Am 28.02.2013 um 11:23 hat Stefan Hajnoczi geschrieben: > On Wed, Feb 27, 2013 at 06:25:49PM +0100, Kevin Wolf wrote: > > Instead of constantly keeping complaining that we need this big -blockdev > > things, let's start attacking individual parts of the project. Here is the > > first part, allowing block drivers to provide additional -drive options. > > > > Any options that isn't processed by the block layer is passed to the driver > > which can use them. If it doesn't, you get an error message like today. At > > the > > end of this series you can specify: > > > > -drive file=test.qcow2,lazy_refcounts=on > > > > This is still quite rough and more of a quick hack, but I'd like to get some > > feedback on the general approach and for example if at least the user > > interface > > is acceptable. I thought -drive already mixes so many things, messing a bit > > more with it can't make things much worse, but you may disagree. > > Quick comment before diving into the patches: > > The consequence of this syntax is that option name collisions may become > a problem in the future. The chance is low but when you string together > a protocol with a format there is already a chance that both > BlockDrivers want an option. This is the multiple inheritance problem > in object oriented language: did the user mean to set both options? > Just one and which? etc
Yeah, I wasn't planning to allow that. Options are for the format. If you want to address the protocol, we can use a similar syntax as suggested below for backing files, like 'file.discard=ignore'. > However, when we get -blockdev this is no longer an issue. And in the > meantime this patch series seems to add a useful feature. More importantly, I believe it's the only way to get closer to the real -blockdev. We have to do things incrementally. > > Before merging this, I'll look into using QemuOpts a bit more (the manual > > parsing of the option in qcow2 definitely has to go away) and possibly allow > > specifying options for backing files or the protocol as well with a syntax > > like > > "backing.lazy_refcounts=on". If all options starts using this, maybe even > > something like "backing.cache=writeback" could be made to work. > > Introducing a new <foo>.<option> namespace pushes the necessity for > -blockdev farther into the future. Yes, that's the dangerous thing about it. :-) But we can't wait another five years to get the functionality... Kevin
