git.ozlabs.org Git - ccan/blob - ccan/tal/tal.c

   1 /* Licensed under BSD-MIT - see LICENSE file for details */
   2 #include <ccan/tal/tal.h>
   3 #include <ccan/compiler/compiler.h>
   4 #include <ccan/list/list.h>
   5 #include <ccan/take/take.h>
   6 #include <assert.h>
   7 #include <stdio.h>
   8 #include <stdarg.h>
   9 #include <stddef.h>
  10 #include <string.h>
  11 #include <limits.h>
  12 #include <errno.h>
  13
  14 //#define TAL_DEBUG 1
  15
  16 /* 32-bit type field, first byte 0 in either endianness. */
  17 enum prop_type {
  18         CHILDREN = 0x00c1d500,
  19         DESTRUCTOR = 0x00de5700,
  20         NAME = 0x00111100,
  21         NOTIFIER = 0x00071f00
  22 };
  23
  24 struct tal_hdr {
  25         struct list_node list;
  26         struct prop_hdr *prop;
  27         struct children *parent_child;
  28 };
  29
  30 struct prop_hdr {
  31         enum prop_type type;
  32         struct prop_hdr *next;
  33 };
  34
  35 struct children {
  36         struct prop_hdr hdr; /* CHILDREN */
  37         struct tal_hdr *parent;
  38         struct list_head children; /* Head of siblings. */
  39 };
  40
  41 struct destructor {
  42         struct prop_hdr hdr; /* DESTRUCTOR */
  43         void (*destroy)(void *me);
  44 };
  45
  46 struct name {
  47         struct prop_hdr hdr; /* NAME */
  48         char name[];
  49 };
  50
  51 struct notifier {
  52         struct prop_hdr hdr; /* NOTIFIER */
  53         enum tal_notify_type types;
  54         void (*notifyfn)(tal_t *, enum tal_notify_type, void *);
  55 };
  56
  57 static struct {
  58         struct tal_hdr hdr;
  59         struct children c;
  60 } null_parent = { { { &null_parent.hdr.list, &null_parent.hdr.list },
  61                     &null_parent.c.hdr, NULL },
  62                   { { CHILDREN, NULL },
  63                     &null_parent.hdr,
  64                     { { &null_parent.c.children.n,
  65                         &null_parent.c.children.n } }
  66                   }
  67 };
  68
  69
  70 static void *(*allocfn)(size_t size) = malloc;
  71 static void *(*resizefn)(void *, size_t size) = realloc;
  72 static void (*freefn)(void *) = free;
  73 static void (*errorfn)(const char *msg) = (void *)abort;
  74
  75 static inline void COLD call_error(const char *msg)
  76 {
  77         errorfn(msg);
  78 }
  79
  80 static bool get_destroying_bit(struct children *parent_child)
  81 {
  82         return (size_t)parent_child & 1;
  83 }
  84
  85 static void set_destroying_bit(struct children **parent_child)
  86 {
  87         *parent_child = (void *)((size_t)*parent_child | 1);
  88 }
  89
  90 static struct children *ignore_destroying_bit(struct children *parent_child)
  91 {
  92         return (void *)((size_t)parent_child & ~(size_t)1);
  93 }
  94
  95 static bool initialized = false;
  96
  97 /* This means valgrind can see leaks. */
  98 static void tal_cleanup(void)
  99 {
 100         struct tal_hdr *i;
 101
 102         while ((i = list_top(&null_parent.c.children, struct tal_hdr, list)))
 103                 list_del(&i->list);
 104
 105         /* Cleanup any taken pointers. */
 106         take_cleanup();
 107 }
 108
 109 /* For allocation failures inside ccan/take */
 110 static void take_alloc_failed(const void *p)
 111 {
 112         tal_free(p);
 113 }
 114
 115 /* We carefully start all real properties with a zero byte. */
 116 static bool is_literal(const struct prop_hdr *prop)
 117 {
 118         return ((char *)prop)[0] != 0;
 119 }
 120
 121 #ifndef NDEBUG
 122 static const void *bounds_start, *bounds_end;
 123
 124 static void update_bounds(const void *new, size_t size)
 125 {
 126         if (unlikely(!bounds_start)) {
 127                 bounds_start = new;
 128                 bounds_end = (char *)new + size;
 129         } else if (new < bounds_start)
 130                 bounds_start = new;
 131         else if ((char *)new + size > (char *)bounds_end)
