Re: [Qemu-devel] [RFC PATCH 03/17] block: add discard properties to BlockDriverInfo

[Kevin Wolf <kwolf@redhat.com>]

Am 08.03.2012 18:15, schrieb Paolo Bonzini:
> In the next patches we will declare the guest's semantics for discard
> to be "always zero the data".  We need to know whether the operation
> need to be emulated or can be passed down.  For this purpose we need
> to know the semantics of the operation and its granularity.
> 
> The granularity may not be related to the cluster size (for example
> "raw" does not have a cluster size), so add it separately.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block.h       |    4 ++++
>  block/qcow2.c |    2 ++
>  qemu-io.c     |    5 ++++-
>  3 files changed, 10 insertions(+), 1 deletions(-)
> 
> diff --git a/block.h b/block.h
> index 48d0bf3..7feda73 100644
> --- a/block.h
> +++ b/block.h
> @@ -15,6 +15,10 @@ typedef struct BlockDriverInfo {
>      int cluster_size;
>      /* offset at which the VM state can be saved (0 if not possible) */
>      int64_t vm_state_offset;
> +    /* whether discard is guaranteed to zero bytes */
> +    bool discard_zeroes_data;
> +    /* discard granularity in sectors */
> +    int discard_granularity;

Why not in bytes? The arbitrary 512 byte units used in the block layer
were probably not the best idea ever and we shouldn't spread it further.

Kevin