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

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.