 132                 bounds_end = (char *)new + size;
 133 }
 134
 135 static bool in_bounds(const void *p)
 136 {
 137         return !p
 138                 || (p >= (void *)&null_parent && p <= (void *)(&null_parent + 1))
 139                 || (p >= bounds_start && p <= bounds_end);
 140 }
 141 #else
 142 static void update_bounds(const void *new, size_t size)
 143 {
 144 }
 145
 146 static bool in_bounds(const void *p)
 147 {
 148         return true;
 149 }
 150 #endif
 151
 152 static void check_bounds(const void *p)
 153 {
 154         if (!in_bounds(p))
 155                 call_error("Not a valid header");
 156 }
 157
 158 static struct tal_hdr *to_tal_hdr(const void *ctx)
 159 {
 160         struct tal_hdr *t;
 161
 162         t = (struct tal_hdr *)((char *)ctx - sizeof(struct tal_hdr));
 163         check_bounds(t);
 164         check_bounds(ignore_destroying_bit(t->parent_child));
 165         check_bounds(t->list.next);
 166         check_bounds(t->list.prev);
 167         if (t->prop && !is_literal(t->prop))
 168                 check_bounds(t->prop);
 169         return t;
 170 }
 171
 172 static struct tal_hdr *to_tal_hdr_or_null(const void *ctx)
 173 {
 174         if (!ctx)
 175                 return &null_parent.hdr;
 176         return to_tal_hdr(ctx);
 177 }
 178
 179 static void *from_tal_hdr(const struct tal_hdr *hdr)
 180 {
 181         return (void *)(hdr + 1);
 182 }
 183
 184 #ifdef TAL_DEBUG
 185 static void *from_tal_hdr_or_null(struct tal_hdr *hdr)
 186 {
 187         if (hdr == &null_parent.hdr)
 188                 return NULL;
 189         return from_tal_hdr(hdr);
 190 }
 191
 192 static struct tal_hdr *debug_tal(struct tal_hdr *tal)
 193 {
 194         tal_check(from_tal_hdr_or_null(tal), "TAL_DEBUG ");
 195         return tal;
 196 }
 197 #else
 198 static struct tal_hdr *debug_tal(struct tal_hdr *tal)
 199 {
 200         return tal;
 201 }
 202 #endif
 203
 204 static void notify(const struct tal_hdr *ctx,
 205                    enum tal_notify_type type, const void *info)
 206 {
 207         const struct prop_hdr *p;
 208
 209         for (p = ctx->prop; p; p = p->next) {
 210                 struct notifier *n;
 211
 212                 if (is_literal(p))
 213                         break;
 214                 if (p->type != NOTIFIER)
 215                         continue;
 216                 n = (struct notifier *)p;
 217                 if (n->types & type)
 218                         n->notifyfn(from_tal_hdr(ctx), type, (void *)info);
 219         }
 220 }
 221
 222 static void *allocate(size_t size)
 223 {
 224         void *ret;
 225
 226         /* Don't hand silly sizes to malloc. */
 227         if (size >> (CHAR_BIT*sizeof(size) - 1)) {
 228                 call_error("allocation size overflow");
 229                 return NULL;
 230         }
 231
 232         ret = allocfn(size);
 233         if (!ret)
 234                 call_error("allocation failed");
 235         else
 236                 update_bounds(ret, size);
 237         return ret;
 238 }
 239
 240 static struct prop_hdr **find_property_ptr(const struct tal_hdr *t,
 241                                            enum prop_type type)
 242 {
 243         struct prop_hdr **p;
 244
 245         for (p = (struct prop_hdr **)&t->prop; *p; p = &(*p)->next) {
 246                 if (is_literal(*p)) {
 247                         if (type == NAME)
 248                                 return p;
 249                         break;
 250                 }
 251                 if ((*p)->type == type)
 252                         return p;
 253         }
 254         return NULL;
 255 }
 256
 257 static void *find_property(const struct tal_hdr *parent, enum prop_type type)
 258 {
 259         struct prop_hdr **p = find_property_ptr(parent, type);
 260
 261         if (p)
 262                 return *p;
 263         return NULL;
 264 }
 265
 266 static void init_property(struct prop_hdr *hdr,
