src/util/ralloc.c

   1 /*
   2  * Copyright © 2010 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  21  * DEALINGS IN THE SOFTWARE.
  22  */
  23
  24 #include <assert.h>
  25 #include <stdlib.h>
  26 #include <stdarg.h>
  27 #include <stdio.h>
  28 #include <string.h>
  29 #include <stdint.h>
  30
  31 /* Some versions of MinGW are missing _vscprintf's declaration, although they
  32  * still provide the symbol in the import library. */
  33 #ifdef __MINGW32__
  34 _CRTIMP int _vscprintf(const char *format, va_list argptr);
  35 #endif
  36
  37 #include "ralloc.h"
  38
  39 #ifndef va_copy
  40 #ifdef __va_copy
  41 #define va_copy(dest, src) __va_copy((dest), (src))
  42 #else
  43 #define va_copy(dest, src) (dest) = (src)
  44 #endif
  45 #endif
  46
  47 #define CANARY 0x5A1106
  48
  49 /* Align the header's size so that ralloc() allocations will return with the
  50  * same alignment as a libc malloc would have (8 on 32-bit GLIBC, 16 on
  51  * 64-bit), avoiding performance penalities on x86 and alignment faults on
  52  * ARM.
  53  */
  54 struct
  55 #ifdef _MSC_VER
  56  __declspec(align(8))
  57 #elif defined(__LP64__)
  58  __attribute__((aligned(16)))
  59 #else
  60  __attribute__((aligned(8)))
  61 #endif
  62    ralloc_header
  63 {
  64 #ifndef NDEBUG
  65    /* A canary value used to determine whether a pointer is ralloc'd. */
  66    unsigned canary;
  67 #endif
  68
  69    struct ralloc_header *parent;
  70
  71    /* The first child (head of a linked list) */
  72    struct ralloc_header *child;
  73
  74    /* Linked list of siblings */
  75    struct ralloc_header *prev;
  76    struct ralloc_header *next;
  77
  78    void (*destructor)(void *);
  79 };
  80
  81 typedef struct ralloc_header ralloc_header;
  82
  83 static void unlink_block(ralloc_header *info);
  84 static void unsafe_free(ralloc_header *info);
  85
  86 static ralloc_header *
  87 get_header(const void *ptr)
  88 {
  89    ralloc_header *info = (ralloc_header *) (((char *) ptr) -
  90                                             sizeof(ralloc_header));
  91    assert(info->canary == CANARY);
  92    return info;
  93 }
  94
  95 #define PTR_FROM_HEADER(info) (((char *) info) + sizeof(ralloc_header))
  96
  97 static void
  98 add_child(ralloc_header *parent, ralloc_header *info)
  99 {
 100    if (parent != NULL) {
 101       info->parent = parent;
 102       info->next = parent->child;
 103       parent->child = info;
 104
 105       if (info->next != NULL)
 106          info->next->prev = info;
 107    }
 108 }
 109
 110 void *
 111 ralloc_context(const void *ctx)
 112 {
 113    return ralloc_size(ctx, 0);
 114 }
 115
 116 void *
 117 ralloc_size(const void *ctx, size_t size)
 118 {
 119    void *block = malloc(size + sizeof(ralloc_header));
 120    ralloc_header *info;
 121    ralloc_header *parent;
 122
 123    if (unlikely(block == NULL))
 124       return NULL;
 125
 126    info = (ralloc_header *) block;
 127    /* measurements have shown that calloc is slower (because of
 128     * the multiplication overflow checking?), so clear things
 129     * manually
 130     */
 131    info->parent = NULL;
 132    info->child = NULL;
 133    info->prev = NULL;
 134    info->next = NULL;
 135    info->destructor = NULL;
 136
 137    parent = ctx != NULL ? get_header(ctx) : NULL;
 138
 139    add_child(parent, info);
 140
 141 #ifndef NDEBUG
 142    info->canary = CANARY;
 143 #endif
 144
 145    return PTR_FROM_HEADER(info);
 146 }
 147
 148 void *
