pack-write.c

   1 #include "cache.h"
   2 #include "pack.h"
   3 #include "csum-file.h"
   4
   5 uint32_t pack_idx_default_version = 2;
   6 uint32_t pack_idx_off32_limit = 0x7fffffff;
   7
   8 static int sha1_compare(const void *_a, const void *_b)
   9 {
  10         struct pack_idx_entry *a = *(struct pack_idx_entry **)_a;
  11         struct pack_idx_entry *b = *(struct pack_idx_entry **)_b;
  12         return hashcmp(a->sha1, b->sha1);
  13 }
  14
  15 /*
  16  * On entry *sha1 contains the pack content SHA1 hash, on exit it is
  17  * the SHA1 hash of sorted object names. The objects array passed in
  18  * will be sorted by SHA1 on exit.
  19  */
  20 const char *write_idx_file(const char *index_name, struct pack_idx_entry **objects,
  21                            int nr_objects, unsigned char *sha1)
  22 {
  23         struct sha1file *f;
  24         struct pack_idx_entry **sorted_by_sha, **list, **last;
  25         off_t last_obj_offset = 0;
  26         uint32_t array[256];
  27         int i, fd;
  28         git_SHA_CTX ctx;
  29         uint32_t index_version;
  30
  31         if (nr_objects) {
  32                 sorted_by_sha = objects;
  33                 list = sorted_by_sha;
  34                 last = sorted_by_sha + nr_objects;
  35                 for (i = 0; i < nr_objects; ++i) {
  36                         if (objects[i]->offset > last_obj_offset)
  37                                 last_obj_offset = objects[i]->offset;
  38                 }
  39                 qsort(sorted_by_sha, nr_objects, sizeof(sorted_by_sha[0]),
  40                       sha1_compare);
  41         }
  42         else
  43                 sorted_by_sha = list = last = NULL;
  44
  45         if (!index_name) {
  46                 static char tmpfile[PATH_MAX];
  47                 fd = odb_mkstemp(tmpfile, sizeof(tmpfile), "pack/tmp_idx_XXXXXX");
  48                 index_name = xstrdup(tmpfile);
  49         } else {
  50                 unlink(index_name);
  51                 fd = open(index_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
  52         }
  53         if (fd < 0)
  54                 die_errno("unable to create '%s'", index_name);
  55         f = sha1fd(fd, index_name);
  56
  57         /* if last object's offset is >= 2^31 we should use index V2 */
  58         index_version = (last_obj_offset >> 31) ? 2 : pack_idx_default_version;
  59
  60         /* index versions 2 and above need a header */
  61         if (index_version >= 2) {
  62                 struct pack_idx_header hdr;
  63                 hdr.idx_signature = htonl(PACK_IDX_SIGNATURE);
  64                 hdr.idx_version = htonl(index_version);
  65                 sha1write(f, &hdr, sizeof(hdr));
  66         }
  67
  68         /*
  69          * Write the first-level table (the list is sorted,
  70          * but we use a 256-entry lookup to be able to avoid
  71          * having to do eight extra binary search iterations).
  72          */
  73         for (i = 0; i < 256; i++) {
  74                 struct pack_idx_entry **next = list;
  75                 while (next < last) {
  76                         struct pack_idx_entry *obj = *next;
  77                         if (obj->sha1[0] != i)
  78                                 break;
  79                         next++;
  80                 }
  81                 array[i] = htonl(next - sorted_by_sha);
  82                 list = next;
  83         }
  84         sha1write(f, array, 256 * 4);
  85
  86         /* compute the SHA1 hash of sorted object names. */
  87         git_SHA1_Init(&ctx);
  88
  89         /*
  90          * Write the actual SHA1 entries..
