mutex_t counter_mutex;
#define counter_lock()          lock_mutex(&counter_mutex)
#define counter_unlock()        unlock_mutex(&counter_mutex)

static pthread_mutex_t work_mutex;
#define work_lock()             lock_mutex(&work_mutex)
#define work_unlock()           unlock_mutex(&work_mutex)

static pthread_mutex_t deepest_delta_mutex;
#define deepest_delta_lock()    lock_mutex(&deepest_delta_mutex)
#define deepest_delta_unlock()  unlock_mutex(&deepest_delta_mutex)

static pthread_key_t key;

static inline void lock_mutex(pthread_mutex_t *mutex)
{
        if (threads_active)
                pthread_mutex_lock(mutex);
}

static inline void unlock_mutex(pthread_mutex_t *mutex)
{
        if (threads_active)
                pthread_mutex_unlock(mutex);
}

/*
 * Mutex and conditional variable can't be statically-initialized on Windows.
 */
static void init_thread(void)
{
        int i;
        init_recursive_mutex(&read_mutex);
        pthread_mutex_init(&counter_mutex, NULL);
        pthread_mutex_init(&work_mutex, NULL);
        if (show_stat)
                pthread_mutex_init(&deepest_delta_mutex, NULL);
        pthread_key_create(&key, NULL);
        CALLOC_ARRAY(thread_data, nr_threads);
        for (i = 0; i < nr_threads; i++) {
                thread_data[i].pack_fd = xopen(curr_pack, O_RDONLY);
        }

        threads_active = 1;
}

static void cleanup_thread(void)
{
        int i;
        if (!threads_active)
                return;
        threads_active = 0;
        pthread_mutex_destroy(&read_mutex);
        pthread_mutex_destroy(&counter_mutex);
        pthread_mutex_destroy(&work_mutex);
        if (show_stat)
                pthread_mutex_destroy(&deepest_delta_mutex);
        for (i = 0; i < nr_threads; i++)
                close(thread_data[i].pack_fd);
        pthread_key_delete(key);
        free(thread_data);
}

static int mark_link(struct object *obj, enum object_type type,
                     void *data, struct fsck_options *options)
{
        if (!obj)
                return -1;

        if (type != OBJ_ANY && obj->type != type)
                die(_("object type mismatch at %s"), oid_to_hex(&obj->oid));

        obj->flags |= FLAG_LINK;
        return 0;
}

/* The content of each linked object must have been checked
   or it must be already present in the object database */
static unsigned check_object(struct object *obj)
{
        if (!obj)
                return 0;

        if (!(obj->flags & FLAG_LINK))
                return 0;

        if (!(obj->flags & FLAG_CHECKED)) {
                unsigned long size;
                int type = oid_object_info(the_repository, &obj->oid, &size);
                if (type <= 0)
                        die(_("did not receive expected object %s"),
                              oid_to_hex(&obj->oid));
                if (type != obj->type)
                        die(_("object %s: expected type %s, found %s"),
                            oid_to_hex(&obj->oid),
                            type_name(obj->type), type_name(type));
                obj->flags |= FLAG_CHECKED;
                return 1;
        }

        return 0;
}

static unsigned check_objects(void)
{
        unsigned i, max, foreign_nr = 0;

        max = get_max_object_index();

        if (verbose)
                progress = start_delayed_progress(_("Checking objects"), max);

        for (i = 0; i < max; i++) {
                foreign_nr += check_object(get_indexed_object(i));
                display_progress(progress, i + 1);
        }

        stop_progress(&progress);
        return foreign_nr;
}


/* Discard current buffer used content. */
static void flush(void)
{
        if (input_offset) {
                if (output_fd >= 0)
                        write_or_die(output_fd, input_buffer, input_offset);
                the_hash_algo->update_fn(&input_ctx, input_buffer, input_offset);
                memmove(input_buffer, input_buffer + input_offset, input_len);
                input_offset = 0;
        }
}

/*
 * Make sure at least "min" bytes are available in the buffer, and
 * return the pointer to the buffer.
 */
static void *fill(int min)
{
        if (min <= input_len)
                return input_buffer + input_offset;
        if (min > sizeof(input_buffer))
                die(Q_("cannot fill %d byte",
                       "cannot fill %d bytes",
                       min),
                    min);
        flush();
        do {
                ssize_t ret = xread(input_fd, input_buffer + input_len,
                                sizeof(input_buffer) - input_len);
                if (ret <= 0) {
                        if (!ret)
                                die(_("early EOF"));
                        die_errno(_("read error on input"));
                }
                input_len += ret;
                if (from_stdin)
                        display_throughput(progress, consumed_bytes + input_len);
        } while (input_len < min);
        return input_buffer;
}

static void use(int bytes)
{
        if (bytes > input_len)
                die(_("used more bytes than were available"));
        input_crc32 = crc32(input_crc32, input_buffer + input_offset, bytes);
        input_len -= bytes;
        input_offset += bytes;

        /* make sure off_t is sufficiently large not to wrap */
        if (signed_add_overflows(consumed_bytes, bytes))
                die(_("pack too large for current definition of off_t"));
        consumed_bytes += bytes;
        if (max_input_size && consumed_bytes > max_input_size) {
                struct strbuf size_limit = STRBUF_INIT;
                strbuf_humanise_bytes(&size_limit, max_input_size);
                die(_("pack exceeds maximum allowed size (%s)"),
                    size_limit.buf);
        }
}

static const char *open_pack_file(const char *pack_name)
{
        if (from_stdin) {
                input_fd = 0;
                if (!pack_name) {
                        struct strbuf tmp_file = STRBUF_INIT;
                        output_fd = odb_mkstemp(&tmp_file,
                                                "pack/tmp_pack_XXXXXX");
                        pack_name = strbuf_detach(&tmp_file, NULL);
                } else {
                        output_fd = xopen(pack_name, O_CREAT|O_EXCL|O_RDWR, 0600);
                }
                nothread_data.pack_fd = output_fd;
        } else {
                input_fd = xopen(pack_name, O_RDONLY);
                output_fd = -1;
                nothread_data.pack_fd = input_fd;
        }
        the_hash_algo->init_fn(&input_ctx);
        return pack_name;
}

static void parse_pack_header(void)
{
        struct pack_header *hdr = fill(sizeof(struct pack_header));

        /* Header consistency check */
        if (hdr->hdr_signature != htonl(PACK_SIGNATURE))
                die(_("pack signature mismatch"));
        if (!pack_version_ok(hdr->hdr_version))
                die(_("pack version %"PRIu32" unsupported"),
                        ntohl(hdr->hdr_version));

        nr_objects = ntohl(hdr->hdr_entries);
        use(sizeof(struct pack_header));
}

__attribute__((format (printf, 2, 3)))
static NORETURN void bad_object(off_t offset, const char *format, ...)
{
        va_list params;
        char buf[1024];

        va_start(params, format);
        vsnprintf(buf, sizeof(buf), format, params);
        va_end(params);
        die(_("pack has bad object at offset %"PRIuMAX": %s"),
            (uintmax_t)offset, buf);
}

static inline struct thread_local *get_thread_data(void)
{
        if (HAVE_THREADS) {
                if (threads_active)
                        return pthread_getspecific(key);
                assert(!threads_active &&
                       "This should only be reached when all threads are gone");
        }
        return &nothread_data;
}

static void set_thread_data(struct thread_local *data)
{
        if (threads_active)
                pthread_setspecific(key, data);
}

