qemu/migration/qemu-file.c
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   1/*
   2 * QEMU System Emulator
   3 *
   4 * Copyright (c) 2003-2008 Fabrice Bellard
   5 *
   6 * Permission is hereby granted, free of charge, to any person obtaining a copy
   7 * of this software and associated documentation files (the "Software"), to deal
   8 * in the Software without restriction, including without limitation the rights
   9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10 * copies of the Software, and to permit persons to whom the Software is
  11 * furnished to do so, subject to the following conditions:
  12 *
  13 * The above copyright notice and this permission notice shall be included in
  14 * all copies or substantial portions of the Software.
  15 *
  16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22 * THE SOFTWARE.
  23 */
  24#include "qemu/osdep.h"
  25#include <zlib.h>
  26#include "qemu/error-report.h"
  27#include "qemu/iov.h"
  28#include "migration.h"
  29#include "qemu-file.h"
  30#include "trace.h"
  31#include "qapi/error.h"
  32
  33#define IO_BUF_SIZE 32768
  34#define MAX_IOV_SIZE MIN_CONST(IOV_MAX, 64)
  35
  36struct QEMUFile {
  37    const QEMUFileOps *ops;
  38    const QEMUFileHooks *hooks;
  39    void *opaque;
  40
  41    int64_t bytes_xfer;
  42    int64_t xfer_limit;
  43
  44    int64_t pos; /* start of buffer when writing, end of buffer
  45                    when reading */
  46    int buf_index;
  47    int buf_size; /* 0 when writing */
  48    uint8_t buf[IO_BUF_SIZE];
  49
  50    DECLARE_BITMAP(may_free, MAX_IOV_SIZE);
  51    struct iovec iov[MAX_IOV_SIZE];
  52    unsigned int iovcnt;
  53
  54    int last_error;
  55    Error *last_error_obj;
  56    /* has the file has been shutdown */
  57    bool shutdown;
  58};
  59
  60/*
  61 * Stop a file from being read/written - not all backing files can do this
  62 * typically only sockets can.
  63 */
  64int qemu_file_shutdown(QEMUFile *f)
  65{
  66    int ret;
  67
  68    f->shutdown = true;
  69    if (!f->ops->shut_down) {
  70        return -ENOSYS;
  71    }
  72    ret = f->ops->shut_down(f->opaque, true, true, NULL);
  73
  74    if (!f->last_error) {
  75        qemu_file_set_error(f, -EIO);
  76    }
  77    return ret;
  78}
  79
  80/*
  81 * Result: QEMUFile* for a 'return path' for comms in the opposite direction
  82 *         NULL if not available
  83 */
  84QEMUFile *qemu_file_get_return_path(QEMUFile *f)
  85{
  86    if (!f->ops->get_return_path) {
  87        return NULL;
  88    }
  89    return f->ops->get_return_path(f->opaque);
  90}
  91
  92bool qemu_file_mode_is_not_valid(const char *mode)
  93{
  94    if (mode == NULL ||
  95        (mode[0] != 'r' && mode[0] != 'w') ||
  96        mode[1] != 'b' || mode[2] != 0) {
  97        fprintf(stderr, "qemu_fopen: Argument validity check failed\n");
  98        return true;
  99    }
 100
 101    return false;
 102}
 103
 104QEMUFile *qemu_fopen_ops(void *opaque, const QEMUFileOps *ops)
 105{
 106    QEMUFile *f;
 107
 108    f = g_new0(QEMUFile, 1);
 109
 110    f->opaque = opaque;
 111    f->ops = ops;
 112    return f;
 113}
 114
 115
 116void qemu_file_set_hooks(QEMUFile *f, const QEMUFileHooks *hooks)
 117{
 118    f->hooks = hooks;
 119}
 120
 121/*
 122 * Get last error for stream f with optional Error*
 123 *
 124 * Return negative error value if there has been an error on previous
 125 * operations, return 0 if no error happened.
