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Date: Tue, 28 Jun 2016 13:47:07 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 07/11] block: optimization
 blk_pwrite_compressed()
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To: "Denis V. Lunev" <den@openvz.org>
Cc: qemu-devel@nongnu.org, Pavel Butsykin <pbutsykin@virtuozzo.com>, Jeff Cody <jcody@redhat.com>, Markus Armbruster <armbru@redhat.com>, Eric Blake <eblake@redhat.com>, John Snow <jsnow@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>

Am 31.05.2016 um 11:15 hat Denis V. Lunev geschrieben:
> From: Pavel Butsykin <pbutsykin@virtuozzo.com>
> 
> For bdrv_pwrite_compressed() it looks like most of the code creating coroutine
> is duplicated in blk_prw(). So we can just add a flag(BDRV_REQ_WRITE_COMPRESSED)
> and use the blk_prw() as a generic one.
> 
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Jeff Cody <jcody@redhat.com>
> CC: Markus Armbruster <armbru@redhat.com>
> CC: Eric Blake <eblake@redhat.com>
> CC: John Snow <jsnow@redhat.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Kevin Wolf <kwolf@redhat.com>

Oh, so you already do use a flag. Nice. :-)

> diff --git a/block/block-backend.c b/block/block-backend.c
> index 3c1fc50..9e1c793 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -785,7 +785,11 @@ int coroutine_fn blk_co_pwritev(BlockBackend *blk, int64_t offset,
>          flags |= BDRV_REQ_FUA;
>      }
>  
> -    return bdrv_co_pwritev(blk_bs(blk), offset, bytes, qiov, flags);
> +    if (flags & BDRV_REQ_WRITE_COMPRESSED) {
> +        return bdrv_co_pwritev_compressed(blk_bs(blk), offset, bytes, qiov);
> +    } else {
> +        return bdrv_co_pwritev(blk_bs(blk), offset, bytes, qiov, flags);
> +    }
>  }

If you move the processing of the flag inside bdrv_co_pwritev(), where I
think it belongs anyway, you could use the flag from the start (by going
through bdrv_prwv_co()) instead of temporarily introducing your own
coroutine wrapper. I think that would make the initial conversion
patches quite a bit simpler.

Kevin