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Date: Thu, 27 Mar 2014 15:17:41 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] block/iscsi: speed up read for unallocated
	sectors
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To: Peter Lieven <pl@kamp.de>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, ronniesahlberg@gmail.com, stefanha@redhat.com

Il 27/03/2014 14:43, Peter Lieven ha scritto:
>
> +static void iscsi_allocationmap_set(IscsiLun *iscsilun, int64_t sector_num,
> +                                    int nb_sectors)
> +{
> +    if (!iscsilun->cluster_sectors) {
> +        return;
> +    }
> +    bitmap_set(iscsilun->allocationmap,
> +               sector_num / iscsilun->cluster_sectors,
> +               DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
> +}
> +
> +static void iscsi_allocationmap_clear(IscsiLun *iscsilun, int64_t sector_num,
> +                                      int nb_sectors)
> +{
> +    if (!iscsilun->cluster_sectors) {
> +        return;
> +    }
> +    bitmap_clear(iscsilun->allocationmap,
> +                 sector_num / iscsilun->cluster_sectors,
> +                 DIV_ROUND_UP(nb_sectors, iscsilun->cluster_sectors));
> +}
> +

Here you need to round the other way, because partial clusters are not 
unmapped:

	cluster_num = DIV_ROUND_UP(sector_num, iscsi->cluster_sectors);
	nb_clusters = (sector_num + nb_sectors) / iscsi->cluster_sectors
		- cluster_num;
	bitmap_clear(iscsilun->allocationmap, cluster_num, nb_clusters);

Paolo