Re: [Qemu-devel] [RFC V6 18/33] qcow2: Extract qcow2_add_feature and qcow2_remove_feature.

[Stefan Hajnoczi]

On Wed, Feb 06, 2013 at 01:31:51PM +0100, Benoît Canet wrote:
> diff --git a/block/qcow2.c b/block/qcow2.c
> index e48f0b0..ad202fa 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -239,61 +239,72 @@ static void report_unsupported_feature(BlockDriverState 
> *bs,
>  }
>  
>  /*
> - * Sets the dirty bit and flushes afterwards if necessary.
> + * Sets the an incompatible feature bit and flushes afterwards if necessary.
>   *
>   * The incompatible_features bit is only set if the image file header was
>   * updated successfully.  Therefore it is not required to check the return
>   * value of this function.
>   */
> -int qcow2_mark_dirty(BlockDriverState *bs)
> +static int qcow2_add_feature(BlockDriverState *bs,
> +                             QCow2IncompatibleFeature feature)

qcow2_set_incompat_feature() - it only operates on
s->incompatible_features and the name should reflect that.

>  {
>      BDRVQcowState *s = bs->opaque;
>      uint64_t val;
> -    int ret;
> +    int ret = 0;
>  
>      assert(s->qcow_version >= 3);
>  
> -    if (s->incompatible_features & QCOW2_INCOMPAT_DIRTY) {
> -        return 0; /* already dirty */
> +    if (s->incompatible_features & feature) {
> +        return 0; /* already added */
>      }
>  
> -    val = cpu_to_be64(s->incompatible_features | QCOW2_INCOMPAT_DIRTY);
> +    val = cpu_to_be64(s->incompatible_features | feature);
>      ret = bdrv_pwrite(bs->file, offsetof(QCowHeader, incompatible_features),
>                        &val, sizeof(val));
>      if (ret < 0) {
>          return ret;
>      }
> -    ret = bdrv_flush(bs->file);
> -    if (ret < 0) {
> -        return ret;
> -    }
>  
> -    /* Only treat image as dirty if the header was updated successfully */
> -    s->incompatible_features |= QCOW2_INCOMPAT_DIRTY;
> +    /* Only treat image as having the feature if the header was updated
> +     * successfully
> +     */
> +    s->incompatible_features |= feature;
>      return 0;
>  }
>  
> +int qcow2_mark_dirty(BlockDriverState *bs)
> +{
> +    return qcow2_add_feature(bs, QCOW2_INCOMPAT_DIRTY);
> +}

Feel free to replace callers with qcow2_set_incompat_feature(bs,
QCOW2_INCOMPAT_DIRTY) instead of adding a wrapper function.

> +static int qcow2_mark_clean(BlockDriverState *bs)
> +{
> +    return qcow2_remove_feature(bs, QCOW2_INCOMPAT_DIRTY);
> +}

Same here.