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Date: Mon, 01 Jun 2015 18:10:12 +0200
From: Max Reitz <mreitz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/3] qcow2: Set MIN_L2_CACHE_SIZE to 2
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To: qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-stable@nongnu.org, Alberto Garcia <berto@igalia.com>, qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>

On 01.06.2015 18:09, Max Reitz wrote:
> The L2 cache must cover at least two L2 tables, because during COW two
> L2 tables are accessed simultaneously.
>
> Reported-by: Alexander Graf <agraf@suse.de>
> Cc: qemu-stable <qemu-stable@nongnu.org>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>   block/qcow2.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 0076512..aa20022 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -62,7 +62,8 @@
>   #define MIN_CLUSTER_BITS 9
>   #define MAX_CLUSTER_BITS 21
>   
> -#define MIN_L2_CACHE_SIZE 1 /* cluster */
> +/* Must be at least 2 to cover COW */
> +#define MIN_L2_CACHE_SIZE 2 /* clusters */
>   
>   /* Must be at least 4 to cover all cases of refcount table growth */
>   #define MIN_REFCOUNT_CACHE_SIZE 4 /* clusters */

Of course git send-email ignored the qemu-stable line... CC-ing manually.

Max