notes.c

   1 #include "cache.h"
   2 #include "notes.h"
   3 #include "blob.h"
   4 #include "tree.h"
   5 #include "utf8.h"
   6 #include "strbuf.h"
   7 #include "tree-walk.h"
   8
   9 /*
  10  * Use a non-balancing simple 16-tree structure with struct int_node as
  11  * internal nodes, and struct leaf_node as leaf nodes. Each int_node has a
  12  * 16-array of pointers to its children.
  13  * The bottom 2 bits of each pointer is used to identify the pointer type
  14  * - ptr & 3 == 0 - NULL pointer, assert(ptr == NULL)
  15  * - ptr & 3 == 1 - pointer to next internal node - cast to struct int_node *
  16  * - ptr & 3 == 2 - pointer to note entry - cast to struct leaf_node *
  17  * - ptr & 3 == 3 - pointer to subtree entry - cast to struct leaf_node *
  18  *
  19  * The root node is a statically allocated struct int_node.
  20  */
  21 struct int_node {
  22         void *a[16];
  23 };
  24
  25 /*
  26  * Leaf nodes come in two variants, note entries and subtree entries,
  27  * distinguished by the LSb of the leaf node pointer (see above).
  28  * As a note entry, the key is the SHA1 of the referenced object, and the
  29  * value is the SHA1 of the note object.
  30  * As a subtree entry, the key is the prefix SHA1 (w/trailing NULs) of the
  31  * referenced object, using the last byte of the key to store the length of
  32  * the prefix. The value is the SHA1 of the tree object containing the notes
  33  * subtree.
  34  */
  35 struct leaf_node {
  36         unsigned char key_sha1[20];
  37         unsigned char val_sha1[20];
  38 };
  39
  40 /*
  41  * A notes tree may contain entries that are not notes, and that do not follow
  42  * the naming conventions of notes. There are typically none/few of these, but
  43  * we still need to keep track of them. Keep a simple linked list sorted alpha-
  44  * betically on the non-note path. The list is populated when parsing tree
  45  * objects in load_subtree(), and the non-notes are correctly written back into
  46  * the tree objects produced by write_notes_tree().
  47  */
  48 struct non_note {
  49         struct non_note *next; /* grounded (last->next == NULL) */
  50         char *path;
  51         unsigned int mode;
  52         unsigned char sha1[20];
  53 };
  54
  55 #define PTR_TYPE_NULL     0
  56 #define PTR_TYPE_INTERNAL 1
  57 #define PTR_TYPE_NOTE     2
  58 #define PTR_TYPE_SUBTREE  3
  59
  60 #define GET_PTR_TYPE(ptr)       ((uintptr_t) (ptr) & 3)
  61 #define CLR_PTR_TYPE(ptr)       ((void *) ((uintptr_t) (ptr) & ~3))
  62 #define SET_PTR_TYPE(ptr, type) ((void *) ((uintptr_t) (ptr) | (type)))
  63
  64 #define GET_NIBBLE(n, sha1) (((sha1[(n) >> 1]) >> ((~(n) & 0x01) << 2)) & 0x0f)
  65
  66 #define SUBTREE_SHA1_PREFIXCMP(key_sha1, subtree_sha1) \
  67         (memcmp(key_sha1, subtree_sha1, subtree_sha1[19]))
  68
  69 struct notes_tree default_notes_tree;
  70
  71 static void load_subtree(struct notes_tree *t, struct leaf_node *subtree,
  72                 struct int_node *node, unsigned int n);
  73
  74 /*
  75  * Search the tree until the appropriate location for the given key is found:
  76  * 1. Start at the root node, with n = 0
  77  * 2. If a[0] at the current level is a matching subtree entry, unpack that
  78  *    subtree entry and remove it; restart search at the current level.
  79  * 3. Use the nth nibble of the key as an index into a:
  80  *    - If a[n] is an int_node, recurse from #2 into that node and increment n
  81  *    - If a matching subtree entry, unpack that subtree entry (and remove it);
  82  *      restart search at the current level.
  83  *    - Otherwise, we have found one of the following:
  84  *      - a subtree entry which does not match the key
  85  *      - a note entry which may or may not match the key
  86  *      - an unused leaf node (NULL)
  87  *      In any case, set *tree and *n, and return pointer to the tree location.
  88  */
  89 static void **note_tree_search(struct notes_tree *t, struct int_node **tree,
  90                 unsigned char *n, const unsigned char *key_sha1)
  91 {
  92         struct leaf_node *l;
  93         unsigned char i;
  94         void *p = (*tree)->a[0];
  95
  96         if (GET_PTR_TYPE(p) == PTR_TYPE_SUBTREE) {
  97                 l = (struct leaf_node *) CLR_PTR_TYPE(p);
  98                 if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_sha1)) {
  99                         /* unpack tree and resume search */
 100                         (*tree)->a[0] = NULL;
 101                         load_subtree(t, l, *tree, *n);
 102                         free(l);
 103                         return note_tree_search(t, tree, n, key_sha1);
 104                 }
 105         }
 106
 107         i = GET_NIBBLE(*n, key_sha1);
 108         p = (*tree)->a[i];
 109         switch (GET_PTR_TYPE(p)) {
 110         case PTR_TYPE_INTERNAL:
 111                 *tree = CLR_PTR_TYPE(p);
 112                 (*n)++;
 113                 return note_tree_search(t, tree, n, key_sha1);
 114         case PTR_TYPE_SUBTREE:
 115                 l = (struct leaf_node *) CLR_PTR_TYPE(p);
 116                 if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_sha1)) {
 117                         /* unpack tree and resume search */
 118                         (*tree)->a[i] = NULL;
 119                         load_subtree(t, l, *tree, *n);
 120                         free(l);
 121                         return note_tree_search(t, tree, n, key_sha1);
 122                 }
 123                 /* fall through */
 124         default:
 125                 return &((*tree)->a[i]);
 126         }
 127 }
 128
 129 /*
 130  * To find a leaf_node:
 131  * Search to the tree location appropriate for the given key:
 132  * If a note entry with matching key, return the note entry, else return NULL.