 126 * Optional, it returns Error* in errp, but it may be NULL even if return value
 127 * is not 0.
 128 *
 129 */
 130int qemu_file_get_error_obj(QEMUFile *f, Error **errp)
 131{
 132    if (errp) {
 133        *errp = f->last_error_obj ? error_copy(f->last_error_obj) : NULL;
 134    }
 135    return f->last_error;
 136}
 137
 138/*
 139 * Set the last error for stream f with optional Error*
 140 */
 141void qemu_file_set_error_obj(QEMUFile *f, int ret, Error *err)
 142{
 143    if (f->last_error == 0 && ret) {
 144        f->last_error = ret;
 145        error_propagate(&f->last_error_obj, err);
 146    } else if (err) {
 147        error_report_err(err);
 148    }
 149}
 150
 151/*
 152 * Get last error for stream f
 153 *
 154 * Return negative error value if there has been an error on previous
 155 * operations, return 0 if no error happened.
 156 *
 157 */
 158int qemu_file_get_error(QEMUFile *f)
 159{
 160    return qemu_file_get_error_obj(f, NULL);
 161}
 162
 163/*
 164 * Set the last error for stream f
 165 */
 166void qemu_file_set_error(QEMUFile *f, int ret)
 167{
 168    qemu_file_set_error_obj(f, ret, NULL);
 169}
 170
 171bool qemu_file_is_writable(QEMUFile *f)
 172{
 173    return f->ops->writev_buffer;
 174}
 175
 176static void qemu_iovec_release_ram(QEMUFile *f)
 177{
 178    struct iovec iov;
 179    unsigned long idx;
 180
 181    /* Find and release all the contiguous memory ranges marked as may_free. */
 182    idx = find_next_bit(f->may_free, f->iovcnt, 0);
 183    if (idx >= f->iovcnt) {
 184        return;
 185    }
 186    iov = f->iov[idx];
 187
 188    /* The madvise() in the loop is called for iov within a continuous range and
 189     * then reinitialize the iov. And in the end, madvise() is called for the
 190     * last iov.
 191     */
 192    while ((idx = find_next_bit(f->may_free, f->iovcnt, idx + 1)) < f->iovcnt) {
 193        /* check for adjacent buffer and coalesce them */
 194        if (iov.iov_base + iov.iov_len == f->iov[idx].iov_base) {
 195            iov.iov_len += f->iov[idx].iov_len;
 196            continue;
 197        }
 198        if (qemu_madvise(iov.iov_base, iov.iov_len, QEMU_MADV_DONTNEED) < 0) {
 199            error_report("migrate: madvise DONTNEED failed %p %zd: %s",
 200                         iov.iov_base, iov.iov_len, strerror(errno));
 201        }
 202        iov = f->iov[idx];
 203    }
 204    if (qemu_madvise(iov.iov_base, iov.iov_len, QEMU_MADV_DONTNEED) < 0) {
 205            error_report("migrate: madvise DONTNEED failed %p %zd: %s",
 206                         iov.iov_base, iov.iov_len, strerror(errno));
 207    }
 208    memset(f->may_free, 0, sizeof(f->may_free));
 209}
 210
 211/**
 212 * Flushes QEMUFile buffer
 213 *
 214 * This will flush all pending data. If data was only partially flushed, it
 215 * will set an error state.
 216 */
 217void qemu_fflush(QEMUFile *f)
 218{
 219    ssize_t ret = 0;
 220    ssize_t expect = 0;
 221    Error *local_error = NULL;
 222
 223    if (!qemu_file_is_writable(f)) {
 224        return;
 225    }
 226
 227    if (f->shutdown) {
 228        return;
 229    }
 230    if (f->iovcnt > 0) {
 231        expect = iov_size(f->iov, f->iovcnt);
 232        ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos,
 233                                    &local_error);
 234
 235        qemu_iovec_release_ram(f);
 236    }
 237
 238    if (ret >= 0) {
 239        f->pos += ret;
 240    }
 241    /* We expect the QEMUFile write impl to send the full
 242     * data set we requested, so sanity check that.
