Re: [Qemu-devel] [PATCH v2 3/7] vmdk: Factor out metadata loading code out of get_cluster_offset()

[Fam Zheng <famz@redhat.com>]

On Sat, 03/25 16:48, Ashijeet Acharya wrote:
> Move the cluster tables loading code out of the existing
> get_cluster_offset() function and implement it in separate

Now it's renamed to vmdk_perform_cow() in previous patch, the commit message
following it should be updated.

> get_cluster_table() and vmdk_L2load() functions. This patch will help
> us avoid code duplication in future patches of this series.
> 
> Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
> ---
>  block/vmdk.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 99 insertions(+)
> 
> diff --git a/block/vmdk.c b/block/vmdk.c
> index f5fda2c..a42322e 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -1037,6 +1037,105 @@ static void vmdk_refresh_limits(BlockDriverState *bs, Error **errp)
>  }
>  
>  /*
> + * vmdk_L2load

Personally, I think vmdk_l2load is good enough, the upper case doesn't add
readability but makes it slightly harder to type.

> + *
> + * Loads a new L2 table into memory. If the table is in the cache, the cache
> + * is used; otherwise the L2 table is loaded from the image file.
> + *
> + * Returns:
> + *   VMDK_OK:       on success
> + *   VMDK_ERROR:    in error cases
> + */
> +static int vmdk_L2load(VmdkExtent *extent, uint64_t offset, int l2_offset,
> +                       uint32_t **new_l2_table, int *new_l2_index)
> +{
> +    int min_index, i, j;
> +    uint32_t *l2_table;
> +    uint32_t min_count;
> +
> +    for (i = 0; i < L2_CACHE_SIZE; i++) {
> +        if (l2_offset == extent->l2_cache_offsets[i]) {
> +            /* increment the hit count */
> +            if (++extent->l2_cache_counts[i] == 0xffffffff) {

Please use UINT32_MAX.

> +                for (j = 0; j < L2_CACHE_SIZE; j++) {
> +                    extent->l2_cache_counts[j] >>= 1;
> +                }
> +            }
> +            l2_table = extent->l2_cache + (i * extent->l2_size);
> +            goto found;
> +        }
> +    }
> +    /* not found: load a new entry in the least used one */
> +    min_index = 0;
> +    min_count = 0xffffffff;

Please use UINT32_MAX.

> +    for (i = 0; i < L2_CACHE_SIZE; i++) {
> +        if (extent->l2_cache_counts[i] < min_count) {
> +            min_count = extent->l2_cache_counts[i];
> +            min_index = i;
> +        }
> +    }
> +    l2_table = extent->l2_cache + (min_index * extent->l2_size);
> +    if (bdrv_pread(extent->file,
> +                (int64_t)l2_offset * 512,
> +                l2_table,
> +                extent->l2_size * sizeof(uint32_t)
> +            ) != extent->l2_size * sizeof(uint32_t)) {
> +        return VMDK_ERROR;
> +    }
> +
> +    extent->l2_cache_offsets[min_index] = l2_offset;
> +    extent->l2_cache_counts[min_index] = 1;
> +found:
> +    *new_l2_index = ((offset >> 9) / extent->cluster_sectors) % extent->l2_size;
> +    *new_l2_table = l2_table;
> +
> +    return VMDK_OK;
> +}
> +
> +/*
> + * get_cluster_table
> + *
> + * for a given offset, load (and allocate if needed) the l2 table.
> + *
> + * Returns:
> + *   VMDK_OK:        on success
> + *
> + *   VMDK_UNALLOC:   if cluster is not mapped
> + *
> + *   VMDK_ERROR:     in error cases
> + */
> +static int get_cluster_table(VmdkExtent *extent, uint64_t offset,
> +                             int *new_l1_index, int *new_l2_offset,
> +                             int *new_l2_index, uint32_t **new_l2_table)

Again, a static function must be introduced with the code change where it is
used, at least for once. It keeps the compiler happy (-Wunused-function) and
makes reviewing easy.

> +{
> +    int l1_index, l2_offset, l2_index;
> +    uint32_t *l2_table;
> +    int ret;
> +
> +    offset -= (extent->end_sector - extent->sectors) * SECTOR_SIZE;
> +    l1_index = (offset >> 9) / extent->l1_entry_sectors;
> +    if (l1_index >= extent->l1_size) {
> +        return VMDK_ERROR;
> +    }
> +    l2_offset = extent->l1_table[l1_index];
> +    if (!l2_offset) {
> +        return VMDK_UNALLOC;
> +    }
> +
> +    ret = vmdk_L2load(extent, offset, l2_offset, &l2_table, &l2_index);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    *new_l1_index = l1_index;
> +    *new_l2_offset = l2_offset;
> +    *new_l2_index = l2_index;
> +    *new_l2_table = l2_table;
> +
> +    return VMDK_OK;
> +}
> +
> +/*
>   * vmdk_perform_cow
>   *
>   * Copy backing file's cluster that covers @sector_num, otherwise write zero,
> -- 
> 2.6.2
> 
> 

Fam