static void free_base_data(struct base_data *c)
{
        if (c->data) {
                FREE_AND_NULL(c->data);
                base_cache_used -= c->size;
        }
}

static void prune_base_data(struct base_data *retain)
{
        struct list_head *pos;

        if (base_cache_used <= base_cache_limit)
                return;

        list_for_each_prev(pos, &done_head) {
                struct base_data *b = list_entry(pos, struct base_data, list);
                if (b->retain_data || b == retain)
                        continue;
                if (b->data) {
                        free_base_data(b);
                        if (base_cache_used <= base_cache_limit)
                                return;
                }
        }

        list_for_each_prev(pos, &work_head) {
                struct base_data *b = list_entry(pos, struct base_data, list);
                if (b->retain_data || b == retain)
                        continue;
                if (b->data) {
                        free_base_data(b);
                        if (base_cache_used <= base_cache_limit)
                                return;
                }
        }
}

static int is_delta_type(enum object_type type)
{
        return (type == OBJ_REF_DELTA || type == OBJ_OFS_DELTA);
}

static void *unpack_entry_data(off_t offset, unsigned long size,
                               enum object_type type, struct object_id *oid)
{
        static char fixed_buf[8192];
        int status;
        git_zstream stream;
        void *buf;
        git_hash_ctx c;
        char hdr[32];
        int hdrlen;

        if (!is_delta_type(type)) {
                hdrlen = format_object_header(hdr, sizeof(hdr), type, size);
                the_hash_algo->init_fn(&c);
                the_hash_algo->update_fn(&c, hdr, hdrlen);
        } else
                oid = NULL;
        if (type == OBJ_BLOB && size > big_file_threshold)
                buf = fixed_buf;
        else
                buf = xmallocz(size);

        memset(&stream, 0, sizeof(stream));
        git_inflate_init(&stream);
        stream.next_out = buf;
        stream.avail_out = buf == fixed_buf ? sizeof(fixed_buf) : size;

        do {
                unsigned char *last_out = stream.next_out;
                stream.next_in = fill(1);
                stream.avail_in = input_len;
                status = git_inflate(&stream, 0);
                use(input_len - stream.avail_in);
                if (oid)
                        the_hash_algo->update_fn(&c, last_out, stream.next_out - last_out);
                if (buf == fixed_buf) {
                        stream.next_out = buf;
                        stream.avail_out = sizeof(fixed_buf);
                }
        } while (status == Z_OK);
        if (stream.total_out != size || status != Z_STREAM_END)
                bad_object(offset, _("inflate returned %d"), status);
        git_inflate_end(&stream);
        if (oid)
                the_hash_algo->final_oid_fn(oid, &c);
        return buf == fixed_buf ? NULL : buf;
}

static void *unpack_raw_entry(struct object_entry *obj,
                              off_t *ofs_offset,
                              struct object_id *ref_oid,
                              struct object_id *oid)
{
        unsigned char *p;
        unsigned long size, c;
        off_t base_offset;
        unsigned shift;
        void *data;

        obj->idx.offset = consumed_bytes;
        input_crc32 = crc32(0, NULL, 0);

        p = fill(1);
        c = *p;
        use(1);
        obj->type = (c >> 4) & 7;
        size = (c & 15);
        shift = 4;
        while (c & 0x80) {
                p = fill(1);
                c = *p;
                use(1);
                size += (c & 0x7f) << shift;
                shift += 7;
        }
        obj->size = size;

        switch (obj->type) {
        case OBJ_REF_DELTA:
                oidread(ref_oid, fill(the_hash_algo->rawsz));
                use(the_hash_algo->rawsz);
                break;
        case OBJ_OFS_DELTA:
                p = fill(1);
                c = *p;
                use(1);
                base_offset = c & 127;
                while (c & 128) {
                        base_offset += 1;
                        if (!base_offset || MSB(base_offset, 7))
                                bad_object(obj->idx.offset, _("offset value overflow for delta base object"));
                        p = fill(1);
                        c = *p;
                        use(1);
                        base_offset = (base_offset << 7) + (c & 127);
                }
                *ofs_offset = obj->idx.offset - base_offset;
                if (*ofs_offset <= 0 || *ofs_offset >= obj->idx.offset)
                        bad_object(obj->idx.offset, _("delta base offset is out of bound"));
                break;
        case OBJ_COMMIT:
        case OBJ_TREE:
        case OBJ_BLOB:
        case OBJ_TAG:
                break;
        default:
                bad_object(obj->idx.offset, _("unknown object type %d"), obj->type);
        }
        obj->hdr_size = consumed_bytes - obj->idx.offset;

        data = unpack_entry_data(obj->idx.offset, obj->size, obj->type, oid);
        obj->idx.crc32 = input_crc32;
        return data;
}

static void *unpack_data(struct object_entry *obj,
                         int (*consume)(const unsigned char *, unsigned long, void *),
                         void *cb_data)
{
        off_t from = obj[0].idx.offset + obj[0].hdr_size;
        off_t len = obj[1].idx.offset - from;
        unsigned char *data, *inbuf;
        git_zstream stream;
        int status;

        data = xmallocz(consume ? 64*1024 : obj->size);
        inbuf = xmalloc((len < 64*1024) ? (int)len : 64*1024);

        memset(&stream, 0, sizeof(stream));
        git_inflate_init(&stream);
        stream.next_out = data;
        stream.avail_out = consume ? 64*1024 : obj->size;

        do {
                ssize_t n = (len < 64*1024) ? (ssize_t)len : 64*1024;
                n = xpread(get_thread_data()->pack_fd, inbuf, n, from);
                if (n < 0)
                        die_errno(_("cannot pread pack file"));
                if (!n)
                        die(Q_("premature end of pack file, %"PRIuMAX" byte missing",
                               "premature end of pack file, %"PRIuMAX" bytes missing",
                               len),
                            (uintmax_t)len);
                from += n;
                len -= n;
                stream.next_in = inbuf;
                stream.avail_in = n;
                if (!consume)
                        status = git_inflate(&stream, 0);
                else {
                        do {
                                status = git_inflate(&stream, 0);
                                if (consume(data, stream.next_out - data, cb_data)) {
                                        free(inbuf);
                                        free(data);
                                        return NULL;
                                }
                                stream.next_out = data;
                                stream.avail_out = 64*1024;
                        } while (status == Z_OK && stream.avail_in);
                }
        } while (len && status == Z_OK && !stream.avail_in);

        /* This has been inflated OK when first encountered, so... */
        if (status != Z_STREAM_END || stream.total_out != obj->size)
                die(_("serious inflate inconsistency"));

        git_inflate_end(&stream);
        free(inbuf);
        if (consume) {
                FREE_AND_NULL(data);
        }
        return data;
}

static void *get_data_from_pack(struct object_entry *obj)
{
        return unpack_data(obj, NULL, NULL);
}

static int compare_ofs_delta_bases(off_t offset1, off_t offset2,
                                   enum object_type type1,
                                   enum object_type type2)
{
        int cmp = type1 - type2;
        if (cmp)
                return cmp;
        return offset1 < offset2 ? -1 :
               offset1 > offset2 ?  1 :
               0;
}

static int find_ofs_delta(const off_t offset)
{
        int first = 0, last = nr_ofs_deltas;

        while (first < last) {
                int next = first + (last - first) / 2;
                struct ofs_delta_entry *delta = &ofs_deltas[next];
                int cmp;