 267                           struct tal_hdr *parent,
 268                           enum prop_type type)
 269 {
 270         hdr->type = type;
 271         hdr->next = parent->prop;
 272         parent->prop = hdr;
 273 }
 274
 275 static struct destructor *add_destructor_property(struct tal_hdr *t,
 276                                                   void (*destroy)(void *))
 277 {
 278         struct destructor *prop = allocate(sizeof(*prop));
 279         if (prop) {
 280                 init_property(&prop->hdr, t, DESTRUCTOR);
 281                 prop->destroy = destroy;
 282         }
 283         return prop;
 284 }
 285
 286 static bool del_destructor_property(struct tal_hdr *t,
 287                                     void (*destroy)(void *))
 288 {
 289         struct prop_hdr **p;
 290
 291         for (p = (struct prop_hdr **)&t->prop; *p; p = &(*p)->next) {
 292                 struct destructor *d;
 293
 294                 if (is_literal(*p))
 295                         break;
 296                 if ((*p)->type != DESTRUCTOR)
 297                         continue;
 298                 d = (struct destructor *)*p;
 299                 if (d->destroy == destroy) {
 300                         *p = (*p)->next;
 301                         freefn(d);
 302                         return true;
 303                 }
 304         }
 305         return false;
 306 }
 307
 308 static struct notifier *add_notifier_property(struct tal_hdr *t,
 309                                               enum tal_notify_type types,
 310                                               void (*fn)(void *,
 311                                                          enum tal_notify_type,
 312                                                          void *))
 313 {
 314         struct notifier *prop = allocate(sizeof(*prop));
 315         if (prop) {
 316                 init_property(&prop->hdr, t, NOTIFIER);
 317                 prop->types = types;
 318                 prop->notifyfn = fn;
 319         }
 320         return prop;
 321 }
 322
 323 static bool del_notifier_property(struct tal_hdr *t,
 324                                   void (*fn)(tal_t *,
 325                                              enum tal_notify_type, void *))
 326 {
 327         struct prop_hdr **p;
 328
 329         for (p = (struct prop_hdr **)&t->prop; *p; p = &(*p)->next) {
 330                 struct notifier *n;
 331
 332                 if (is_literal(*p))
 333                         break;
 334                 if ((*p)->type != NOTIFIER)
 335                         continue;
 336                 n = (struct notifier *)*p;
 337                 if (n->notifyfn == fn) {
 338                         *p = (*p)->next;
 339                         freefn(n);
 340                         return true;
 341                 }
 342         }
 343         return false;
 344 }
 345
 346 static struct name *add_name_property(struct tal_hdr *t, const char *name)
 347 {
 348         struct name *prop;
 349
 350         prop = allocate(sizeof(*prop) + strlen(name) + 1);
 351         if (prop) {
 352                 init_property(&prop->hdr, t, NAME);
 353                 strcpy(prop->name, name);
 354         }
 355         return prop;
 356 }
 357
 358 static struct children *add_child_property(struct tal_hdr *parent,
 359                                            struct tal_hdr *child)
 360 {
 361         struct children *prop = allocate(sizeof(*prop));
 362         if (prop) {
 363                 init_property(&prop->hdr, parent, CHILDREN);
 364                 prop->parent = parent;
 365                 list_head_init(&prop->children);
 366         }
 367         return prop;
 368 }
 369
 370 static bool add_child(struct tal_hdr *parent, struct tal_hdr *child)
 371 {
 372         struct children *children = find_property(parent, CHILDREN);
 373
 374         if (!children) {
 375                 if (unlikely(!initialized)) {
 376                         atexit(tal_cleanup);