 243     */
 244    if (ret != expect) {
 245        qemu_file_set_error_obj(f, ret < 0 ? ret : -EIO, local_error);
 246    }
 247    f->buf_index = 0;
 248    f->iovcnt = 0;
 249}
 250
 251void ram_control_before_iterate(QEMUFile *f, uint64_t flags)
 252{
 253    int ret = 0;
 254
 255    if (f->hooks && f->hooks->before_ram_iterate) {
 256        ret = f->hooks->before_ram_iterate(f, f->opaque, flags, NULL);
 257        if (ret < 0) {
 258            qemu_file_set_error(f, ret);
 259        }
 260    }
 261}
 262
 263void ram_control_after_iterate(QEMUFile *f, uint64_t flags)
 264{
 265    int ret = 0;
 266
 267    if (f->hooks && f->hooks->after_ram_iterate) {
 268        ret = f->hooks->after_ram_iterate(f, f->opaque, flags, NULL);
 269        if (ret < 0) {
 270            qemu_file_set_error(f, ret);
 271        }
 272    }
 273}
 274
 275void ram_control_load_hook(QEMUFile *f, uint64_t flags, void *data)
 276{
 277    int ret = -EINVAL;
 278
 279    if (f->hooks && f->hooks->hook_ram_load) {
 280        ret = f->hooks->hook_ram_load(f, f->opaque, flags, data);
 281        if (ret < 0) {
 282            qemu_file_set_error(f, ret);
 283        }
 284    } else {
 285        /*
 286         * Hook is a hook specifically requested by the source sending a flag
 287         * that expects there to be a hook on the destination.
 288         */
 289        if (flags == RAM_CONTROL_HOOK) {
 290            qemu_file_set_error(f, ret);
 291        }
 292    }
 293}
 294
 295size_t ram_control_save_page(QEMUFile *f, ram_addr_t block_offset,
 296                             ram_addr_t offset, size_t size,
 297                             uint64_t *bytes_sent)
 298{
 299    if (f->hooks && f->hooks->save_page) {
 300        int ret = f->hooks->save_page(f, f->opaque, block_offset,
 301                                      offset, size, bytes_sent);
 302        if (ret != RAM_SAVE_CONTROL_NOT_SUPP) {
 303            f->bytes_xfer += size;
 304        }
 305
 306        if (ret != RAM_SAVE_CONTROL_DELAYED &&
 307            ret != RAM_SAVE_CONTROL_NOT_SUPP) {
 308            if (bytes_sent && *bytes_sent > 0) {
 309                qemu_update_position(f, *bytes_sent);
 310            } else if (ret < 0) {
 311                qemu_file_set_error(f, ret);
 312            }
 313        }
 314
 315        return ret;
 316    }
 317
 318    return RAM_SAVE_CONTROL_NOT_SUPP;
 319}
 320
 321/*
 322 * Attempt to fill the buffer from the underlying file
 323 * Returns the number of bytes read, or negative value for an error.
 324 *
 325 * Note that it can return a partially full buffer even in a not error/not EOF
 326 * case if the underlying file descriptor gives a short read, and that can
 327 * happen even on a blocking fd.