                cmp = compare_ofs_delta_bases(offset, delta->offset,
                                              OBJ_OFS_DELTA,
                                              objects[delta->obj_no].type);
                if (!cmp)
                        return next;
                if (cmp < 0) {
                        last = next;
                        continue;
                }
                first = next+1;
        }
        return -first-1;
}

static void find_ofs_delta_children(off_t offset,
                                    int *first_index, int *last_index)
{
        int first = find_ofs_delta(offset);
        int last = first;
        int end = nr_ofs_deltas - 1;

        if (first < 0) {
                *first_index = 0;
                *last_index = -1;
                return;
        }
        while (first > 0 && ofs_deltas[first - 1].offset == offset)
                --first;
        while (last < end && ofs_deltas[last + 1].offset == offset)
                ++last;
        *first_index = first;
        *last_index = last;
}

static int compare_ref_delta_bases(const struct object_id *oid1,
                                   const struct object_id *oid2,
                                   enum object_type type1,
                                   enum object_type type2)
{
        int cmp = type1 - type2;
        if (cmp)
                return cmp;
        return oidcmp(oid1, oid2);
}

static int find_ref_delta(const struct object_id *oid)
{
        int first = 0, last = nr_ref_deltas;

        while (first < last) {
                int next = first + (last - first) / 2;
                struct ref_delta_entry *delta = &ref_deltas[next];
                int cmp;

                cmp = compare_ref_delta_bases(oid, &delta->oid,
                                              OBJ_REF_DELTA,
                                              objects[delta->obj_no].type);
                if (!cmp)
                        return next;
                if (cmp < 0) {
                        last = next;
                        continue;
                }
                first = next+1;
        }
        return -first-1;
}

static void find_ref_delta_children(const struct object_id *oid,
                                    int *first_index, int *last_index)
{
        int first = find_ref_delta(oid);
        int last = first;
        int end = nr_ref_deltas - 1;

        if (first < 0) {
                *first_index = 0;
                *last_index = -1;
                return;
        }
        while (first > 0 && oideq(&ref_deltas[first - 1].oid, oid))
                --first;
        while (last < end && oideq(&ref_deltas[last + 1].oid, oid))
                ++last;
        *first_index = first;
        *last_index = last;
}

struct compare_data {
        struct object_entry *entry;
        struct git_istream *st;
        unsigned char *buf;
        unsigned long buf_size;
};

static int compare_objects(const unsigned char *buf, unsigned long size,
                           void *cb_data)
{
        struct compare_data *data = cb_data;

        if (data->buf_size < size) {
                free(data->buf);
                data->buf = xmalloc(size);
                data->buf_size = size;
        }

        while (size) {
                ssize_t len = read_istream(data->st, data->buf, size);
                if (len == 0)
                        die(_("SHA1 COLLISION FOUND WITH %s !"),
                            oid_to_hex(&data->entry->idx.oid));
                if (len < 0)
                        die(_("unable to read %s"),
                            oid_to_hex(&data->entry->idx.oid));
                if (memcmp(buf, data->buf, len))
                        die(_("SHA1 COLLISION FOUND WITH %s !"),
                            oid_to_hex(&data->entry->idx.oid));
                size -= len;
                buf += len;
        }
        return 0;
}

static int check_collison(struct object_entry *entry)
{
        struct compare_data data;
        enum object_type type;
        unsigned long size;

        if (entry->size <= big_file_threshold || entry->type != OBJ_BLOB)
                return -1;

        memset(&data, 0, sizeof(data));
        data.entry = entry;
        data.st = open_istream(the_repository, &entry->idx.oid, &type, &size,
                               NULL);
        if (!data.st)
                return -1;
        if (size != entry->size || type != entry->type)
                die(_("SHA1 COLLISION FOUND WITH %s !"),
                    oid_to_hex(&entry->idx.oid));
        unpack_data(entry, compare_objects, &data);
        close_istream(data.st);
        free(data.buf);
        return 0;
}

static void sha1_object(const void *data, struct object_entry *obj_entry,
                        unsigned long size, enum object_type type,
                        const struct object_id *oid)
{
        void *new_data = NULL;
        int collision_test_needed = 0;

        assert(data || obj_entry);

        if (startup_info->have_repository) {
                read_lock();
                collision_test_needed =
                        repo_has_object_file_with_flags(the_repository, oid,
                                                        OBJECT_INFO_QUICK);
                read_unlock();
        }

        if (collision_test_needed && !data) {
                read_lock();
                if (!check_collison(obj_entry))
                        collision_test_needed = 0;
                read_unlock();
        }
        if (collision_test_needed) {
                void *has_data;
                enum object_type has_type;
                unsigned long has_size;
                read_lock();
                has_type = oid_object_info(the_repository, oid, &has_size);
                if (has_type < 0)
                        die(_("cannot read existing object info %s"), oid_to_hex(oid));
                if (has_type != type || has_size != size)
                        die(_("SHA1 COLLISION FOUND WITH %s !"), oid_to_hex(oid));
                has_data = repo_read_object_file(the_repository, oid,
                                                 &has_type, &has_size);
                read_unlock();
                if (!data)
                        data = new_data = get_data_from_pack(obj_entry);
                if (!has_data)
                        die(_("cannot read existing object %s"), oid_to_hex(oid));
                if (size != has_size || type != has_type ||
                    memcmp(data, has_data, size) != 0)
                        die(_("SHA1 COLLISION FOUND WITH %s !"), oid_to_hex(oid));
                free(has_data);
        }

        if (strict || do_fsck_object) {
                read_lock();
                if (type == OBJ_BLOB) {
                        struct blob *blob = lookup_blob(the_repository, oid);
                        if (blob)
                                blob->object.flags |= FLAG_CHECKED;
                        else
                                die(_("invalid blob object %s"), oid_to_hex(oid));
                        if (do_fsck_object &&
                            fsck_object(&blob->object, (void *)data, size, &fsck_options))
                                die(_("fsck error in packed object"));
                } else {
                        struct object *obj;
                        int eaten;
                        void *buf = (void *) data;

                        assert(data && "data can only be NULL for large _blobs_");

                        /*
                         * we do not need to free the memory here, as the
                         * buf is deleted by the caller.
                         */
                        obj = parse_object_buffer(the_repository, oid, type,
                                                  size, buf,
                                                  &eaten);
                        if (!obj)
                                die(_("invalid %s"), type_name(type));
                        if (do_fsck_object &&
                            fsck_object(obj, buf, size, &fsck_options))
                                die(_("fsck error in packed object"));
                        if (strict && fsck_walk(obj, NULL, &fsck_options))
                                die(_("Not all child objects of %s are reachable"), oid_to_hex(&obj->oid));

