Re: [Qemu-devel] [PATCH 1/2] qcow2: Drop REFCOUNT_SHIFT

["Benoît Canet" <benoit.canet@irqsave.net>]

The Friday 29 Aug 2014 à 23:45:26 (+0200), Max Reitz wrote :
> With BDRVQcowState.refcount_block_bits, we don't need REFCOUNT_SHIFT
> anymore.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2-refcount.c | 32 ++++++++++++++------------------
>  block/qcow2.c          |  2 +-
>  block/qcow2.h          |  2 --
>  3 files changed, 15 insertions(+), 21 deletions(-)
> 
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 29136ee..cd6f5a0 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -102,7 +102,7 @@ static int get_refcount(BlockDriverState *bs, int64_t cluster_index)
>      uint16_t *refcount_block;
>      uint16_t refcount;
>  
> -    refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
> +    refcount_table_index = cluster_index >> s->refcount_block_bits;
>      if (refcount_table_index >= s->refcount_table_size)
>          return 0;
>      refcount_block_offset =
> @@ -116,8 +116,7 @@ static int get_refcount(BlockDriverState *bs, int64_t cluster_index)
>          return ret;
>      }
>  
> -    block_index = cluster_index &
> -        ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
> +    block_index = cluster_index & (s->refcount_block_size - 1);
>      refcount = be16_to_cpu(refcount_block[block_index]);
>  
>      ret = qcow2_cache_put(bs, s->refcount_block_cache,
> @@ -152,8 +151,8 @@ static unsigned int next_refcount_table_size(BDRVQcowState *s,
>  static int in_same_refcount_block(BDRVQcowState *s, uint64_t offset_a,
>      uint64_t offset_b)
>  {
> -    uint64_t block_a = offset_a >> (2 * s->cluster_bits - REFCOUNT_SHIFT);
> -    uint64_t block_b = offset_b >> (2 * s->cluster_bits - REFCOUNT_SHIFT);
> +    uint64_t block_a = offset_a >> (s->cluster_bits + s->refcount_block_bits);
> +    uint64_t block_b = offset_b >> (s->cluster_bits + s->refcount_block_bits);
>  
>      return (block_a == block_b);
>  }
> @@ -174,7 +173,7 @@ static int alloc_refcount_block(BlockDriverState *bs,
>      BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC);
>  
>      /* Find the refcount block for the given cluster */
> -    refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
> +    refcount_table_index = cluster_index >> s->refcount_block_bits;
>  
>      if (refcount_table_index < s->refcount_table_size) {
>  
> @@ -243,7 +242,7 @@ static int alloc_refcount_block(BlockDriverState *bs,
>  
>          /* The block describes itself, need to update the cache */
>          int block_index = (new_block >> s->cluster_bits) &
> -            ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
> +            (s->refcount_block_size - 1);
>          (*refcount_block)[block_index] = cpu_to_be16(1);
>      } else {
>          /* Described somewhere else. This can recurse at most twice before we
> @@ -315,8 +314,7 @@ static int alloc_refcount_block(BlockDriverState *bs,
>      BLKDBG_EVENT(bs->file, BLKDBG_REFTABLE_GROW);
>  
>      /* Calculate the number of refcount blocks needed so far */
> -    uint64_t refcount_block_clusters = 1 << (s->cluster_bits - REFCOUNT_SHIFT);
> -    uint64_t blocks_used = DIV_ROUND_UP(cluster_index, refcount_block_clusters);
> +    uint64_t blocks_used = DIV_ROUND_UP(cluster_index, s->refcount_block_size);
>  
>      if (blocks_used > QCOW_MAX_REFTABLE_SIZE / sizeof(uint64_t)) {
>          return -EFBIG;
> @@ -330,14 +328,14 @@ static int alloc_refcount_block(BlockDriverState *bs,
>          uint64_t table_clusters =
>              size_to_clusters(s, table_size * sizeof(uint64_t));
>          blocks_clusters = 1 +
> -            ((table_clusters + refcount_block_clusters - 1)
> -            / refcount_block_clusters);
> +            ((table_clusters + s->refcount_block_size - 1)
> +            / s->refcount_block_size);
>          uint64_t meta_clusters = table_clusters + blocks_clusters;
>  
>          last_table_size = table_size;
>          table_size = next_refcount_table_size(s, blocks_used +
> -            ((meta_clusters + refcount_block_clusters - 1)
> -            / refcount_block_clusters));
> +            ((meta_clusters + s->refcount_block_size - 1)
> +            / s->refcount_block_size));
>  
>      } while (last_table_size != table_size);
>  
> @@ -347,7 +345,7 @@ static int alloc_refcount_block(BlockDriverState *bs,
>  #endif
>  
>      /* Create the new refcount table and blocks */
> -    uint64_t meta_offset = (blocks_used * refcount_block_clusters) *
> +    uint64_t meta_offset = (blocks_used * s->refcount_block_size) *
>          s->cluster_size;
>      uint64_t table_offset = meta_offset + blocks_clusters * s->cluster_size;
>      uint64_t *new_table = g_try_new0(uint64_t, table_size);
> @@ -546,8 +544,7 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
>      {
>          int block_index, refcount;
>          int64_t cluster_index = cluster_offset >> s->cluster_bits;
> -        int64_t table_index =
> -            cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
> +        int64_t table_index = cluster_index >> s->refcount_block_bits;
>  
>          /* Load the refcount block and allocate it if needed */
>          if (table_index != old_table_index) {
> @@ -569,8 +566,7 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
>          qcow2_cache_entry_mark_dirty(s->refcount_block_cache, refcount_block);
>  
>          /* we can update the count and save it */
> -        block_index = cluster_index &
> -            ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
> +        block_index = cluster_index & (s->refcount_block_size - 1);
>  
>          refcount = be16_to_cpu(refcount_block[block_index]);
>          refcount += addend;
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 82bca88..cdbcb81 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1799,7 +1799,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
>          .l1_size                    = cpu_to_be32(0),
>          .refcount_table_offset      = cpu_to_be64(cluster_size),
>          .refcount_table_clusters    = cpu_to_be32(1),
> -        .refcount_order             = cpu_to_be32(3 + REFCOUNT_SHIFT),
> +        .refcount_order             = cpu_to_be32(4),
>          .header_length              = cpu_to_be32(sizeof(*header)),
>      };
>  
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 7c01fb7..5b099cb 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -59,8 +59,6 @@
>  /* The cluster reads as all zeros */
>  #define QCOW_OFLAG_ZERO (1ULL << 0)
>  
> -#define REFCOUNT_SHIFT 1 /* refcount size is 2 bytes */
> -
>  #define MIN_CLUSTER_BITS 9
>  #define MAX_CLUSTER_BITS 21
>  
> -- 
> 2.1.0
> 
> 

Putting Jun Li in copy because he just wrote a patch using it.