 133  */
 134 static struct leaf_node *note_tree_find(struct notes_tree *t,
 135                 struct int_node *tree, unsigned char n,
 136                 const unsigned char *key_sha1)
 137 {
 138         void **p = note_tree_search(t, &tree, &n, key_sha1);
 139         if (GET_PTR_TYPE(*p) == PTR_TYPE_NOTE) {
 140                 struct leaf_node *l = (struct leaf_node *) CLR_PTR_TYPE(*p);
 141                 if (!hashcmp(key_sha1, l->key_sha1))
 142                         return l;
 143         }
 144         return NULL;
 145 }
 146
 147 /*
 148  * To insert a leaf_node:
 149  * Search to the tree location appropriate for the given leaf_node's key:
 150  * - If location is unused (NULL), store the tweaked pointer directly there
 151  * - If location holds a note entry that matches the note-to-be-inserted, then
 152  *   combine the two notes (by calling the given combine_notes function).
 153  * - If location holds a note entry that matches the subtree-to-be-inserted,
 154  *   then unpack the subtree-to-be-inserted into the location.
 155  * - If location holds a matching subtree entry, unpack the subtree at that
 156  *   location, and restart the insert operation from that level.
 157  * - Else, create a new int_node, holding both the node-at-location and the
 158  *   node-to-be-inserted, and store the new int_node into the location.
 159  */
 160 static void note_tree_insert(struct notes_tree *t, struct int_node *tree,
 161                 unsigned char n, struct leaf_node *entry, unsigned char type,
 162                 combine_notes_fn combine_notes)
 163 {
 164         struct int_node *new_node;
 165         struct leaf_node *l;
 166         void **p = note_tree_search(t, &tree, &n, entry->key_sha1);
 167
 168         assert(GET_PTR_TYPE(entry) == 0); /* no type bits set */
 169         l = (struct leaf_node *) CLR_PTR_TYPE(*p);
 170         switch (GET_PTR_TYPE(*p)) {
 171         case PTR_TYPE_NULL:
 172                 assert(!*p);
 173                 *p = SET_PTR_TYPE(entry, type);
 174                 return;
 175         case PTR_TYPE_NOTE:
 176                 switch (type) {
 177                 case PTR_TYPE_NOTE:
 178                         if (!hashcmp(l->key_sha1, entry->key_sha1)) {
 179                                 /* skip concatenation if l == entry */
 180                                 if (!hashcmp(l->val_sha1, entry->val_sha1))
 181                                         return;
 182
 183                                 if (combine_notes(l->val_sha1, entry->val_sha1))
 184                                         die("failed to combine notes %s and %s"
 185                                             " for object %s",
 186                                             sha1_to_hex(l->val_sha1),
 187                                             sha1_to_hex(entry->val_sha1),
 188                                             sha1_to_hex(l->key_sha1));
 189                                 free(entry);
 190                                 return;
 191                         }
 192                         break;
 193                 case PTR_TYPE_SUBTREE:
 194                         if (!SUBTREE_SHA1_PREFIXCMP(l->key_sha1,
 195                                                     entry->key_sha1)) {
 196                                 /* unpack 'entry' */
 197                                 load_subtree(t, entry, tree, n);
 198                                 free(entry);
 199                                 return;
 200                         }
 201                         break;
 202                 }
 203                 break;
 204         case PTR_TYPE_SUBTREE:
 205                 if (!SUBTREE_SHA1_PREFIXCMP(entry->key_sha1, l->key_sha1)) {
 206                         /* unpack 'l' and restart insert */
 207                         *p = NULL;
 208                         load_subtree(t, l, tree, n);
 209                         free(l);
 210                         note_tree_insert(t, tree, n, entry, type,
 211                                          combine_notes);
 212                         return;
 213                 }
 214                 break;
 215         }
 216
 217         /* non-matching leaf_node */
 218         assert(GET_PTR_TYPE(*p) == PTR_TYPE_NOTE ||
 219                GET_PTR_TYPE(*p) == PTR_TYPE_SUBTREE);
 220         new_node = (struct int_node *) xcalloc(sizeof(struct int_node), 1);
 221         note_tree_insert(t, new_node, n + 1, l, GET_PTR_TYPE(*p),
 222                          combine_notes);
 223         *p = SET_PTR_TYPE(new_node, PTR_TYPE_INTERNAL);
 224         note_tree_insert(t, new_node, n + 1, entry, type, combine_notes);
 225 }
 226
 227 /*
 228  * How to consolidate an int_node:
 229  * If there are > 1 non-NULL entries, give up and return non-zero.
