Re: [for-4.2 PATCH 3/6] replay: update docs for record/replay with block devices

[Kevin Wolf <kwolf@redhat.com>]

Am 11.10.2019 um 08:10 hat Pavel Dovgalyuk geschrieben:
> > From: Kevin Wolf [mailto:kwolf@redhat.com]
> > Am 25.09.2019 um 11:02 hat Pavel Dovgalyuk geschrieben:
> > > I started playing with -blockdev: added new blockdev for blkreplay and
> > > constructed the following command line:
> > >
> > > -blockdev driver=file,filename=disk.img,node-name=hd0
> > > -blockdev driver=blkreplay,file=hd0,node-name=hd0-rr
> > > -device virtio-blk-device,drive=hd0-rr
> > >
> > > However, I get an error: "Could not open 'disk.img': Permission denied"
> > > Everything works when I use this file in '-drive' parameter.
> > > What am I doing wrong?
> > 
> > The reason why I didn't reply immediately is because I don't see
> > anything wrong in the options you used.
> > 
> > Just to confirm, do you still get the same error when you use only the
> > first -blockdev option and no other options at all?
> 
> Ok, I tried again and got different error, which was caused by incorrect
> QAPI schema for blkreplay.
> Now it seems ok, but I still can't boot.

Hm... Are you actually using a raw image? If not, you need the format
driver, too, and would end up with something like:

 -blockdev driver=file,filename=disk.qcow2,node-name=hd0
 -blockdev driver=qcow2,file=hd0,node-name=hd0-qcow2
 -blockdev driver=blkreplay,file=hd0-qcow2,node-name=hd0-rr
 -device virtio-blk-device,drive=hd0-rr

(The first two can be combined into a single option by using a syntax
like file.driver=file,file.filename=disk.qcow2, but defining each node
separately is a bit cleaner.)

> > I've now tried out the options you gave, and it does fail for me, but
> > with a different error:
> > 
> >     qemu-system-x86_64: -blockdev driver=blkreplay,file=hd0,node-name=hd0-rr: Invalid
> > parameter 'blkreplay'
> > 
> > This one is because the QAPI schema doesn't know blkreplay and should
> > easily be fixed by adding a blkreplay field to BlockdevOptions.
> 
> Right, I added the following schema:
> 
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2832,8 +2832,8 @@
>  # Since: 2.9
>  ##
>  { 'enum': 'BlockdevDriver',
> -  'data': [ 'blkdebug', 'blklogwrites', 'blkverify', 'bochs', 'cloop',
> -            'copy-on-read', 'dmg', 'file', 'ftp', 'ftps', 'gluster',
> +  'data': [ 'blkdebug', 'blklogwrites', 'blkreplay', 'blkverify', 'bochs',
> +            'cloop', 'copy-on-read', 'dmg', 'file', 'ftp', 'ftps', 'gluster',
>              'host_cdrom', 'host_device', 'http', 'https', 'iscsi', 'luks',
>              'nbd', 'nfs', 'null-aio', 'null-co', 'nvme', 'parallels', 'qcow',
>              'qcow2', 'qed', 'quorum', 'raw', 'rbd',

Please add a '@blkreplay: Since 4.2' note to the comment, too.

> @@ -3446,6 +3446,18 @@
>    'data': { 'test': 'BlockdevRef',
>              'raw': 'BlockdevRef' } }
>  
> +##
> +# @BlockdevOptionsBlkreplay:
> +#
> +# Driver specific block device options for blkreplay.
> +#
> +# @image:     disk image which should be controlled with blkreplay
> +#
> +# Since: 4.2
> +##
> +{ 'struct': 'BlockdevOptionsBlkreplay',
> +  'data': { 'image': 'BlockdevRef' } }
> +
>  ##
>  # @QuorumReadPattern:
>  #
> @@ -3973,6 +3985,7 @@
>        'blkdebug':   'BlockdevOptionsBlkdebug',
>        'blklogwrites':'BlockdevOptionsBlklogwrites',
>        'blkverify':  'BlockdevOptionsBlkverify',
> +      'blkreplay':  'BlockdevOptionsBlkreplay',
>        'bochs':      'BlockdevOptionsGenericFormat',
>        'cloop':      'BlockdevOptionsGenericFormat',
>        'copy-on-read':'BlockdevOptionsGenericFormat',

Otherwise, this looks good to me. Can you turn it into a proper patch?

> > As soft freeze is coming closer, I'm considering taking this series as
> > it is (it's wrong in parts, but the old state is probably even more
> > wrong) and letting you fix up these checks on top. What do you think?
> 
> That sounds reasonable.

Okay, then that's what I will do.

Kevin