                        if (obj->type == OBJ_TREE) {
                                struct tree *item = (struct tree *) obj;
                                item->buffer = NULL;
                                obj->parsed = 0;
                        }
                        if (obj->type == OBJ_COMMIT) {
                                struct commit *commit = (struct commit *) obj;
                                if (detach_commit_buffer(commit, NULL) != data)
                                        BUG("parse_object_buffer transmogrified our buffer");
                        }
                        obj->flags |= FLAG_CHECKED;
                }
                read_unlock();
        }

        free(new_data);
}

/*
 * Ensure that this node has been reconstructed and return its contents.
 *
 * In the typical and best case, this node would already be reconstructed
 * (through the invocation to resolve_delta() in threaded_second_pass()) and it
 * would not be pruned. However, if pruning of this node was necessary due to
 * reaching delta_base_cache_limit, this function will find the closest
 * ancestor with reconstructed data that has not been pruned (or if there is
 * none, the ultimate base object), and reconstruct each node in the delta
 * chain in order to generate the reconstructed data for this node.
 */
static void *get_base_data(struct base_data *c)
{
        if (!c->data) {
                struct object_entry *obj = c->obj;
                struct base_data **delta = NULL;
                int delta_nr = 0, delta_alloc = 0;

                while (is_delta_type(c->obj->type) && !c->data) {
                        ALLOC_GROW(delta, delta_nr + 1, delta_alloc);
                        delta[delta_nr++] = c;
                        c = c->base;
                }
                if (!delta_nr) {
                        c->data = get_data_from_pack(obj);
                        c->size = obj->size;
                        base_cache_used += c->size;
                        prune_base_data(c);
                }
                for (; delta_nr > 0; delta_nr--) {
                        void *base, *raw;
                        c = delta[delta_nr - 1];
                        obj = c->obj;
                        base = get_base_data(c->base);
                        raw = get_data_from_pack(obj);
                        c->data = patch_delta(
                                base, c->base->size,
                                raw, obj->size,
                                &c->size);
                        free(raw);
                        if (!c->data)
                                bad_object(obj->idx.offset, _("failed to apply delta"));
                        base_cache_used += c->size;
                        prune_base_data(c);
                }
                free(delta);
        }
        return c->data;
}

static struct base_data *make_base(struct object_entry *obj,
                                   struct base_data *parent)
{
        struct base_data *base = xcalloc(1, sizeof(struct base_data));
        base->base = parent;
        base->obj = obj;
        find_ref_delta_children(&obj->idx.oid,
                                &base->ref_first, &base->ref_last);
        find_ofs_delta_children(obj->idx.offset,
                                &base->ofs_first, &base->ofs_last);
        base->children_remaining = base->ref_last - base->ref_first +
                base->ofs_last - base->ofs_first + 2;
        return base;
}

static struct base_data *resolve_delta(struct object_entry *delta_obj,
                                       struct base_data *base)
{
        void *delta_data, *result_data;
        struct base_data *result;
        unsigned long result_size;

        if (show_stat) {
                int i = delta_obj - objects;
                int j = base->obj - objects;
                obj_stat[i].delta_depth = obj_stat[j].delta_depth + 1;
                deepest_delta_lock();
                if (deepest_delta < obj_stat[i].delta_depth)
                        deepest_delta = obj_stat[i].delta_depth;
                deepest_delta_unlock();
                obj_stat[i].base_object_no = j;
        }
        delta_data = get_data_from_pack(delta_obj);
        assert(base->data);
        result_data = patch_delta(base->data, base->size,
                                  delta_data, delta_obj->size, &result_size);
        free(delta_data);
        if (!result_data)
                bad_object(delta_obj->idx.offset, _("failed to apply delta"));
        hash_object_file(the_hash_algo, result_data, result_size,
                         delta_obj->real_type, &delta_obj->idx.oid);
        sha1_object(result_data, NULL, result_size, delta_obj->real_type,
                    &delta_obj->idx.oid);

        result = make_base(delta_obj, base);
        result->data = result_data;
        result->size = result_size;

        counter_lock();
        nr_resolved_deltas++;
        counter_unlock();

        return result;
}

static int compare_ofs_delta_entry(const void *a, const void *b)
{
        const struct ofs_delta_entry *delta_a = a;
        const struct ofs_delta_entry *delta_b = b;

        return delta_a->offset < delta_b->offset ? -1 :
               delta_a->offset > delta_b->offset ?  1 :
               0;
}

static int compare_ref_delta_entry(const void *a, const void *b)
{
        const struct ref_delta_entry *delta_a = a;
        const struct ref_delta_entry *delta_b = b;

        return oidcmp(&delta_a->oid, &delta_b->oid);
}

static void *threaded_second_pass(void *data)
{
        if (data)
                set_thread_data(data);
        for (;;) {
                struct base_data *parent = NULL;
                struct object_entry *child_obj;
                struct base_data *child;

                counter_lock();
                display_progress(progress, nr_resolved_deltas);
                counter_unlock();

                work_lock();
                if (list_empty(&work_head)) {
                        /*
                         * Take an object from the object array.
                         */
                        while (nr_dispatched < nr_objects &&
                               is_delta_type(objects[nr_dispatched].type))
                                nr_dispatched++;
                        if (nr_dispatched >= nr_objects) {
                                work_unlock();
                                break;
                        }
                        child_obj = &objects[nr_dispatched++];
                } else {
                        /*
                         * Peek at the top of the stack, and take a child from
                         * it.
                         */
                        parent = list_first_entry(&work_head, struct base_data,
                                                  list);

                        if (parent->ref_first <= parent->ref_last) {
                                int offset = ref_deltas[parent->ref_first++].obj_no;
                                child_obj = objects + offset;
                                if (child_obj->real_type != OBJ_REF_DELTA)
                                        die("REF_DELTA at offset %"PRIuMAX" already resolved (duplicate base %s?)",
                                            (uintmax_t) child_obj->idx.offset,
                                            oid_to_hex(&parent->obj->idx.oid));
                                child_obj->real_type = parent->obj->real_type;
                        } else {
                                child_obj = objects +
                                        ofs_deltas[parent->ofs_first++].obj_no;
                                assert(child_obj->real_type == OBJ_OFS_DELTA);
                                child_obj->real_type = parent->obj->real_type;
                        }

                        if (parent->ref_first > parent->ref_last &&
                            parent->ofs_first > parent->ofs_last) {
                                /*
                                 * This parent has run out of children, so move
                                 * it to done_head.
                                 */
                                list_del(&parent->list);
                                list_add(&parent->list, &done_head);
                        }

                        /*
                         * Ensure that the parent has data, since we will need
                         * it later.
                         *
                         * NEEDSWORK: If parent data needs to be reloaded, this
                         * prolongs the time that the current thread spends in
                         * the mutex. A mitigating factor is that parent data
                         * needs to be reloaded only if the delta base cache
                         * limit is exceeded, so in the typical case, this does
                         * not happen.
                         */
                        get_base_data(parent);
                        parent->retain_data++;
                }
                work_unlock();

                if (parent) {
                        child = resolve_delta(child_obj, parent);
                        if (!child->children_remaining)
                                FREE_AND_NULL(child->data);
                } else {
                        child = make_base(child_obj, NULL);
                        if (child->children_remaining) {
                                /*
                                 * Since this child has its own delta children,
                                 * we will need this data in the future.
                                 * Inflate now so that future iterations will
                                 * have access to this object's data while
                                 * outside the work mutex.
                                 */
                                child->data = get_data_from_pack(child_obj);
                                child->size = child_obj->size;
                        }
                }

                work_lock();
                if (parent)
                        parent->retain_data--;
                if (child->data) {
                        /*
                         * This child has its own children, so add it to
                         * work_head.
                         */
                        list_add(&child->list, &work_head);
                        base_cache_used += child->size;
                        prune_base_data(NULL);
                        free_base_data(child);
                } else {
                        /*
                         * This child does not have its own children. It may be
                         * the last descendant of its ancestors; free those
                         * that we can.
                         */
                        struct base_data *p = parent;

                        while (p) {
                                struct base_data *next_p;

                                p->children_remaining--;
                                if (p->children_remaining)
                                        break;

                                next_p = p->base;
                                free_base_data(p);
                                list_del(&p->list);
                                free(p);

                                p = next_p;
                        }
                        FREE_AND_NULL(child);
                }
                work_unlock();
        }
        return NULL;
}

