text: /*
   * Image streaming
   *
   * Copyright IBM, Corp. 2011
   *
   * Authors:
   *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
   *
   * This work is licensed under the terms of the GNU LGPL, version 2 or later.
   * See the COPYING.LIB file in the top-level directory.
   *
   */
  
  #include "trace.h"
  #include "block_int.h"
  
  enum {
      /*
       * Size of data buffer for populating the image file.  This should be large
       * enough to process multiple clusters in a single call, so that populating
       * contiguous regions of the image is efficient.
       */
      STREAM_BUFFER_SIZE = 512 * 1024, /* in bytes */
  };
  
  #define SLICE_TIME 100000000ULL /* ns */
  
  typedef struct {
      int64_t next_slice_time;
      uint64_t slice_quota;
      uint64_t dispatched;
  } RateLimit;
  
  static int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
  {
      int64_t delay_ns = 0;
      int64_t now = qemu_get_clock_ns(rt_clock);
  
      if (limit->next_slice_time < now) {
          limit->next_slice_time = now + SLICE_TIME;
          limit->dispatched = 0;
      }
      if (limit->dispatched + n > limit->slice_quota) {
          delay_ns = limit->next_slice_time - now;
      } else {
          limit->dispatched += n;
      }
      return delay_ns;
  }
  
  static void ratelimit_set_speed(RateLimit *limit, uint64_t speed)
  {
      limit->slice_quota = speed / (1000000000ULL / SLICE_TIME);
  }
  
  typedef struct StreamBlockJob {
      BlockJob common;
      RateLimit limit;
      BlockDriverState *base;
      char backing_file_id[1024];
  } StreamBlockJob;
  
  static int coroutine_fn stream_populate(BlockDriverState *bs,
                                          int64_t sector_num, int nb_sectors,
                                          void *buf)
  {
      struct iovec iov = {
          .iov_base = buf,
          .iov_len  = nb_sectors * BDRV_SECTOR_SIZE,
      };
      QEMUIOVector qiov;
  
      qemu_iovec_init_external(&qiov, &iov, 1);
  
      /* Copy-on-read the unallocated clusters */
      return bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, &qiov);
  }
  
  /*
   * Given an image chain: [BASE] -> [INTER1] -> [INTER2] -> [TOP]
   *
   * Return true if the given sector is allocated in top.
   * Return false if the given sector is allocated in intermediate images.
   * Return true otherwise.
   *
   * 'pnum' is set to the number of sectors (including and immediately following
   *  the specified sector) that are known to be in the same
   *  allocated/unallocated state.
   *
   */
  static int coroutine_fn is_allocated_base(BlockDriverState *top,
                                            BlockDriverState *base,
                                            int64_t sector_num,
                                            int nb_sectors, int *pnum)
  {
      BlockDriverState *intermediate;
      int ret, n;
  
      ret = bdrv_co_is_allocated(top, sector_num, nb_sectors, &n);
      if (ret) {
          *pnum = n;
          return ret;
      }
  
      /*
       * Is the unallocated chunk [sector_num, n] also
       * unallocated between base and top?
       */
      intermediate = top->backing_hd;
  
      while (intermediate) {
          int pnum_inter;
  
          /* reached base */
          if (intermediate == base) {
              *pnum = n;
              return 1;
          }
          ret = bdrv_co_is_allocated(intermediate, sector_num, nb_sectors,
                                     &pnum_inter);
          if (ret < 0) {
              return ret;
          } else if (ret) {
              *pnum = pnum_inter;
              return 0;
          }
  
          /*
           * [sector_num, nb_sectors] is unallocated on top but intermediate
           * might have
           *
           * [sector_num+x, nr_sectors] allocated.
           */
          if (n > pnum_inter) {
              n = pnum_inter;
          }
  
          intermediate = intermediate->backing_hd;
      }
  
      return 1;
  }
  
  static void coroutine_fn stream_run(void *opaque)
  {
      StreamBlockJob *s = opaque;
      BlockDriverState *bs = s->common.bs;
      BlockDriverState *base = s->base;
      int64_t sector_num, end;
      int ret = 0;
      int n;
      void *buf;
  
      s->common.len = bdrv_getlength(bs);
      if (s->common.len < 0) {
          block_job_complete(&s->common, s->common.len);
          return;
      }
  
      end = s->common.len >> BDRV_SECTOR_BITS;
      buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE);
  
      /* Turn on copy-on-read for the whole block device so that guest read
       * requests help us make progress.  Only do this when copying the entire
       * backing chain since the copy-on-read operation does not take base into
       * account.
       */
      if (!base) {
          bdrv_enable_copy_on_read(bs);
      }
  
      for (sector_num = 0; sector_num < end; sector_num += n) {
  retry:
          if (block_job_is_cancelled(&s->common)) {
              break;
          }
  
  
          if (base) {
              ret = is_allocated_base(bs, base, sector_num,
                                      STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE, &n);
          } else {
              ret = bdrv_co_is_allocated(bs, sector_num,
                                         STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE,
                                         &n);
          }
          trace_stream_one_iteration(s, sector_num, n, ret);
          if (ret == 0) {
              if (s->common.speed) {
                  uint64_t delay_ns = ratelimit_calculate_delay(&s->limit, n);
                  if (delay_ns > 0) {
                      co_sleep_ns(rt_clock, delay_ns);
  
                      /* Recheck cancellation and that sectors are unallocated */
                      goto retry;
                  }
              }
              ret = stream_populate(bs, sector_num, n, buf);
          }
          if (ret < 0) {
              break;
          }
          ret = 0;
  
          /* Publish progress */
          s->common.offset += n * BDRV_SECTOR_SIZE;
  
          /* Note that even when no rate limit is applied we need to yield
           * with no pending I/O here so that qemu_aio_flush() returns.
           */
          co_sleep_ns(rt_clock, 0);
      }
  
      if (!base) {
          bdrv_disable_copy_on_read(bs);
      }
  
      if (sector_num == end && ret == 0) {
          const char *base_id = NULL;
          if (base) {
              base_id = s->backing_file_id;
          }
          ret = bdrv_change_backing_file(bs, base_id, NULL);
      }
  
      qemu_vfree(buf);
      block_job_complete(&s->common, ret);
  }
  
  static int stream_set_speed(BlockJob *job, int64_t value)
  {
      StreamBlockJob *s = container_of(job, StreamBlockJob, common);
  
      if (value < 0) {
          return -EINVAL;
      }
      job->speed = value;
      ratelimit_set_speed(&s->limit, value / BDRV_SECTOR_SIZE);
      return 0;
  }
  
  static BlockJobType stream_job_type = {
      .instance_size = sizeof(StreamBlockJob),
      .job_type      = "stream",
      .set_speed     = stream_set_speed,
  };
  
  int stream_start(BlockDriverState *bs, BlockDriverState *base,
                   const char *base_id, BlockDriverCompletionFunc *cb,
                   void *opaque)
  {
      StreamBlockJob *s;
      Coroutine *co;
  
      s = block_job_create(&stream_job_type, bs, cb, opaque);
      if (!s) {
          return -EBUSY; /* bs must already be in use */
      }
  
      s->base = base;
      if (base_id) {
          pstrcpy(s->backing_file_id, sizeof(s->backing_file_id), base_id);
      }
  
      co = qemu_coroutine_create(stream_run);
      trace_stream_start(bs, base, s, co, opaque);
      qemu_coroutine_enter(co, s);
      return 0;
  }
  