qemu

qemu-file.c (23695B)

---

 /*
  * QEMU System Emulator
  *
  * Copyright (c) 2003-2008 Fabrice Bellard
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
 #include "qemu/osdep.h"
 #include <zlib.h>
 #include "qemu/madvise.h"
 #include "qemu/error-report.h"
 #include "qemu/iov.h"
 #include "migration.h"
 #include "qemu-file.h"
 #include "trace.h"
 #include "qapi/error.h"
 
 #define IO_BUF_SIZE 32768
 #define MAX_IOV_SIZE MIN_CONST(IOV_MAX, 64)
 
 struct QEMUFile {
     const QEMUFileHooks *hooks;
     QIOChannel *ioc;
     bool is_writable;
 
     /*
      * Maximum amount of data in bytes to transfer during one
      * rate limiting time window
      */
     int64_t rate_limit_max;
     /*
      * Total amount of data in bytes queued for transfer
      * during this rate limiting time window
      */
     int64_t rate_limit_used;
 
     /* The sum of bytes transferred on the wire */
     int64_t total_transferred;
 
     int buf_index;
     int buf_size; /* 0 when writing */
     uint8_t buf[IO_BUF_SIZE];
 
     DECLARE_BITMAP(may_free, MAX_IOV_SIZE);
     struct iovec iov[MAX_IOV_SIZE];
     unsigned int iovcnt;
 
     int last_error;
     Error *last_error_obj;
     /* has the file has been shutdown */
     bool shutdown;
 };
 
 /*
  * Stop a file from being read/written - not all backing files can do this
  * typically only sockets can.
  *
  * TODO: convert to propagate Error objects instead of squashing
  * to a fixed errno value
  */
 int qemu_file_shutdown(QEMUFile *f)
 {
     int ret = 0;
 
     f->shutdown = true;
 
     /*
      * We must set qemufile error before the real shutdown(), otherwise
      * there can be a race window where we thought IO all went though
      * (because last_error==NULL) but actually IO has already stopped.
      *
      * If without correct ordering, the race can happen like this:
      *
      *      page receiver                     other thread
      *      -------------                     ------------
      *      qemu_get_buffer()
      *                                        do shutdown()
      *        returns 0 (buffer all zero)
      *        (we didn't check this retcode)
      *      try to detect IO error
      *        last_error==NULL, IO okay
      *      install ALL-ZERO page
      *                                        set last_error
      *      --> guest crash!
      */
     if (!f->last_error) {
         qemu_file_set_error(f, -EIO);
     }
 
     if (!qio_channel_has_feature(f->ioc,
                                  QIO_CHANNEL_FEATURE_SHUTDOWN)) {
         return -ENOSYS;
     }
 
     if (qio_channel_shutdown(f->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL) < 0) {
         ret = -EIO;
     }
 
     return ret;
 }
 
 bool qemu_file_mode_is_not_valid(const char *mode)
 {
     if (mode == NULL ||
         (mode[0] != 'r' && mode[0] != 'w') ||
         mode[1] != 'b' || mode[2] != 0) {
         fprintf(stderr, "qemu_fopen: Argument validity check failed\n");
         return true;
     }
 
     return false;
 }
 
 static QEMUFile *qemu_file_new_impl(QIOChannel *ioc, bool is_writable)
 {
     QEMUFile *f;
 
     f = g_new0(QEMUFile, 1);
 
     object_ref(ioc);
     f->ioc = ioc;
     f->is_writable = is_writable;
 
     return f;
 }
 
 /*
  * Result: QEMUFile* for a 'return path' for comms in the opposite direction
  *         NULL if not available
  */
 QEMUFile *qemu_file_get_return_path(QEMUFile *f)
 {
     return qemu_file_new_impl(f->ioc, !f->is_writable);
 }
 
 QEMUFile *qemu_file_new_output(QIOChannel *ioc)
 {
     return qemu_file_new_impl(ioc, true);
 }
 
 QEMUFile *qemu_file_new_input(QIOChannel *ioc)
 {
     return qemu_file_new_impl(ioc, false);
 }
 
 void qemu_file_set_hooks(QEMUFile *f, const QEMUFileHooks *hooks)
 {
     f->hooks = hooks;
 }
 
