Re: [Qemu-devel] [PATCH v3 11/20] mirror: Switch mirror_do_read() to byte-based

[Jeff Cody <jcody@redhat.com>]

On Tue, Jun 27, 2017 at 02:24:49PM -0500, Eric Blake wrote:
> We are gradually converting to byte-based interfaces, as they are
> easier to reason about than sector-based.  Convert another internal
> function (no semantic change).
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> Reviewed-by: John Snow <jsnow@redhat.com>
> 

Reviewed-by: Jeff Cody <jcody@redhat.com>

> ---
> v2: rebase to earlier changes
> ---
>  block/mirror.c | 75 ++++++++++++++++++++++++++--------------------------------
>  1 file changed, 33 insertions(+), 42 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 1a4602a..81ff784 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -196,7 +196,7 @@ static inline int mirror_clip_sectors(MirrorBlockJob *s,
>  /* Round offset and/or bytes to target cluster if COW is needed, and
>   * return the offset of the adjusted tail against original. */
>  static int mirror_cow_align(MirrorBlockJob *s, int64_t *offset,
> -                            unsigned int *bytes)
> +                            uint64_t *bytes)
>  {
>      bool need_cow;
>      int ret = 0;
> @@ -204,6 +204,7 @@ static int mirror_cow_align(MirrorBlockJob *s, int64_t *offset,
>      unsigned int align_bytes = *bytes;
>      int max_bytes = s->granularity * s->max_iov;
> 
> +    assert(*bytes < INT_MAX);
>      need_cow = !test_bit(*offset / s->granularity, s->cow_bitmap);
>      need_cow |= !test_bit((*offset + *bytes - 1) / s->granularity,
>                            s->cow_bitmap);
> @@ -239,59 +240,50 @@ static inline void mirror_wait_for_io(MirrorBlockJob *s)
>  }
> 
>  /* Submit async read while handling COW.
> - * Returns: The number of sectors copied after and including sector_num,
> - *          excluding any sectors copied prior to sector_num due to alignment.
> - *          This will be nb_sectors if no alignment is necessary, or
> - *          (new_end - sector_num) if tail is rounded up or down due to
> + * Returns: The number of bytes copied after and including offset,
> + *          excluding any bytes copied prior to offset due to alignment.
> + *          This will be @bytes if no alignment is necessary, or
> + *          (new_end - offset) if tail is rounded up or down due to
>   *          alignment or buffer limit.
>   */
> -static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,
> -                          int nb_sectors)
> +static uint64_t mirror_do_read(MirrorBlockJob *s, int64_t offset,
> +                               uint64_t bytes)
>  {
>      BlockBackend *source = s->common.blk;
> -    int sectors_per_chunk, nb_chunks;
> -    int ret;
> +    int nb_chunks;
> +    uint64_t ret;
>      MirrorOp *op;
> -    int max_sectors;
> +    uint64_t max_bytes;
> 
> -    sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
> -    max_sectors = sectors_per_chunk * s->max_iov;
> +    max_bytes = s->granularity * s->max_iov;
> 
>      /* We can only handle as much as buf_size at a time. */
> -    nb_sectors = MIN(s->buf_size >> BDRV_SECTOR_BITS, nb_sectors);
> -    nb_sectors = MIN(max_sectors, nb_sectors);
> -    assert(nb_sectors);
> -    assert(nb_sectors < BDRV_REQUEST_MAX_SECTORS);
> -    ret = nb_sectors;
> +    bytes = MIN(s->buf_size, MIN(max_bytes, bytes));
> +    assert(bytes);
> +    assert(bytes < BDRV_REQUEST_MAX_BYTES);
> +    ret = bytes;
> 
>      if (s->cow_bitmap) {
> -        int64_t offset = sector_num * BDRV_SECTOR_SIZE;