 230  * Otherwise replace the int_node at the given index in the given parent node
 231  * with the only entry (or a NULL entry if no entries) from the given tree,
 232  * and return 0.
 233  */
 234 static int note_tree_consolidate(struct int_node *tree,
 235         struct int_node *parent, unsigned char index)
 236 {
 237         unsigned int i;
 238         void *p = NULL;
 239
 240         assert(tree && parent);
 241         assert(CLR_PTR_TYPE(parent->a[index]) == tree);
 242
 243         for (i = 0; i < 16; i++) {
 244                 if (GET_PTR_TYPE(tree->a[i]) != PTR_TYPE_NULL) {
 245                         if (p) /* more than one entry */
 246                                 return -2;
 247                         p = tree->a[i];
 248                 }
 249         }
 250
 251         /* replace tree with p in parent[index] */
 252         parent->a[index] = p;
 253         free(tree);
 254         return 0;
 255 }
 256
 257 /*
 258  * To remove a leaf_node:
 259  * Search to the tree location appropriate for the given leaf_node's key:
 260  * - If location does not hold a matching entry, abort and do nothing.
 261  * - Replace the matching leaf_node with a NULL entry (and free the leaf_node).
 262  * - Consolidate int_nodes repeatedly, while walking up the tree towards root.
 263  */
 264 static void note_tree_remove(struct notes_tree *t, struct int_node *tree,
 265                 unsigned char n, struct leaf_node *entry)
 266 {
 267         struct leaf_node *l;
 268         struct int_node *parent_stack[20];
 269         unsigned char i, j;
 270         void **p = note_tree_search(t, &tree, &n, entry->key_sha1);
 271
 272         assert(GET_PTR_TYPE(entry) == 0); /* no type bits set */
 273         if (GET_PTR_TYPE(*p) != PTR_TYPE_NOTE)
 274                 return; /* type mismatch, nothing to remove */
 275         l = (struct leaf_node *) CLR_PTR_TYPE(*p);
 276         if (hashcmp(l->key_sha1, entry->key_sha1))
 277                 return; /* key mismatch, nothing to remove */
 278
 279         /* we have found a matching entry */
 280         free(l);
 281         *p = SET_PTR_TYPE(NULL, PTR_TYPE_NULL);
 282
 283         /* consolidate this tree level, and parent levels, if possible */
 284         if (!n)
 285                 return; /* cannot consolidate top level */
 286         /* first, build stack of ancestors between root and current node */
 287         parent_stack[0] = t->root;
 288         for (i = 0; i < n; i++) {
 289                 j = GET_NIBBLE(i, entry->key_sha1);
 290                 parent_stack[i + 1] = CLR_PTR_TYPE(parent_stack[i]->a[j]);
 291         }
 292         assert(i == n && parent_stack[i] == tree);
 293         /* next, unwind stack until note_tree_consolidate() is done */
 294         while (i > 0 &&
 295                !note_tree_consolidate(parent_stack[i], parent_stack[i - 1],
 296                                       GET_NIBBLE(i - 1, entry->key_sha1)))
 297                 i--;
 298 }
 299
 300 /* Free the entire notes data contained in the given tree */
 301 static void note_tree_free(struct int_node *tree)
 302 {
 303         unsigned int i;
 304         for (i = 0; i < 16; i++) {
 305                 void *p = tree->a[i];
 306                 switch (GET_PTR_TYPE(p)) {
 307                 case PTR_TYPE_INTERNAL:
 308                         note_tree_free(CLR_PTR_TYPE(p));
 309                         /* fall through */
 310                 case PTR_TYPE_NOTE:
 311                 case PTR_TYPE_SUBTREE:
 312                         free(CLR_PTR_TYPE(p));
 313                 }
 314         }
 315 }
 316
 317 /*
 318  * Convert a partial SHA1 hex string to the corresponding partial SHA1 value.
 319  * - hex      - Partial SHA1 segment in ASCII hex format
 320  * - hex_len  - Length of above segment. Must be multiple of 2 between 0 and 40
 321  * - sha1     - Partial SHA1 value is written here
 322  * - sha1_len - Max #bytes to store in sha1, Must be >= hex_len / 2, and < 20
 323  * Returns -1 on error (invalid arguments or invalid SHA1 (not in hex format)).
 324  * Otherwise, returns number of bytes written to sha1 (i.e. hex_len / 2).
 325  * Pads sha1 with NULs up to sha1_len (not included in returned length).