 377                         take_allocfail(take_alloc_failed);
 378                         initialized = true;
 379                 }
 380                 children = add_child_property(parent, child);
 381                 if (!children)
 382                         return false;
 383         }
 384         list_add(&children->children, &child->list);
 385         child->parent_child = children;
 386         return true;
 387 }
 388
 389 static void del_tree(struct tal_hdr *t, const tal_t *orig)
 390 {
 391         struct prop_hdr **prop, *p, *next;
 392
 393         /* Already being destroyed?  Don't loop. */
 394         if (unlikely(get_destroying_bit(t->parent_child)))
 395                 return;
 396
 397         set_destroying_bit(&t->parent_child);
 398
 399         /* Carefully call destructors, removing as we go. */
 400         while ((prop = find_property_ptr(t, DESTRUCTOR))) {
 401                 struct destructor *d = (struct destructor *)*prop;
 402                 d->destroy(from_tal_hdr(t));
 403                 *prop = d->hdr.next;
 404                 freefn(d);
 405         }
 406
 407         /* Call free notifiers. */
 408         notify(t, TAL_NOTIFY_FREE, (tal_t *)orig);
 409
 410         /* Now free children and groups. */
 411         prop = find_property_ptr(t, CHILDREN);
 412         if (prop) {
 413                 struct tal_hdr *i;
 414                 struct children *c = (struct children *)*prop;
 415
 416                 while ((i = list_top(&c->children, struct tal_hdr, list))) {
 417                         list_del(&i->list);
 418                         del_tree(i, orig);
 419                 }
 420         }
 421
 422         /* Finally free our properties. */
 423         for (p = t->prop; p && !is_literal(p); p = next) {
 424                 next = p->next;
 425                 freefn(p);
 426         }
 427         freefn(t);
 428 }
 429
 430 void *tal_alloc_(const tal_t *ctx, size_t size, bool clear, const char *label)
 431 {
 432         struct tal_hdr *child, *parent = debug_tal(to_tal_hdr_or_null(ctx));
 433
 434         child = allocate(sizeof(struct tal_hdr) + size);
 435         if (!child)
 436                 return NULL;
 437         if (clear)
 438                 memset(from_tal_hdr(child), 0, size);
 439         child->prop = (void *)label;
 440         if (!add_child(parent, child)) {
 441                 freefn(child);
 442                 return NULL;
 443         }
 444         debug_tal(parent);
 445         notify(parent, TAL_NOTIFY_ADD_CHILD, from_tal_hdr(debug_tal(child)));
 446         return from_tal_hdr(debug_tal(child));
 447 }
 448
 449 void *tal_free(const tal_t *ctx)
 450 {
 451         if (ctx) {
 452                 struct tal_hdr *t;
 453                 int saved_errno = errno;
 454                 t = debug_tal(to_tal_hdr(ctx));
 455                 notify(ignore_destroying_bit(t->parent_child)->parent,
 456                        TAL_NOTIFY_DEL_CHILD, ctx);
 457                 list_del(&t->list);
 458                 del_tree(t, ctx);
 459                 errno = saved_errno;
 460         }
 461         return NULL;
 462 }
 463
 464 void *tal_steal_(const tal_t *new_parent, const tal_t *ctx)
 465 {
 466         if (ctx) {
 467                 struct tal_hdr *newpar, *t, *old_parent;
 468
 469                 newpar = debug_tal(to_tal_hdr_or_null(new_parent));
 470                 t = debug_tal(to_tal_hdr(ctx));
 471
 472                 /* Unlink it from old parent. */
 473                 list_del(&t->list);
 474                 old_parent = ignore_destroying_bit(t->parent_child)->parent;
 475
 476                 if (unlikely(!add_child(newpar, t))) {
 477                         /* We can always add to old parent, becuase it has a
 478                          * children property already. */
 479                         if (!add_child(old_parent, t))
 480                                 abort();
