Documentation/technical: describe bitmap lookup table extension

[git/debian.git] / pack-write.c

#include "cache.h"
#include "pack.h"
#include "csum-file.h"
#include "remote.h"
#include "chunk-format.h"
#include "pack-mtimes.h"
#include "oidmap.h"
#include "chunk-format.h"
#include "pack-objects.h"

void reset_pack_idx_option(struct pack_idx_option *opts)
{
        memset(opts, 0, sizeof(*opts));
        opts->version = 2;
        opts->off32_limit = 0x7fffffff;
}

static int sha1_compare(const void *_a, const void *_b)
{
        struct pack_idx_entry *a = *(struct pack_idx_entry **)_a;
        struct pack_idx_entry *b = *(struct pack_idx_entry **)_b;
        return oidcmp(&a->oid, &b->oid);
}

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 int need_large_offset(off_t offset, const struct pack_idx_option *opts)
{
        uint32_t ofsval;

        if ((offset >> 31) || (opts->off32_limit < offset))
                return 1;
        if (!opts->anomaly_nr)
                return 0;
        ofsval = offset;
        return !!bsearch(&ofsval, opts->anomaly, opts->anomaly_nr,
                         sizeof(ofsval), cmp_uint32);
}

/*
 * The *sha1 contains the pack content SHA1 hash.
 * The objects array passed in will be sorted by SHA1 on exit.
 */
const char *write_idx_file(const char *index_name, struct pack_idx_entry **objects,
                           int nr_objects, const struct pack_idx_option *opts,
                           const unsigned char *sha1)
{
        struct hashfile *f;
        struct pack_idx_entry **sorted_by_sha, **list, **last;
        off_t last_obj_offset = 0;
        int i, fd;
        uint32_t index_version;

        if (nr_objects) {
                sorted_by_sha = objects;
                list = sorted_by_sha;
                last = sorted_by_sha + nr_objects;
                for (i = 0; i < nr_objects; ++i) {
                        if (objects[i]->offset > last_obj_offset)
                                last_obj_offset = objects[i]->offset;
                }
                QSORT(sorted_by_sha, nr_objects, sha1_compare);
        }
        else
                sorted_by_sha = list = last = NULL;

        if (opts->flags & WRITE_IDX_VERIFY) {
                assert(index_name);
                f = hashfd_check(index_name);
        } else {
                if (!index_name) {
                        struct strbuf tmp_file = STRBUF_INIT;
                        fd = odb_mkstemp(&tmp_file, "pack/tmp_idx_XXXXXX");
                        index_name = strbuf_detach(&tmp_file, NULL);
                } else {
                        unlink(index_name);
                        fd = xopen(index_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
                }
                f = hashfd(fd, index_name);
        }

        /* if last object's offset is >= 2^31 we should use index V2 */
        index_version = need_large_offset(last_obj_offset, opts) ? 2 : opts->version;

        /* index versions 2 and above need a header */
        if (index_version >= 2) {
                struct pack_idx_header hdr;
                hdr.idx_signature = htonl(PACK_IDX_SIGNATURE);
                hdr.idx_version = htonl(index_version);
                hashwrite(f, &hdr, sizeof(hdr));
        }

        /*
         * Write the first-level table (the list is sorted,
         * but we use a 256-entry lookup to be able to avoid
         * having to do eight extra binary search iterations).
         */
        for (i = 0; i < 256; i++) {
                struct pack_idx_entry **next = list;
                while (next < last) {
                        struct pack_idx_entry *obj = *next;
                        if (obj->oid.hash[0] != i)
                                break;
                        next++;
                }
                hashwrite_be32(f, next - sorted_by_sha);
                list = next;
        }

        /*
         * Write the actual SHA1 entries..
         */
        list = sorted_by_sha;
        for (i = 0; i < nr_objects; i++) {
                struct pack_idx_entry *obj = *list++;
                if (index_version < 2)
                        hashwrite_be32(f, obj->offset);
                hashwrite(f, obj->oid.hash, the_hash_algo->rawsz);
                if ((opts->flags & WRITE_IDX_STRICT) &&
                    (i && oideq(&list[-2]->oid, &obj->oid)))
                        die("The same object %s appears twice in the pack",
                            oid_to_hex(&obj->oid));
        }

        if (index_version >= 2) {
                unsigned int nr_large_offset = 0;