 328 */
 329static ssize_t qemu_fill_buffer(QEMUFile *f)
 330{
 331    int len;
 332    int pending;
 333    Error *local_error = NULL;
 334
 335    assert(!qemu_file_is_writable(f));
 336
 337    pending = f->buf_size - f->buf_index;
 338    if (pending > 0) {
 339        memmove(f->buf, f->buf + f->buf_index, pending);
 340    }
 341    f->buf_index = 0;
 342    f->buf_size = pending;
 343
 344    if (f->shutdown) {
 345        return 0;
 346    }
 347
 348    len = f->ops->get_buffer(f->opaque, f->buf + pending, f->pos,
 349                             IO_BUF_SIZE - pending, &local_error);
 350    if (len > 0) {
 351        f->buf_size += len;
 352        f->pos += len;
 353    } else if (len == 0) {
 354        qemu_file_set_error_obj(f, -EIO, local_error);
 355    } else if (len != -EAGAIN) {
 356        qemu_file_set_error_obj(f, len, local_error);
 357    } else {
 358        error_free(local_error);
 359    }
 360
 361    return len;
 362}
 363
 364void qemu_update_position(QEMUFile *f, size_t size)
 365{
 366    f->pos += size;
 367}
 368
 369/** Closes the file
 370 *
 371 * Returns negative error value if any error happened on previous operations or
 372 * while closing the file. Returns 0 or positive number on success.
 373 *
 374 * The meaning of return value on success depends on the specific backend
 375 * being used.
 376 */
 377int qemu_fclose(QEMUFile *f)
 378{
 379    int ret;
 380    qemu_fflush(f);
 381    ret = qemu_file_get_error(f);
 382
 383    if (f->ops->close) {
 384        int ret2 = f->ops->close(f->opaque, NULL);
 385        if (ret >= 0) {
 386            ret = ret2;
 387        }
 388    }
 389    /* If any error was spotted before closing, we should report it
 390     * instead of the close() return value.
 391     */
 392    if (f->last_error) {
 393        ret = f->last_error;
 394    }
 395    error_free(f->last_error_obj);
 396    g_free(f);
 397    trace_qemu_file_fclose();
 398    return ret;
 399}
 400
 401/*
 402 * Add buf to iovec. Do flush if iovec is full.
 403 *
 404 * Return values:
 405 * 1 iovec is full and flushed
 406 * 0 iovec is not flushed
 407 *
 408 */
 409static int add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size,
 410                        bool may_free)
 411{
 412    /* check for adjacent buffer and coalesce them */
 413    if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base +
 414        f->iov[f->iovcnt - 1].iov_len &&
 415        may_free == test_bit(f->iovcnt - 1, f->may_free))
 416    {
 417        f->iov[f->iovcnt - 1].iov_len += size;
 418    } else {
 419        if (may_free) {
 420            set_bit(f->iovcnt, f->may_free);
 421        }
 422        f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
 423        f->iov[f->iovcnt++].iov_len = size;
 424    }
 425
 426    if (f->iovcnt >= MAX_IOV_SIZE) {
 427        qemu_fflush(f);
 428        return 1;
 429    }
 430
 431    return 0;
 432}
 433
 434static void add_buf_to_iovec(QEMUFile *f, size_t len)
 435{
 436    if (!add_to_iovec(f, f->buf + f->buf_index, len, false)) {
 437        f->buf_index += len;
 438        if (f->buf_index == IO_BUF_SIZE) {
 439            qemu_fflush(f);
 440        }
 441    }
 442}
 443
 444void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size,
 445                           bool may_free)
 446{
 447    if (f->last_error) {
 448        return;
 449    }
 450
 451    f->bytes_xfer += size;
 452    add_to_iovec(f, buf, size, may_free);
 453}
 454
 455void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size)
 456{
 457    size_t l;
 458
 459    if (f->last_error) {
 460        return;
 461    }
 462
 463    while (size > 0) {
 464        l = IO_BUF_SIZE - f->buf_index;
 465        if (l > size) {
 466            l = size;
 467        }
 468        memcpy(f->buf + f->buf_index, buf, l);
 469        f->bytes_xfer += l;
 470        add_buf_to_iovec(f, l);
 471        if (qemu_file_get_error(f)) {
 472            break;
 473        }
 474        buf += l;
 475        size -= l;
 476    }
 477}
 478
 479void qemu_put_byte(QEMUFile *f, int v)
 480{
 481    if (f->last_error) {
 482        return;
 483    }
 484
 485    f->buf[f->buf_index] = v;
 486    f->bytes_xfer++;
 487    add_buf_to_iovec(f, 1);
 488}
 489
 490void qemu_file_skip(QEMUFile *f, int size)
 491{
 492    if (f->buf_index + size <= f->buf_size) {
 493        f->buf_index += size;
 494    }
 495}
 496
 497/*
 498 * Read 'size' bytes from file (at 'offset') without moving the
 499 * pointer and set 'buf' to point to that data.