 481                         return NULL;
 482                 }
 483                 debug_tal(newpar);
 484                 notify(t, TAL_NOTIFY_STEAL, new_parent);
 485         }
 486         return (void *)ctx;
 487 }
 488
 489 bool tal_add_destructor_(tal_t *ctx, void (*destroy)(void *me))
 490 {
 491         tal_t *t = debug_tal(to_tal_hdr(ctx));
 492         return add_destructor_property(t, destroy);
 493 }
 494
 495 bool tal_add_notifier_(tal_t *ctx, enum tal_notify_type types,
 496                        void (*callback)(tal_t *, enum tal_notify_type, void *))
 497 {
 498         tal_t *t = debug_tal(to_tal_hdr(ctx));
 499         struct notifier *n;
 500
 501         assert(types);
 502         assert((types & ~(TAL_NOTIFY_FREE | TAL_NOTIFY_STEAL | TAL_NOTIFY_MOVE
 503                           | TAL_NOTIFY_RESIZE | TAL_NOTIFY_RENAME
 504                           | TAL_NOTIFY_ADD_CHILD | TAL_NOTIFY_DEL_CHILD
 505                           | TAL_NOTIFY_ADD_NOTIFIER
 506                           | TAL_NOTIFY_DEL_NOTIFIER)) == 0);
 507
 508         /* Don't call notifier about itself: set types after! */
 509         n = add_notifier_property(t, 0, callback);
 510         if (unlikely(!n))
 511                 return false;
 512
 513         notify(t, TAL_NOTIFY_ADD_NOTIFIER, callback);
 514         n->types = types;
 515         return true;
 516 }
 517
 518 bool tal_del_notifier_(tal_t *ctx,
 519                        void (*callback)(tal_t *, enum tal_notify_type, void *))
 520 {
 521         struct tal_hdr *t = debug_tal(to_tal_hdr(ctx));
 522         bool ret;
 523
 524         ret = del_notifier_property(t, callback);
 525         if (ret)
 526                 notify(t, TAL_NOTIFY_DEL_NOTIFIER, callback);
 527         return ret;
 528 }
 529
 530 bool tal_del_destructor_(tal_t *ctx, void (*destroy)(void *me))
 531 {
 532         struct tal_hdr *t = debug_tal(to_tal_hdr(ctx));
 533         return del_destructor_property(t, destroy);
 534 }
 535
 536 bool tal_set_name_(tal_t *ctx, const char *name, bool literal)
 537 {
 538         struct tal_hdr *t = debug_tal(to_tal_hdr(ctx));
 539         struct prop_hdr **prop = find_property_ptr(t, NAME);
 540
 541         /* Get rid of any old name */
 542         if (prop) {
 543                 struct name *name = (struct name *)*prop;
 544                 if (is_literal(&name->hdr))
 545                         *prop = NULL;
 546                 else {
 547                         *prop = name->hdr.next;
 548                         freefn(name);
 549                 }
 550         }
 551
 552         if (literal && name[0]) {
 553                 struct prop_hdr **p;
 554
 555                 /* Append literal. */
 556                 for (p = &t->prop; *p && !is_literal(*p); p = &(*p)->next);
 557                 *p = (struct prop_hdr *)name;
 558         } else if (!add_name_property(t, name))
 559                 return false;
 560
 561         debug_tal(t);
 562         notify(t, TAL_NOTIFY_RENAME, name);
 563         return true;
 564 }
 565
 566 const char *tal_name(const tal_t *t)
 567 {
 568         struct name *n;
 569
 570         n = find_property(debug_tal(to_tal_hdr(t)), NAME);
 571         if (!n)
 572                 return NULL;
 573
 574         if (is_literal(&n->hdr))
 575                 return (const char *)n;
 576         return n->name;
 577 }
 578
 579 /* Start one past first child: make stopping natural in circ. list. */
 580 static struct tal_hdr *first_child(struct tal_hdr *parent)
 581 {
 582         struct children *child;
 583
 584         child = find_property(parent, CHILDREN);
 585         if (!child)
 586                 return NULL;
 587
 588         return list_top(&child->children, struct tal_hdr, list);
 589 }
 590
 591 tal_t *tal_first(const tal_t *root)
 592 {
 593         struct tal_hdr *c, *t = debug_tal(to_tal_hdr_or_null(root));
 594
 595         c = first_child(t);
 596         if (!c)
 597                 return NULL;
