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Date: Mon, 20 May 2013 13:30:37 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to
	block driver
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org, dietmar@proxmox.com, imain@redhat.com, xiawenc@linux.vnet.ibm.com

Il 15/05/2013 16:34, Stefan Hajnoczi ha scritto:
> +    wait_for_overlapping_requests(job, start, end);
> +    cow_request_begin(&cow_request, job, start, end);
> +
> +    for (; start < end; start++) {
> +        if (hbitmap_get(job->bitmap, start)) {
> +            DPRINTF("brdv_co_backup_cow skip C%" PRId64 "\n", start);
> +            continue; /* already copied */
> +        }
> +
> +        /* immediately set bitmap (avoid coroutine race) */
> +        hbitmap_set(job->bitmap, start, 1);
> +

HBitmap already has code for finding the next set bit, but you're not
using it.

If you reverse the direction of the bitmap, you can use an HBitmapIter here:

> 
> +    start = 0;
> +    end = DIV_ROUND_UP(bdrv_getlength(bs) / BDRV_SECTOR_SIZE,
> +                       BACKUP_BLOCKS_PER_CLUSTER);
> +
> +    job->bitmap = hbitmap_alloc(end, 0);
> +
> +    before_write = bdrv_add_before_write_cb(bs, backup_before_write);
> +
> +    DPRINTF("backup_run start %s %" PRId64 " %" PRId64 "\n",
> +            bdrv_get_device_name(bs), start, end);
> +
> +    for (; start < end; start++) {

... instead of iterating through each item manually.

Paolo

> +        if (block_job_is_cancelled(&job->common)) {
> +            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)) {
> +            break;
> +        }
> +
> +        DPRINTF("backup_run loop C%" PRId64 "\n", start);
> +
> +        ret = backup_do_cow(bs, start * BACKUP_BLOCKS_PER_CLUSTER, 1);
> +        if (ret < 0) {
> +            break;
> +        }
> +
> +        /* Publish progress */
> +        job->common.offset += BACKUP_CLUSTER_SIZE;
> +    }