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

[Kevin Wolf]

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