 326  */
 327 static int get_sha1_hex_segment(const char *hex, unsigned int hex_len,
 328                 unsigned char *sha1, unsigned int sha1_len)
 329 {
 330         unsigned int i, len = hex_len >> 1;
 331         if (hex_len % 2 != 0 || len > sha1_len)
 332                 return -1;
 333         for (i = 0; i < len; i++) {
 334                 unsigned int val = (hexval(hex[0]) << 4) | hexval(hex[1]);
 335                 if (val & ~0xff)
 336                         return -1;
 337                 *sha1++ = val;
 338                 hex += 2;
 339         }
 340         for (; i < sha1_len; i++)
 341                 *sha1++ = 0;
 342         return len;
 343 }
 344
 345 static int non_note_cmp(const struct non_note *a, const struct non_note *b)
 346 {
 347         return strcmp(a->path, b->path);
 348 }
 349
 350 static void add_non_note(struct notes_tree *t, const char *path,
 351                 unsigned int mode, const unsigned char *sha1)
 352 {
 353         struct non_note *p = t->prev_non_note, *n;
 354         n = (struct non_note *) xmalloc(sizeof(struct non_note));
 355         n->next = NULL;
 356         n->path = xstrdup(path);
 357         n->mode = mode;
 358         hashcpy(n->sha1, sha1);
 359         t->prev_non_note = n;
 360
 361         if (!t->first_non_note) {
 362                 t->first_non_note = n;
 363                 return;
 364         }
 365
 366         if (non_note_cmp(p, n) < 0)
 367                 ; /* do nothing  */
 368         else if (non_note_cmp(t->first_non_note, n) <= 0)
 369                 p = t->first_non_note;
 370         else {
 371                 /* n sorts before t->first_non_note */
 372                 n->next = t->first_non_note;
 373                 t->first_non_note = n;
 374                 return;
 375         }
 376
 377         /* n sorts equal or after p */
 378         while (p->next && non_note_cmp(p->next, n) <= 0)
 379                 p = p->next;
 380
 381         if (non_note_cmp(p, n) == 0) { /* n ~= p; overwrite p with n */
 382                 assert(strcmp(p->path, n->path) == 0);
 383                 p->mode = n->mode;
 384                 hashcpy(p->sha1, n->sha1);
 385                 free(n);
 386                 t->prev_non_note = p;
 387                 return;
 388         }
 389
 390         /* n sorts between p and p->next */
 391         n->next = p->next;
 392         p->next = n;
 393 }
 394
 395 static void load_subtree(struct notes_tree *t, struct leaf_node *subtree,
 396                 struct int_node *node, unsigned int n)
 397 {
 398         unsigned char object_sha1[20];
 399         unsigned int prefix_len;
 400         void *buf;
 401         struct tree_desc desc;
 402         struct name_entry entry;
 403         int len, path_len;
 404         unsigned char type;
 405         struct leaf_node *l;
 406
 407         buf = fill_tree_descriptor(&desc, subtree->val_sha1);
 408         if (!buf)
 409                 die("Could not read %s for notes-index",
 410                      sha1_to_hex(subtree->val_sha1));
 411
 412         prefix_len = subtree->key_sha1[19];
 413         assert(prefix_len * 2 >= n);
 414         memcpy(object_sha1, subtree->key_sha1, prefix_len);
 415         while (tree_entry(&desc, &entry)) {
 416                 path_len = strlen(entry.path);
 417                 len = get_sha1_hex_segment(entry.path, path_len,
 418                                 object_sha1 + prefix_len, 20 - prefix_len);
 419                 if (len < 0)
 420                         goto handle_non_note; /* entry.path is not a SHA1 */
 421                 len += prefix_len;
 422
 423                 /*
 424                  * If object SHA1 is complete (len == 20), assume note object
 425                  * If object SHA1 is incomplete (len < 20), and current
 426                  * component consists of 2 hex chars, assume note subtree
 427                  */
 428                 if (len <= 20) {
 429                         type = PTR_TYPE_NOTE;
 430                         l = (struct leaf_node *)
 431                                 xcalloc(sizeof(struct leaf_node), 1);
 432                         hashcpy(l->key_sha1, object_sha1);
 433                         hashcpy(l->val_sha1, entry.sha1);
 434                         if (len < 20) {
 435                                 if (!S_ISDIR(entry.mode) || path_len != 2)
 436                                         goto handle_non_note; /* not subtree */
 437                                 l->key_sha1[19] = (unsigned char) len;
 438                                 type = PTR_TYPE_SUBTREE;
 439                         }
 440                         note_tree_insert(t, node, n, l, type,
 441                                          combine_notes_concatenate);
 442                 }
 443                 continue;
 444
 445 handle_non_note:
 446                 /*
 447                  * Determine full path for this non-note entry:
 448                  * The filename is already found in entry.path, but the
 449                  * directory part of the path must be deduced from the subtree
 450                  * containing this entry. We assume here that the overall notes
 451                  * tree follows a strict byte-based progressive fanout
 452                  * structure (i.e. using 2/38, 2/2/36, etc. fanouts, and not
 453                  * e.g. 4/36 fanout). This means that if a non-note is found at
 454                  * path "dead/beef", the following code will register it as
 455                  * being found on "de/ad/beef".
 456                  * On the other hand, if you use such non-obvious non-note
 457                  * paths in the middle of a notes tree, you deserve what's
 458                  * coming to you ;). Note that for non-notes that are not
 459                  * SHA1-like at the top level, there will be no problems.
 460                  *
 461                  * To conclude, it is strongly advised to make sure non-notes
 462                  * have at least one non-hex character in the top-level path
 463                  * component.
 464                  */
 465                 {
 466                         char non_note_path[PATH_MAX];
 467                         char *p = non_note_path;
 468                         const char *q = sha1_to_hex(subtree->key_sha1);
 469                         int i;
 470                         for (i = 0; i < prefix_len; i++) {
 471                                 *p++ = *q++;
 472                                 *p++ = *q++;
 473                                 *p++ = '/';
 474                         }
 475                         strcpy(p, entry.path);
 476                         add_non_note(t, non_note_path, entry.mode, entry.sha1);
 477                 }
 478         }
 479         free(buf);
 480 }
 481
 482 /*
 483  * Determine optimal on-disk fanout for this part of the notes tree
 484  *
 485  * Given a (sub)tree and the level in the internal tree structure, determine
 486  * whether or not the given existing fanout should be expanded for this
 487  * (sub)tree.