                /* write the crc32 table */
                list = sorted_by_sha;
                for (i = 0; i < nr_objects; i++) {
                        struct pack_idx_entry *obj = *list++;
                        hashwrite_be32(f, obj->crc32);
                }

                /* write the 32-bit offset table */
                list = sorted_by_sha;
                for (i = 0; i < nr_objects; i++) {
                        struct pack_idx_entry *obj = *list++;
                        uint32_t offset;

                        offset = (need_large_offset(obj->offset, opts)
                                  ? (0x80000000 | nr_large_offset++)
                                  : obj->offset);
                        hashwrite_be32(f, offset);
                }

                /* write the large offset table */
                list = sorted_by_sha;
                while (nr_large_offset) {
                        struct pack_idx_entry *obj = *list++;
                        uint64_t offset = obj->offset;

                        if (!need_large_offset(offset, opts))
                                continue;
                        hashwrite_be64(f, offset);
                        nr_large_offset--;
                }
        }

        hashwrite(f, sha1, the_hash_algo->rawsz);
        finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
                          CSUM_HASH_IN_STREAM | CSUM_CLOSE |
                          ((opts->flags & WRITE_IDX_VERIFY) ? 0 : CSUM_FSYNC));
        return index_name;
}

static int pack_order_cmp(const void *va, const void *vb, void *ctx)
{
        struct pack_idx_entry **objects = ctx;

        off_t oa = objects[*(uint32_t*)va]->offset;
        off_t ob = objects[*(uint32_t*)vb]->offset;

        if (oa < ob)
                return -1;
        if (oa > ob)
                return 1;
        return 0;
}

static void write_rev_header(struct hashfile *f)
{
        hashwrite_be32(f, RIDX_SIGNATURE);
        hashwrite_be32(f, RIDX_VERSION);
        hashwrite_be32(f, oid_version(the_hash_algo));
}

static void write_rev_index_positions(struct hashfile *f,
                                      uint32_t *pack_order,
                                      uint32_t nr_objects)
{
        uint32_t i;
        for (i = 0; i < nr_objects; i++)
                hashwrite_be32(f, pack_order[i]);
}

static void write_rev_trailer(struct hashfile *f, const unsigned char *hash)
{
        hashwrite(f, hash, the_hash_algo->rawsz);
}

const char *write_rev_file(const char *rev_name,
                           struct pack_idx_entry **objects,
                           uint32_t nr_objects,
                           const unsigned char *hash,
                           unsigned flags)
{
        uint32_t *pack_order;
        uint32_t i;
        const char *ret;

        if (!(flags & WRITE_REV) && !(flags & WRITE_REV_VERIFY))
                return NULL;

        ALLOC_ARRAY(pack_order, nr_objects);
        for (i = 0; i < nr_objects; i++)
                pack_order[i] = i;
        QSORT_S(pack_order, nr_objects, pack_order_cmp, objects);

        ret = write_rev_file_order(rev_name, pack_order, nr_objects, hash,
                                   flags);

        free(pack_order);

        return ret;
}

const char *write_rev_file_order(const char *rev_name,
                                 uint32_t *pack_order,
                                 uint32_t nr_objects,
                                 const unsigned char *hash,
                                 unsigned flags)
{
        struct hashfile *f;
        int fd;

        if ((flags & WRITE_REV) && (flags & WRITE_REV_VERIFY))
                die(_("cannot both write and verify reverse index"));

        if (flags & WRITE_REV) {
                if (!rev_name) {
                        struct strbuf tmp_file = STRBUF_INIT;
                        fd = odb_mkstemp(&tmp_file, "pack/tmp_rev_XXXXXX");
                        rev_name = strbuf_detach(&tmp_file, NULL);
                } else {
                        unlink(rev_name);
                        fd = xopen(rev_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
                }
                f = hashfd(fd, rev_name);
        } else if (flags & WRITE_REV_VERIFY) {
                struct stat statbuf;
                if (stat(rev_name, &statbuf)) {
                        if (errno == ENOENT) {
                                /* .rev files are optional */
                                return NULL;
                        } else
                                die_errno(_("could not stat: %s"), rev_name);
                }
                f = hashfd_check(rev_name);
        } else
                return NULL;

