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 #ifdef DEBUG
  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 #ifdef DEBUG
  92    assert(info->canary == CANARY);
  93 #endif
  94    return info;
  95 }
  96
  97 #define PTR_FROM_HEADER(info) (((char *) info) + sizeof(ralloc_header))
  98
  99 static void
 100 add_child(ralloc_header *parent, ralloc_header *info)
 101 {
 102    if (parent != NULL) {
 103       info->parent = parent;
 104       info->next = parent->child;
 105       parent->child = info;
 106
 107       if (info->next != NULL)
 108          info->next->prev = info;
 109    }
 110 }
 111
 112 void *
 113 ralloc_context(const void *ctx)
 114 {
 115    return ralloc_size(ctx, 0);
 116 }
 117
 118 void *
 119 ralloc_size(const void *ctx, size_t size)
 120 {
 121    void *block = malloc(size + sizeof(ralloc_header));
 122    ralloc_header *info;
 123    ralloc_header *parent;
 124
 125    if (unlikely(block == NULL))
 126       return NULL;
 127
 128    info = (ralloc_header *) block;
 129    /* measurements have shown that calloc is slower (because of
 130     * the multiplication overflow checking?), so clear things
 131     * manually
 132     */
 133    info->parent = NULL;
 134    info->child = NULL;
 135    info->prev = NULL;
 136    info->next = NULL;
 137    info->destructor = NULL;
 138
 139    parent = ctx != NULL ? get_header(ctx) : NULL;
 140
 141    add_child(parent, info);
 142
 143 #ifdef DEBUG
 144    info->canary = CANARY;
 145 #endif
 146
 147    return PTR_FROM_HEADER(info);
 148 }
 149
 150 void *
 151 rzalloc_size(const void *ctx, size_t size)
 152 {
 153    void *ptr = ralloc_size(ctx, size);
 154
 155    if (likely(ptr))
 156       memset(ptr, 0, size);
 157
 158    return ptr;
 159 }
 160
 161 /* helper function - assumes ptr != NULL */
 162 static void *
 163 resize(void *ptr, size_t size)
 164 {
 165    ralloc_header *child, *old, *info;
 166
 167    old = get_header(ptr);
 168    info = realloc(old, size + sizeof(ralloc_header));
 169
 170    if (info == NULL)
 171       return NULL;
 172
 173    /* Update parent and sibling's links to the reallocated node. */
 174    if (info != old && info->parent != NULL) {
 175       if (info->parent->child == old)
 176          info->parent->child = info;
 177
 178       if (info->prev != NULL)
 179          info->prev->next = info;
 180
 181       if (info->next != NULL)
 182          info->next->prev = info;
 183    }
 184
 185    /* Update child->parent links for all children */
 186    for (child = info->child; child != NULL; child = child->next)
 187       child->parent = info;
 188
 189    return PTR_FROM_HEADER(info);
 190 }
 191
 192 void *
 193 reralloc_size(const void *ctx, void *ptr, size_t size)
 194 {
 195    if (unlikely(ptr == NULL))
 196       return ralloc_size(ctx, size);
 197
 198    assert(ralloc_parent(ptr) == ctx);
 199    return resize(ptr, size);
 200 }
 201
 202 void *
 203 ralloc_array_size(const void *ctx, size_t size, unsigned count)
 204 {
 205    if (count > SIZE_MAX/size)
 206       return NULL;
 207
 208    return ralloc_size(ctx, size * count);
 209 }
 210
 211 void *
 212 rzalloc_array_size(const void *ctx, size_t size, unsigned count)
 213 {
 214    if (count > SIZE_MAX/size)
 215       return NULL;
 216
 217    return rzalloc_size(ctx, size * count);
 218 }
 219
 220 void *
 221 reralloc_array_size(const void *ctx, void *ptr, size_t size, unsigned count)
 222 {
 223    if (count > SIZE_MAX/size)
 224       return NULL;
 225