 488  *
 489  * Values of the 'fanout' variable:
 490  * - 0: No fanout (all notes are stored directly in the root notes tree)
 491  * - 1: 2/38 fanout
 492  * - 2: 2/2/36 fanout
 493  * - 3: 2/2/2/34 fanout
 494  * etc.
 495  */
 496 static unsigned char determine_fanout(struct int_node *tree, unsigned char n,
 497                 unsigned char fanout)
 498 {
 499         /*
 500          * The following is a simple heuristic that works well in practice:
 501          * For each even-numbered 16-tree level (remember that each on-disk
 502          * fanout level corresponds to _two_ 16-tree levels), peek at all 16
 503          * entries at that tree level. If all of them are either int_nodes or
 504          * subtree entries, then there are likely plenty of notes below this
 505          * level, so we return an incremented fanout.
 506          */
 507         unsigned int i;
 508         if ((n % 2) || (n > 2 * fanout))
 509                 return fanout;
 510         for (i = 0; i < 16; i++) {
 511                 switch (GET_PTR_TYPE(tree->a[i])) {
 512                 case PTR_TYPE_SUBTREE:
 513                 case PTR_TYPE_INTERNAL:
 514                         continue;
 515                 default:
 516                         return fanout;
 517                 }
 518         }
 519         return fanout + 1;
 520 }
 521
 522 static void construct_path_with_fanout(const unsigned char *sha1,
 523                 unsigned char fanout, char *path)
 524 {
 525         unsigned int i = 0, j = 0;
 526         const char *hex_sha1 = sha1_to_hex(sha1);
 527         assert(fanout < 20);
 528         while (fanout) {
 529                 path[i++] = hex_sha1[j++];
 530                 path[i++] = hex_sha1[j++];
 531                 path[i++] = '/';
 532                 fanout--;
 533         }
 534         strcpy(path + i, hex_sha1 + j);
 535 }
 536
 537 static int for_each_note_helper(struct notes_tree *t, struct int_node *tree,
 538                 unsigned char n, unsigned char fanout, int flags,
 539                 each_note_fn fn, void *cb_data)
 540 {
 541         unsigned int i;
 542         void *p;
 543         int ret = 0;
 544         struct leaf_node *l;
 545         static char path[40 + 19 + 1];  /* hex SHA1 + 19 * '/' + NUL */
 546
 547         fanout = determine_fanout(tree, n, fanout);
 548         for (i = 0; i < 16; i++) {
 549 redo:
 550                 p = tree->a[i];
 551                 switch (GET_PTR_TYPE(p)) {
 552                 case PTR_TYPE_INTERNAL:
 553                         /* recurse into int_node */
 554                         ret = for_each_note_helper(t, CLR_PTR_TYPE(p), n + 1,
 555                                 fanout, flags, fn, cb_data);
 556                         break;
 557                 case PTR_TYPE_SUBTREE:
 558                         l = (struct leaf_node *) CLR_PTR_TYPE(p);
 559                         /*
 560                          * Subtree entries in the note tree represent parts of
 561                          * the note tree that have not yet been explored. There
 562                          * is a direct relationship between subtree entries at
 563                          * level 'n' in the tree, and the 'fanout' variable:
 564                          * Subtree entries at level 'n <= 2 * fanout' should be
 565                          * preserved, since they correspond exactly to a fanout
 566                          * directory in the on-disk structure. However, subtree
 567                          * entries at level 'n > 2 * fanout' should NOT be
 568                          * preserved, but rather consolidated into the above
 569                          * notes tree level. We achieve this by unconditionally
 570                          * unpacking subtree entries that exist below the
 571                          * threshold level at 'n = 2 * fanout'.