        write_rev_header(f);

        write_rev_index_positions(f, pack_order, nr_objects);
        write_rev_trailer(f, hash);

        if (rev_name && adjust_shared_perm(rev_name) < 0)
                die(_("failed to make %s readable"), rev_name);

        finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
                          CSUM_HASH_IN_STREAM | CSUM_CLOSE |
                          ((flags & WRITE_IDX_VERIFY) ? 0 : CSUM_FSYNC));

        return rev_name;
}

static void write_mtimes_header(struct hashfile *f)
{
        hashwrite_be32(f, MTIMES_SIGNATURE);
        hashwrite_be32(f, MTIMES_VERSION);
        hashwrite_be32(f, oid_version(the_hash_algo));
}

/*
 * Writes the object mtimes of "objects" for use in a .mtimes file.
 * Note that objects must be in lexicographic (index) order, which is
 * the expected ordering of these values in the .mtimes file.
 */
static void write_mtimes_objects(struct hashfile *f,
                                 struct packing_data *to_pack,
                                 struct pack_idx_entry **objects,
                                 uint32_t nr_objects)
{
        uint32_t i;
        for (i = 0; i < nr_objects; i++) {
                struct object_entry *e = (struct object_entry*)objects[i];
                hashwrite_be32(f, oe_cruft_mtime(to_pack, e));
        }
}

static void write_mtimes_trailer(struct hashfile *f, const unsigned char *hash)
{
        hashwrite(f, hash, the_hash_algo->rawsz);
}

static const char *write_mtimes_file(struct packing_data *to_pack,
                                     struct pack_idx_entry **objects,
                                     uint32_t nr_objects,
                                     const unsigned char *hash)
{
        struct strbuf tmp_file = STRBUF_INIT;
        const char *mtimes_name;
        struct hashfile *f;
        int fd;

        if (!to_pack)
                BUG("cannot call write_mtimes_file with NULL packing_data");

        fd = odb_mkstemp(&tmp_file, "pack/tmp_mtimes_XXXXXX");
        mtimes_name = strbuf_detach(&tmp_file, NULL);
        f = hashfd(fd, mtimes_name);

        write_mtimes_header(f);
        write_mtimes_objects(f, to_pack, objects, nr_objects);
        write_mtimes_trailer(f, hash);

        if (adjust_shared_perm(mtimes_name) < 0)
                die(_("failed to make %s readable"), mtimes_name);

        finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
                          CSUM_HASH_IN_STREAM | CSUM_CLOSE | CSUM_FSYNC);

        return mtimes_name;
}

off_t write_pack_header(struct hashfile *f, uint32_t nr_entries)
{
        struct pack_header hdr;

        hdr.hdr_signature = htonl(PACK_SIGNATURE);
        hdr.hdr_version = htonl(PACK_VERSION);
        hdr.hdr_entries = htonl(nr_entries);
        hashwrite(f, &hdr, sizeof(hdr));
        return sizeof(hdr);
}

/*
 * Update pack header with object_count and compute new SHA1 for pack data
 * associated to pack_fd, and write that SHA1 at the end.  That new SHA1
 * is also returned in new_pack_sha1.
 *
 * If partial_pack_sha1 is non null, then the SHA1 of the existing pack
 * (without the header update) is computed and validated against the
 * one provided in partial_pack_sha1.  The validation is performed at
 * partial_pack_offset bytes in the pack file.  The SHA1 of the remaining
 * data (i.e. from partial_pack_offset to the end) is then computed and
 * returned in partial_pack_sha1.
 *
 * Note that new_pack_sha1 is updated last, so both new_pack_sha1 and
 * partial_pack_sha1 can refer to the same buffer if the caller is not
 * interested in the resulting SHA1 of pack data above partial_pack_offset.
 */
void fixup_pack_header_footer(int pack_fd,
                         unsigned char *new_pack_hash,
                         const char *pack_name,
                         uint32_t object_count,
                         unsigned char *partial_pack_hash,
                         off_t partial_pack_offset)
{
        int aligned_sz, buf_sz = 8 * 1024;
        git_hash_ctx old_hash_ctx, new_hash_ctx;
        struct pack_header hdr;
        char *buf;
        ssize_t read_result;