/*
 * First pass:
 * - find locations of all objects;
 * - calculate SHA1 of all non-delta objects;
 * - remember base (SHA1 or offset) for all deltas.
 */
static void parse_pack_objects(unsigned char *hash)
{
        int i, nr_delays = 0;
        struct ofs_delta_entry *ofs_delta = ofs_deltas;
        struct object_id ref_delta_oid;
        struct stat st;

        if (verbose)
                progress = start_progress(
                                progress_title ? progress_title :
                                from_stdin ? _("Receiving objects") : _("Indexing objects"),
                                nr_objects);
        for (i = 0; i < nr_objects; i++) {
                struct object_entry *obj = &objects[i];
                void *data = unpack_raw_entry(obj, &ofs_delta->offset,
                                              &ref_delta_oid,
                                              &obj->idx.oid);
                obj->real_type = obj->type;
                if (obj->type == OBJ_OFS_DELTA) {
                        nr_ofs_deltas++;
                        ofs_delta->obj_no = i;
                        ofs_delta++;
                } else if (obj->type == OBJ_REF_DELTA) {
                        ALLOC_GROW(ref_deltas, nr_ref_deltas + 1, ref_deltas_alloc);
                        oidcpy(&ref_deltas[nr_ref_deltas].oid, &ref_delta_oid);
                        ref_deltas[nr_ref_deltas].obj_no = i;
                        nr_ref_deltas++;
                } else if (!data) {
                        /* large blobs, check later */
                        obj->real_type = OBJ_BAD;
                        nr_delays++;
                } else
                        sha1_object(data, NULL, obj->size, obj->type,
                                    &obj->idx.oid);
                free(data);
                display_progress(progress, i+1);
        }
        objects[i].idx.offset = consumed_bytes;
        stop_progress(&progress);

        /* Check pack integrity */
        flush();
        the_hash_algo->final_fn(hash, &input_ctx);
        if (!hasheq(fill(the_hash_algo->rawsz), hash))
                die(_("pack is corrupted (SHA1 mismatch)"));
        use(the_hash_algo->rawsz);

        /* If input_fd is a file, we should have reached its end now. */
        if (fstat(input_fd, &st))
                die_errno(_("cannot fstat packfile"));
        if (S_ISREG(st.st_mode) &&
                        lseek(input_fd, 0, SEEK_CUR) - input_len != st.st_size)
                die(_("pack has junk at the end"));

        for (i = 0; i < nr_objects; i++) {
                struct object_entry *obj = &objects[i];
                if (obj->real_type != OBJ_BAD)
                        continue;
                obj->real_type = obj->type;
                sha1_object(NULL, obj, obj->size, obj->type,
                            &obj->idx.oid);
                nr_delays--;
        }
        if (nr_delays)
                die(_("confusion beyond insanity in parse_pack_objects()"));
}

/*
 * Second pass:
 * - for all non-delta objects, look if it is used as a base for
 *   deltas;
 * - if used as a base, uncompress the object and apply all deltas,
 *   recursively checking if the resulting object is used as a base
 *   for some more deltas.
 */
static void resolve_deltas(void)
{
        int i;

        if (!nr_ofs_deltas && !nr_ref_deltas)
                return;

        /* Sort deltas by base SHA1/offset for fast searching */
        QSORT(ofs_deltas, nr_ofs_deltas, compare_ofs_delta_entry);
        QSORT(ref_deltas, nr_ref_deltas, compare_ref_delta_entry);

        if (verbose || show_resolving_progress)
                progress = start_progress(_("Resolving deltas"),
                                          nr_ref_deltas + nr_ofs_deltas);

        nr_dispatched = 0;
        base_cache_limit = delta_base_cache_limit * nr_threads;
        if (nr_threads > 1 || getenv("GIT_FORCE_THREADS")) {
                init_thread();
                for (i = 0; i < nr_threads; i++) {
                        int ret = pthread_create(&thread_data[i].thread, NULL,
                                                 threaded_second_pass, thread_data + i);
                        if (ret)
                                die(_("unable to create thread: %s"),
                                    strerror(ret));
                }
                for (i = 0; i < nr_threads; i++)
                        pthread_join(thread_data[i].thread, NULL);
                cleanup_thread();
                return;
        }
        threaded_second_pass(&nothread_data);
}

/*
 * Third pass:
 * - append objects to convert thin pack to full pack if required
 * - write the final pack hash
 */
static void fix_unresolved_deltas(struct hashfile *f);
static void conclude_pack(int fix_thin_pack, const char *curr_pack, unsigned char *pack_hash)
{
        if (nr_ref_deltas + nr_ofs_deltas == nr_resolved_deltas) {
                stop_progress(&progress);
                /* Flush remaining pack final hash. */
                flush();
                return;
        }

        if (fix_thin_pack) {
                struct hashfile *f;
                unsigned char read_hash[GIT_MAX_RAWSZ], tail_hash[GIT_MAX_RAWSZ];
                struct strbuf msg = STRBUF_INIT;
                int nr_unresolved = nr_ofs_deltas + nr_ref_deltas - nr_resolved_deltas;
                int nr_objects_initial = nr_objects;
                if (nr_unresolved <= 0)
                        die(_("confusion beyond insanity"));
                REALLOC_ARRAY(objects, nr_objects + nr_unresolved + 1);
                memset(objects + nr_objects + 1, 0,
                       nr_unresolved * sizeof(*objects));
                f = hashfd(output_fd, curr_pack);
                fix_unresolved_deltas(f);
                strbuf_addf(&msg, Q_("completed with %d local object",
                                     "completed with %d local objects",
                                     nr_objects - nr_objects_initial),
                            nr_objects - nr_objects_initial);
                stop_progress_msg(&progress, msg.buf);
                strbuf_release(&msg);
                finalize_hashfile(f, tail_hash, FSYNC_COMPONENT_PACK, 0);
                hashcpy(read_hash, pack_hash);
                fixup_pack_header_footer(output_fd, pack_hash,
                                         curr_pack, nr_objects,
                                         read_hash, consumed_bytes-the_hash_algo->rawsz);
                if (!hasheq(read_hash, tail_hash))
                        die(_("Unexpected tail checksum for %s "
                              "(disk corruption?)"), curr_pack);
        }
        if (nr_ofs_deltas + nr_ref_deltas != nr_resolved_deltas)
                die(Q_("pack has %d unresolved delta",
                       "pack has %d unresolved deltas",
                       nr_ofs_deltas + nr_ref_deltas - nr_resolved_deltas),
                    nr_ofs_deltas + nr_ref_deltas - nr_resolved_deltas);
}

static int write_compressed(struct hashfile *f, void *in, unsigned int size)
{
        git_zstream stream;
        int status;
        unsigned char outbuf[4096];

        git_deflate_init(&stream, zlib_compression_level);
        stream.next_in = in;
        stream.avail_in = size;

        do {
                stream.next_out = outbuf;
                stream.avail_out = sizeof(outbuf);
                status = git_deflate(&stream, Z_FINISH);
                hashwrite(f, outbuf, sizeof(outbuf) - stream.avail_out);
        } while (status == Z_OK);

        if (status != Z_STREAM_END)
                die(_("unable to deflate appended object (%d)"), status);
        size = stream.total_out;
        git_deflate_end(&stream);
        return size;
}

static struct object_entry *append_obj_to_pack(struct hashfile *f,
                               const unsigned char *sha1, void *buf,
                               unsigned long size, enum object_type type)
{
        struct object_entry *obj = &objects[nr_objects++];
        unsigned char header[10];
        unsigned long s = size;
        int n = 0;
        unsigned char c = (type << 4) | (s & 15);
        s >>= 4;
        while (s) {
                header[n++] = c | 0x80;
                c = s & 0x7f;
                s >>= 7;
        }
        header[n++] = c;
        crc32_begin(f);
        hashwrite(f, header, n);
        obj[0].size = size;
        obj[0].hdr_size = n;
        obj[0].type = type;
        obj[0].real_type = type;
        obj[1].idx.offset = obj[0].idx.offset + n;
        obj[1].idx.offset += write_compressed(f, buf, size);
        obj[0].idx.crc32 = crc32_end(f);
        hashflush(f);
        oidread(&obj->idx.oid, sha1);
        return obj;
}

static int delta_pos_compare(const void *_a, const void *_b)
{
        struct ref_delta_entry *a = *(struct ref_delta_entry **)_a;
        struct ref_delta_entry *b = *(struct ref_delta_entry **)_b;
        return a->obj_no - b->obj_no;
}

static void fix_unresolved_deltas(struct hashfile *f)
{
        struct ref_delta_entry **sorted_by_pos;
        int i;