 226    return reralloc_size(ctx, ptr, size * count);
 227 }
 228
 229 void
 230 ralloc_free(void *ptr)
 231 {
 232    ralloc_header *info;
 233
 234    if (ptr == NULL)
 235       return;
 236
 237    info = get_header(ptr);
 238    unlink_block(info);
 239    unsafe_free(info);
 240 }
 241
 242 static void
 243 unlink_block(ralloc_header *info)
 244 {
 245    /* Unlink from parent & siblings */
 246    if (info->parent != NULL) {
 247       if (info->parent->child == info)
 248          info->parent->child = info->next;
 249
 250       if (info->prev != NULL)
 251          info->prev->next = info->next;
 252
 253       if (info->next != NULL)
 254          info->next->prev = info->prev;
 255    }
 256    info->parent = NULL;
 257    info->prev = NULL;
 258    info->next = NULL;
 259 }
 260
 261 static void
 262 unsafe_free(ralloc_header *info)
 263 {
 264    /* Recursively free any children...don't waste time unlinking them. */
 265    ralloc_header *temp;
 266    while (info->child != NULL) {
 267       temp = info->child;
 268       info->child = temp->next;
 269       unsafe_free(temp);
 270    }
 271
 272    /* Free the block itself.  Call the destructor first, if any. */
 273    if (info->destructor != NULL)
 274       info->destructor(PTR_FROM_HEADER(info));
 275
 276    free(info);
 277 }
 278
 279 void
 280 ralloc_steal(const void *new_ctx, void *ptr)
 281 {
 282    ralloc_header *info, *parent;
 283
 284    if (unlikely(ptr == NULL))
 285       return;
 286
 287    info = get_header(ptr);
 288    parent = get_header(new_ctx);
 289
 290    unlink_block(info);
 291
 292    add_child(parent, info);
 293 }
 294
 295 void
 296 ralloc_adopt(const void *new_ctx, void *old_ctx)
 297 {
 298    ralloc_header *new_info, *old_info, *child;
 299
 300    if (unlikely(old_ctx == NULL))
 301       return;
 302
 303    old_info = get_header(old_ctx);
 304    new_info = get_header(new_ctx);
 305
 306    /* If there are no children, bail. */
 307    if (unlikely(old_info->child == NULL))
 308       return;
 309
 310    /* Set all the children's parent to new_ctx; get a pointer to the last child. */
 311    for (child = old_info->child; child->next != NULL; child = child->next) {
 312       child->parent = new_info;
 313    }
 314
 315    /* Connect the two lists together; parent them to new_ctx; make old_ctx empty. */
 316    child->next = new_info->child;
 317    child->parent = new_info;
 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 ALIGN_POT(x, y) (((x) + (y) - 1) & ~((y) - 1))
 555
 556 #define MIN_LINEAR_BUFSIZE 2048
 557 #define SUBALLOC_ALIGNMENT sizeof(uintptr_t)
 558 #define LMAGIC 0x87b9c7d3
 559
 560 struct linear_header {
 561 #ifdef DEBUG
 562    unsigned magic;   /* for debugging */
 563 #endif
 564    unsigned offset;  /* points to the first unused byte in the buffer */
 565    unsigned size;    /* size of the buffer */
 566    void *ralloc_parent;          /* new buffers will use this */
 567    struct linear_header *next;   /* next buffer if we have more */
 568    struct linear_header *latest; /* the only buffer that has free space */
 569
 570    /* After this structure, the buffer begins.
 571     * Each suballocation consists of linear_size_chunk as its header followed
 572     * by the suballocation, so it goes:
 573     *
 574     * - linear_size_chunk
 575     * - allocated space
 576     * - linear_size_chunk
 577     * - allocated space
 578     * etc.
 579     *
 580     * linear_size_chunk is only needed by linear_realloc.