 149 rzalloc_size(const void *ctx, size_t size)
 150 {
 151    void *ptr = ralloc_size(ctx, size);
 152
 153    if (likely(ptr))
 154       memset(ptr, 0, size);
 155
 156    return ptr;
 157 }
 158
 159 /* helper function - assumes ptr != NULL */
 160 static void *
 161 resize(void *ptr, size_t size)
 162 {
 163    ralloc_header *child, *old, *info;
 164
 165    old = get_header(ptr);
 166    info = realloc(old, size + sizeof(ralloc_header));
 167
 168    if (info == NULL)
 169       return NULL;
 170
 171    /* Update parent and sibling's links to the reallocated node. */
 172    if (info != old && info->parent != NULL) {
 173       if (info->parent->child == old)
 174          info->parent->child = info;
 175
 176       if (info->prev != NULL)
 177          info->prev->next = info;
 178
 179       if (info->next != NULL)
 180          info->next->prev = info;
 181    }
 182
 183    /* Update child->parent links for all children */
 184    for (child = info->child; child != NULL; child = child->next)
 185       child->parent = info;
 186
 187    return PTR_FROM_HEADER(info);
 188 }
 189
 190 void *
 191 reralloc_size(const void *ctx, void *ptr, size_t size)
 192 {
 193    if (unlikely(ptr == NULL))
 194       return ralloc_size(ctx, size);
 195
 196    assert(ralloc_parent(ptr) == ctx);
 197    return resize(ptr, size);
 198 }
 199
 200 void *
 201 ralloc_array_size(const void *ctx, size_t size, unsigned count)
 202 {
 203    if (count > SIZE_MAX/size)
 204       return NULL;
 205
 206    return ralloc_size(ctx, size * count);
 207 }
 208
 209 void *
 210 rzalloc_array_size(const void *ctx, size_t size, unsigned count)
 211 {
 212    if (count > SIZE_MAX/size)
 213       return NULL;
 214
 215    return rzalloc_size(ctx, size * count);
 216 }
 217
 218 void *
 219 reralloc_array_size(const void *ctx, void *ptr, size_t size, unsigned count)
 220 {
 221    if (count > SIZE_MAX/size)
 222       return NULL;
 223
 224    return reralloc_size(ctx, ptr, size * count);
 225 }
 226
 227 void
 228 ralloc_free(void *ptr)
 229 {
 230    ralloc_header *info;
 231
 232    if (ptr == NULL)
 233       return;
 234
 235    info = get_header(ptr);
 236    unlink_block(info);
 237    unsafe_free(info);
 238 }
 239
 240 static void
 241 unlink_block(ralloc_header *info)
 242 {
 243    /* Unlink from parent & siblings */
 244    if (info->parent != NULL) {
 245       if (info->parent->child == info)
 246          info->parent->child = info->next;
 247
 248       if (info->prev != NULL)
 249          info->prev->next = info->next;
 250
 251       if (info->next != NULL)
 252          info->next->prev = info->prev;
 253    }
 254    info->parent = NULL;
 255    info->prev = NULL;
 256    info->next = NULL;
 257 }
 258
 259 static void
 260 unsafe_free(ralloc_header *info)
 261 {
 262    /* Recursively free any children...don't waste time unlinking them. */
 263    ralloc_header *temp;
 264    while (info->child != NULL) {
 265       temp = info->child;
 266       info->child = temp->next;
 267       unsafe_free(temp);
 268    }
 269
 270    /* Free the block itself.  Call the destructor first, if any. */
 271    if (info->destructor != NULL)
 272       info->destructor(PTR_FROM_HEADER(info));
 273
 274    free(info);
 275 }
 276
 277 void
 278 ralloc_steal(const void *new_ctx, void *ptr)
 279 {
 280    ralloc_header *info, *parent;
 281
 282    if (unlikely(ptr == NULL))
 283       return;
 284
 285    info = get_header(ptr);
 286    parent = new_ctx ? get_header(new_ctx) : NULL;
 287
 288    unlink_block(info);