        the_hash_algo->init_fn(&old_hash_ctx);
        the_hash_algo->init_fn(&new_hash_ctx);

        if (lseek(pack_fd, 0, SEEK_SET) != 0)
                die_errno("Failed seeking to start of '%s'", pack_name);
        read_result = read_in_full(pack_fd, &hdr, sizeof(hdr));
        if (read_result < 0)
                die_errno("Unable to reread header of '%s'", pack_name);
        else if (read_result != sizeof(hdr))
                die_errno("Unexpected short read for header of '%s'",
                          pack_name);
        if (lseek(pack_fd, 0, SEEK_SET) != 0)
                die_errno("Failed seeking to start of '%s'", pack_name);
        the_hash_algo->update_fn(&old_hash_ctx, &hdr, sizeof(hdr));
        hdr.hdr_entries = htonl(object_count);
        the_hash_algo->update_fn(&new_hash_ctx, &hdr, sizeof(hdr));
        write_or_die(pack_fd, &hdr, sizeof(hdr));
        partial_pack_offset -= sizeof(hdr);

        buf = xmalloc(buf_sz);
        aligned_sz = buf_sz - sizeof(hdr);
        for (;;) {
                ssize_t m, n;
                m = (partial_pack_hash && partial_pack_offset < aligned_sz) ?
                        partial_pack_offset : aligned_sz;
                n = xread(pack_fd, buf, m);
                if (!n)
                        break;
                if (n < 0)
                        die_errno("Failed to checksum '%s'", pack_name);
                the_hash_algo->update_fn(&new_hash_ctx, buf, n);

                aligned_sz -= n;
                if (!aligned_sz)
                        aligned_sz = buf_sz;

                if (!partial_pack_hash)
                        continue;

                the_hash_algo->update_fn(&old_hash_ctx, buf, n);
                partial_pack_offset -= n;
                if (partial_pack_offset == 0) {
                        unsigned char hash[GIT_MAX_RAWSZ];
                        the_hash_algo->final_fn(hash, &old_hash_ctx);
                        if (!hasheq(hash, partial_pack_hash))
                                die("Unexpected checksum for %s "
                                    "(disk corruption?)", pack_name);
                        /*
                         * Now let's compute the SHA1 of the remainder of the
                         * pack, which also means making partial_pack_offset
                         * big enough not to matter anymore.
                         */
                        the_hash_algo->init_fn(&old_hash_ctx);
                        partial_pack_offset = ~partial_pack_offset;
                        partial_pack_offset -= MSB(partial_pack_offset, 1);
                }
        }
        free(buf);

        if (partial_pack_hash)
                the_hash_algo->final_fn(partial_pack_hash, &old_hash_ctx);
        the_hash_algo->final_fn(new_pack_hash, &new_hash_ctx);
        write_or_die(pack_fd, new_pack_hash, the_hash_algo->rawsz);
        fsync_component_or_die(FSYNC_COMPONENT_PACK, pack_fd, pack_name);
}

char *index_pack_lockfile(int ip_out, int *is_well_formed)
{
        char packname[GIT_MAX_HEXSZ + 6];
        const int len = the_hash_algo->hexsz + 6;

        /*
         * The first thing we expect from index-pack's output
         * is "pack\t%40s\n" or "keep\t%40s\n" (46 bytes) where
         * %40s is the newly created pack SHA1 name.  In the "keep"
         * case, we need it to remove the corresponding .keep file
         * later on.  If we don't get that then tough luck with it.
         */
        if (read_in_full(ip_out, packname, len) == len && packname[len-1] == '\n') {
                const char *name;

                if (is_well_formed)
                        *is_well_formed = 1;
                packname[len-1] = 0;
                if (skip_prefix(packname, "keep\t", &name))
                        return xstrfmt("%s/pack/pack-%s.keep",
                                       get_object_directory(), name);
                return NULL;
        }
        if (is_well_formed)
                *is_well_formed = 0;
        return NULL;
}

