Re: [Qemu-devel] [PATCH] qcow2: Define and use QCOW2_COMPRESSED_SECTOR_SIZE

[Stefano Garzarella]

The patch LGTM, just a comment below.

On Fri, May 10, 2019 at 07:22:54PM +0300, Alberto Garcia wrote:
> When an L2 table entry points to a compressed cluster the space used
> by the data is specified in 512-byte sectors. This size is independent
> from BDRV_SECTOR_SIZE and is specific to the qcow2 file format.
> 
> The QCOW2_COMPRESSED_SECTOR_SIZE constant defined in this patch makes
> this explicit.
> 
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  block/qcow2-cluster.c  |  5 +++--
>  block/qcow2-refcount.c | 25 ++++++++++++++-----------
>  block/qcow2.c          |  3 ++-
>  block/qcow2.h          |  4 ++++
>  4 files changed, 23 insertions(+), 14 deletions(-)
> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 974a4e8656..b36f4aa84a 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -796,8 +796,9 @@ int 
> qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
>          return cluster_offset;
>      }
>  
> -    nb_csectors = ((cluster_offset + compressed_size - 1) >> 9) -
> -                  (cluster_offset >> 9);
> +    nb_csectors =
> +        (cluster_offset + compressed_size - 1) / 
> QCOW2_COMPRESSED_SECTOR_SIZE -
> +        (cluster_offset / QCOW2_COMPRESSED_SECTOR_SIZE);
>  
>      cluster_offset |= QCOW_OFLAG_COMPRESSED |
>                        ((uint64_t)nb_csectors << s->csize_shift);
> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index fa7ac1f7cb..780bd49a00 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -1172,12 +1172,11 @@ void qcow2_free_any_clusters(BlockDriverState *bs, 
> uint64_t l2_entry,
>      switch (ctype) {
>      case QCOW2_CLUSTER_COMPRESSED:
>          {
> -            int nb_csectors;
> -            nb_csectors = ((l2_entry >> s->csize_shift) &
> -                           s->csize_mask) + 1;
> -            qcow2_free_clusters(bs,
> -                (l2_entry & s->cluster_offset_mask) & ~511,
> -                nb_csectors * 512, type);
> +            int64_t offset = (l2_entry & s->cluster_offset_mask)
> +                & QCOW2_COMPRESSED_SECTOR_MASK;
> +            int size = QCOW2_COMPRESSED_SECTOR_SIZE *
> +                (((l2_entry >> s->csize_shift) & s->csize_mask) + 1);

What about using int64_t type for the 'size' variable?
(because the qcow2_free_clusters() 'size' parameter is int64_t)

> +            qcow2_free_clusters(bs, offset, size, type);
>          }
>          break;
>      case QCOW2_CLUSTER_NORMAL:
> @@ -1317,9 +1316,12 @@ int qcow2_update_snapshot_refcount(BlockDriverState 
> *bs,
>                          nb_csectors = ((entry >> s->csize_shift) &
>                                         s->csize_mask) + 1;
>                          if (addend != 0) {
> +                            uint64_t coffset = (entry & 
> s->cluster_offset_mask)
> +                                & QCOW2_COMPRESSED_SECTOR_MASK;
>                              ret = update_refcount(
> -                                bs, (entry & s->cluster_offset_mask) & ~511,
> -                                nb_csectors * 512, abs(addend), addend < 0,
> +                                bs, coffset,
> +                                nb_csectors * QCOW2_COMPRESSED_SECTOR_SIZE,
> +                                abs(addend), addend < 0,
>                                  QCOW2_DISCARD_SNAPSHOT);
>                              if (ret < 0) {
>                                  goto fail;
> @@ -1635,9 +1637,10 @@ static int check_refcounts_l2(BlockDriverState *bs, 
> BdrvCheckResult *res,
>              nb_csectors = ((l2_entry >> s->csize_shift) &
>                             s->csize_mask) + 1;
>              l2_entry &= s->cluster_offset_mask;
> -            ret = qcow2_inc_refcounts_imrt(bs, res,
> -                                           refcount_table, 
> refcount_table_size,
> -                                           l2_entry & ~511, nb_csectors * 
> 512);
> +            ret = qcow2_inc_refcounts_imrt(
> +                bs, res, refcount_table, refcount_table_size,
> +                l2_entry & QCOW2_COMPRESSED_SECTOR_MASK,
> +                nb_csectors * QCOW2_COMPRESSED_SECTOR_SIZE);
>              if (ret < 0) {
>                  goto fail;
>              }
> diff --git a/block/qcow2.c b/block/qcow2.c
> index a520d116ef..80679a84d2 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -4188,7 +4188,8 @@ qcow2_co_preadv_compressed(BlockDriverState *bs,
>  
>      coffset = file_cluster_offset & s->cluster_offset_mask;
>      nb_csectors = ((file_cluster_offset >> s->csize_shift) & s->csize_mask) 
> + 1;
> -    csize = nb_csectors * 512 - (coffset & 511);
> +    csize = nb_csectors * QCOW2_COMPRESSED_SECTOR_SIZE -
> +        (coffset & ~QCOW2_COMPRESSED_SECTOR_MASK);
>  
>      buf = g_try_malloc(csize);
>      if (!buf) {
> diff --git a/block/qcow2.h b/block/qcow2.h
> index fdee297f33..7e796877d6 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -74,6 +74,10 @@
>  #define MIN_CLUSTER_BITS 9
>  #define MAX_CLUSTER_BITS 21
>  
> +/* Defined in the qcow2 spec (compressed cluster descriptor) */
> +#define QCOW2_COMPRESSED_SECTOR_SIZE 512U
> +#define QCOW2_COMPRESSED_SECTOR_MASK (~(QCOW2_COMPRESSED_SECTOR_SIZE - 1))
> +
>  /* Must be at least 2 to cover COW */
>  #define MIN_L2_CACHE_SIZE 2 /* cache entries */
>