 289
 290    add_child(parent, info);
 291 }
 292
 293 void
 294 ralloc_adopt(const void *new_ctx, void *old_ctx)
 295 {
 296    ralloc_header *new_info, *old_info, *child;
 297
 298    if (unlikely(old_ctx == NULL))
 299       return;
 300
 301    old_info = get_header(old_ctx);
 302    new_info = get_header(new_ctx);
 303
 304    /* If there are no children, bail. */
 305    if (unlikely(old_info->child == NULL))
 306       return;
 307
 308    /* Set all the children's parent to new_ctx; get a pointer to the last child. */
 309    for (child = old_info->child; child->next != NULL; child = child->next) {
 310       child->parent = new_info;
 311    }
 312    child->parent = new_info;
 313
 314    /* Connect the two lists together; parent them to new_ctx; make old_ctx empty. */
 315    child->next = new_info->child;
 316    if (child->next)
 317       child->next->prev = child;
 318    new_info->child = old_info->child;
 319    old_info->child = NULL;
 320 }
 321
 322 void *
 323 ralloc_parent(const void *ptr)
 324 {
 325    ralloc_header *info;
 326
 327    if (unlikely(ptr == NULL))
 328       return NULL;
 329
 330    info = get_header(ptr);
 331    return info->parent ? PTR_FROM_HEADER(info->parent) : NULL;
 332 }
 333
 334 void
 335 ralloc_set_destructor(const void *ptr, void(*destructor)(void *))
 336 {
 337    ralloc_header *info = get_header(ptr);
 338    info->destructor = destructor;
 339 }
 340
 341 char *
 342 ralloc_strdup(const void *ctx, const char *str)
 343 {
 344    size_t n;
 345    char *ptr;
 346
 347    if (unlikely(str == NULL))
 348       return NULL;
 349
 350    n = strlen(str);
 351    ptr = ralloc_array(ctx, char, n + 1);
 352    memcpy(ptr, str, n);
 353    ptr[n] = '\0';
 354    return ptr;
 355 }
 356
 357 char *
 358 ralloc_strndup(const void *ctx, const char *str, size_t max)
 359 {
 360    size_t n;
 361    char *ptr;
 362
 363    if (unlikely(str == NULL))
 364       return NULL;
 365
 366    n = strnlen(str, max);
 367    ptr = ralloc_array(ctx, char, n + 1);
 368    memcpy(ptr, str, n);
 369    ptr[n] = '\0';
 370    return ptr;
 371 }
 372
 373 /* helper routine for strcat/strncat - n is the exact amount to copy */
 374 static bool
 375 cat(char **dest, const char *str, size_t n)
 376 {
 377    char *both;
 378    size_t existing_length;
 379    assert(dest != NULL && *dest != NULL);
 380
 381    existing_length = strlen(*dest);
 382    both = resize(*dest, existing_length + n + 1);
 383    if (unlikely(both == NULL))
 384       return false;
 385
 386    memcpy(both + existing_length, str, n);
 387    both[existing_length + n] = '\0';
 388
 389    *dest = both;
 390    return true;
 391 }
 392
 393
 394 bool
 395 ralloc_strcat(char **dest, const char *str)
 396 {
 397    return cat(dest, str, strlen(str));
 398 }
 399
 400 bool
 401 ralloc_strncat(char **dest, const char *str, size_t n)
 402 {
 403    return cat(dest, str, strnlen(str, n));
 404 }
 405
 406 bool
 407 ralloc_str_append(char **dest, const char *str,
 408                   size_t existing_length, size_t str_size)
 409 {
 410    char *both;
 411    assert(dest != NULL && *dest != NULL);
 412
 413    both = resize(*dest, existing_length + str_size + 1);
 414    if (unlikely(both == NULL))
 415       return false;
 416
 417    memcpy(both + existing_length, str, str_size);
 418    both[existing_length + str_size] = '\0';
 419
 420    *dest = both;
 421
 422    return true;
 423 }
 424
 425 char *
 426 ralloc_asprintf(const void *ctx, const char *fmt, ...)
