On 2018-02-27 10:34, Fam Zheng wrote:
> On Mon, 01/22 23:08, Max Reitz wrote:
>> @@ -1151,7 +1285,48 @@ static int coroutine_fn
>> bdrv_mirror_top_preadv(BlockDriverState *bs,
>> static int coroutine_fn bdrv_mirror_top_pwritev(BlockDriverState *bs,
>> uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
>> {
>> - return bdrv_co_pwritev(bs->backing, offset, bytes, qiov, flags);
>> + MirrorOp *op = NULL;
>> + MirrorBDSOpaque *s = bs->opaque;
>> + QEMUIOVector bounce_qiov;
>> + void *bounce_buf;
>> + int ret = 0;
>> + bool copy_to_target;
>> +
>> + copy_to_target = s->job->ret >= 0 &&
>> + s->job->copy_mode == MIRROR_COPY_MODE_WRITE_BLOCKING;
>> +
>> + if (copy_to_target) {
>> + /* The guest might concurrently modify the data to write; but
>> + * the data on source and destination must match, so we have
>> + * to use a bounce buffer if we are going to write to the
>> + * target now. */
>> + bounce_buf = qemu_blockalign(bs, bytes);
>> + iov_to_buf_full(qiov->iov, qiov->niov, 0, bounce_buf, bytes);
>
> Quorum doesn't use a bounce buffer, so I think we can get away without it
> too: a
> guest concurrently modifying the buffer isn't a concern in practice.
>
>> +
>> + qemu_iovec_init(&bounce_qiov, 1);
>> + qemu_iovec_add(&bounce_qiov, bounce_buf, bytes);
>> + qiov = &bounce_qiov;
>> +
>> + op = active_write_prepare(s->job, offset, bytes);
>> + }
>> +
>> + ret = bdrv_co_pwritev(bs->backing, offset, bytes, qiov, flags);
>> + if (ret < 0) {
>> + goto out;
>> + }
>> +
>> + if (copy_to_target) {
>> + do_sync_target_write(s->job, offset, bytes, qiov, flags);
>> + }
>> +
>> +out:
>> + if (copy_to_target) {
>> + active_write_settle(op);
>> +
>> + qemu_iovec_destroy(&bounce_qiov);
>> + qemu_vfree(bounce_buf);
>> + }
>> + return ret;
>> }
>>
>> static int coroutine_fn bdrv_mirror_top_flush(BlockDriverState *bs)
>
> Don't you need to update bdrv_mirror_top_pdiscard and bdrv_mirror_top_pwritev
> too?Now that you mention it... Max
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