 /*
  * Get last error for stream f with optional Error*
  *
  * Return negative error value if there has been an error on previous
  * operations, return 0 if no error happened.
  * Optional, it returns Error* in errp, but it may be NULL even if return value
  * is not 0.
  *
  */
 int qemu_file_get_error_obj(QEMUFile *f, Error **errp)
 {
     if (errp) {
         *errp = f->last_error_obj ? error_copy(f->last_error_obj) : NULL;
     }
     return f->last_error;
 }
 
 /*
  * Get last error for either stream f1 or f2 with optional Error*.
  * The error returned (non-zero) can be either from f1 or f2.
  *
  * If any of the qemufile* is NULL, then skip the check on that file.
  *
  * When there is no error on both qemufile, zero is returned.
  */
 int qemu_file_get_error_obj_any(QEMUFile *f1, QEMUFile *f2, Error **errp)
 {
     int ret = 0;
 
     if (f1) {
         ret = qemu_file_get_error_obj(f1, errp);
         /* If there's already error detected, return */
         if (ret) {
             return ret;
         }
     }
 
     if (f2) {
         ret = qemu_file_get_error_obj(f2, errp);
     }
 
     return ret;
 }
 
 /*
  * Set the last error for stream f with optional Error*
  */
 void qemu_file_set_error_obj(QEMUFile *f, int ret, Error *err)
 {
     if (f->last_error == 0 && ret) {
         f->last_error = ret;
         error_propagate(&f->last_error_obj, err);
     } else if (err) {
         error_report_err(err);
     }
 }
 
 /*
  * Get last error for stream f
  *
  * Return negative error value if there has been an error on previous
  * operations, return 0 if no error happened.
  *
  */
 int qemu_file_get_error(QEMUFile *f)
 {
     return qemu_file_get_error_obj(f, NULL);
 }
 
 /*
  * Set the last error for stream f
  */
 void qemu_file_set_error(QEMUFile *f, int ret)
 {
     qemu_file_set_error_obj(f, ret, NULL);
 }
 
 bool qemu_file_is_writable(QEMUFile *f)
 {
     return f->is_writable;
 }
 
 static void qemu_iovec_release_ram(QEMUFile *f)
 {
     struct iovec iov;
     unsigned long idx;
 
     /* Find and release all the contiguous memory ranges marked as may_free. */
     idx = find_next_bit(f->may_free, f->iovcnt, 0);
     if (idx >= f->iovcnt) {
         return;
     }
     iov = f->iov[idx];
 
     /* The madvise() in the loop is called for iov within a continuous range and
      * then reinitialize the iov. And in the end, madvise() is called for the
      * last iov.
      */
     while ((idx = find_next_bit(f->may_free, f->iovcnt, idx + 1)) < f->iovcnt) {
         /* check for adjacent buffer and coalesce them */
         if (iov.iov_base + iov.iov_len == f->iov[idx].iov_base) {
             iov.iov_len += f->iov[idx].iov_len;
             continue;
         }
         if (qemu_madvise(iov.iov_base, iov.iov_len, QEMU_MADV_DONTNEED) < 0) {
             error_report("migrate: madvise DONTNEED failed %p %zd: %s",
                          iov.iov_base, iov.iov_len, strerror(errno));
         }
         iov = f->iov[idx];
     }
     if (qemu_madvise(iov.iov_base, iov.iov_len, QEMU_MADV_DONTNEED) < 0) {
             error_report("migrate: madvise DONTNEED failed %p %zd: %s",
                          iov.iov_base, iov.iov_len, strerror(errno));
     }
     memset(f->may_free, 0, sizeof(f->may_free));
 }
 
 
 /**
  * Flushes QEMUFile buffer
  *
  * This will flush all pending data. If data was only partially flushed, it
  * will set an error state.
  */
 void qemu_fflush(QEMUFile *f)
 {
     if (!qemu_file_is_writable(f)) {
         return;
     }
 
     if (f->shutdown) {
         return;
     }
     if (f->iovcnt > 0) {
         Error *local_error = NULL;
         if (qio_channel_writev_all(f->ioc,
                                    f->iov, f->iovcnt,
                                    &local_error) < 0) {
             qemu_file_set_error_obj(f, -EIO, local_error);
         } else {
             f->total_transferred += iov_size(f->iov, f->iovcnt);
         }
 
         qemu_iovec_release_ram(f);
     }
 
     f->buf_index = 0;
     f->iovcnt = 0;
 }
 
 void ram_control_before_iterate(QEMUFile *f, uint64_t flags)
 {
     int ret = 0;
 