 427 {
 428    char *ptr;
 429    va_list args;
 430    va_start(args, fmt);
 431    ptr = ralloc_vasprintf(ctx, fmt, args);
 432    va_end(args);
 433    return ptr;
 434 }
 435
 436 /* Return the length of the string that would be generated by a printf-style
 437  * format and argument list, not including the \0 byte.
 438  */
 439 static size_t
 440 printf_length(const char *fmt, va_list untouched_args)
 441 {
 442    int size;
 443    char junk;
 444
 445    /* Make a copy of the va_list so the original caller can still use it */
 446    va_list args;
 447    va_copy(args, untouched_args);
 448
 449 #ifdef _WIN32
 450    /* We need to use _vcsprintf to calculate the size as vsnprintf returns -1
 451     * if the number of characters to write is greater than count.
 452     */
 453    size = _vscprintf(fmt, args);
 454    (void)junk;
 455 #else
 456    size = vsnprintf(&junk, 1, fmt, args);
 457 #endif
 458    assert(size >= 0);
 459
 460    va_end(args);
 461
 462    return size;
 463 }
 464
 465 char *
 466 ralloc_vasprintf(const void *ctx, const char *fmt, va_list args)
 467 {
 468    size_t size = printf_length(fmt, args) + 1;
 469
 470    char *ptr = ralloc_size(ctx, size);
 471    if (ptr != NULL)
 472       vsnprintf(ptr, size, fmt, args);
 473
 474    return ptr;
 475 }
 476
 477 bool
 478 ralloc_asprintf_append(char **str, const char *fmt, ...)
 479 {
 480    bool success;
 481    va_list args;
 482    va_start(args, fmt);
 483    success = ralloc_vasprintf_append(str, fmt, args);
 484    va_end(args);
 485    return success;
 486 }
 487
 488 bool
 489 ralloc_vasprintf_append(char **str, const char *fmt, va_list args)
 490 {
 491    size_t existing_length;
 492    assert(str != NULL);
 493    existing_length = *str ? strlen(*str) : 0;
 494    return ralloc_vasprintf_rewrite_tail(str, &existing_length, fmt, args);
 495 }
 496
 497 bool
 498 ralloc_asprintf_rewrite_tail(char **str, size_t *start, const char *fmt, ...)
 499 {
 500    bool success;
 501    va_list args;
 502    va_start(args, fmt);
 503    success = ralloc_vasprintf_rewrite_tail(str, start, fmt, args);
 504    va_end(args);
 505    return success;
 506 }
 507
 508 bool
 509 ralloc_vasprintf_rewrite_tail(char **str, size_t *start, const char *fmt,
 510                               va_list args)
 511 {
 512    size_t new_length;
 513    char *ptr;
 514
 515    assert(str != NULL);
 516
 517    if (unlikely(*str == NULL)) {
 518       // Assuming a NULL context is probably bad, but it's expected behavior.
 519       *str = ralloc_vasprintf(NULL, fmt, args);
 520       *start = strlen(*str);
 521       return true;
 522    }
 523
 524    new_length = printf_length(fmt, args);
 525
 526    ptr = resize(*str, *start + new_length + 1);
 527    if (unlikely(ptr == NULL))
 528       return false;
 529
 530    vsnprintf(ptr + *start, new_length + 1, fmt, args);
 531    *str = ptr;
 532    *start += new_length;
 533    return true;
 534 }
 535
 536 /***************************************************************************
 537  * Linear allocator for short-lived allocations.