 500 *
 501 * It will return size bytes unless there was an error, in which case it will
 502 * return as many as it managed to read (assuming blocking fd's which
 503 * all current QEMUFile are)
 504 */
 505size_t qemu_peek_buffer(QEMUFile *f, uint8_t **buf, size_t size, size_t offset)
 506{
 507    ssize_t pending;
 508    size_t index;
 509
 510    assert(!qemu_file_is_writable(f));
 511    assert(offset < IO_BUF_SIZE);
 512    assert(size <= IO_BUF_SIZE - offset);
 513
 514    /* The 1st byte to read from */
 515    index = f->buf_index + offset;
 516    /* The number of available bytes starting at index */
 517    pending = f->buf_size - index;
 518
 519    /*
 520     * qemu_fill_buffer might return just a few bytes, even when there isn't
 521     * an error, so loop collecting them until we get enough.
 522     */
 523    while (pending < size) {
 524        int received = qemu_fill_buffer(f);
 525
 526        if (received <= 0) {
 527            break;
 528        }
 529
 530        index = f->buf_index + offset;
 531        pending = f->buf_size - index;
 532    }
 533
 534    if (pending <= 0) {
 535        return 0;
 536    }
 537    if (size > pending) {
 538        size = pending;
 539    }
 540
 541    *buf = f->buf + index;
 542    return size;
 543}
 544
 545/*
 546 * Read 'size' bytes of data from the file into buf.
 547 * 'size' can be larger than the internal buffer.
 548 *
 549 * It will return size bytes unless there was an error, in which case it will
 550 * return as many as it managed to read (assuming blocking fd's which
 551 * all current QEMUFile are)
 552 */
 553size_t qemu_get_buffer(QEMUFile *f, uint8_t *buf, size_t size)
 554{
 555    size_t pending = size;
 556    size_t done = 0;
 557
 558    while (pending > 0) {
 559        size_t res;
 560        uint8_t *src;
 561
 562        res = qemu_peek_buffer(f, &src, MIN(pending, IO_BUF_SIZE), 0);
 563        if (res == 0) {
 564            return done;
 565        }
 566        memcpy(buf, src, res);
 567        qemu_file_skip(f, res);
 568        buf += res;
 569        pending -= res;
 570        done += res;
 571    }
 572    return done;
 573}
 574
 575/*
 576 * Read 'size' bytes of data from the file.
 577 * 'size' can be larger than the internal buffer.
 578 *
 579 * The data:
 580 *   may be held on an internal buffer (in which case *buf is updated
 581 *     to point to it) that is valid until the next qemu_file operation.
 582 * OR
 583 *   will be copied to the *buf that was passed in.
 584 *
 585 * The code tries to avoid the copy if possible.
 586 *
 587 * It will return size bytes unless there was an error, in which case it will
 588 * return as many as it managed to read (assuming blocking fd's which
 589 * all current QEMUFile are)
 590 *
 591 * Note: Since **buf may get changed, the caller should take care to
 592 *       keep a pointer to the original buffer if it needs to deallocate it.