 572                          */
 573                         if (n <= 2 * fanout &&
 574                             flags & FOR_EACH_NOTE_YIELD_SUBTREES) {
 575                                 /* invoke callback with subtree */
 576                                 unsigned int path_len =
 577                                         l->key_sha1[19] * 2 + fanout;
 578                                 assert(path_len < 40 + 19);
 579                                 construct_path_with_fanout(l->key_sha1, fanout,
 580                                                            path);
 581                                 /* Create trailing slash, if needed */
 582                                 if (path[path_len - 1] != '/')
 583                                         path[path_len++] = '/';
 584                                 path[path_len] = '\0';
 585                                 ret = fn(l->key_sha1, l->val_sha1, path,
 586                                          cb_data);
 587                         }
 588                         if (n > fanout * 2 ||
 589                             !(flags & FOR_EACH_NOTE_DONT_UNPACK_SUBTREES)) {
 590                                 /* unpack subtree and resume traversal */
 591                                 tree->a[i] = NULL;
 592                                 load_subtree(t, l, tree, n);
 593                                 free(l);
 594                                 goto redo;
 595                         }
 596                         break;
 597                 case PTR_TYPE_NOTE:
 598                         l = (struct leaf_node *) CLR_PTR_TYPE(p);
 599                         construct_path_with_fanout(l->key_sha1, fanout, path);
 600                         ret = fn(l->key_sha1, l->val_sha1, path, cb_data);
 601                         break;
 602                 }
 603                 if (ret)
 604                         return ret;
 605         }
 606         return 0;
 607 }
 608
 609 struct tree_write_stack {
 610         struct tree_write_stack *next;
 611         struct strbuf buf;
 612         char path[2]; /* path to subtree in next, if any */
 613 };
 614
 615 static inline int matches_tree_write_stack(struct tree_write_stack *tws,
 616                 const char *full_path)
 617 {
 618         return  full_path[0] == tws->path[0] &&
 619                 full_path[1] == tws->path[1] &&
 620                 full_path[2] == '/';
 621 }
 622
 623 static void write_tree_entry(struct strbuf *buf, unsigned int mode,
 624                 const char *path, unsigned int path_len, const
 625                 unsigned char *sha1)
 626 {
 627         strbuf_addf(buf, "%o %.*s%c", mode, path_len, path, '\0');
 628         strbuf_add(buf, sha1, 20);
 629 }
 630
 631 static void tree_write_stack_init_subtree(struct tree_write_stack *tws,
 632                 const char *path)
 633 {
 634         struct tree_write_stack *n;
 635         assert(!tws->next);
 636         assert(tws->path[0] == '\0' && tws->path[1] == '\0');
 637         n = (struct tree_write_stack *)
 638                 xmalloc(sizeof(struct tree_write_stack));
 639         n->next = NULL;
 640         strbuf_init(&n->buf, 256 * (32 + 40)); /* assume 256 entries per tree */
 641         n->path[0] = n->path[1] = '\0';
 642         tws->next = n;
 643         tws->path[0] = path[0];
 644         tws->path[1] = path[1];
 645 }
 646
 647 static int tree_write_stack_finish_subtree(struct tree_write_stack *tws)
 648 {
 649         int ret;
 650         struct tree_write_stack *n = tws->next;
 651         unsigned char s[20];
 652         if (n) {
 653                 ret = tree_write_stack_finish_subtree(n);
 654                 if (ret)
 655                         return ret;
 656                 ret = write_sha1_file(n->buf.buf, n->buf.len, tree_type, s);
 657                 if (ret)
 658                         return ret;
 659                 strbuf_release(&n->buf);
 660                 free(n);
 661                 tws->next = NULL;
 662                 write_tree_entry(&tws->buf, 040000, tws->path, 2, s);
 663                 tws->path[0] = tws->path[1] = '\0';
 664         }
 665         return 0;
 666 }
 667
 668 static int write_each_note_helper(struct tree_write_stack *tws,
 669                 const char *path, unsigned int mode,
 670                 const unsigned char *sha1)
 671 {
 672         size_t path_len = strlen(path);
 673         unsigned int n = 0;
 674         int ret;
 675
 676         /* Determine common part of tree write stack */
 677         while (tws && 3 * n < path_len &&
 678                matches_tree_write_stack(tws, path + 3 * n)) {
 679                 n++;
 680                 tws = tws->next;
 681         }
 682
 683         /* tws point to last matching tree_write_stack entry */
 684         ret = tree_write_stack_finish_subtree(tws);
 685         if (ret)
 686                 return ret;
 687
 688         /* Start subtrees needed to satisfy path */
 689         while (3 * n + 2 < path_len && path[3 * n + 2] == '/') {
 690                 tree_write_stack_init_subtree(tws, path + 3 * n);
 691                 n++;
 692                 tws = tws->next;
 693         }
 694
 695         /* There should be no more directory components in the given path */
 696         assert(memchr(path + 3 * n, '/', path_len - (3 * n)) == NULL);
 697
 698         /* Finally add given entry to the current tree object */
 699         write_tree_entry(&tws->buf, mode, path + 3 * n, path_len - (3 * n),
 700                          sha1);
 701
 702         return 0;
 703 }
 704
 705 struct write_each_note_data {
 706         struct tree_write_stack *root;
 707         struct non_note *next_non_note;
 708 };
 709
 710 static int write_each_non_note_until(const char *note_path,
 711                 struct write_each_note_data *d)
 712 {
 713         struct non_note *n = d->next_non_note;
