Re: [Xen-devel] [RFC] Virtual disk configuration, PV vs. emulated, backward compatibility etc

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Tue, 2010-07-27 at 21:41 +0100, Pasi KÃrkkÃinen wrote:
> > Backward compatible disk configuration
> > --------------------------------------
> > 
> > Given the above configuration options several short hands are
> defined
> > for backwards compatibility with existing configuration files and
> > guests.
> > 
> > These will be implemented by a straight textual substitution before
> > parsing the configuration.
> > 
> >         hda => d0p0,pv=true,emul=ide0.0,_vdevice=3:0
> >         hdb => d1p0,pv=true,emul=ide0.1,_vdevice=3:64
> >         hdc => d2p0,pv=true,emul=ide1.0,_vdevice=22:0
> >         hdd => d3p0,pv=true,emul=ide1.1,_vdevice=22:64
> > 
> >         xvda => d0p0,pv=true,emul=_ide0.0,_vdevice=202:0
> >         xvdb => d1p0,pv=true,emul=_ide0.1,_vdevice=202:16
> >         xvdc => d2p0,pv=true,emul=_ide1.0,_vdevice=202:32
> >         xvdd => d3p0,pv=true,emul=_ide1.1,_vdevice=202:64
> >         xvde => d4p0,pv=true,emul=none,_vdevice=202:80
> >         ...
> >         xvdo => d15p0,pv=true,emul=none,_vdevice=202:240
> >         xvdp => d16p0,pv=true,emul=none
> >         ...
> >         xvdz => d25,pv=true,emul=none
> >         
> >         xvda[1..15] =>
> >         d0p[1..15],pv=true,emul=_ide0.0,_vdevice=202:[0..15]
> >         xvdb[1..15] => etc
> > 
> > Note that all the above are Linux (guest) specific.
> > 
> > The sd* syntax is not covered. It's unclear if this is used in the 
> > wild or what the existing semantics of emul= are for SCSI devices.
> > If someone cares to investigate the existing behaviour then it can 
> > be added.
> >
> 
> sd* devices are still often used for Xen PV domUs..
> (yeah, people should use xvd*, but many people still have sd*). 

Thanks. We can therefore add to the shorthands (emul=none unless anyone
knows better):

        sda => d0p0,pv=true,emul=none,_vdevice=8:0
        sdb => d1p0,pv=true,emul=none,_vdevice=8:16
        sdc => d2p0,pv=true,emul=none,_vdevice=8:32
        sdd => d3p0,pv=true,emul=none,_vdevice=8:48
        ...
        sdp => d15p0,pv=true,emul=none,_vdevice=8:240
        sdq => d16p0,pv=true,emul=none,_vdevice=65:0
        sdr => d17p0,pv=true,emul=none,_vdevice=65:16
        ... etc through:
        ... ... major 65 (sdq ->sdaf)
        ... ... major 66 (sdag->sdav)
        ... ... major 67 (sdaw->sdbl)
        ... ... major 68 (sdbm->sdcr)
        ... ... major 69 (sdcc->sdcr)
        ... ... major 70 (sdcs->sddh)
        ... ... major 71 (sddi->sddx)
        sddx => d127p0,pv=true,emul=none,_vdevice=71:240

(perhaps supporting all these is overkill ;-))

Ian. 


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