Re: [Qemu-devel] [Fwd: [PATCH v2] vpc: Implement bdrv_co_get_block_status()]

[Peter Lieven <pl@kamp.de>]

Am 18.02.2015 um 21:57 schrieb Peter Lieven:
> This implements bdrv_co_get_block_status() for VHD images. This can
> significantly speed up qemu-img convert operation because only with this
> function implemented sparseness can be considered. (Before, converting a
> 1 TB empty image took several minutes for me, now it's instantaneous.)
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/vpc.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 48 insertions(+), 2 deletions(-)
>
> diff --git a/block/vpc.c b/block/vpc.c
> index 7fddbf0..1533b6a 100644
> --- a/block/vpc.c
> +++ b/block/vpc.c
> @@ -597,6 +597,51 @@ static coroutine_fn int vpc_co_write(BlockDriverState
> *bs, int64_t sector_num,
>      return ret;
>  }
>
> +static int64_t coroutine_fn vpc_co_get_block_status(BlockDriverState *bs,
> +        int64_t sector_num, int nb_sectors, int *pnum)
> +{
> +    BDRVVPCState *s = bs->opaque;
> +    VHDFooter *footer = (VHDFooter*) s->footer_buf;
> +    int64_t start, offset, next;
> +    bool allocated;
> +    int n;
> +
> +    if (be32_to_cpu(footer->type) == VHD_FIXED) {
> +        *pnum = nb_sectors;
> +        return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_DATA |
> +               (sector_num << BDRV_SECTOR_BITS);
> +    }
> +
> +    offset = get_sector_offset(bs, sector_num, 0);
> +    start = offset;
> +    allocated = (offset != -1);
> +    *pnum = 0;
> +
> +    do {
> +        /* All sectors in a block are contiguous (without using the
> bitmap) */
> +        n = ROUND_UP(sector_num + 1, s->block_size / BDRV_SECTOR_SIZE)
> +          - sector_num;
> +        n = MIN(n, nb_sectors);
> +
> +        *pnum += n;
> +        sector_num += n;
> +        nb_sectors -= n;
> +        next = start + (*pnum * BDRV_SECTOR_SIZE);
> +
> +        if (nb_sectors == 0) {
> +            break;
> +        }
> +
> +        offset = get_sector_offset(bs, sector_num, 0);
> +    } while ((allocated && offset == next) || (!allocated && offset == -1));
> +
> +    if (allocated) {
> +        return BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | start;
> +    } else {
> +        return 0;

Shouldn't this be

 return BDRV_BLOCK_ZERO;

?

vpc_read memsets all blocks with offset == -1 to 0x00.

Not for this patch, but couldn't we use your new function to signifincantly speed up
reading of continous allocated areas in vpc_read?

Peter