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From: "Pavel Dovgalyuk" <dovgaluk@ispras.ru>
References: <20160301110732.10104.2019.stgit@PASHA-ISP>
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	<20160309114321.GE5205@noname.redhat.com>
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Date: Thu, 10 Mar 2016 09:15:36 +0300
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Subject: Re: [Qemu-devel] [PATCH v3 5/5] replay: introduce block devices
	record/replay
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To: 'Kevin Wolf' <kwolf@redhat.com>, '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, stefanha@redhat.com, pbonzini@redhat.com, batuzovk@ispras.ru, alex.bennee@linaro.org, fred.konrad@greensocs.com

> From: Kevin Wolf [mailto:kwolf@redhat.com]
> Am 01.03.2016 um 12:08 hat Pavel Dovgalyuk geschrieben:
> > This patch introduces block driver that implement recording
> > and replaying of block devices' operations.
> > All block completion operations are added to the queue.
> > Queue is flushed at checkpoints and information about processed requests
> > is recorded to the log. In replay phase the queue is matched with
> > events read from the log. Therefore block devices requests are processed
> > deterministically.
> >
> > Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
> 
> I like this new version much better than the old one. :-)

Thanks for reviewing!

> > +static int blkreplay_open(BlockDriverState *bs, QDict *options, int flags,
> > +                          Error **errp)
> > +{
> > +    Error *local_err = NULL;
> > +    int ret;
> > +
> > +    /* Open the image file */
> > +    bs->file = bdrv_open_child(NULL, options, "image",
> > +                               bs, &child_file, false, &local_err);
> > +    if (local_err) {
> > +        ret = -EINVAL;
> > +        error_propagate(errp, local_err);
> > +        goto fail;
> > +    }
> > +
> > +    ret = 0;
> > +fail:
> > +    if (ret < 0) {
> > +        bdrv_unref_child(bs, bs->file);
> 
> This is unnecessary because in error cases, bdrv_open_child() returns
> NULL. On the other hand, bdrv_unref_child() accepts a NULL child and
> just doesn't do anything then, so it's harmless.

Right, but this may be useful in case of future changes (if something else
will be initialized here).

Pavel Dovgalyuk