Re: [Qemu-devel] [PATCH 2/6] qcow2: simplify qcow2_cache_put() and qcow2_cache_entry_mark_dirty()

[Eric Blake <eblake@redhat.com>]

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On 04/30/2015 04:11 AM, Alberto Garcia wrote:
> Since all tables are now stored together, it is possible to obtain
> the position of a particular table directly from its address, so the
> operation becomes O(1).
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/qcow2-cache.c | 22 +++++-----------------
>  1 file changed, 5 insertions(+), 17 deletions(-)
> 
> diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
> index 586880b..d3274f4 100644
> --- a/block/qcow2-cache.c
> +++ b/block/qcow2-cache.c
> @@ -335,16 +335,12 @@ int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
>  
>  int qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table)
>  {
> -    int i;
> +    int i = (*table - c->table_array) / c->table_size;

Arithmetic on void* is not portable.

>  void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table)
>  {
> -    int i;
> -
> -    for (i = 0; i < c->size; i++) {
> -        if (table_addr(c, i) == table) {
> -            goto found;
> -        }
> -    }
> -    abort();
> -
> -found:
> +    int i = (table - c->table_array) / c->table_size;

and again.

> +    assert(c->entries[i].offset != 0);
>      c->entries[i].dirty = true;
>  }
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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