 581     */
 582 };
 583
 584 struct linear_size_chunk {
 585    unsigned size; /* for realloc */
 586    unsigned _padding;
 587 };
 588
 589 typedef struct linear_header linear_header;
 590 typedef struct linear_size_chunk linear_size_chunk;
 591
 592 #define LINEAR_PARENT_TO_HEADER(parent) \
 593    (linear_header*) \
 594    ((char*)(parent) - sizeof(linear_size_chunk) - sizeof(linear_header))
 595
 596 /* Allocate the linear buffer with its header. */
 597 static linear_header *
 598 create_linear_node(void *ralloc_ctx, unsigned min_size)
 599 {
 600    linear_header *node;
 601
 602    min_size += sizeof(linear_size_chunk);
 603
 604    if (likely(min_size < MIN_LINEAR_BUFSIZE))
 605       min_size = MIN_LINEAR_BUFSIZE;
 606
 607    node = ralloc_size(ralloc_ctx, sizeof(linear_header) + min_size);
 608    if (unlikely(!node))
 609       return NULL;
 610
 611 #ifdef DEBUG
 612    node->magic = LMAGIC;
 613 #endif
 614    node->offset = 0;
 615    node->size = min_size;
 616    node->ralloc_parent = ralloc_ctx;
 617    node->next = NULL;
 618    node->latest = node;
 619    return node;
 620 }
 621
 622 void *
 623 linear_alloc_child(void *parent, unsigned size)
 624 {
 625    linear_header *first = LINEAR_PARENT_TO_HEADER(parent);
 626    linear_header *latest = first->latest;
 627    linear_header *new_node;
 628    linear_size_chunk *ptr;
 629    unsigned full_size;
 630
 631    assert(first->magic == LMAGIC);
 632    assert(!latest->next);
 633
 634    size = ALIGN_POT(size, SUBALLOC_ALIGNMENT);
 635    full_size = sizeof(linear_size_chunk) + size;
 636
 637    if (unlikely(latest->offset + full_size > latest->size)) {
 638       /* allocate a new node */
 639       new_node = create_linear_node(latest->ralloc_parent, size);
 640       if (unlikely(!new_node))
 641          return NULL;
 642
 643       first->latest = new_node;
 644       latest->latest = new_node;
 645       latest->next = new_node;
 646       latest = new_node;
 647    }
 648
 649    ptr = (linear_size_chunk *)((char*)&latest[1] + latest->offset);
 650    ptr->size = size;
 651    latest->offset += full_size;
 652    return &ptr[1];
 653 }
 654
 655 void *
 656 linear_alloc_parent(void *ralloc_ctx, unsigned size)
 657 {
 658    linear_header *node;
 659
 660    if (unlikely(!ralloc_ctx))
 661       return NULL;
 662
 663    size = ALIGN_POT(size, SUBALLOC_ALIGNMENT);
 664
 665    node = create_linear_node(ralloc_ctx, size);
 666    if (unlikely(!node))
 667       return NULL;
 668
 669    return linear_alloc_child((char*)node +
 670                              sizeof(linear_header) +
 671                              sizeof(linear_size_chunk), size);
 672 }
 673
 674 void *
 675 linear_zalloc_child(void *parent, unsigned size)
 676 {
 677    void *ptr = linear_alloc_child(parent, size);
 678
 679    if (likely(ptr))
 680       memset(ptr, 0, size);
 681    return ptr;
 682 }
 683
 684 void *
 685 linear_zalloc_parent(void *parent, unsigned size)
 686 {
 687    void *ptr = linear_alloc_parent(parent, size);
 688
 689    if (likely(ptr))
 690       memset(ptr, 0, size);
 691    return ptr;
 692 }
 693
 694 void
 695 linear_free_parent(void *ptr)
 696 {
 697    linear_header *node;
 698
 699    if (unlikely(!ptr))
 700       return;
 701
 702    node = LINEAR_PARENT_TO_HEADER(ptr);
 703    assert(node->magic == LMAGIC);
 704
 705    while (node) {
 706       void *ptr = node;
 707
 708       node = node->next;
 709       ralloc_free(ptr);
 710    }
 711 }
 712
 713 void
 714 ralloc_steal_linear_parent(void *new_ralloc_ctx, void *ptr)
 715 {
 716    linear_header *node;
 717
 718    if (unlikely(!ptr))
 719       return;
 720
 721    node = LINEAR_PARENT_TO_HEADER(ptr);
 722    assert(node->magic == LMAGIC);
 723
 724    while (node) {
 725       ralloc_steal(new_ralloc_ctx, node);
 726       node->ralloc_parent = new_ralloc_ctx;
 727       node = node->next;
 728    }
 729 }
 730
 731 void *
 732 ralloc_parent_of_linear_parent(void *ptr)
 733 {
 734    linear_header *node = LINEAR_PARENT_TO_HEADER(ptr);
 735    assert(node->magic == LMAGIC);
 736    return node->ralloc_parent;
 737 }
 738
 739 void *
 740 linear_realloc(void *parent, void *old, unsigned new_size)
 741 {
 742    unsigned old_size = 0;
 743    ralloc_header *new_ptr;
 744
 745    new_ptr = linear_alloc_child(parent, new_size);
 746
 747    if (unlikely(!old))
 748       return new_ptr;
 749
 750    old_size = ((linear_size_chunk*)old)[-1].size;
 751
 752    if (likely(new_ptr && old_size))
 753       memcpy(new_ptr, old, MIN2(old_size, new_size));
 754
 755    return new_ptr;
 756 }
 757
 758 /* All code below is pretty much copied from ralloc and only the alloc
 759  * calls are different.