  91          */
  92         list = sorted_by_sha;
  93         for (i = 0; i < nr_objects; i++) {
  94                 struct pack_idx_entry *obj = *list++;
  95                 if (index_version < 2) {
  96                         uint32_t offset = htonl(obj->offset);
  97                         sha1write(f, &offset, 4);
  98                 }
  99                 sha1write(f, obj->sha1, 20);
 100                 git_SHA1_Update(&ctx, obj->sha1, 20);
 101         }
 102
 103         if (index_version >= 2) {
 104                 unsigned int nr_large_offset = 0;
 105
 106                 /* write the crc32 table */
 107                 list = sorted_by_sha;
 108                 for (i = 0; i < nr_objects; i++) {
 109                         struct pack_idx_entry *obj = *list++;
 110                         uint32_t crc32_val = htonl(obj->crc32);
 111                         sha1write(f, &crc32_val, 4);
 112                 }
 113
 114                 /* write the 32-bit offset table */
 115                 list = sorted_by_sha;
 116                 for (i = 0; i < nr_objects; i++) {
 117                         struct pack_idx_entry *obj = *list++;
 118                         uint32_t offset = (obj->offset <= pack_idx_off32_limit) ?
 119                                 obj->offset : (0x80000000 | nr_large_offset++);
 120                         offset = htonl(offset);
 121                         sha1write(f, &offset, 4);
 122                 }
 123
 124                 /* write the large offset table */
 125                 list = sorted_by_sha;
 126                 while (nr_large_offset) {
 127                         struct pack_idx_entry *obj = *list++;
 128                         uint64_t offset = obj->offset;
 129                         if (offset > pack_idx_off32_limit) {
 130                                 uint32_t split[2];
 131                                 split[0] = htonl(offset >> 32);
 132                                 split[1] = htonl(offset & 0xffffffff);
 133                                 sha1write(f, split, 8);
 134                                 nr_large_offset--;
 135                         }
 136                 }
 137         }
 138
 139         sha1write(f, sha1, 20);
 140         sha1close(f, NULL, CSUM_FSYNC);
 141         git_SHA1_Final(sha1, &ctx);
 142         return index_name;
 143 }
 144
 145 /*
 146  * Update pack header with object_count and compute new SHA1 for pack data
 147  * associated to pack_fd, and write that SHA1 at the end.  That new SHA1
 148  * is also returned in new_pack_sha1.
 149  *
 150  * If partial_pack_sha1 is non null, then the SHA1 of the existing pack
 151  * (without the header update) is computed and validated against the
 152  * one provided in partial_pack_sha1.  The validation is performed at
 153  * partial_pack_offset bytes in the pack file.  The SHA1 of the remaining
 154  * data (i.e. from partial_pack_offset to the end) is then computed and
 155  * returned in partial_pack_sha1.
 156  *
 157  * Note that new_pack_sha1 is updated last, so both new_pack_sha1 and
 158  * partial_pack_sha1 can refer to the same buffer if the caller is not
 159  * interested in the resulting SHA1 of pack data above partial_pack_offset.
 160  */
 161 void fixup_pack_header_footer(int pack_fd,
 162                          unsigned char *new_pack_sha1,
 163                          const char *pack_name,
 164                          uint32_t object_count,
 165                          unsigned char *partial_pack_sha1,
 166                          off_t partial_pack_offset)
 167 {
 168         int aligned_sz, buf_sz = 8 * 1024;
 169         git_SHA_CTX old_sha1_ctx, new_sha1_ctx;
 170         struct pack_header hdr;
 171         char *buf;
 172
 173         git_SHA1_Init(&old_sha1_ctx);
 174         git_SHA1_Init(&new_sha1_ctx);
 175
 176         if (lseek(pack_fd, 0, SEEK_SET) != 0)
 177                 die_errno("Failed seeking to start of '%s'", pack_name);
 178         if (read_in_full(pack_fd, &hdr, sizeof(hdr)) != sizeof(hdr))
 179                 die_errno("Unable to reread header of '%s'", pack_name);
 180         if (lseek(pack_fd, 0, SEEK_SET) != 0)
 181                 die_errno("Failed seeking to start of '%s'", pack_name);
 182         git_SHA1_Update(&old_sha1_ctx, &hdr, sizeof(hdr));
 183         hdr.hdr_entries = htonl(object_count);
 184         git_SHA1_Update(&new_sha1_ctx, &hdr, sizeof(hdr));
 185         write_or_die(pack_fd, &hdr, sizeof(hdr));
 186         partial_pack_offset -= sizeof(hdr);
 187
 188         buf = xmalloc(buf_sz);
 189         aligned_sz = buf_sz - sizeof(hdr);
 190         for (;;) {
 191                 ssize_t m, n;
 192                 m = (partial_pack_sha1 && partial_pack_offset < aligned_sz) ?