     if (f->hooks && f->hooks->before_ram_iterate) {
         ret = f->hooks->before_ram_iterate(f, flags, NULL);
         if (ret < 0) {
             qemu_file_set_error(f, ret);
         }
     }
 }
 
 void ram_control_after_iterate(QEMUFile *f, uint64_t flags)
 {
     int ret = 0;
 
     if (f->hooks && f->hooks->after_ram_iterate) {
         ret = f->hooks->after_ram_iterate(f, flags, NULL);
         if (ret < 0) {
             qemu_file_set_error(f, ret);
         }
     }
 }
 
 void ram_control_load_hook(QEMUFile *f, uint64_t flags, void *data)
 {
     int ret = -EINVAL;
 
     if (f->hooks && f->hooks->hook_ram_load) {
         ret = f->hooks->hook_ram_load(f, flags, data);
         if (ret < 0) {
             qemu_file_set_error(f, ret);
         }
     } else {
         /*
          * Hook is a hook specifically requested by the source sending a flag
          * that expects there to be a hook on the destination.
          */
         if (flags == RAM_CONTROL_HOOK) {
             qemu_file_set_error(f, ret);
         }
     }
 }
 
 size_t ram_control_save_page(QEMUFile *f, ram_addr_t block_offset,
                              ram_addr_t offset, size_t size,
                              uint64_t *bytes_sent)
 {
     if (f->hooks && f->hooks->save_page) {
         int ret = f->hooks->save_page(f, block_offset,
                                       offset, size, bytes_sent);
         if (ret != RAM_SAVE_CONTROL_NOT_SUPP) {
             f->rate_limit_used += size;
         }
 
         if (ret != RAM_SAVE_CONTROL_DELAYED &&
             ret != RAM_SAVE_CONTROL_NOT_SUPP) {
             if (bytes_sent && *bytes_sent > 0) {
                 qemu_file_credit_transfer(f, *bytes_sent);
             } else if (ret < 0) {
                 qemu_file_set_error(f, ret);
             }
         }
 
         return ret;
     }
 
     return RAM_SAVE_CONTROL_NOT_SUPP;
 }
 
 /*
  * Attempt to fill the buffer from the underlying file
  * Returns the number of bytes read, or negative value for an error.
  *
  * Note that it can return a partially full buffer even in a not error/not EOF
  * case if the underlying file descriptor gives a short read, and that can
  * happen even on a blocking fd.
  */
 static ssize_t qemu_fill_buffer(QEMUFile *f)
 {
     int len;
     int pending;
     Error *local_error = NULL;
 
     assert(!qemu_file_is_writable(f));
 
     pending = f->buf_size - f->buf_index;
     if (pending > 0) {
         memmove(f->buf, f->buf + f->buf_index, pending);
     }
     f->buf_index = 0;
     f->buf_size = pending;
 
     if (f->shutdown) {
         return 0;
     }
 
     do {
         len = qio_channel_read(f->ioc,
                                (char *)f->buf + pending,
                                IO_BUF_SIZE - pending,
                                &local_error);
         if (len == QIO_CHANNEL_ERR_BLOCK) {
             if (qemu_in_coroutine()) {
                 qio_channel_yield(f->ioc, G_IO_IN);
             } else {
                 qio_channel_wait(f->ioc, G_IO_IN);
             }
         } else if (len < 0) {
             len = -EIO;
         }
     } while (len == QIO_CHANNEL_ERR_BLOCK);
 
     if (len > 0) {
         f->buf_size += len;
         f->total_transferred += len;
     } else if (len == 0) {
         qemu_file_set_error_obj(f, -EIO, local_error);
     } else {
         qemu_file_set_error_obj(f, len, local_error);
     }
 
     return len;
 }
 
 void qemu_file_credit_transfer(QEMUFile *f, size_t size)
 {
     f->total_transferred += size;
 }
 
 /** Closes the file
  *
  * Returns negative error value if any error happened on previous operations or
  * while closing the file. Returns 0 or positive number on success.
  *
  * The meaning of return value on success depends on the specific backend
  * being used.
  */
 int qemu_fclose(QEMUFile *f)
 {
     int ret, ret2;
     qemu_fflush(f);
     ret = qemu_file_get_error(f);
 
     ret2 = qio_channel_close(f->ioc, NULL);
     if (ret >= 0) {
         ret = ret2;
     }
     g_clear_pointer(&f->ioc, object_unref);
 