/*
 * The per-object header is a pretty dense thing, which is
 *  - first byte: low four bits are "size", then three bits of "type",
 *    and the high bit is "size continues".
 *  - each byte afterwards: low seven bits are size continuation,
 *    with the high bit being "size continues"
 */
int encode_in_pack_object_header(unsigned char *hdr, int hdr_len,
                                 enum object_type type, uintmax_t size)
{
        int n = 1;
        unsigned char c;

        if (type < OBJ_COMMIT || type > OBJ_REF_DELTA)
                die("bad type %d", type);

        c = (type << 4) | (size & 15);
        size >>= 4;
        while (size) {
                if (n == hdr_len)
                        die("object size is too enormous to format");
                *hdr++ = c | 0x80;
                c = size & 0x7f;
                size >>= 7;
                n++;
        }
        *hdr = c;
        return n;
}

struct hashfile *create_tmp_packfile(char **pack_tmp_name)
{
        struct strbuf tmpname = STRBUF_INIT;
        int fd;

        fd = odb_mkstemp(&tmpname, "pack/tmp_pack_XXXXXX");
        *pack_tmp_name = strbuf_detach(&tmpname, NULL);
        return hashfd(fd, *pack_tmp_name);
}

static void rename_tmp_packfile(struct strbuf *name_prefix, const char *source,
                                const char *ext)
{
        size_t name_prefix_len = name_prefix->len;

        strbuf_addstr(name_prefix, ext);
        if (rename(source, name_prefix->buf))
                die_errno("unable to rename temporary file to '%s'",
                          name_prefix->buf);
        strbuf_setlen(name_prefix, name_prefix_len);
}

void rename_tmp_packfile_idx(struct strbuf *name_buffer,
                             char **idx_tmp_name)
{
        rename_tmp_packfile(name_buffer, *idx_tmp_name, "idx");
}

void stage_tmp_packfiles(struct strbuf *name_buffer,
                         const char *pack_tmp_name,
                         struct pack_idx_entry **written_list,
                         uint32_t nr_written,
                         struct packing_data *to_pack,
                         struct pack_idx_option *pack_idx_opts,
                         unsigned char hash[],
                         char **idx_tmp_name)
{
        const char *rev_tmp_name = NULL;
        const char *mtimes_tmp_name = NULL;

        if (adjust_shared_perm(pack_tmp_name))
                die_errno("unable to make temporary pack file readable");

        *idx_tmp_name = (char *)write_idx_file(NULL, written_list, nr_written,
                                               pack_idx_opts, hash);
        if (adjust_shared_perm(*idx_tmp_name))
                die_errno("unable to make temporary index file readable");

        rev_tmp_name = write_rev_file(NULL, written_list, nr_written, hash,
                                      pack_idx_opts->flags);

        if (pack_idx_opts->flags & WRITE_MTIMES) {
                mtimes_tmp_name = write_mtimes_file(to_pack, written_list,
                                                    nr_written,
                                                    hash);
        }

        rename_tmp_packfile(name_buffer, pack_tmp_name, "pack");
        if (rev_tmp_name)
                rename_tmp_packfile(name_buffer, rev_tmp_name, "rev");
        if (mtimes_tmp_name)
                rename_tmp_packfile(name_buffer, mtimes_tmp_name, "mtimes");
}

void write_promisor_file(const char *promisor_name, struct ref **sought, int nr_sought)
{
        int i, err;
        FILE *output = xfopen(promisor_name, "w");

        for (i = 0; i < nr_sought; i++)
                fprintf(output, "%s %s\n", oid_to_hex(&sought[i]->old_oid),
                        sought[i]->name);

        err = ferror(output);
        err |= fclose(output);
        if (err)
                die(_("could not write '%s' promisor file"), promisor_name);
}