Re: [Qemu-block] [PATCH v2 2/2] backup: Use copy offloading

[Stefan Hajnoczi]

On Tue, Jun 05, 2018 at 04:07:10PM +0800, Fam Zheng wrote:
> The implementation is similar to the 'qemu-img convert'. In the
> beginning of the job, offloaded copy is attempted. If it fails, further
> I/O will go through the existing bounce buffer code path.
> 
> Signed-off-by: Fam Zheng <address@hidden>

Nice, this has become much more readable.

> +/* Copy range to target and return the bytes copied. If error occured, 
> return a
> + * negative error number. */
> +static int backup_cow_with_offload(BackupBlockJob *job,

coroutine_fn

> +                                   int64_t start,
> +                                   int64_t end,
> +                                   bool is_write_notifier)
> +{
> +    int ret;
> +    int nr_clusters;
> +    BlockBackend *blk = job->common.blk;
> +    int nbytes;
> +
> +    assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
> +    nbytes = MIN(job->copy_range_size, end - start);
> +    nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
> +    hbitmap_reset(job->copy_bitmap, start / job->cluster_size,
> +                  nr_clusters);
> +    ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
> +                            is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0);
> +    if (ret < 0) {
> +        job->use_copy_range = false;

This is not necessary since backup_do_cow() also sets it to false.  This
function doesn't need to know about job->use_copy_range.

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