     /* If any error was spotted before closing, we should report it
      * instead of the close() return value.
      */
     if (f->last_error) {
         ret = f->last_error;
     }
     error_free(f->last_error_obj);
     g_free(f);
     trace_qemu_file_fclose();
     return ret;
 }
 
 /*
  * Add buf to iovec. Do flush if iovec is full.
  *
  * Return values:
  * 1 iovec is full and flushed
  * 0 iovec is not flushed
  *
  */
 static int add_to_iovec(QEMUFile *f, const uint8_t *buf, size_t size,
                         bool may_free)
 {
     /* check for adjacent buffer and coalesce them */
     if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base +
         f->iov[f->iovcnt - 1].iov_len &&
         may_free == test_bit(f->iovcnt - 1, f->may_free))
     {
         f->iov[f->iovcnt - 1].iov_len += size;
     } else {
         if (f->iovcnt >= MAX_IOV_SIZE) {
             /* Should only happen if a previous fflush failed */
             assert(f->shutdown || !qemu_file_is_writable(f));
             return 1;
         }
         if (may_free) {
             set_bit(f->iovcnt, f->may_free);
         }
         f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
         f->iov[f->iovcnt++].iov_len = size;
     }
 
     if (f->iovcnt >= MAX_IOV_SIZE) {
         qemu_fflush(f);
         return 1;
     }
 
     return 0;
 }
 
 static void add_buf_to_iovec(QEMUFile *f, size_t len)
 {
     if (!add_to_iovec(f, f->buf + f->buf_index, len, false)) {
         f->buf_index += len;
         if (f->buf_index == IO_BUF_SIZE) {
             qemu_fflush(f);
         }
     }
 }
 
 void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, size_t size,
                            bool may_free)
 {
     if (f->last_error) {
         return;
     }
 
     f->rate_limit_used += size;
     add_to_iovec(f, buf, size, may_free);
 }
 
 void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, size_t size)
 {
     size_t l;
 
     if (f->last_error) {
         return;
     }
 
     while (size > 0) {
         l = IO_BUF_SIZE - f->buf_index;
         if (l > size) {
             l = size;
         }
         memcpy(f->buf + f->buf_index, buf, l);
         f->rate_limit_used += l;
         add_buf_to_iovec(f, l);
         if (qemu_file_get_error(f)) {
             break;
         }
         buf += l;
         size -= l;
     }
 }
 
 void qemu_put_byte(QEMUFile *f, int v)
 {
     if (f->last_error) {
         return;
     }
 
     f->buf[f->buf_index] = v;
     f->rate_limit_used++;
     add_buf_to_iovec(f, 1);
 }
 
 void qemu_file_skip(QEMUFile *f, int size)
 {
     if (f->buf_index + size <= f->buf_size) {
         f->buf_index += size;
     }
 }
 
 /*
  * Read 'size' bytes from file (at 'offset') without moving the
  * pointer and set 'buf' to point to that data.
  *
  * It will return size bytes unless there was an error, in which case it will
  * return as many as it managed to read (assuming blocking fd's which
  * all current QEMUFile are)
  */
 size_t qemu_peek_buffer(QEMUFile *f, uint8_t **buf, size_t size, size_t offset)
 {
     ssize_t pending;
     size_t index;
 
     assert(!qemu_file_is_writable(f));
     assert(offset < IO_BUF_SIZE);
     assert(size <= IO_BUF_SIZE - offset);
 
     /* The 1st byte to read from */
     index = f->buf_index + offset;
     /* The number of available bytes starting at index */
     pending = f->buf_size - index;
 
     /*
      * qemu_fill_buffer might return just a few bytes, even when there isn't
      * an error, so loop collecting them until we get enough.
      */
     while (pending < size) {
         int received = qemu_fill_buffer(f);
 
         if (received <= 0) {
             break;
         }
 
         index = f->buf_index + offset;
         pending = f->buf_size - index;
     }
 
     if (pending <= 0) {
         return 0;
     }
     if (size > pending) {
         size = pending;
     }
 