 714         int cmp, ret;
 715         while (n && (!note_path || (cmp = strcmp(n->path, note_path)) <= 0)) {
 716                 if (note_path && cmp == 0)
 717                         ; /* do nothing, prefer note to non-note */
 718                 else {
 719                         ret = write_each_note_helper(d->root, n->path, n->mode,
 720                                                      n->sha1);
 721                         if (ret)
 722                                 return ret;
 723                 }
 724                 n = n->next;
 725         }
 726         d->next_non_note = n;
 727         return 0;
 728 }
 729
 730 static int write_each_note(const unsigned char *object_sha1,
 731                 const unsigned char *note_sha1, char *note_path,
 732                 void *cb_data)
 733 {
 734         struct write_each_note_data *d =
 735                 (struct write_each_note_data *) cb_data;
 736         size_t note_path_len = strlen(note_path);
 737         unsigned int mode = 0100644;
 738
 739         if (note_path[note_path_len - 1] == '/') {
 740                 /* subtree entry */
 741                 note_path_len--;
 742                 note_path[note_path_len] = '\0';
 743                 mode = 040000;
 744         }
 745         assert(note_path_len <= 40 + 19);
 746
 747         /* Weave non-note entries into note entries */
 748         return  write_each_non_note_until(note_path, d) ||
 749                 write_each_note_helper(d->root, note_path, mode, note_sha1);
 750 }
 751
 752 struct note_delete_list {
 753         struct note_delete_list *next;
 754         const unsigned char *sha1;
 755 };
 756
 757 static int prune_notes_helper(const unsigned char *object_sha1,
 758                 const unsigned char *note_sha1, char *note_path,
 759                 void *cb_data)
 760 {
 761         struct note_delete_list **l = (struct note_delete_list **) cb_data;
 762         struct note_delete_list *n;
 763
 764         if (has_sha1_file(object_sha1))
 765                 return 0; /* nothing to do for this note */
 766
 767         /* failed to find object => prune this note */
 768         n = (struct note_delete_list *) xmalloc(sizeof(*n));
 769         n->next = *l;
 770         n->sha1 = object_sha1;
 771         *l = n;
 772         return 0;
 773 }
 774
 775 int combine_notes_concatenate(unsigned char *cur_sha1,
 776                 const unsigned char *new_sha1)
 777 {
 778         char *cur_msg = NULL, *new_msg = NULL, *buf;
 779         unsigned long cur_len, new_len, buf_len;
 780         enum object_type cur_type, new_type;
 781         int ret;
 782
 783         /* read in both note blob objects */
 784         if (!is_null_sha1(new_sha1))
 785                 new_msg = read_sha1_file(new_sha1, &new_type, &new_len);
 786         if (!new_msg || !new_len || new_type != OBJ_BLOB) {
 787                 free(new_msg);
 788                 return 0;
 789         }
 790         if (!is_null_sha1(cur_sha1))
 791                 cur_msg = read_sha1_file(cur_sha1, &cur_type, &cur_len);
 792         if (!cur_msg || !cur_len || cur_type != OBJ_BLOB) {
 793                 free(cur_msg);
 794                 free(new_msg);
 795                 hashcpy(cur_sha1, new_sha1);
 796                 return 0;
 797         }
 798
 799         /* we will separate the notes by a newline anyway */
 800         if (cur_msg[cur_len - 1] == '\n')
 801                 cur_len--;
 802
 803         /* concatenate cur_msg and new_msg into buf */
 804         buf_len = cur_len + 1 + new_len;
 805         buf = (char *) xmalloc(buf_len);
 806         memcpy(buf, cur_msg, cur_len);
 807         buf[cur_len] = '\n';
 808         memcpy(buf + cur_len + 1, new_msg, new_len);
 809         free(cur_msg);
 810         free(new_msg);
 811
 812         /* create a new blob object from buf */
 813         ret = write_sha1_file(buf, buf_len, blob_type, cur_sha1);
 814         free(buf);
 815         return ret;
 816 }
 817
 818 int combine_notes_overwrite(unsigned char *cur_sha1,
 819                 const unsigned char *new_sha1)
 820 {
 821         hashcpy(cur_sha1, new_sha1);
 822         return 0;
 823 }
 824
 825 int combine_notes_ignore(unsigned char *cur_sha1,
 826                 const unsigned char *new_sha1)
 827 {
 828         return 0;
 829 }
 830
 831 void init_notes(struct notes_tree *t, const char *notes_ref,
 832                 combine_notes_fn combine_notes, int flags)
 833 {
 834         unsigned char sha1[20], object_sha1[20];
 835         unsigned mode;
 836         struct leaf_node root_tree;
 837
 838         if (!t)
 839                 t = &default_notes_tree;
 840         assert(!t->initialized);
 841
 842         if (!notes_ref)
 843                 notes_ref = getenv(GIT_NOTES_REF_ENVIRONMENT);
 844         if (!notes_ref)
 845                 notes_ref = notes_ref_name; /* value of core.notesRef config */
 846         if (!notes_ref)
 847                 notes_ref = GIT_NOTES_DEFAULT_REF;
 848
 849         if (!combine_notes)
 850                 combine_notes = combine_notes_concatenate;
 851
 852         t->root = (struct int_node *) xcalloc(sizeof(struct int_node), 1);
 853         t->first_non_note = NULL;
 854         t->prev_non_note = NULL;
 855         t->ref = notes_ref ? xstrdup(notes_ref) : NULL;
 856         t->combine_notes = combine_notes;
 857         t->initialized = 1;
 858
 859         if (flags & NOTES_INIT_EMPTY || !notes_ref ||
 860             read_ref(notes_ref, object_sha1))
 861                 return;
 862         if (get_tree_entry(object_sha1, "", sha1, &mode))
 863                 die("Failed to read notes tree referenced by %s (%s)",
 864                     notes_ref, object_sha1);
 865
 866         hashclr(root_tree.key_sha1);
 867         hashcpy(root_tree.val_sha1, sha1);
 868         load_subtree(t, &root_tree, t->root, 0);