        /*
         * Since many unresolved deltas may well be themselves base objects
         * for more unresolved deltas, we really want to include the
         * smallest number of base objects that would cover as much delta
         * as possible by picking the
         * trunc deltas first, allowing for other deltas to resolve without
         * additional base objects.  Since most base objects are to be found
         * before deltas depending on them, a good heuristic is to start
         * resolving deltas in the same order as their position in the pack.
         */
        ALLOC_ARRAY(sorted_by_pos, nr_ref_deltas);
        for (i = 0; i < nr_ref_deltas; i++)
                sorted_by_pos[i] = &ref_deltas[i];
        QSORT(sorted_by_pos, nr_ref_deltas, delta_pos_compare);

        if (repo_has_promisor_remote(the_repository)) {
                /*
                 * Prefetch the delta bases.
                 */
                struct oid_array to_fetch = OID_ARRAY_INIT;
                for (i = 0; i < nr_ref_deltas; i++) {
                        struct ref_delta_entry *d = sorted_by_pos[i];
                        if (!oid_object_info_extended(the_repository, &d->oid,
                                                      NULL,
                                                      OBJECT_INFO_FOR_PREFETCH))
                                continue;
                        oid_array_append(&to_fetch, &d->oid);
                }
                promisor_remote_get_direct(the_repository,
                                           to_fetch.oid, to_fetch.nr);
                oid_array_clear(&to_fetch);
        }

        for (i = 0; i < nr_ref_deltas; i++) {
                struct ref_delta_entry *d = sorted_by_pos[i];
                enum object_type type;
                void *data;
                unsigned long size;

                if (objects[d->obj_no].real_type != OBJ_REF_DELTA)
                        continue;
                data = repo_read_object_file(the_repository, &d->oid, &type,
                                             &size);
                if (!data)
                        continue;

                if (check_object_signature(the_repository, &d->oid, data, size,
                                           type) < 0)
                        die(_("local object %s is corrupt"), oid_to_hex(&d->oid));

                /*
                 * Add this as an object to the objects array and call
                 * threaded_second_pass() (which will pick up the added
                 * object).
                 */
                append_obj_to_pack(f, d->oid.hash, data, size, type);
                free(data);
                threaded_second_pass(NULL);

                display_progress(progress, nr_resolved_deltas);
        }
        free(sorted_by_pos);
}

static const char *derive_filename(const char *pack_name, const char *strip,
                                   const char *suffix, struct strbuf *buf)
{
        size_t len;
        if (!strip_suffix(pack_name, strip, &len) || !len ||
            pack_name[len - 1] != '.')
                die(_("packfile name '%s' does not end with '.%s'"),
                    pack_name, strip);
        strbuf_add(buf, pack_name, len);
        strbuf_addstr(buf, suffix);
        return buf->buf;
}

static void write_special_file(const char *suffix, const char *msg,
                               const char *pack_name, const unsigned char *hash,
                               const char **report)
{
        struct strbuf name_buf = STRBUF_INIT;
        const char *filename;
        int fd;
        int msg_len = strlen(msg);

        if (pack_name)
                filename = derive_filename(pack_name, "pack", suffix, &name_buf);
        else
                filename = odb_pack_name(&name_buf, hash, suffix);

        fd = odb_pack_keep(filename);
        if (fd < 0) {
                if (errno != EEXIST)
                        die_errno(_("cannot write %s file '%s'"),
                                  suffix, filename);
        } else {
                if (msg_len > 0) {
                        write_or_die(fd, msg, msg_len);
                        write_or_die(fd, "\n", 1);
                }
                if (close(fd) != 0)
                        die_errno(_("cannot close written %s file '%s'"),
                                  suffix, filename);
                if (report)
                        *report = suffix;
        }
        strbuf_release(&name_buf);
}

static void rename_tmp_packfile(const char **final_name,
                                const char *curr_name,
                                struct strbuf *name, unsigned char *hash,
                                const char *ext, int make_read_only_if_same)
{
        if (*final_name != curr_name) {
                if (!*final_name)
                        *final_name = odb_pack_name(name, hash, ext);
                if (finalize_object_file(curr_name, *final_name))
                        die(_("unable to rename temporary '*.%s' file to '%s'"),
                            ext, *final_name);
        } else if (make_read_only_if_same) {
                chmod(*final_name, 0444);
        }
}

static void final(const char *final_pack_name, const char *curr_pack_name,
                  const char *final_index_name, const char *curr_index_name,
                  const char *final_rev_index_name, const char *curr_rev_index_name,
                  const char *keep_msg, const char *promisor_msg,
                  unsigned char *hash)
{
        const char *report = "pack";
        struct strbuf pack_name = STRBUF_INIT;
        struct strbuf index_name = STRBUF_INIT;
        struct strbuf rev_index_name = STRBUF_INIT;
        int err;

        if (!from_stdin) {
                close(input_fd);
        } else {
                fsync_component_or_die(FSYNC_COMPONENT_PACK, output_fd, curr_pack_name);
                err = close(output_fd);
                if (err)
                        die_errno(_("error while closing pack file"));
        }

        if (keep_msg)
                write_special_file("keep", keep_msg, final_pack_name, hash,
                                   &report);
        if (promisor_msg)
                write_special_file("promisor", promisor_msg, final_pack_name,
                                   hash, NULL);

        rename_tmp_packfile(&final_pack_name, curr_pack_name, &pack_name,
                            hash, "pack", from_stdin);
        if (curr_rev_index_name)
                rename_tmp_packfile(&final_rev_index_name, curr_rev_index_name,
                                    &rev_index_name, hash, "rev", 1);
        rename_tmp_packfile(&final_index_name, curr_index_name, &index_name,
                            hash, "idx", 1);

        if (do_fsck_object) {
                struct packed_git *p;
                p = add_packed_git(final_index_name, strlen(final_index_name), 0);
                if (p)
                        install_packed_git(the_repository, p);
        }

        if (!from_stdin) {
                printf("%s\n", hash_to_hex(hash));
        } else {
                struct strbuf buf = STRBUF_INIT;

                strbuf_addf(&buf, "%s\t%s\n", report, hash_to_hex(hash));
                write_or_die(1, buf.buf, buf.len);
                strbuf_release(&buf);