     *buf = f->buf + index;
     return size;
 }
 
 /*
  * Read 'size' bytes of data from the file into buf.
  * 'size' can be larger than the internal buffer.
  *
  * It will return size bytes unless there was an error, in which case it will
  * return as many as it managed to read (assuming blocking fd's which
  * all current QEMUFile are)
  */
 size_t qemu_get_buffer(QEMUFile *f, uint8_t *buf, size_t size)
 {
     size_t pending = size;
     size_t done = 0;
 
     while (pending > 0) {
         size_t res;
         uint8_t *src;
 
         res = qemu_peek_buffer(f, &src, MIN(pending, IO_BUF_SIZE), 0);
         if (res == 0) {
             return done;
         }
         memcpy(buf, src, res);
         qemu_file_skip(f, res);
         buf += res;
         pending -= res;
         done += res;
     }
     return done;
 }
 
 /*
  * Read 'size' bytes of data from the file.
  * 'size' can be larger than the internal buffer.
  *
  * The data:
  *   may be held on an internal buffer (in which case *buf is updated
  *     to point to it) that is valid until the next qemu_file operation.
  * OR
  *   will be copied to the *buf that was passed in.
  *
  * The code tries to avoid the copy if possible.
  *
  * It will return size bytes unless there was an error, in which case it will
  * return as many as it managed to read (assuming blocking fd's which
  * all current QEMUFile are)
  *
  * Note: Since **buf may get changed, the caller should take care to
  *       keep a pointer to the original buffer if it needs to deallocate it.
  */
 size_t qemu_get_buffer_in_place(QEMUFile *f, uint8_t **buf, size_t size)
 {
     if (size < IO_BUF_SIZE) {
         size_t res;
         uint8_t *src = NULL;
 
         res = qemu_peek_buffer(f, &src, size, 0);
 
         if (res == size) {
             qemu_file_skip(f, res);
             *buf = src;
             return res;
         }
     }
 
     return qemu_get_buffer(f, *buf, size);
 }
 
 /*
  * Peeks a single byte from the buffer; this isn't guaranteed to work if
  * offset leaves a gap after the previous read/peeked data.
  */
 int qemu_peek_byte(QEMUFile *f, int offset)
 {
     int index = f->buf_index + offset;
 
     assert(!qemu_file_is_writable(f));
     assert(offset < IO_BUF_SIZE);
 
     if (index >= f->buf_size) {
         qemu_fill_buffer(f);
         index = f->buf_index + offset;
         if (index >= f->buf_size) {
             return 0;
         }
     }
     return f->buf[index];
 }
 
 int qemu_get_byte(QEMUFile *f)
 {
     int result;
 
     result = qemu_peek_byte(f, 0);
     qemu_file_skip(f, 1);
     return result;
 }
 
 int64_t qemu_file_total_transferred_fast(QEMUFile *f)
 {
     int64_t ret = f->total_transferred;
     int i;
 
     for (i = 0; i < f->iovcnt; i++) {
         ret += f->iov[i].iov_len;
     }
 
     return ret;
 }
 
 int64_t qemu_file_total_transferred(QEMUFile *f)
 {
     qemu_fflush(f);
     return f->total_transferred;
 }
 
 int qemu_file_rate_limit(QEMUFile *f)
 {
     if (f->shutdown) {
         return 1;
     }
     if (qemu_file_get_error(f)) {
         return 1;
     }
     if (f->rate_limit_max > 0 && f->rate_limit_used > f->rate_limit_max) {
         return 1;
     }
     return 0;
 }
 
 int64_t qemu_file_get_rate_limit(QEMUFile *f)
 {
     return f->rate_limit_max;
 }
 
 void qemu_file_set_rate_limit(QEMUFile *f, int64_t limit)
 {
     f->rate_limit_max = limit;
 }
 
 void qemu_file_reset_rate_limit(QEMUFile *f)
 {
     f->rate_limit_used = 0;
 }
 
 void qemu_file_acct_rate_limit(QEMUFile *f, int64_t len)
 {
     f->rate_limit_used += len;
 }
 
 void qemu_put_be16(QEMUFile *f, unsigned int v)
 {
     qemu_put_byte(f, v >> 8);
     qemu_put_byte(f, v);
 }
 
 void qemu_put_be32(QEMUFile *f, unsigned int v)
 {
     qemu_put_byte(f, v >> 24);
     qemu_put_byte(f, v >> 16);
     qemu_put_byte(f, v >> 8);
     qemu_put_byte(f, v);
 }
 