 193                         partial_pack_offset : aligned_sz;
 194                 n = xread(pack_fd, buf, m);
 195                 if (!n)
 196                         break;
 197                 if (n < 0)
 198                         die_errno("Failed to checksum '%s'", pack_name);
 199                 git_SHA1_Update(&new_sha1_ctx, buf, n);
 200
 201                 aligned_sz -= n;
 202                 if (!aligned_sz)
 203                         aligned_sz = buf_sz;
 204
 205                 if (!partial_pack_sha1)
 206                         continue;
 207
 208                 git_SHA1_Update(&old_sha1_ctx, buf, n);
 209                 partial_pack_offset -= n;
 210                 if (partial_pack_offset == 0) {
 211                         unsigned char sha1[20];
 212                         git_SHA1_Final(sha1, &old_sha1_ctx);
 213                         if (hashcmp(sha1, partial_pack_sha1) != 0)
 214                                 die("Unexpected checksum for %s "
 215                                     "(disk corruption?)", pack_name);
 216                         /*
 217                          * Now let's compute the SHA1 of the remainder of the
 218                          * pack, which also means making partial_pack_offset
 219                          * big enough not to matter anymore.
 220                          */
 221                         git_SHA1_Init(&old_sha1_ctx);
 222                         partial_pack_offset = ~partial_pack_offset;
 223                         partial_pack_offset -= MSB(partial_pack_offset, 1);
 224                 }
 225         }
 226         free(buf);
 227
 228         if (partial_pack_sha1)
 229                 git_SHA1_Final(partial_pack_sha1, &old_sha1_ctx);
 230         git_SHA1_Final(new_pack_sha1, &new_sha1_ctx);
 231         write_or_die(pack_fd, new_pack_sha1, 20);
 232         fsync_or_die(pack_fd, pack_name);
 233 }
 234
 235 char *index_pack_lockfile(int ip_out)
 236 {
 237         char packname[46];
 238
 239         /*
 240          * The first thing we expect from index-pack's output
 241          * is "pack\t%40s\n" or "keep\t%40s\n" (46 bytes) where
 242          * %40s is the newly created pack SHA1 name.  In the "keep"
 243          * case, we need it to remove the corresponding .keep file
 244          * later on.  If we don't get that then tough luck with it.
 245          */
 246         if (read_in_full(ip_out, packname, 46) == 46 && packname[45] == '\n' &&
 247             memcmp(packname, "keep\t", 5) == 0) {
 248                 char path[PATH_MAX];
 249                 packname[45] = 0;
 250                 snprintf(path, sizeof(path), "%s/pack/pack-%s.keep",
 251                          get_object_directory(), packname + 5);
 252                 return xstrdup(path);
 253         }
 254         return NULL;
 255 }
 256
 257 /*
 258  * The per-object header is a pretty dense thing, which is
 259  *  - first byte: low four bits are "size", then three bits of "type",
 260  *    and the high bit is "size continues".
 261  *  - each byte afterwards: low seven bits are size continuation,
 262  *    with the high bit being "size continues"
 263  */
 264 int encode_in_pack_object_header(enum object_type type, uintmax_t size, unsigned char *hdr)
 265 {
 266         int n = 1;
 267         unsigned char c;
 268
 269         if (type < OBJ_COMMIT || type > OBJ_REF_DELTA)
 270                 die("bad type %d", type);
 271
 272         c = (type << 4) | (size & 15);
 273         size >>= 4;
 274         while (size) {
 275                 *hdr++ = c | 0x80;
 276                 c = size & 0x7f;
 277                 size >>= 7;
 278                 n++;
 279         }
 280         *hdr = c;
 281         return n;
 282 }