 538  ***************************************************************************
 539  *
 540  * The allocator consists of a parent node (2K buffer), which requires
 541  * a ralloc parent, and child nodes (allocations). Child nodes can't be freed
 542  * directly, because the parent doesn't track them. You have to release
 543  * the parent node in order to release all its children.
 544  *
 545  * The allocator uses a fixed-sized buffer with a monotonically increasing
 546  * offset after each allocation. If the buffer is all used, another buffer
 547  * is allocated, sharing the same ralloc parent, so all buffers are at
 548  * the same level in the ralloc hierarchy.
 549  *
 550  * The linear parent node is always the first buffer and keeps track of all
 551  * other buffers.
 552  */
 553
 554 #define MIN_LINEAR_BUFSIZE 2048
 555 #define SUBALLOC_ALIGNMENT 8
 556 #define LMAGIC 0x87b9c7d3
 557
 558 struct
 559 #ifdef _MSC_VER
 560  __declspec(align(8))
 561 #elif defined(__LP64__)
 562  __attribute__((aligned(16)))
 563 #else
 564  __attribute__((aligned(8)))
 565 #endif
 566    linear_header {
 567 #ifndef NDEBUG
 568    unsigned magic;   /* for debugging */
 569 #endif
 570    unsigned offset;  /* points to the first unused byte in the buffer */
 571    unsigned size;    /* size of the buffer */
 572    void *ralloc_parent;          /* new buffers will use this */
 573    struct linear_header *next;   /* next buffer if we have more */
 574    struct linear_header *latest; /* the only buffer that has free space */
 575
 576    /* After this structure, the buffer begins.
 577     * Each suballocation consists of linear_size_chunk as its header followed
 578     * by the suballocation, so it goes:
 579     *
 580     * - linear_size_chunk
 581     * - allocated space
 582     * - linear_size_chunk
 583     * - allocated space
 584     * etc.
 585     *
 586     * linear_size_chunk is only needed by linear_realloc.
 587     */
 588 };
 589
 590 struct linear_size_chunk {
 591    unsigned size; /* for realloc */
 592    unsigned _padding;
 593 };
 594
 595 typedef struct linear_header linear_header;
 596 typedef struct linear_size_chunk linear_size_chunk;
 597
 598 #define LINEAR_PARENT_TO_HEADER(parent) \
 599    (linear_header*) \
 600    ((char*)(parent) - sizeof(linear_size_chunk) - sizeof(linear_header))
 601
 602 /* Allocate the linear buffer with its header. */
 603 static linear_header *
 604 create_linear_node(void *ralloc_ctx, unsigned min_size)
 605 {
 606    linear_header *node;
 607
 608    min_size += sizeof(linear_size_chunk);
 609
 610    if (likely(min_size < MIN_LINEAR_BUFSIZE))
 611       min_size = MIN_LINEAR_BUFSIZE;
 612
 613    node = ralloc_size(ralloc_ctx, sizeof(linear_header) + min_size);
 614    if (unlikely(!node))
 615       return NULL;
 616
 617 #ifndef NDEBUG
 618    node->magic = LMAGIC;
 619 #endif
 620    node->offset = 0;
 621    node->size = min_size;
 622    node->ralloc_parent = ralloc_ctx;
 623    node->next = NULL;
 624    node->latest = node;
 625    return node;
 626 }
 627
 628 void *
 629 linear_alloc_child(void *parent, unsigned size)
 630 {
 631    linear_header *first = LINEAR_PARENT_TO_HEADER(parent);
 632    linear_header *latest = first->latest;
 633    linear_header *new_node;
 634    linear_size_chunk *ptr;
 635    unsigned full_size;
 636
