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