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Re: [Qemu-block] [PATCH 1/1] mirror: fix improperly filled copy_bitmap f
From: |
Jeff Cody |
Subject: |
Re: [Qemu-block] [PATCH 1/1] mirror: fix improperly filled copy_bitmap for mirror block job |
Date: |
Wed, 7 Sep 2016 02:15:44 -0400 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Tue, Sep 06, 2016 at 06:11:19PM +0300, Denis V. Lunev wrote:
> bdrv_is_allocated_above() returns true in the case if qcow2 even for
> completely zeroed areas as BDRV_BLOCK_ALLOCATED flag is set in both
> cases.
Hi Denis,
Not just qcow2. BDRV_BLOCK_ALLOCATED for a layer means the content of the
block is defined by that layer (even if that is a zero block, that doesn't
mean it is unallocated). This applies to all image formats.
> Though we have completely zeroed out the image just above or it was
> already zeroed.
This is only true if we are in 'sync = full' mode.
> The patch stops using bdrv_is_allocated_above() wrapper and switches to
> bdrv_get_block_status_above() to distinguish zeroed areas and areas with
> data to avoid extra IO operations, which could be VERY slow.
For 'sync = top', we need to make sure to appropriately allocate the sector,
even if it is BDRV_BLOCK_ZERO.
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Jeff Cody <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Max Reitz <address@hidden>
> ---
> block/mirror.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/block/mirror.c b/block/mirror.c
> index e0b3f41..87edbd8 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -552,7 +552,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob
> *s)
> BlockDriverState *base = s->base;
> BlockDriverState *bs = blk_bs(s->common.blk);
> BlockDriverState *target_bs = blk_bs(s->target);
> - int ret, n;
> + int n;
>
> end = s->bdev_length / BDRV_SECTOR_SIZE;
>
> @@ -590,6 +590,8 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob
> *s)
> /* Just to make sure we are not exceeding int limit. */
> int nb_sectors = MIN(INT_MAX >> BDRV_SECTOR_BITS,
> end - sector_num);
> + int64_t status;
> + BlockDriverState *file;
>
> mirror_throttle(s);
>
> @@ -597,13 +599,14 @@ static int coroutine_fn
> mirror_dirty_init(MirrorBlockJob *s)
> return 0;
> }
>
> - ret = bdrv_is_allocated_above(bs, base, sector_num, nb_sectors, &n);
> - if (ret < 0) {
> - return ret;
> + status = bdrv_get_block_status_above(bs, base, sector_num,
> + nb_sectors, &n, &file);
> + if (status < 0) {
> + return status;
> }
>
> assert(n > 0);
> - if (ret == 1) {
> + if (status & BDRV_BLOCK_DATA) {
I think this patch would work if this was changed to something like this:
mark_dirty = base == NULL ? status & BDRV_BLOCK_DATA : /* 'full' */
status & BDRV_BLOCK_ALLOCATED;
if (mark_dirty) {
Thanks,
Jeff
> bdrv_set_dirty_bitmap(s->dirty_bitmap, sector_num, n);
> }
> sector_num += n;
> --
> 2.7.4
>