 637    assert(first->magic == LMAGIC);
 638    assert(!latest->next);
 639
 640    size = ALIGN_POT(size, SUBALLOC_ALIGNMENT);
 641    full_size = sizeof(linear_size_chunk) + size;
 642
 643    if (unlikely(latest->offset + full_size > latest->size)) {
 644       /* allocate a new node */
 645       new_node = create_linear_node(latest->ralloc_parent, size);
 646       if (unlikely(!new_node))
 647          return NULL;
 648
 649       first->latest = new_node;
 650       latest->latest = new_node;
 651       latest->next = new_node;
 652       latest = new_node;
 653    }
 654
 655    ptr = (linear_size_chunk *)((char*)&latest[1] + latest->offset);
 656    ptr->size = size;
 657    latest->offset += full_size;
 658
 659    assert((uintptr_t)&ptr[1] % SUBALLOC_ALIGNMENT == 0);
 660    return &ptr[1];
 661 }
 662
 663 void *
 664 linear_alloc_parent(void *ralloc_ctx, unsigned size)
 665 {
 666    linear_header *node;
 667
 668    if (unlikely(!ralloc_ctx))
 669       return NULL;
 670
 671    size = ALIGN_POT(size, SUBALLOC_ALIGNMENT);
 672
 673    node = create_linear_node(ralloc_ctx, size);
 674    if (unlikely(!node))
 675       return NULL;
 676
 677    return linear_alloc_child((char*)node +
 678                              sizeof(linear_header) +
 679                              sizeof(linear_size_chunk), size);
 680 }
 681
 682 void *
 683 linear_zalloc_child(void *parent, unsigned size)
 684 {
 685    void *ptr = linear_alloc_child(parent, size);
 686
 687    if (likely(ptr))
 688       memset(ptr, 0, size);
 689    return ptr;
 690 }
 691
 692 void *
 693 linear_zalloc_parent(void *parent, unsigned size)
 694 {
 695    void *ptr = linear_alloc_parent(parent, size);
 696
 697    if (likely(ptr))
 698       memset(ptr, 0, size);
 699    return ptr;
 700 }
 701
 702 void
 703 linear_free_parent(void *ptr)
 704 {
 705    linear_header *node;
 706
 707    if (unlikely(!ptr))
 708       return;
 709
 710    node = LINEAR_PARENT_TO_HEADER(ptr);
 711    assert(node->magic == LMAGIC);
 712
 713    while (node) {
 714       void *ptr = node;
 715
 716       node = node->next;
 717       ralloc_free(ptr);
 718    }
 719 }
 720
 721 void
 722 ralloc_steal_linear_parent(void *new_ralloc_ctx, void *ptr)
 723 {
 724    linear_header *node;
 725
 726    if (unlikely(!ptr))
 727       return;
 728
 729    node = LINEAR_PARENT_TO_HEADER(ptr);
 730    assert(node->magic == LMAGIC);
 731
 732    while (node) {
 733       ralloc_steal(new_ralloc_ctx, node);
 734       node->ralloc_parent = new_ralloc_ctx;
 735       node = node->next;
 736    }
 737 }
 738
 739 void *
 740 ralloc_parent_of_linear_parent(void *ptr)
 741 {
 742    linear_header *node = LINEAR_PARENT_TO_HEADER(ptr);
 743    assert(node->magic == LMAGIC);
 744    return node->ralloc_parent;
 745 }
 746
 747 void *
 748 linear_realloc(void *parent, void *old, unsigned new_size)
 749 {
 750    unsigned old_size = 0;
 751    ralloc_header *new_ptr;
 752
 753    new_ptr = linear_alloc_child(parent, new_size);
 754
 755    if (unlikely(!old))
 756       return new_ptr;
 757
 758    old_size = ((linear_size_chunk*)old)[-1].size;
 759
 760    if (likely(new_ptr && old_size))
 761       memcpy(new_ptr, old, MIN2(old_size, new_size));
 762
 763    return new_ptr;
 764 }
 765
 766 /* All code below is pretty much copied from ralloc and only the alloc
 767  * calls are different.