 void qemu_put_be64(QEMUFile *f, uint64_t v)
 {
     qemu_put_be32(f, v >> 32);
     qemu_put_be32(f, v);
 }
 
 unsigned int qemu_get_be16(QEMUFile *f)
 {
     unsigned int v;
     v = qemu_get_byte(f) << 8;
     v |= qemu_get_byte(f);
     return v;
 }
 
 unsigned int qemu_get_be32(QEMUFile *f)
 {
     unsigned int v;
     v = (unsigned int)qemu_get_byte(f) << 24;
     v |= qemu_get_byte(f) << 16;
     v |= qemu_get_byte(f) << 8;
     v |= qemu_get_byte(f);
     return v;
 }
 
 uint64_t qemu_get_be64(QEMUFile *f)
 {
     uint64_t v;
     v = (uint64_t)qemu_get_be32(f) << 32;
     v |= qemu_get_be32(f);
     return v;
 }
 
 /* return the size after compression, or negative value on error */
 static int qemu_compress_data(z_stream *stream, uint8_t *dest, size_t dest_len,
                               const uint8_t *source, size_t source_len)
 {
     int err;
 
     err = deflateReset(stream);
     if (err != Z_OK) {
         return -1;
     }
 
     stream->avail_in = source_len;
     stream->next_in = (uint8_t *)source;
     stream->avail_out = dest_len;
     stream->next_out = dest;
 
     err = deflate(stream, Z_FINISH);
     if (err != Z_STREAM_END) {
         return -1;
     }
 
     return stream->next_out - dest;
 }
 
 /* Compress size bytes of data start at p and store the compressed
  * data to the buffer of f.
  *
  * Since the file is dummy file with empty_ops, return -1 if f has no space to
  * save the compressed data.
  */
 ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream,
                                   const uint8_t *p, size_t size)
 {
     ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
 
     if (blen < compressBound(size)) {
         return -1;
     }
 
     blen = qemu_compress_data(stream, f->buf + f->buf_index + sizeof(int32_t),
                               blen, p, size);
     if (blen < 0) {
         return -1;
     }
 
     qemu_put_be32(f, blen);
     add_buf_to_iovec(f, blen);
     return blen + sizeof(int32_t);
 }
 
 /* Put the data in the buffer of f_src to the buffer of f_des, and
  * then reset the buf_index of f_src to 0.
  */
 
 int qemu_put_qemu_file(QEMUFile *f_des, QEMUFile *f_src)
 {
     int len = 0;
 
     if (f_src->buf_index > 0) {
         len = f_src->buf_index;
         qemu_put_buffer(f_des, f_src->buf, f_src->buf_index);
         f_src->buf_index = 0;
         f_src->iovcnt = 0;
     }
     return len;
 }
 
 /*
  * Get a string whose length is determined by a single preceding byte
  * A preallocated 256 byte buffer must be passed in.
  * Returns: len on success and a 0 terminated string in the buffer
  *          else 0
  *          (Note a 0 length string will return 0 either way)
  */
 size_t qemu_get_counted_string(QEMUFile *f, char buf[256])
 {
     size_t len = qemu_get_byte(f);
     size_t res = qemu_get_buffer(f, (uint8_t *)buf, len);
 
     buf[res] = 0;
 
     return res == len ? res : 0;
 }
 
 /*
  * Put a string with one preceding byte containing its length. The length of
  * the string should be less than 256.
  */
 void qemu_put_counted_string(QEMUFile *f, const char *str)
 {
     size_t len = strlen(str);
 
     assert(len < 256);
     qemu_put_byte(f, len);
     qemu_put_buffer(f, (const uint8_t *)str, len);
 }
 
 /*
  * Set the blocking state of the QEMUFile.
  * Note: On some transports the OS only keeps a single blocking state for
  *       both directions, and thus changing the blocking on the main
  *       QEMUFile can also affect the return path.
  */
 void qemu_file_set_blocking(QEMUFile *f, bool block)
 {
     qio_channel_set_blocking(f->ioc, block, NULL);
 }
 
 /*
  * qemu_file_get_ioc:
  *
  * Get the ioc object for the file, without incrementing
  * the reference count.
  *
  * Returns: the ioc object
  */
 QIOChannel *qemu_file_get_ioc(QEMUFile *file)
 {
     return file->ioc;
 }