Re: [Qemu-devel] [PATCH v3 13/39] qcow2: Add l2_slice_size field to BDRVQcow2State

[Max Reitz <mreitz@redhat.com>]

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On 2018-01-26 15:59, Alberto Garcia wrote:
> The BDRVQcow2State structure contains an l2_size field, which stores
> the number of 64-bit entries in an L2 table.
> 
> For efficiency reasons we want to be able to load slices instead of
> full L2 tables, so we need to know how many entries an L2 slice can
> hold.
> 
> An L2 slice is the portion of an L2 table that is loaded by the qcow2
> cache. At the moment that cache can only load complete tables,
> therefore an L2 slice has the same size as an L2 table (one cluster)
> and l2_size == l2_slice_size.
> 
> Later we'll allow smaller slices, but until then we have to use this
> new l2_slice_size field to make the rest of the code ready for that.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>  block/qcow2.c | 3 +++
>  block/qcow2.h | 1 +
>  2 files changed, 4 insertions(+)

Am I missing something or does this patch miss setting l2_slice_size in
qcow2_do_open()?

Max

> diff --git a/block/qcow2.c b/block/qcow2.c
> index e2d4bf7ad5..78f067cae7 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -805,6 +805,7 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
>  typedef struct Qcow2ReopenState {
>      Qcow2Cache *l2_table_cache;
>      Qcow2Cache *refcount_block_cache;
> +    int l2_slice_size; /* Number of entries in a slice of the L2 table */
>      bool use_lazy_refcounts;
>      int overlap_check;
>      bool discard_passthrough[QCOW2_DISCARD_MAX];
> @@ -886,6 +887,7 @@ static int qcow2_update_options_prepare(BlockDriverState *bs,
>          }
>      }
>  
> +    r->l2_slice_size = s->cluster_size / sizeof(uint64_t);
>      r->l2_table_cache = qcow2_cache_create(bs, l2_cache_size);
>      r->refcount_block_cache = qcow2_cache_create(bs, refcount_cache_size);
>      if (r->l2_table_cache == NULL || r->refcount_block_cache == NULL) {
> @@ -1049,6 +1051,7 @@ static void qcow2_update_options_commit(BlockDriverState *bs,
>      }
>      s->l2_table_cache = r->l2_table_cache;
>      s->refcount_block_cache = r->refcount_block_cache;
> +    s->l2_slice_size = r->l2_slice_size;
>  
>      s->overlap_check = r->overlap_check;
>      s->use_lazy_refcounts = r->use_lazy_refcounts;
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 0559afbc63..e0aee88811 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -251,6 +251,7 @@ typedef struct BDRVQcow2State {
>      int cluster_bits;
>      int cluster_size;
>      int cluster_sectors;
> +    int l2_slice_size;
>      int l2_bits;
>      int l2_size;
>      int l1_size;
> 



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