 598         return from_tal_hdr(c);
 599 }
 600
 601 tal_t *tal_next(const tal_t *root, const tal_t *prev)
 602 {
 603         struct tal_hdr *c, *t = debug_tal(to_tal_hdr(prev)), *top;
 604
 605         /* Children? */
 606         c = first_child(t);
 607         if (c)
 608                 return from_tal_hdr(c);
 609
 610         top = to_tal_hdr_or_null(root);
 611         do {
 612                 struct tal_hdr *next;
 613                 struct list_node *end;
 614
 615                 end = &ignore_destroying_bit(t->parent_child)->children.n;
 616
 617                 next = list_entry(t->list.next, struct tal_hdr, list);
 618                 if (&next->list != end)
 619                         return from_tal_hdr(next);
 620
 621                 /* OK, go back to parent. */
 622                 t = ignore_destroying_bit(t->parent_child)->parent;
 623         } while (t != top);
 624
 625         return NULL;
 626 }
 627
 628 tal_t *tal_parent(const tal_t *ctx)
 629 {
 630         struct tal_hdr *t;
 631
 632         if (!ctx)
 633                 return NULL;
 634
 635         t = debug_tal(to_tal_hdr(ctx));
 636         if (ignore_destroying_bit(t->parent_child)->parent == &null_parent.hdr)
 637                 return NULL;
 638         return from_tal_hdr(ignore_destroying_bit(t->parent_child)->parent);
 639 }
 640
 641 bool tal_resize_(tal_t **ctxp, size_t size)
 642 {
 643         struct tal_hdr *old_t, *t;
 644         struct children *child;
 645
 646         old_t = debug_tal(to_tal_hdr(*ctxp));
 647
 648         /* Don't hand silly sizes to realloc. */
 649         if (size >> (CHAR_BIT*sizeof(size) - 1)) {
 650                 call_error("Reallocation size overflow");
 651                 return false;
 652         }
 653
 654         t = resizefn(old_t, size + sizeof(struct tal_hdr));
 655         if (!t) {
 656                 call_error("Reallocation failure");
 657                 return false;
 658         }
 659
 660         /* If it didn't move, we're done! */
 661         if (t != old_t) {
 662                 update_bounds(t, size + sizeof(struct tal_hdr));
 663
 664                 /* Fix up linked list pointers. */
 665                 if (list_entry(t->list.next, struct tal_hdr, list) != old_t)
 666                         t->list.next->prev = t->list.prev->next = &t->list;
 667
 668                 /* Fix up child property's parent pointer. */
 669                 child = find_property(t, CHILDREN);
 670                 if (child) {
 671                         assert(child->parent == old_t);
 672                         child->parent = t;
 673                 }
 674                 *ctxp = from_tal_hdr(debug_tal(t));
 675                 notify(t, TAL_NOTIFY_MOVE, from_tal_hdr(old_t));
 676         }
 677         notify(t, TAL_NOTIFY_RESIZE, (void *)size);
 678
 679         return true;
 680 }
 681
 682 char *tal_strdup(const tal_t *ctx, const char *p)
 683 {
 684         /* We have to let through NULL for take(). */
 685         return tal_dup(ctx, char, p, p ? strlen(p) + 1: 1, 0);
 686 }
 687
 688 char *tal_strndup(const tal_t *ctx, const char *p, size_t n)
 689 {
 690         size_t len;
 691         char *ret;
 692
 693         /* We have to let through NULL for take(). */
 694         if (likely(p)) {
 695                 len = strlen(p);
 696                 if (len > n)
 697                         len = n;
 698         } else
 699                 len = n;
 700
 701         ret = tal_dup(ctx, char, p, len, 1);
 702         if (ret)
 703                 ret[len] = '\0';
 704         return ret;
 705 }
 706
 707 void *tal_dup_(const tal_t *ctx, const void *p, size_t n, size_t extra,
 708                const char *label)
 709 {
 710         void *ret;
 711
 712         /* Beware overflow! */
 713         if (n + extra < n || n + extra + sizeof(struct tal_hdr) < n) {
 714                 call_error("dup size overflow");
 715                 if (taken(p))
