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References: <20180118115158.17219-1-edgar.kaziakhmedov@virtuozzo.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <1b55edad-f820-6898-1630-ccc76e6c4845@redhat.com>
Date: Thu, 18 Jan 2018 13:09:42 +0100
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Subject: Re: [Qemu-devel] [PATCH 1/1] nbd: implement bdrv_get_info callback
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To: Edgar Kaziakhmedov <edgar.kaziakhmedov@virtuozzo.com>, qemu-block@nongnu.org
Cc: qemu-devel@nongnu.org, eblake@redhat.com, kwolf@redhat.com, mreitz@redhat.com, den@openvz.org, vsementsov@virtuozzo.com

On 18/01/2018 12:51, Edgar Kaziakhmedov wrote:
> 
> +static int nbd_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
> +{
> +    if (bs->supported_zero_flags & BDRV_REQ_MAY_UNMAP) {
> +        bdi->can_write_zeroes_with_unmap = true;
> +    }
> +    return 0;
> +}
> +

Other drivers set the flag always, while NBD only sets it if the server
knows the flag.

I think NBD is more correct, so:

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

However, it would be nice to remove can_write_zeroes_with_unmap from
BlockDriverInfo, and make bdrv_can_write_zeroes_with_unmap just return
!!(bs->supported_zero_flags & BDRV_REQ_MAY_UNMAP).  Kevin, what do you
think?

Paolo