Re: [Qemu-devel] [PATCH 07/12] block: introduce bdrv_zeroize

[Peter Lieven <pl@kamp.de>]

On 13.09.2013 12:25, Peter Lieven wrote:
> this patch adds a call to completely zero out a block device.
> the operation is speed up by checking the block status and
> only writing zeroes to the device if they currently do not
> return zeroes. optionally the zero writing can be speed up
> by setting the flag BDRV_REQ_MAY_UNMAP to emulate the zero
> write by unmapping if the driver supports it.
>
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>   block.c               |   45 +++++++++++++++++++++++++++++++++++++++++++++
>   include/block/block.h |    1 +
>   2 files changed, 46 insertions(+)
>
> diff --git a/block.c b/block.c
> index 6f498fc..76a6621 100644
> --- a/block.c
> +++ b/block.c
> @@ -2342,6 +2342,51 @@ int bdrv_write_zeroes(BlockDriverState *bs, int64_t sector_num,
>                         BDRV_REQ_ZERO_WRITE | flags);
>   }
>   
> +int bdrv_zeroize(BlockDriverState *bs, BdrvRequestFlags flags)
> +{
> +    BlockDriverInfo bdi;
> +    int64_t target_size = bdrv_getlength(bs) / BDRV_SECTOR_SIZE;
> +    int64_t ret, nb_sectors, sector_num = 0;
> +    int n;
> +    /* split the write requests into 1MB chunks if the driver
> +     * does not return a maximal size via bdi */
> +    int max_write_zeroes = 1 << (20 - BDRV_SECTOR_BITS);
> +    if (bdrv_get_info(bs, &bdi) == 0 &&
> +        bdi.max_write_zeroes > 0) {
> +        max_write_zeroes = bdi.max_write_zeroes;
> +    }
> +    for (;;) {
> +        nb_sectors = target_size - sector_num;
> +        if (nb_sectors <= 0) {
> +            return 0;
> +        }
> +        if (nb_sectors > INT_MAX) {
> +            nb_sectors = INT_MAX;
> +        }
> +        ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &n);
forgot to check for ret < 0 here.

Peter