 716                         tal_free(p);
 717                 return NULL;
 718         }
 719
 720         if (taken(p)) {
 721                 if (unlikely(!p))
 722                         return NULL;
 723                 if (unlikely(!tal_resize_((void **)&p, n + extra)))
 724                         return tal_free(p);
 725                 if (unlikely(!tal_steal(ctx, p)))
 726                         return tal_free(p);
 727                 return (void *)p;
 728         }
 729         ret = tal_alloc_(ctx, n + extra, false, label);
 730         if (ret)
 731                 memcpy(ret, p, n);
 732         return ret;
 733 }
 734
 735 char *tal_asprintf(const tal_t *ctx, const char *fmt, ...)
 736 {
 737         va_list ap;
 738         char *ret;
 739
 740         va_start(ap, fmt);
 741         ret = tal_vasprintf(ctx, fmt, ap);
 742         va_end(ap);
 743
 744         return ret;
 745 }
 746
 747 char *tal_vasprintf(const tal_t *ctx, const char *fmt, va_list ap)
 748 {
 749         size_t max;
 750         char *buf;
 751         int ret;
 752
 753         if (!fmt && taken(fmt))
 754                 return NULL;
 755
 756         /* A decent guess to start. */
 757         max = strlen(fmt) * 2;
 758         buf = tal_arr(ctx, char, max);
 759         while (buf) {
 760                 va_list ap2;
 761
 762                 va_copy(ap2, ap);
 763                 ret = vsnprintf(buf, max, fmt, ap2);
 764                 va_end(ap2);
 765
 766                 if (ret < max)
 767                         break;
 768                 if (!tal_resize(&buf, max *= 2))
 769                         buf = tal_free(buf);
 770         }
 771         if (taken(fmt))
 772                 tal_free(fmt);
 773         return buf;
 774 }
 775
 776 void tal_set_backend(void *(*alloc_fn)(size_t size),
 777                      void *(*resize_fn)(void *, size_t size),
 778                      void (*free_fn)(void *),
 779                      void (*error_fn)(const char *msg))
 780 {
 781         if (alloc_fn)
 782                 allocfn = alloc_fn;
 783         if (resize_fn)
 784                 resizefn = resize_fn;
 785         if (free_fn)
 786                 freefn = free_fn;
 787         if (error_fn)
 788                 errorfn = error_fn;
 789 }
 790
 791 #ifdef CCAN_TAL_DEBUG
 792 static void dump_node(unsigned int indent, const struct tal_hdr *t)
 793 {
 794         unsigned int i;
 795         const struct prop_hdr *p;
 796
 797         for (i = 0; i < indent; i++)
 798                 printf("  ");
 799         printf("%p", t);
 800         for (p = t->prop; p; p = p->next) {
 801                 struct children *c;
 802                 struct destructor *d;
 803                 struct name *n;
 804                 struct notifier *no;
 805                 if (is_literal(p)) {
 806                         printf(" \"%s\"", (const char *)p);
 807                         break;
 808                 }
 809                 switch (p->type) {
 810                 case CHILDREN:
 811                         c = (struct children *)p;
 812                         printf(" CHILDREN(%p):parent=%p,children={%p,%p}\n",
 813                                p, c->parent,
 814                                c->children.n.prev, c->children.n.next);
 815                         break;
 816                 case DESTRUCTOR:
 817                         d = (struct destructor *)p;
 818                         printf(" DESTRUCTOR(%p):fn=%p", p, d->destroy);
 819                         break;
 820                 case NAME:
 821                         n = (struct name *)p;
 822                         printf(" NAME(%p):%s", p, n->name);
 823                         break;
 824                 case NOTIFIER:
 825                         no = (struct notifier *)p;
 826                         printf(" NOTIFIER(%p):fn=%p", p, no->notifyfn);
 827                         break;
 828                 default:
