Re: [Qemu-devel] [PATCH v2 4/4] replay: introduce block devices record/replay

From: Stefan Hajnoczi <stefanha@redhat.com>
To: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Cc: edgar.iglesias@xilinx.com, peter.maydell@linaro.org,
	igor.rubinov@gmail.com, mark.burton@greensocs.com,
	real@ispras.ru, hines@cert.org, qemu-devel@nongnu.org,
	maria.klimushenkova@ispras.ru, kwolf@redhat.com,
	pbonzini@redhat.com, batuzovk@ispras.ru, alex.bennee@linaro.org,
	fred.konrad@greensocs.com
Subject: Re: [Qemu-devel] [PATCH v2 4/4] replay: introduce block devices record/replay
Date: Thu, 11 Feb 2016 09:56:05 +0000	[thread overview]
Message-ID: <20160211095605.GB4647@stefanha-x1.localdomain> (raw)
In-Reply-To: <20160210091323.10024.5684.stgit@PASHA-ISP>

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On Wed, Feb 10, 2016 at 12:13:23PM +0300, Pavel Dovgalyuk wrote:
> @@ -784,7 +798,11 @@ BlockAIOCB *blk_aio_flush(BlockBackend *blk,
>          return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM);
>      }
>  
> -    return bdrv_aio_flush(blk->bs, cb, opaque);
> +    if (replay_mode == REPLAY_MODE_NONE) {
> +        return bdrv_aio_flush(blk->bs, cb, opaque);
> +    } else {
> +        return replay_aio_flush(blk->bs, cb, opaque);
> +    }
>  }

I am only looking at this patch in isolation and am not familiar with
the record/replay work, but these changes appear invasive.  In order for
record/replay to keep working in the future, everyone touching block
layer code must be familiar with the principles of how record/replay
works.  This patch does not include documentation.

Can you point me to documentation that explains the how record replay
works?

Thanks,
Stefan

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