                /*
                 * Let's just mimic git-unpack-objects here and write
                 * the last part of the input buffer to stdout.
                 */
                while (input_len) {
                        err = xwrite(1, input_buffer + input_offset, input_len);
                        if (err <= 0)
                                break;
                        input_len -= err;
                        input_offset += err;
                }
        }

        strbuf_release(&rev_index_name);
        strbuf_release(&index_name);
        strbuf_release(&pack_name);
}

static int git_index_pack_config(const char *k, const char *v, void *cb)
{
        struct pack_idx_option *opts = cb;

        if (!strcmp(k, "pack.indexversion")) {
                opts->version = git_config_int(k, v);
                if (opts->version > 2)
                        die(_("bad pack.indexVersion=%"PRIu32), opts->version);
                return 0;
        }
        if (!strcmp(k, "pack.threads")) {
                nr_threads = git_config_int(k, v);
                if (nr_threads < 0)
                        die(_("invalid number of threads specified (%d)"),
                            nr_threads);
                if (!HAVE_THREADS && nr_threads != 1) {
                        warning(_("no threads support, ignoring %s"), k);
                        nr_threads = 1;
                }
                return 0;
        }
        if (!strcmp(k, "pack.writereverseindex")) {
                if (git_config_bool(k, v))
                        opts->flags |= WRITE_REV;
                else
                        opts->flags &= ~WRITE_REV;
        }
        return git_default_config(k, v, cb);
}

static int cmp_uint32(const void *a_, const void *b_)
{
        uint32_t a = *((uint32_t *)a_);
        uint32_t b = *((uint32_t *)b_);

        return (a < b) ? -1 : (a != b);
}

static void read_v2_anomalous_offsets(struct packed_git *p,
                                      struct pack_idx_option *opts)
{
        const uint32_t *idx1, *idx2;
        uint32_t i;

        /* The address of the 4-byte offset table */
        idx1 = (((const uint32_t *)((const uint8_t *)p->index_data + p->crc_offset))
                + (size_t)p->num_objects /* CRC32 table */
                );

        /* The address of the 8-byte offset table */
        idx2 = idx1 + p->num_objects;

        for (i = 0; i < p->num_objects; i++) {
                uint32_t off = ntohl(idx1[i]);
                if (!(off & 0x80000000))
                        continue;
                off = off & 0x7fffffff;
                check_pack_index_ptr(p, &idx2[off * 2]);
                if (idx2[off * 2])
                        continue;
                /*
                 * The real offset is ntohl(idx2[off * 2]) in high 4
                 * octets, and ntohl(idx2[off * 2 + 1]) in low 4
                 * octets.  But idx2[off * 2] is Zero!!!
                 */
                ALLOC_GROW(opts->anomaly, opts->anomaly_nr + 1, opts->anomaly_alloc);
                opts->anomaly[opts->anomaly_nr++] = ntohl(idx2[off * 2 + 1]);
        }

        QSORT(opts->anomaly, opts->anomaly_nr, cmp_uint32);
}

static void read_idx_option(struct pack_idx_option *opts, const char *pack_name)
{
        struct packed_git *p = add_packed_git(pack_name, strlen(pack_name), 1);

        if (!p)
                die(_("Cannot open existing pack file '%s'"), pack_name);
        if (open_pack_index(p))
                die(_("Cannot open existing pack idx file for '%s'"), pack_name);

        /* Read the attributes from the existing idx file */
        opts->version = p->index_version;

        if (opts->version == 2)
                read_v2_anomalous_offsets(p, opts);

        /*
         * Get rid of the idx file as we do not need it anymore.
         * NEEDSWORK: extract this bit from free_pack_by_name() in
         * object-file.c, perhaps?  It shouldn't matter very much as we
         * know we haven't installed this pack (hence we never have
         * read anything from it).
         */
        close_pack_index(p);
        free(p);
}

static void show_pack_info(int stat_only)
{
        int i, baseobjects = nr_objects - nr_ref_deltas - nr_ofs_deltas;
        unsigned long *chain_histogram = NULL;

        if (deepest_delta)
                CALLOC_ARRAY(chain_histogram, deepest_delta);

        for (i = 0; i < nr_objects; i++) {
                struct object_entry *obj = &objects[i];

                if (is_delta_type(obj->type))
                        chain_histogram[obj_stat[i].delta_depth - 1]++;
                if (stat_only)
                        continue;
                printf("%s %-6s %"PRIuMAX" %"PRIuMAX" %"PRIuMAX,
                       oid_to_hex(&obj->idx.oid),
                       type_name(obj->real_type), (uintmax_t)obj->size,
                       (uintmax_t)(obj[1].idx.offset - obj->idx.offset),
                       (uintmax_t)obj->idx.offset);
                if (is_delta_type(obj->type)) {
                        struct object_entry *bobj = &objects[obj_stat[i].base_object_no];
                        printf(" %u %s", obj_stat[i].delta_depth,
                               oid_to_hex(&bobj->idx.oid));
                }
                putchar('\n');
        }

        if (baseobjects)
                printf_ln(Q_("non delta: %d object",
                             "non delta: %d objects",
                             baseobjects),
                          baseobjects);
        for (i = 0; i < deepest_delta; i++) {
                if (!chain_histogram[i])
                        continue;
                printf_ln(Q_("chain length = %d: %lu object",
                             "chain length = %d: %lu objects",
                             chain_histogram[i]),
                          i + 1,
                          chain_histogram[i]);
        }
        free(chain_histogram);
}

int cmd_index_pack(int argc, const char **argv, const char *prefix)
{
        int i, fix_thin_pack = 0, verify = 0, stat_only = 0, rev_index;
        const char *curr_index;
        const char *curr_rev_index = NULL;
        const char *index_name = NULL, *pack_name = NULL, *rev_index_name = NULL;
        const char *keep_msg = NULL;
        const char *promisor_msg = NULL;
        struct strbuf index_name_buf = STRBUF_INIT;
        struct strbuf rev_index_name_buf = STRBUF_INIT;
        struct pack_idx_entry **idx_objects;
        struct pack_idx_option opts;
        unsigned char pack_hash[GIT_MAX_RAWSZ];
        unsigned foreign_nr = 1;        /* zero is a "good" value, assume bad */
        int report_end_of_input = 0;
        int hash_algo = 0;

        /*
         * index-pack never needs to fetch missing objects except when
         * REF_DELTA bases are missing (which are explicitly handled). It only
         * accesses the repo to do hash collision checks and to check which
         * REF_DELTA bases need to be fetched.
         */
        fetch_if_missing = 0;

        if (argc == 2 && !strcmp(argv[1], "-h"))
                usage(index_pack_usage);

        disable_replace_refs();
        fsck_options.walk = mark_link;

        reset_pack_idx_option(&opts);
        opts.flags |= WRITE_REV;
        git_config(git_index_pack_config, &opts);
        if (prefix && chdir(prefix))
                die(_("Cannot come back to cwd"));

        if (git_env_bool(GIT_TEST_NO_WRITE_REV_INDEX, 0))
                rev_index = 0;
        else
                rev_index = !!(opts.flags & (WRITE_REV_VERIFY | WRITE_REV));

        for (i = 1; i < argc; i++) {
                const char *arg = argv[i];

