Re: [Qemu-block] [PATCH] proto: add 'shift' extension.

[Vladimir Sementsov-Ogievskiy]

On 28.09.2016 11:56, Kevin Wolf wrote:
> Am 28.09.2016 um 10:37 hat Denis V. Lunev geschrieben:
> > On 09/28/2016 11:34 AM, Kevin Wolf wrote:
> > > Am 27.09.2016 um 20:59 hat Denis V. Lunev geschrieben:
> > > > On 09/27/2016 08:04 PM, Paolo Bonzini wrote:
> > > > > On 27/09/2016 15:28, Denis V. Lunev wrote:
> > > > > > On 09/27/2016 03:07 PM, Paolo Bonzini wrote:
> > > > > > > ----- Original Message -----
> > > > > > > > From: "Denis V. Lunev" <address@hidden>
> > > > > > > > To: "Paolo Bonzini" <address@hidden>
> > > > > > > > Cc: "Vladimir Sementsov-Ogievskiy" <address@hidden>, address@hidden, 
> > > > > > > > address@hidden,
> > > > > > > > address@hidden, address@hidden, address@hidden, address@hidden, address@hidden,
> > > > > > > > address@hidden
> > > > > > > > Sent: Tuesday, September 27, 2016 12:25:54 PM
> > > > > > > > Subject: Re: [PATCH] proto: add 'shift' extension.
> > > > > > > >
> > > > > > > > On 09/27/2016 01:15 PM, Paolo Bonzini wrote:
> > > > > > > > > > We could go in a different direction and export flag
> > > > > > > > > > 'has_zero_init' which will report that the storage is
> > > > > > > > > > initialized with all zeroes at the moment. In this
> > > > > > > > > > case mirroring code will not fall into this
> > > > > > > > > > branch.
> > > > > > > > > Why don't you add the zero_init flag to QEMU's NBD driver instead?
> > > > > > > > for all cases without knowing real backend on the server side?
> > > > > > > > I think this would be wrong.
> > > > > > > Add it to the command line, and leave it to libvirt or the user to
> > > > > > > pass "-drive file.driver=nbd,...,file.zero-init=on".
> > > > > > I have started with something very similar for 'drive-mirror' command.
> > > > > > We have added additional flag for this to improve migration speed
> > > > > > and this was rejected.
> > > > > You can add it through the filename path too, through a URI option
> > > > > "nbd://...?zero-init=on".
> > > > >
> > > > > Paolo
> > > > ha, cool idea! Thanks!
> > > What's the advantage of writing "?zero-init=on" instead of
> > > ",zero-init=on"? Doesn't it only add more string parsing code for no
> > > benefit?
> > >
> > > Kevin
> > Here I appreciate the idea to pass command line options in the
> > target file name. Will it be performed via comma or '?' - there
> > is no difference for us. We will check and use what is already
> > implemented.
> >
> > The most important for us is an approach.
> For me, too. With commas it's not part of the file name that must be
> parsed out of the string, but a separate option, which is the much
> cleaner approach.
>
> The good thing is that the conversion of NBD to individual options has
> progressed far enough that you wouldn't even be able to implement the
> URL extension without implementing the separate option, too. :-)
> (Because all the URL parser does is splitting the URL into individual
> options before passing them to nbd_open().)
>
> Kevin

Just note: we can use json instead of url, like this: virsh 
qemu-monitor-command backup-vm 
'{"execute":"drive-backup","arguments":{"device": "disk", "target": 
"json://{\"driver\":\"nbd\",\"host\":\"127.0.0.1\",\"port\":\"10809\",\"zero-init\":\"on\"}", 
"mode": "existing", "sync": "full"}}'

--
Best regards,
Vladimir