Re: [Qemu-devel] [PATCH v3 14/20] backup: Switch BackupBlockJob to byte-based

[Jeff Cody <jcody@redhat.com>]

On Tue, Jun 27, 2017 at 02:24:52PM -0500, Eric Blake wrote:
> We are gradually converting to byte-based interfaces, as they are
> easier to reason about than sector-based.  Continue by converting an
> internal structure (no semantic change), and all references to
> tracking progress.  Drop a redundant local variable bytes_per_cluster.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> Reviewed-by: John Snow <jsnow@redhat.com>
> 

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

> ---
> v2: no change
> ---
>  block/backup.c | 33 +++++++++++++++------------------
>  1 file changed, 15 insertions(+), 18 deletions(-)
> 
> diff --git a/block/backup.c b/block/backup.c
> index 06431ac..4e64710 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -39,7 +39,7 @@ typedef struct BackupBlockJob {
>      BlockdevOnError on_source_error;
>      BlockdevOnError on_target_error;
>      CoRwlock flush_rwlock;
> -    uint64_t sectors_read;
> +    uint64_t bytes_read;
>      unsigned long *done_bitmap;
>      int64_t cluster_size;
>      bool compress;
> @@ -102,16 +102,15 @@ static int coroutine_fn backup_do_cow(BackupBlockJob *job,
>      void *bounce_buffer = NULL;
>      int ret = 0;
>      int64_t sectors_per_cluster = cluster_size_sectors(job);
> -    int64_t bytes_per_cluster = sectors_per_cluster * BDRV_SECTOR_SIZE;
> -    int64_t start, end;
> -    int n;
> +    int64_t start, end; /* clusters */
> +    int n; /* bytes */
> 
>      qemu_co_rwlock_rdlock(&job->flush_rwlock);
> 
>      start = sector_num / sectors_per_cluster;
>      end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster);
> 
> -    trace_backup_do_cow_enter(job, start * bytes_per_cluster,
> +    trace_backup_do_cow_enter(job, start * job->cluster_size,
>                                sector_num * BDRV_SECTOR_SIZE,
>                                nb_sectors * BDRV_SECTOR_SIZE);
> 
> @@ -120,28 +119,27 @@ static int coroutine_fn backup_do_cow(BackupBlockJob *job,
> 
>      for (; start < end; start++) {
>          if (test_bit(start, job->done_bitmap)) {
> -            trace_backup_do_cow_skip(job, start * bytes_per_cluster);
> +            trace_backup_do_cow_skip(job, start * job->cluster_size);
>              continue; /* already copied */
>          }
> 
> -        trace_backup_do_cow_process(job, start * bytes_per_cluster);
> +        trace_backup_do_cow_process(job, start * job->cluster_size);
> 
> -        n = MIN(sectors_per_cluster,
> -                job->common.len / BDRV_SECTOR_SIZE -
> -                start * sectors_per_cluster);
> +        n = MIN(job->cluster_size,
> +                job->common.len - start * job->cluster_size);
> 
>          if (!bounce_buffer) {
>              bounce_buffer = blk_blockalign(blk, job->cluster_size);
>          }
>          iov.iov_base = bounce_buffer;
> -        iov.iov_len = n * BDRV_SECTOR_SIZE;
> +        iov.iov_len = n;
>          qemu_iovec_init_external(&bounce_qiov, &iov, 1);
> 
>          ret = blk_co_preadv(blk, start * job->cluster_size,
>                              bounce_qiov.size, &bounce_qiov,
>                              is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0);
>          if (ret < 0) {
> -            trace_backup_do_cow_read_fail(job, start * bytes_per_cluster, ret);
> +            trace_backup_do_cow_read_fail(job, start * job->cluster_size, ret);
>              if (error_is_read) {
>                  *error_is_read = true;
>              }
> @@ -157,7 +155,7 @@ static int coroutine_fn backup_do_cow(BackupBlockJob *job,
>                                   job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
>          }
>          if (ret < 0) {
> -            trace_backup_do_cow_write_fail(job, start * bytes_per_cluster, ret);
> +            trace_backup_do_cow_write_fail(job, start * job->cluster_size, ret);
>              if (error_is_read) {
>                  *error_is_read = false;
>              }
> @@ -169,8 +167,8 @@ static int coroutine_fn backup_do_cow(BackupBlockJob *job,
>          /* Publish progress, guest I/O counts as progress too.  Note that the
>           * offset field is an opaque progress value, it is not a disk offset.
>           */
> -        job->sectors_read += n;
> -        job->common.offset += n * BDRV_SECTOR_SIZE;
> +        job->bytes_read += n;
> +        job->common.offset += n;
>      }
> 
>  out:
> @@ -363,9 +361,8 @@ static bool coroutine_fn yield_and_check(BackupBlockJob *job)
>       */
>      if (job->common.speed) {
>          uint64_t delay_ns = ratelimit_calculate_delay(&job->limit,
> -                                                      job->sectors_read *
> -                                                      BDRV_SECTOR_SIZE);
> -        job->sectors_read = 0;
> +                                                      job->bytes_read);
> +        job->bytes_read = 0;
>          block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, delay_ns);
>      } else {
>          block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, 0);
> -- 
> 2.9.4
>