                if (*arg == '-') {
                        if (!strcmp(arg, "--stdin")) {
                                from_stdin = 1;
                        } else if (!strcmp(arg, "--fix-thin")) {
                                fix_thin_pack = 1;
                        } else if (skip_to_optional_arg(arg, "--strict", &arg)) {
                                strict = 1;
                                do_fsck_object = 1;
                                fsck_set_msg_types(&fsck_options, arg);
                        } else if (!strcmp(arg, "--check-self-contained-and-connected")) {
                                strict = 1;
                                check_self_contained_and_connected = 1;
                        } else if (!strcmp(arg, "--fsck-objects")) {
                                do_fsck_object = 1;
                        } else if (!strcmp(arg, "--verify")) {
                                verify = 1;
                        } else if (!strcmp(arg, "--verify-stat")) {
                                verify = 1;
                                show_stat = 1;
                        } else if (!strcmp(arg, "--verify-stat-only")) {
                                verify = 1;
                                show_stat = 1;
                                stat_only = 1;
                        } else if (skip_to_optional_arg(arg, "--keep", &keep_msg)) {
                                ; /* nothing to do */
                        } else if (skip_to_optional_arg(arg, "--promisor", &promisor_msg)) {
                                ; /* already parsed */
                        } else if (starts_with(arg, "--threads=")) {
                                char *end;
                                nr_threads = strtoul(arg+10, &end, 0);
                                if (!arg[10] || *end || nr_threads < 0)
                                        usage(index_pack_usage);
                                if (!HAVE_THREADS && nr_threads != 1) {
                                        warning(_("no threads support, ignoring %s"), arg);
                                        nr_threads = 1;
                                }
                        } else if (starts_with(arg, "--pack_header=")) {
                                struct pack_header *hdr;
                                char *c;

                                hdr = (struct pack_header *)input_buffer;
                                hdr->hdr_signature = htonl(PACK_SIGNATURE);
                                hdr->hdr_version = htonl(strtoul(arg + 14, &c, 10));
                                if (*c != ',')
                                        die(_("bad %s"), arg);
                                hdr->hdr_entries = htonl(strtoul(c + 1, &c, 10));
                                if (*c)
                                        die(_("bad %s"), arg);
                                input_len = sizeof(*hdr);
                        } else if (!strcmp(arg, "-v")) {
                                verbose = 1;
                        } else if (!strcmp(arg, "--progress-title")) {
                                if (progress_title || (i+1) >= argc)
                                        usage(index_pack_usage);
                                progress_title = argv[++i];
                        } else if (!strcmp(arg, "--show-resolving-progress")) {
                                show_resolving_progress = 1;
                        } else if (!strcmp(arg, "--report-end-of-input")) {
                                report_end_of_input = 1;
                        } else if (!strcmp(arg, "-o")) {
                                if (index_name || (i+1) >= argc)
                                        usage(index_pack_usage);
                                index_name = argv[++i];
                        } else if (starts_with(arg, "--index-version=")) {
                                char *c;
                                opts.version = strtoul(arg + 16, &c, 10);
                                if (opts.version > 2)
                                        die(_("bad %s"), arg);
                                if (*c == ',')
                                        opts.off32_limit = strtoul(c+1, &c, 0);
                                if (*c || opts.off32_limit & 0x80000000)
                                        die(_("bad %s"), arg);
                        } else if (skip_prefix(arg, "--max-input-size=", &arg)) {
                                max_input_size = strtoumax(arg, NULL, 10);
                        } else if (skip_prefix(arg, "--object-format=", &arg)) {
                                hash_algo = hash_algo_by_name(arg);
                                if (hash_algo == GIT_HASH_UNKNOWN)
                                        die(_("unknown hash algorithm '%s'"), arg);
                                repo_set_hash_algo(the_repository, hash_algo);
                        } else if (!strcmp(arg, "--rev-index")) {
                                rev_index = 1;
                        } else if (!strcmp(arg, "--no-rev-index")) {
                                rev_index = 0;
                        } else
                                usage(index_pack_usage);
                        continue;
                }

                if (pack_name)
                        usage(index_pack_usage);
                pack_name = arg;
        }

        if (!pack_name && !from_stdin)
                usage(index_pack_usage);
        if (fix_thin_pack && !from_stdin)
                die(_("the option '%s' requires '%s'"), "--fix-thin", "--stdin");
        if (from_stdin && !startup_info->have_repository)
                die(_("--stdin requires a git repository"));
        if (from_stdin && hash_algo)
                die(_("options '%s' and '%s' cannot be used together"), "--object-format", "--stdin");
        if (!index_name && pack_name)
                index_name = derive_filename(pack_name, "pack", "idx", &index_name_buf);

        opts.flags &= ~(WRITE_REV | WRITE_REV_VERIFY);
        if (rev_index) {
                opts.flags |= verify ? WRITE_REV_VERIFY : WRITE_REV;
                if (index_name)
                        rev_index_name = derive_filename(index_name,
                                                         "idx", "rev",
                                                         &rev_index_name_buf);
        }

        if (verify) {
                if (!index_name)
                        die(_("--verify with no packfile name given"));
                read_idx_option(&opts, index_name);
                opts.flags |= WRITE_IDX_VERIFY | WRITE_IDX_STRICT;
        }
        if (strict)
                opts.flags |= WRITE_IDX_STRICT;

        if (HAVE_THREADS && !nr_threads) {
                nr_threads = online_cpus();
                /*
                 * Experiments show that going above 20 threads doesn't help,
                 * no matter how many cores you have. Below that, we tend to
                 * max at half the number of online_cpus(), presumably because
                 * half of those are hyperthreads rather than full cores. We'll
                 * never reduce the level below "3", though, to match a
                 * historical value that nobody complained about.
                 */
                if (nr_threads < 4)
                        ; /* too few cores to consider capping */
                else if (nr_threads < 6)
                        nr_threads = 3; /* historic cap */
                else if (nr_threads < 40)
                        nr_threads /= 2;
                else
                        nr_threads = 20; /* hard cap */
        }

        curr_pack = open_pack_file(pack_name);
        parse_pack_header();
        CALLOC_ARRAY(objects, st_add(nr_objects, 1));
        if (show_stat)
                CALLOC_ARRAY(obj_stat, st_add(nr_objects, 1));
        CALLOC_ARRAY(ofs_deltas, nr_objects);
        parse_pack_objects(pack_hash);
        if (report_end_of_input)
                write_in_full(2, "\0", 1);
        resolve_deltas();
        conclude_pack(fix_thin_pack, curr_pack, pack_hash);
        free(ofs_deltas);
        free(ref_deltas);
        if (strict)
                foreign_nr = check_objects();

        if (show_stat)
                show_pack_info(stat_only);

        ALLOC_ARRAY(idx_objects, nr_objects);
        for (i = 0; i < nr_objects; i++)
                idx_objects[i] = &objects[i].idx;
        curr_index = write_idx_file(index_name, idx_objects, nr_objects, &opts, pack_hash);
        if (rev_index)
                curr_rev_index = write_rev_file(rev_index_name, idx_objects,
                                                nr_objects, pack_hash,
                                                opts.flags);
        free(idx_objects);

        if (!verify)
                final(pack_name, curr_pack,
                      index_name, curr_index,
                      rev_index_name, curr_rev_index,
                      keep_msg, promisor_msg,
                      pack_hash);
        else
                close(input_fd);

        if (do_fsck_object && fsck_finish(&fsck_options))
                die(_("fsck error in pack objects"));

        free(opts.anomaly);
        free(objects);
        strbuf_release(&index_name_buf);
        strbuf_release(&rev_index_name_buf);
        if (!pack_name)
                free((void *) curr_pack);
        if (!index_name)
                free((void *) curr_index);
        if (!rev_index_name)
                free((void *) curr_rev_index);

        /*
         * Let the caller know this pack is not self contained
         */
        if (check_self_contained_and_connected && foreign_nr)
                return 1;

        return 0;
}