 593 */
 594size_t qemu_get_buffer_in_place(QEMUFile *f, uint8_t **buf, size_t size)
 595{
 596    if (size < IO_BUF_SIZE) {
 597        size_t res;
 598        uint8_t *src;
 599
 600        res = qemu_peek_buffer(f, &src, size, 0);
 601
 602        if (res == size) {
 603            qemu_file_skip(f, res);
 604            *buf = src;
 605            return res;
 606        }
 607    }
 608
 609    return qemu_get_buffer(f, *buf, size);
 610}
 611
 612/*
 613 * Peeks a single byte from the buffer; this isn't guaranteed to work if
 614 * offset leaves a gap after the previous read/peeked data.
 615 */
 616int qemu_peek_byte(QEMUFile *f, int offset)
 617{
 618    int index = f->buf_index + offset;
 619
 620    assert(!qemu_file_is_writable(f));
 621    assert(offset < IO_BUF_SIZE);
 622
 623    if (index >= f->buf_size) {
 624        qemu_fill_buffer(f);
 625        index = f->buf_index + offset;
 626        if (index >= f->buf_size) {
 627            return 0;
 628        }
 629    }
 630    return f->buf[index];
 631}
 632
 633int qemu_get_byte(QEMUFile *f)
 634{
 635    int result;
 636
 637    result = qemu_peek_byte(f, 0);
 638    qemu_file_skip(f, 1);
 639    return result;
 640}
 641
 642int64_t qemu_ftell_fast(QEMUFile *f)
 643{
 644    int64_t ret = f->pos;
 645    int i;
 646
 647    for (i = 0; i < f->iovcnt; i++) {
 648        ret += f->iov[i].iov_len;
 649    }
 650
 651    return ret;
 652}
 653
 654int64_t qemu_ftell(QEMUFile *f)
 655{
 656    qemu_fflush(f);
 657    return f->pos;
 658}
 659
 660int qemu_file_rate_limit(QEMUFile *f)
 661{
 662    if (f->shutdown) {
 663        return 1;
 664    }
 665    if (qemu_file_get_error(f)) {
 666        return 1;
 667    }
 668    if (f->xfer_limit > 0 && f->bytes_xfer > f->xfer_limit) {
 669        return 1;
 670    }
 671    return 0;
 672}
 673
 674int64_t qemu_file_get_rate_limit(QEMUFile *f)
 675{
 676    return f->xfer_limit;
 677}
 678
 679void qemu_file_set_rate_limit(QEMUFile *f, int64_t limit)
 680{
 681    f->xfer_limit = limit;
 682}
 683
 684void qemu_file_reset_rate_limit(QEMUFile *f)
 685{
 686    f->bytes_xfer = 0;
 687}
 688
 689void qemu_file_update_transfer(QEMUFile *f, int64_t len)
 690{
 691    f->bytes_xfer += len;
 692}
 693
 694void qemu_put_be16(QEMUFile *f, unsigned int v)
 695{
 696    qemu_put_byte(f, v >> 8);
 697    qemu_put_byte(f, v);
 698}
 699
 700void qemu_put_be32(QEMUFile *f, unsigned int v)
 701{
 702    qemu_put_byte(f, v >> 24);
 703    qemu_put_byte(f, v >> 16);
 704    qemu_put_byte(f, v >> 8);
 705    qemu_put_byte(f, v);
 706}
 707
 708void qemu_put_be64(QEMUFile *f, uint64_t v)
 709{
 710    qemu_put_be32(f, v >> 32);
 711    qemu_put_be32(f, v);
 712}
 713
 714unsigned int qemu_get_be16(QEMUFile *f)
 715{
 716    unsigned int v;
 717    v = qemu_get_byte(f) << 8;
 718    v |= qemu_get_byte(f);
 719    return v;
 720}
 721
 722unsigned int qemu_get_be32(QEMUFile *f)
 723{
 724    unsigned int v;
 725    v = (unsigned int)qemu_get_byte(f) << 24;
 726    v |= qemu_get_byte(f) << 16;
 727    v |= qemu_get_byte(f) << 8;
 728    v |= qemu_get_byte(f);
 729    return v;
 730}
 731
 732uint64_t qemu_get_be64(QEMUFile *f)
 733{
 734    uint64_t v;
 735    v = (uint64_t)qemu_get_be32(f) << 32;
 736    v |= qemu_get_be32(f);
 737    return v;
 738}
 739
 740/* return the size after compression, or negative value on error */
 741static int qemu_compress_data(z_stream *stream, uint8_t *dest, size_t dest_len,
 742                              const uint8_t *source, size_t source_len)
 743{
 744    int err;
 745
 746    err = deflateReset(stream);
 747    if (err != Z_OK) {
 748        return -1;
 749    }
 750
 751    stream->avail_in = source_len;
 752    stream->next_in = (uint8_t *)source;
 753    stream->avail_out = dest_len;
 754    stream->next_out = dest;
 755
 756    err = deflate(stream, Z_FINISH);
 757    if (err != Z_STREAM_END) {
 758        return -1;
 759    }
 760
 761    return stream->next_out - dest;
 762}
 763
 764/* Compress size bytes of data start at p and store the compressed
 765 * data to the buffer of f.