 760  */
 761
 762 char *
 763 linear_strdup(void *parent, const char *str)
 764 {
 765    unsigned n;
 766    char *ptr;
 767
 768    if (unlikely(!str))
 769       return NULL;
 770
 771    n = strlen(str);
 772    ptr = linear_alloc_child(parent, n + 1);
 773    if (unlikely(!ptr))
 774       return NULL;
 775
 776    memcpy(ptr, str, n);
 777    ptr[n] = '\0';
 778    return ptr;
 779 }
 780
 781 char *
 782 linear_asprintf(void *parent, const char *fmt, ...)
 783 {
 784    char *ptr;
 785    va_list args;
 786    va_start(args, fmt);
 787    ptr = linear_vasprintf(parent, fmt, args);
 788    va_end(args);
 789    return ptr;
 790 }
 791
 792 char *
 793 linear_vasprintf(void *parent, const char *fmt, va_list args)
 794 {
 795    unsigned size = printf_length(fmt, args) + 1;
 796
 797    char *ptr = linear_alloc_child(parent, size);
 798    if (ptr != NULL)
 799       vsnprintf(ptr, size, fmt, args);
 800
 801    return ptr;
 802 }
 803
 804 bool
 805 linear_asprintf_append(void *parent, char **str, const char *fmt, ...)
 806 {
 807    bool success;
 808    va_list args;
 809    va_start(args, fmt);
 810    success = linear_vasprintf_append(parent, str, fmt, args);
 811    va_end(args);
 812    return success;
 813 }
 814
 815 bool
 816 linear_vasprintf_append(void *parent, char **str, const char *fmt, va_list args)
 817 {
 818    size_t existing_length;
 819    assert(str != NULL);
 820    existing_length = *str ? strlen(*str) : 0;
 821    return linear_vasprintf_rewrite_tail(parent, str, &existing_length, fmt, args);
 822 }
 823
 824 bool
 825 linear_asprintf_rewrite_tail(void *parent, char **str, size_t *start,
 826                              const char *fmt, ...)
 827 {
 828    bool success;
 829    va_list args;
 830    va_start(args, fmt);
 831    success = linear_vasprintf_rewrite_tail(parent, str, start, fmt, args);
 832    va_end(args);
 833    return success;
 834 }
 835
 836 bool
 837 linear_vasprintf_rewrite_tail(void *parent, char **str, size_t *start,
 838                               const char *fmt, va_list args)
 839 {
 840    size_t new_length;
 841    char *ptr;
 842
 843    assert(str != NULL);
 844
 845    if (unlikely(*str == NULL)) {
 846       *str = linear_vasprintf(parent, fmt, args);
 847       *start = strlen(*str);
 848       return true;
 849    }
 850
 851    new_length = printf_length(fmt, args);
 852
 853    ptr = linear_realloc(parent, *str, *start + new_length + 1);
 854    if (unlikely(ptr == NULL))
 855       return false;
 856
 857    vsnprintf(ptr + *start, new_length + 1, fmt, args);
 858    *str = ptr;
 859    *start += new_length;
 860    return true;
 861 }
 862
 863 /* helper routine for strcat/strncat - n is the exact amount to copy */
 864 static bool
 865 linear_cat(void *parent, char **dest, const char *str, unsigned n)
 866 {
 867    char *both;
 868    unsigned existing_length;
 869    assert(dest != NULL && *dest != NULL);
 870
 871    existing_length = strlen(*dest);
 872    both = linear_realloc(parent, *dest, existing_length + n + 1);
 873    if (unlikely(both == NULL))
 874       return false;
 875
 876    memcpy(both + existing_length, str, n);
 877    both[existing_length + n] = '\0';
 878
 879    *dest = both;
 880    return true;
 881 }
 882
 883 bool
 884 linear_strcat(void *parent, char **dest, const char *str)
 885 {
 886    return linear_cat(parent, dest, str, strlen(str));
 887 }