> -        unsigned int bytes = nb_sectors * BDRV_SECTOR_SIZE;
> -        int gap;
> -
> -        gap = mirror_cow_align(s, &offset, &bytes);
> -        sector_num = offset / BDRV_SECTOR_SIZE;
> -        nb_sectors = bytes / BDRV_SECTOR_SIZE;
> -        ret += gap / BDRV_SECTOR_SIZE;
> +        ret += mirror_cow_align(s, &offset, &bytes);
>      }
> -    assert(nb_sectors << BDRV_SECTOR_BITS <= s->buf_size);
> -    /* The sector range must meet granularity because:
> +    assert(bytes <= s->buf_size);
> +    /* The range will be sector-aligned because:
>       * 1) Caller passes in aligned values;
> -     * 2) mirror_cow_align is used only when target cluster is larger. */
> -    assert(!(sector_num % sectors_per_chunk));
> -    nb_chunks = DIV_ROUND_UP(nb_sectors, sectors_per_chunk);
> +     * 2) mirror_cow_align is used only when target cluster is larger.
> +     * But it might not be cluster-aligned at end-of-file. */
> +    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> +    nb_chunks = DIV_ROUND_UP(bytes, s->granularity);
> 
>      while (s->buf_free_count < nb_chunks) {
> -        trace_mirror_yield_in_flight(s, sector_num * BDRV_SECTOR_SIZE,
> -                                     s->in_flight);
> +        trace_mirror_yield_in_flight(s, offset, s->in_flight);
>          mirror_wait_for_io(s);
>      }
> 
>      /* Allocate a MirrorOp that is used as an AIO callback.  */
>      op = g_new(MirrorOp, 1);
>      op->s = s;
> -    op->offset = sector_num * BDRV_SECTOR_SIZE;
> -    op->bytes = nb_sectors * BDRV_SECTOR_SIZE;
> +    op->offset = offset;
> +    op->bytes = bytes;
> 
>      /* Now make a QEMUIOVector taking enough granularity-sized chunks
>       * from s->buf_free.
> @@ -299,7 +291,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,
>      qemu_iovec_init(&op->qiov, nb_chunks);
>      while (nb_chunks-- > 0) {
>          MirrorBuffer *buf = QSIMPLEQ_FIRST(&s->buf_free);
> -        size_t remaining = nb_sectors * BDRV_SECTOR_SIZE - op->qiov.size;
> +        size_t remaining = bytes - op->qiov.size;
> 
>          QSIMPLEQ_REMOVE_HEAD(&s->buf_free, next);
>          s->buf_free_count--;
> @@ -308,12 +300,10 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,
> 
>      /* Copy the dirty cluster.  */
>      s->in_flight++;
> -    s->bytes_in_flight += nb_sectors * BDRV_SECTOR_SIZE;
> -    trace_mirror_one_iteration(s, sector_num * BDRV_SECTOR_SIZE,
> -                               nb_sectors * BDRV_SECTOR_SIZE);
> +    s->bytes_in_flight += bytes;
> +    trace_mirror_one_iteration(s, offset, bytes);
> 
> -    blk_aio_preadv(source, sector_num * BDRV_SECTOR_SIZE, &op->qiov, 0,
> -                   mirror_read_complete, op);
> +    blk_aio_preadv(source, offset, &op->qiov, 0, mirror_read_complete, op);
>      return ret;
>  }
> 
> @@ -461,8 +451,9 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
>          io_sectors = mirror_clip_sectors(s, sector_num, io_sectors);
>          switch (mirror_method) {
>          case MIRROR_METHOD_COPY:
> -            io_sectors = mirror_do_read(s, sector_num, io_sectors);
> -            io_bytes_acct = io_sectors * BDRV_SECTOR_SIZE;
> +            io_bytes_acct = mirror_do_read(s, sector_num * BDRV_SECTOR_SIZE,
> +                                           io_sectors * BDRV_SECTOR_SIZE);
> +            io_sectors = io_bytes_acct / BDRV_SECTOR_SIZE;
>              break;
>          case MIRROR_METHOD_ZERO:
>          case MIRROR_METHOD_DISCARD:
> -- 
> 2.9.4
>