Re: [Qemu-devel] [Qemu-block] [PATCH v3] block: Turn on "unmap" in active commit

[Stefan Hajnoczi]

On Tue, Sep 27, 2016 at 07:14:52PM +0800, Fam Zheng wrote:
> We already specified BDRV_O_UNMAP when opening images in 'qemu-img
> commit', but didn't turn on the "unmap" in the active commit job. This
> patch fixes that so that zeroed clusters in top image can be discarded
> which is desired in the virt-sparsify use case, where a temporary
> overlay is created and fstrim'ed before commiting back, to free space in
> the original image.
> 
> This also enables it for block-commit.
> 
> Signed-off-by: Fam Zheng <address@hidden>
> ---
> v3: Change the right parameter.
> v2: Add "unmap" to block-commit as well. [Kevin]
> ---
>  block/mirror.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index f9d1fec..8847ec5 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -1042,7 +1042,7 @@ void commit_active_start(const char *job_id, 
> BlockDriverState *bs,
>  
>      mirror_start_job(job_id, bs, base, NULL, speed, 0, 0,
>                       MIRROR_LEAVE_BACKING_CHAIN,
> -                     on_error, on_error, false, cb, opaque, &local_err,
> +                     on_error, on_error, true, cb, opaque, &local_err,
>                       &commit_active_job_driver, false, base, auto_complete);
>      if (local_err) {
>          error_propagate(errp, local_err);

Why is unmap an option at all?

What's wrong with using BDRV_REQ_MAY_UNMAP on all
blk_aio_pwrite_zeroes() calls?

Stefan

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