Re: [Qemu-devel] [PATCH 13/14] commit: Use BlockBackend for I/O

[Max Reitz <mreitz@redhat.com>]

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On 04.05.2016 11:39, Kevin Wolf wrote:
> This changes the commit block job to use the job's BlockBackend for
> performing its I/O. job->bs isn't used by the commit code any more
> afterwards.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/commit.c | 42 +++++++++++++++++++++++++++---------------
>  1 file changed, 27 insertions(+), 15 deletions(-)
> 
> diff --git a/block/commit.c b/block/commit.c
> index f308c8c..863e059 100644
> --- a/block/commit.c
> +++ b/block/commit.c
> @@ -36,28 +36,34 @@ typedef struct CommitBlockJob {
>      BlockJob common;
>      RateLimit limit;
>      BlockDriverState *active;
> -    BlockDriverState *top;
> -    BlockDriverState *base;
> +    BlockBackend *top;
> +    BlockBackend *base;
>      BlockdevOnError on_error;
>      int base_flags;
>      int orig_overlay_flags;
>      char *backing_file_str;
>  } CommitBlockJob;
>  
> -static int coroutine_fn commit_populate(BlockDriverState *bs,
> -                                        BlockDriverState *base,
> +static int coroutine_fn commit_populate(BlockBackend *bs, BlockBackend *base,
>                                          int64_t sector_num, int nb_sectors,
>                                          void *buf)
>  {
>      int ret = 0;
> +    QEMUIOVector qiov;
> +    struct iovec iov = {
> +        .iov_base = (void *)buf,

Why the cast?

> +        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
> +    };
>  
> -    ret = bdrv_read(bs, sector_num, buf, nb_sectors);
> -    if (ret) {
> +    qemu_iovec_init_external(&qiov, &iov, 1);
> +
> +    ret = blk_co_readv(bs, sector_num, nb_sectors, &qiov);
> +    if (ret < 0) {
>          return ret;
>      }
>  
> -    ret = bdrv_write(base, sector_num, buf, nb_sectors);
> -    if (ret) {
> +    ret = blk_co_writev(base, sector_num, nb_sectors, &qiov);
> +    if (ret < 0) {
>          return ret;
>      }
>  
> @@ -73,8 +79,8 @@ static void commit_complete(BlockJob *job, void *opaque)
>      CommitBlockJob *s = container_of(job, CommitBlockJob, common);
>      CommitCompleteData *data = opaque;
>      BlockDriverState *active = s->active;
> -    BlockDriverState *top = s->top;
> -    BlockDriverState *base = s->base;
> +    BlockDriverState *top = blk_bs(s->top);
> +    BlockDriverState *base = blk_bs(s->base);
>      BlockDriverState *overlay_bs;
>      int ret = data->ret;
>  
> @@ -94,6 +100,8 @@ static void commit_complete(BlockJob *job, void *opaque)
>          bdrv_reopen(overlay_bs, s->orig_overlay_flags, NULL);
>      }
>      g_free(s->backing_file_str);
> +    blk_unref(s->top);
> +    blk_unref(s->base);
>      block_job_completed(&s->common, ret);
>      g_free(data);
>  }
> @@ -102,8 +110,8 @@ static void coroutine_fn commit_run(void *opaque)
>  {
>      CommitBlockJob *s = opaque;
>      CommitCompleteData *data;
> -    BlockDriverState *top = s->top;
> -    BlockDriverState *base = s->base;
> +    BlockDriverState *top = blk_bs(s->top);
> +    BlockDriverState *base = blk_bs(s->base);

I think for this function it would definitely be nicer to drop these
variables (or make them BlockBackend pointers) and use them with the
blk_* functions. The only function where this is not possible is
bdrv_is_allocated_above(), and I think it won't be too ugly to use
blk_bs() in its parameter list there.

>      int64_t sector_num, end;
>      int ret = 0;
>      int n = 0;
> @@ -158,7 +166,7 @@ wait:
>                      goto wait;
>                  }
>              }
> -            ret = commit_populate(top, base, sector_num, n, buf);
> +            ret = commit_populate(s->top, s->base, sector_num, n, buf);
>              bytes_written += n * BDRV_SECTOR_SIZE;
>          }
>          if (ret < 0) {
> @@ -253,8 +261,12 @@ void commit_start(BlockDriverState *bs, BlockDriverState *base,
>          return;
>      }
>  
> -    s->base   = base;
> -    s->top    = top;
> +    s->base = blk_new(&error_abort);
> +    blk_insert_bs(s->base, base);
> +
> +    s->top = blk_new(&error_abort);
> +    blk_insert_bs(s->top, top);
> +

But again, this is why I'm hesitant to give an R-b for this patch.

Max

>      s->active = bs;
>  
>      s->base_flags          = orig_base_flags;
> 



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