Re: [Qemu-devel] [PATCH v2 1/3] block: add basic backup support to block driver

[Fam Zheng <famz@redhat.com>]

On Mon, 04/29 09:42, Stefan Hajnoczi wrote:
> +
> +static void coroutine_fn backup_run(void *opaque)
> +{
> +    BackupBlockJob *job = opaque;
> +    BlockDriverState *bs = job->common.bs;
> +    assert(bs);
> +
> +    int64_t start, end;
> +
> +    start = 0;
> +    end = DIV_ROUND_UP(bdrv_getlength(bs) / BDRV_SECTOR_SIZE,
> +                       BACKUP_BLOCKS_PER_CLUSTER);
> +
> +    job->bitmap = hbitmap_alloc(end, 0);
> +
> +    DPRINTF("backup_run start %s %" PRId64 " %" PRId64 "\n",
> +            bdrv_get_device_name(bs), start, end);
> +
> +    int ret = 0;
> +
> +    for (; start < end; start++) {
> +        if (block_job_is_cancelled(&job->common)) {
> +            ret = -1;
> +            break;
> +        }
> +
> +        /* we need to yield so that qemu_aio_flush() returns.
> +         * (without, VM does not reboot)
> +         */
> +        if (job->common.speed) {
> +            uint64_t delay_ns = ratelimit_calculate_delay(
> +                &job->limit, job->sectors_read);
> +            job->sectors_read = 0;
> +            block_job_sleep_ns(&job->common, rt_clock, delay_ns);
> +        } else {
> +            block_job_sleep_ns(&job->common, rt_clock, 0);
> +        }
> +
> +        if (block_job_is_cancelled(&job->common)) {
> +            ret = -1;
> +            break;
> +        }
> +
> +        if (hbitmap_get(job->bitmap, start)) {
> +            continue; /* already copied */
> +        }
> +
> +        DPRINTF("backup_run loop C%" PRId64 "\n", start);
> +
> +        /**
> +         * This triggers a cluster copy
> +         * Note: avoid direct call to brdv_co_backup_cow, because
> +         * this does not call tracked_request_begin()
> +         */
> +        ret = bdrv_co_backup(bs, start*BACKUP_BLOCKS_PER_CLUSTER, 1);
> +        if (ret < 0) {
> +            break;
> +        }
> +        /* Publish progress */
> +        job->common.offset += BACKUP_CLUSTER_SIZE;
> +    }
> +
> +    /* wait until pending backup_do_cow()calls have completed */
> +    qemu_co_rwlock_wrlock(&job->rwlock);
> +    qemu_co_rwlock_unlock(&job->rwlock);
> +
> +    hbitmap_free(job->bitmap);
> +
> +    bdrv_delete(job->target);
> +
> +    DPRINTF("backup_run complete %d\n", ret);
> +    block_job_completed(&job->common, ret);
> +}

What will ret value be when the source block is not aligned to cluster
size?

Fam