Re: [libvirt] [PATCH v2 2/2] add interface for blkio.weight_device

On Thu, Sep 15, 2011 at 08:53:35AM +0100, Daniel P. Berrange wrote: > On Thu, Sep 15, 2011 at 03:31:48PM +0800, Hu Tao wrote: > > > > + > > > > +/** > > > > + * virDomainBlkioWeightDeviceParseXML > > > > + * > > > > + * this function parses a XML node: > > > > + * > > > > + * <device> > > > > + * <major>major</major> > > > > + * <minor>minor</minor> > > > > + * <weight>weight</weight> > > > > + * </device> > > > > + * > > > > + * and fills a virBlkioWeightDevice struct. > > > > + */ > > > > > > I'm not really seeing the benefit in using major, minor in the XML for > > > this. The <disk> element is using the /dev/hda1 path for the host > > > device, so I'd expect the same path to be usable for the block I/O > > > tuning. > > > > > > How does the scope work here, does major,minor have to refer to a block > > > device, or can it refer to a partition ? If we have multiple <device> > > > elements, each giving a different partition on the same device can we > > > set different weight for each partition ? > > > > blkio doesn't support io control on a partition, so I add major, minor > > to refer to a block device as a whole, rather than utilizing the existing > > <disk> element. > > Hmm, well I think we should still just use the '/dev/hda' block device > path. The major/minor numbers cannot be assumed to be stable across > different hosts, so would break migration. Whereas you can use the > /dev/disk/by-{id,path} symlinks for block paths and thus be migration > safe. Good idea. Thanks for the suggestion. To summarize, the XML describing weight_device like this will be acceptable: <device> <id>by-id</id> (or path here) <weight>weight</weight> </device> Should the <device> be changed into <disk> to remind user that the id is in fact a disk id?