root/pack-write.c

DEFINITIONS

1. reset_pack_idx_option
2. sha1_compare
3. cmp_uint32
4. need_large_offset
5. write_idx_file
6. write_pack_header
7. fixup_pack_header_footer
8. index_pack_lockfile
9. encode_in_pack_object_header
10. create_tmp_packfile
11. finish_tmp_packfile

#include "cache.h"
#include "pack.h"
#include "csum-file.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 hashcmp(a->sha1, b->sha1);
}

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);
}

/*
 * On entry *sha1 contains the pack content SHA1 hash, on exit it is
 * the SHA1 hash of sorted object names. 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 sha1file *f;
        struct pack_idx_entry **sorted_by_sha, **list, **last;
        off_t last_obj_offset = 0;
        uint32_t array[256];
        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, sizeof(sorted_by_sha[0]),
                      sha1_compare);
        }
        else
                sorted_by_sha = list = last = NULL;

        if (opts->flags & WRITE_IDX_VERIFY) {
                assert(index_name);
                f = sha1fd_check(index_name);
        } else {
                if (!index_name) {
                        static char tmp_file[PATH_MAX];
                        fd = odb_mkstemp(tmp_file, sizeof(tmp_file), "pack/tmp_idx_XXXXXX");
                        index_name = xstrdup(tmp_file);
                } else {
                        unlink(index_name);
                        fd = open(index_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
                }
                if (fd < 0)
                        die_errno("unable to create '%s'", index_name);
                f = sha1fd(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);
                sha1write(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->sha1[0] != i)
                                break;
                        next++;
                }
                array[i] = htonl(next - sorted_by_sha);
                list = next;
        }
        sha1write(f, array, 256 * 4);

        /*
         * 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) {
                        uint32_t offset = htonl(obj->offset);
                        sha1write(f, &offset, 4);
                }
                sha1write(f, obj->sha1, 20);
                if ((opts->flags & WRITE_IDX_STRICT) &&
                    (i && !hashcmp(list[-2]->sha1, obj->sha1)))
                        die("The same object %s appears twice in the pack",
                            sha1_to_hex(obj->sha1));
        }

        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++;
                        uint32_t crc32_val = htonl(obj->crc32);
                        sha1write(f, &crc32_val, 4);
                }

                /* 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);
                        offset = htonl(offset);
                        sha1write(f, &offset, 4);
                }

                /* write the large offset table */
                list = sorted_by_sha;
                while (nr_large_offset) {
                        struct pack_idx_entry *obj = *list++;
                        uint64_t offset = obj->offset;
                        uint32_t split[2];

                        if (!need_large_offset(offset, opts))
                                continue;
                        split[0] = htonl(offset >> 32);
                        split[1] = htonl(offset & 0xffffffff);
                        sha1write(f, split, 8);
                        nr_large_offset--;
                }
        }

        sha1write(f, sha1, 20);
        sha1close(f, NULL, ((opts->flags & WRITE_IDX_VERIFY)
                            ? CSUM_CLOSE : CSUM_FSYNC));
        return index_name;
}

off_t write_pack_header(struct sha1file *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);
        sha1write(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_sha1,
                         const char *pack_name,
                         uint32_t object_count,
                         unsigned char *partial_pack_sha1,
                         off_t partial_pack_offset)
{
        int aligned_sz, buf_sz = 8 * 1024;
        git_SHA_CTX old_sha1_ctx, new_sha1_ctx;
        struct pack_header hdr;
        char *buf;

        git_SHA1_Init(&old_sha1_ctx);
        git_SHA1_Init(&new_sha1_ctx);

        if (lseek(pack_fd, 0, SEEK_SET) != 0)
                die_errno("Failed seeking to start of '%s'", pack_name);
        if (read_in_full(pack_fd, &hdr, sizeof(hdr)) != sizeof(hdr))
                die_errno("Unable to reread header of '%s'", pack_name);
        if (lseek(pack_fd, 0, SEEK_SET) != 0)
                die_errno("Failed seeking to start of '%s'", pack_name);
        git_SHA1_Update(&old_sha1_ctx, &hdr, sizeof(hdr));
        hdr.hdr_entries = htonl(object_count);
        git_SHA1_Update(&new_sha1_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_sha1 && 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);
                git_SHA1_Update(&new_sha1_ctx, buf, n);

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

                if (!partial_pack_sha1)
                        continue;

                git_SHA1_Update(&old_sha1_ctx, buf, n);
                partial_pack_offset -= n;
                if (partial_pack_offset == 0) {
                        unsigned char sha1[20];
                        git_SHA1_Final(sha1, &old_sha1_ctx);
                        if (hashcmp(sha1, partial_pack_sha1) != 0)
                                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.
                         */
                        git_SHA1_Init(&old_sha1_ctx);
                        partial_pack_offset = ~partial_pack_offset;
                        partial_pack_offset -= MSB(partial_pack_offset, 1);
                }
        }
        free(buf);

        if (partial_pack_sha1)
                git_SHA1_Final(partial_pack_sha1, &old_sha1_ctx);
        git_SHA1_Final(new_pack_sha1, &new_sha1_ctx);
        write_or_die(pack_fd, new_pack_sha1, 20);
        fsync_or_die(pack_fd, pack_name);
}

char *index_pack_lockfile(int ip_out)
{
        char packname[46];

        /*
         * 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, 46) == 46 && packname[45] == '\n') {
                const char *name;
                packname[45] = 0;
                if (skip_prefix(packname, "keep\t", &name))
                        return xstrfmt("%s/pack/pack-%s.keep",
                                       get_object_directory(), name);
        }
        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(enum object_type type, uintmax_t size, unsigned char *hdr)
{
        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) {
                *hdr++ = c | 0x80;
                c = size & 0x7f;
                size >>= 7;
                n++;
        }
        *hdr = c;
        return n;
}

struct sha1file *create_tmp_packfile(char **pack_tmp_name)
{
        char tmpname[PATH_MAX];
        int fd;

        fd = odb_mkstemp(tmpname, sizeof(tmpname), "pack/tmp_pack_XXXXXX");
        *pack_tmp_name = xstrdup(tmpname);
        return sha1fd(fd, *pack_tmp_name);
}

void finish_tmp_packfile(struct strbuf *name_buffer,
                         const char *pack_tmp_name,
                         struct pack_idx_entry **written_list,
                         uint32_t nr_written,
                         struct pack_idx_option *pack_idx_opts,
                         unsigned char sha1[])
{
        const char *idx_tmp_name;
        int basename_len = name_buffer->len;

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

        idx_tmp_name = write_idx_file(NULL, written_list, nr_written,
                                      pack_idx_opts, sha1);
        if (adjust_shared_perm(idx_tmp_name))
                die_errno("unable to make temporary index file readable");

        strbuf_addf(name_buffer, "%s.pack", sha1_to_hex(sha1));
        free_pack_by_name(name_buffer->buf);

        if (rename(pack_tmp_name, name_buffer->buf))
                die_errno("unable to rename temporary pack file");

        strbuf_setlen(name_buffer, basename_len);

        strbuf_addf(name_buffer, "%s.idx", sha1_to_hex(sha1));
        if (rename(idx_tmp_name, name_buffer->buf))
                die_errno("unable to rename temporary index file");

        strbuf_setlen(name_buffer, basename_len);

        free((void *)idx_tmp_name);
}