 766 *
 767 * Since the file is dummy file with empty_ops, return -1 if f has no space to
 768 * save the compressed data.
 769 */
 770ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream,
 771                                  const uint8_t *p, size_t size)
 772{
 773    ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
 774
 775    if (blen < compressBound(size)) {
 776        return -1;
 777    }
 778
 779    blen = qemu_compress_data(stream, f->buf + f->buf_index + sizeof(int32_t),
 780                              blen, p, size);
 781    if (blen < 0) {
 782        return -1;
 783    }
 784
 785    qemu_put_be32(f, blen);
 786    add_buf_to_iovec(f, blen);
 787    return blen + sizeof(int32_t);
 788}
 789
 790/* Put the data in the buffer of f_src to the buffer of f_des, and
 791 * then reset the buf_index of f_src to 0.
 792 */
 793
 794int qemu_put_qemu_file(QEMUFile *f_des, QEMUFile *f_src)
 795{
 796    int len = 0;
 797
 798    if (f_src->buf_index > 0) {
 799        len = f_src->buf_index;
 800        qemu_put_buffer(f_des, f_src->buf, f_src->buf_index);
 801        f_src->buf_index = 0;
 802        f_src->iovcnt = 0;
 803    }
 804    return len;
 805}
 806
 807/*
 808 * Get a string whose length is determined by a single preceding byte
 809 * A preallocated 256 byte buffer must be passed in.
 810 * Returns: len on success and a 0 terminated string in the buffer
 811 *          else 0
 812 *          (Note a 0 length string will return 0 either way)
 813 */
 814size_t qemu_get_counted_string(QEMUFile *f, char buf[256])
 815{
 816    size_t len = qemu_get_byte(f);
 817    size_t res = qemu_get_buffer(f, (uint8_t *)buf, len);
 818
 819    buf[res] = 0;
 820
 821    return res == len ? res : 0;
 822}
 823
 824/*
 825 * Put a string with one preceding byte containing its length. The length of
 826 * the string should be less than 256.
 827 */
 828void qemu_put_counted_string(QEMUFile *f, const char *str)
 829{
 830    size_t len = strlen(str);
 831
 832    assert(len < 256);
 833    qemu_put_byte(f, len);
 834    qemu_put_buffer(f, (const uint8_t *)str, len);
 835}
 836
 837/*
 838 * Set the blocking state of the QEMUFile.
 839 * Note: On some transports the OS only keeps a single blocking state for
 840 *       both directions, and thus changing the blocking on the main
 841 *       QEMUFile can also affect the return path.
 842 */
 843void qemu_file_set_blocking(QEMUFile *f, bool block)
 844{
 845    if (f->ops->set_blocking) {
 846        f->ops->set_blocking(f->opaque, block, NULL);
 847    }
 848}
 849