 829                         printf(" **UNKNOWN(%p):%i**", p, p->type);
 830                 }
 831         }
 832         printf("\n");
 833 }
 834
 835 static void tal_dump_(unsigned int level, const struct tal_hdr *t)
 836 {
 837         struct children *children;
 838
 839         dump_node(level, t);
 840
 841         children = find_property(t, CHILDREN);
 842         if (children) {
 843                 struct tal_hdr *i;
 844
 845                 list_for_each(&children->children, i, list)
 846                         tal_dump_(level + 1, i);
 847         }
 848 }
 849
 850 void tal_dump(void)
 851 {
 852         tal_dump_(0, &null_parent.hdr);
 853 }
 854 #endif /* CCAN_TAL_DEBUG */
 855
 856 #ifndef NDEBUG
 857 static bool check_err(struct tal_hdr *t, const char *errorstr,
 858                       const char *errmsg)
 859 {
 860         if (errorstr) {
 861                 /* Try not to malloc: it may be corrupted. */
 862                 char msg[strlen(errorstr) + 20 + strlen(errmsg) + 1];
 863                 sprintf(msg, "%s:%p %s", errorstr, from_tal_hdr(t), errmsg);
 864                 call_error(msg);
 865         }
 866         return false;
 867 }
 868
 869 static bool check_node(struct children *parent_child,
 870                        struct tal_hdr *t, const char *errorstr)
 871 {
 872         struct prop_hdr *p;
 873         struct name *name = NULL;
 874         struct children *children = NULL;
 875
 876         if (!in_bounds(t))
 877                 return check_err(t, errorstr, "invalid pointer");
 878
 879         if (ignore_destroying_bit(t->parent_child) != parent_child)
 880                 return check_err(t, errorstr, "incorrect parent");
 881
 882         for (p = t->prop; p; p = p->next) {
 883                 if (is_literal(p)) {
 884                         if (name)
 885                                 return check_err(t, errorstr,
 886                                                  "has extra literal");
 887                         name = (struct name *)p;
 888                         break;
 889                 }
 890                 if (!in_bounds(p))
 891                         return check_err(t, errorstr,
 892                                          "has bad property pointer");
 893
 894                 switch (p->type) {
 895                 case CHILDREN:
 896                         if (children)
 897                                 return check_err(t, errorstr,
 898                                                  "has two child nodes");
 899                         children = (struct children *)p;
 900                         break;
 901                 case DESTRUCTOR:
 902                 case NOTIFIER:
 903                         break;
 904                 case NAME:
 905                         if (name)
 906                                 return check_err(t, errorstr,
 907                                                  "has two names");
 908                         name = (struct name *)p;
 909                         break;
 910                 default:
 911                         return check_err(t, errorstr, "has unknown property");
 912                 }
 913         }
 914         if (children) {
 915                 struct tal_hdr *i;
 916
 917                 if (!list_check(&children->children, errorstr))
 918                         return false;
 919                 list_for_each(&children->children, i, list) {
 920                         if (!check_node(children, i, errorstr))
 921                                 return false;
 922                 }
 923         }
 924         return true;
 925 }
 926
 927 bool tal_check(const tal_t *ctx, const char *errorstr)
 928 {
 929         struct tal_hdr *t = to_tal_hdr_or_null(ctx);
 930
 931         return check_node(ignore_destroying_bit(t->parent_child), t, errorstr);
 932 }
 933 #else /* NDEBUG */
 934 bool tal_check(const tal_t *ctx, const char *errorstr)
 935 {
 936         return true;
 937 }
 938 #endif