 869 }
 870
 871 void add_note(struct notes_tree *t, const unsigned char *object_sha1,
 872                 const unsigned char *note_sha1, combine_notes_fn combine_notes)
 873 {
 874         struct leaf_node *l;
 875
 876         if (!t)
 877                 t = &default_notes_tree;
 878         assert(t->initialized);
 879         if (!combine_notes)
 880                 combine_notes = t->combine_notes;
 881         l = (struct leaf_node *) xmalloc(sizeof(struct leaf_node));
 882         hashcpy(l->key_sha1, object_sha1);
 883         hashcpy(l->val_sha1, note_sha1);
 884         note_tree_insert(t, t->root, 0, l, PTR_TYPE_NOTE, combine_notes);
 885 }
 886
 887 void remove_note(struct notes_tree *t, const unsigned char *object_sha1)
 888 {
 889         struct leaf_node l;
 890
 891         if (!t)
 892                 t = &default_notes_tree;
 893         assert(t->initialized);
 894         hashcpy(l.key_sha1, object_sha1);
 895         hashclr(l.val_sha1);
 896         note_tree_remove(t, t->root, 0, &l);
 897 }
 898
 899 const unsigned char *get_note(struct notes_tree *t,
 900                 const unsigned char *object_sha1)
 901 {
 902         struct leaf_node *found;
 903
 904         if (!t)
 905                 t = &default_notes_tree;
 906         assert(t->initialized);
 907         found = note_tree_find(t, t->root, 0, object_sha1);
 908         return found ? found->val_sha1 : NULL;
 909 }
 910
 911 int for_each_note(struct notes_tree *t, int flags, each_note_fn fn,
 912                 void *cb_data)
 913 {
 914         if (!t)
 915                 t = &default_notes_tree;
 916         assert(t->initialized);
 917         return for_each_note_helper(t, t->root, 0, 0, flags, fn, cb_data);
 918 }
 919
 920 int write_notes_tree(struct notes_tree *t, unsigned char *result)
 921 {
 922         struct tree_write_stack root;
 923         struct write_each_note_data cb_data;
 924         int ret;
 925
 926         if (!t)
 927                 t = &default_notes_tree;
 928         assert(t->initialized);
 929
 930         /* Prepare for traversal of current notes tree */
 931         root.next = NULL; /* last forward entry in list is grounded */
 932         strbuf_init(&root.buf, 256 * (32 + 40)); /* assume 256 entries */
 933         root.path[0] = root.path[1] = '\0';
 934         cb_data.root = &root;
 935         cb_data.next_non_note = t->first_non_note;
 936
 937         /* Write tree objects representing current notes tree */
 938         ret = for_each_note(t, FOR_EACH_NOTE_DONT_UNPACK_SUBTREES |
 939                                 FOR_EACH_NOTE_YIELD_SUBTREES,
 940                         write_each_note, &cb_data) ||
 941                 write_each_non_note_until(NULL, &cb_data) ||
 942                 tree_write_stack_finish_subtree(&root) ||
 943                 write_sha1_file(root.buf.buf, root.buf.len, tree_type, result);
 944         strbuf_release(&root.buf);
 945         return ret;
 946 }
 947
 948 void prune_notes(struct notes_tree *t)
 949 {
 950         struct note_delete_list *l = NULL;
 951
 952         if (!t)
 953                 t = &default_notes_tree;
 954         assert(t->initialized);
 955
 956         for_each_note(t, 0, prune_notes_helper, &l);
 957
 958         while (l) {
 959                 remove_note(t, l->sha1);
 960                 l = l->next;
 961         }
 962 }
 963
 964 void free_notes(struct notes_tree *t)
 965 {
 966         if (!t)
 967                 t = &default_notes_tree;
 968         if (t->root)
 969                 note_tree_free(t->root);
 970         free(t->root);
 971         while (t->first_non_note) {
 972                 t->prev_non_note = t->first_non_note->next;
 973                 free(t->first_non_note->path);
 974                 free(t->first_non_note);
 975                 t->first_non_note = t->prev_non_note;
 976         }
 977         free(t->ref);
 978         memset(t, 0, sizeof(struct notes_tree));
 979 }
 980
 981 void format_note(struct notes_tree *t, const unsigned char *object_sha1,
 982                 struct strbuf *sb, const char *output_encoding, int flags)
 983 {
 984         static const char utf8[] = "utf-8";
 985         const unsigned char *sha1;
 986         char *msg, *msg_p;
 987         unsigned long linelen, msglen;
 988         enum object_type type;
 989
 990         if (!t)
 991                 t = &default_notes_tree;
 992         if (!t->initialized)
 993                 init_notes(t, NULL, NULL, 0);
 994
 995         sha1 = get_note(t, object_sha1);
 996         if (!sha1)
 997                 return;
 998
 999         if (!(msg = read_sha1_file(sha1, &type, &msglen)) || !msglen ||
1000                         type != OBJ_BLOB) {
1001                 free(msg);
1002                 return;
1003         }
1004
1005         if (output_encoding && *output_encoding &&
1006                         strcmp(utf8, output_encoding)) {
1007                 char *reencoded = reencode_string(msg, output_encoding, utf8);
1008                 if (reencoded) {
1009                         free(msg);
1010                         msg = reencoded;
1011                         msglen = strlen(msg);
1012                 }
1013         }
1014
1015         /* we will end the annotation by a newline anyway */
1016         if (msglen && msg[msglen - 1] == '\n')
1017                 msglen--;
1018
1019         if (flags & NOTES_SHOW_HEADER)
1020                 strbuf_addstr(sb, "\nNotes:\n");
1021
1022         for (msg_p = msg; msg_p < msg + msglen; msg_p += linelen + 1) {
1023                 linelen = strchrnul(msg_p, '\n') - msg_p;
1024
1025                 if (flags & NOTES_INDENT)
1026                         strbuf_addstr(sb, "    ");
1027                 strbuf_add(sb, msg_p, linelen);
1028                 strbuf_addch(sb, '\n');
1029         }
1030
1031         free(msg);
1032 }