 768  */
 769
 770 char *
 771 linear_strdup(void *parent, const char *str)
 772 {
 773    unsigned n;
 774    char *ptr;
 775
 776    if (unlikely(!str))
 777       return NULL;
 778
 779    n = strlen(str);
 780    ptr = linear_alloc_child(parent, n + 1);
 781    if (unlikely(!ptr))
 782       return NULL;
 783
 784    memcpy(ptr, str, n);
 785    ptr[n] = '\0';
 786    return ptr;
 787 }
 788
 789 char *
 790 linear_asprintf(void *parent, const char *fmt, ...)
 791 {
 792    char *ptr;
 793    va_list args;
 794    va_start(args, fmt);
 795    ptr = linear_vasprintf(parent, fmt, args);
 796    va_end(args);
 797    return ptr;
 798 }
 799
 800 char *
 801 linear_vasprintf(void *parent, const char *fmt, va_list args)
 802 {
 803    unsigned size = printf_length(fmt, args) + 1;
 804
 805    char *ptr = linear_alloc_child(parent, size);
 806    if (ptr != NULL)
 807       vsnprintf(ptr, size, fmt, args);
 808
 809    return ptr;
 810 }
 811
 812 bool
 813 linear_asprintf_append(void *parent, char **str, const char *fmt, ...)
 814 {
 815    bool success;
 816    va_list args;
 817    va_start(args, fmt);
 818    success = linear_vasprintf_append(parent, str, fmt, args);
 819    va_end(args);
 820    return success;
 821 }
 822
 823 bool
 824 linear_vasprintf_append(void *parent, char **str, const char *fmt, va_list args)
 825 {
 826    size_t existing_length;
 827    assert(str != NULL);
 828    existing_length = *str ? strlen(*str) : 0;
 829    return linear_vasprintf_rewrite_tail(parent, str, &existing_length, fmt, args);
 830 }
 831
 832 bool
 833 linear_asprintf_rewrite_tail(void *parent, char **str, size_t *start,
 834                              const char *fmt, ...)
 835 {
 836    bool success;
 837    va_list args;
 838    va_start(args, fmt);
 839    success = linear_vasprintf_rewrite_tail(parent, str, start, fmt, args);
 840    va_end(args);
 841    return success;
 842 }
 843
 844 bool
 845 linear_vasprintf_rewrite_tail(void *parent, char **str, size_t *start,
 846                               const char *fmt, va_list args)
 847 {
 848    size_t new_length;
 849    char *ptr;
 850
 851    assert(str != NULL);
 852
 853    if (unlikely(*str == NULL)) {
 854       *str = linear_vasprintf(parent, fmt, args);
 855       *start = strlen(*str);
 856       return true;
 857    }
 858
 859    new_length = printf_length(fmt, args);
 860
 861    ptr = linear_realloc(parent, *str, *start + new_length + 1);
 862    if (unlikely(ptr == NULL))
 863       return false;
 864
 865    vsnprintf(ptr + *start, new_length + 1, fmt, args);
 866    *str = ptr;
 867    *start += new_length;
 868    return true;
 869 }
 870
 871 /* helper routine for strcat/strncat - n is the exact amount to copy */
 872 static bool
 873 linear_cat(void *parent, char **dest, const char *str, unsigned n)
 874 {
 875    char *both;
 876    unsigned existing_length;
 877    assert(dest != NULL && *dest != NULL);
 878
 879    existing_length = strlen(*dest);
 880    both = linear_realloc(parent, *dest, existing_length + n + 1);
 881    if (unlikely(both == NULL))
 882       return false;
 883
 884    memcpy(both + existing_length, str, n);
 885    both[existing_length + n] = '\0';
 886
 887    *dest = both;
 888    return true;
 889 }
 890
 891 bool
 892 linear_strcat(void *parent, char **dest, const char *str)
 893 {
 894    return linear_cat(parent, dest, str, strlen(str));
 895 }