Re: [Qemu-devel] [RFC]virtio-blk: add disk-name device property

[Fam Zheng]

On Thu, 01/12 15:39, Yang Zhang wrote:
> On 2017/1/12 10:22, Fam Zheng wrote:
> > On Thu, 01/12 09:22, Yang Zhang wrote:
> > > On 2017/1/4 22:44, Stefan Hajnoczi wrote:
> > > > On Tue, Jan 03, 2017 at 10:53:06AM -0600, Eric Blake wrote:
> > > > > On 12/29/2016 08:41 PM, Junkang Fu wrote:
> > > > > > >From 74e913fc41ea98d1dde692175f1e3fb6729342aa Mon Sep 17 00:00:00 
> > > > > > >2001
> > > > > > From: "junkang.fjk" <address@hidden>
> > > > > > Date: Wed, 24 Aug 2016 19:36:53 +0800
> > > > > > Subject: [PATCH] virtio-blk: add disk-name device property
> > > > > > 
> > > > > > Current virtio-blk disk name(ex. /dev/vdb) has nothing to do with 
> > > > > > the
> > > > > > target dev
> > > > > > name specified in libvirt xml file. For example, we may get disk 
> > > > > > name
> > > > > > /dev/vdb in
> > > > > > VM while target dev specified in libvirt xml is vdc.
> > > > > 
> > > > > It's not really libvirt's fault.  The libvirt XML names are for
> > > > > convenience, but nothing on the host side requires the guest to pick 
> > > > > the
> > > > > same naming scheme as the host.
> > > > > 
> > > > > I guess your proposal is to enhance the virtio spec such that clients
> > > > > that are new enough to honor the new addition to the virtio spec will
> > > > > change their name-picking algorithm to use the name provided by the
> > > > > host, rather than their current approach of picking whatever name they
> > > > > feel like, and then enhance libvirt to pass the XML name on down to 
> > > > > the
> > > > > guest?  It might work, but as others have pointed out, it will 
> > > > > require a
> > > > > virtio spec change first.
> > > > 
> > > > This change is unnecessary.  The -device virtio-blk-pci,serial= property
> > > > already exists for this purpose.
> > > 
> > > how about the /dev/vdabc? I guess lots of people prefer to use it instead 
> > > of
> > > /dev/disk/by-id/xxx?
> > 
> > I disagree. Using /dev/sdX has exactly the same issue and that's why fstab 
> > and
> > boot loader etc almost always use UUID or disk label by default because 
> > they are
> > more stable.
> 
> I mean does it also change the /dev/sdX to the name specified in serial=sdX
> or it just show the name under /dev/disk/by-id/

I was saying on real hardware, sata disks can have unstable /dev/sdX naming
across reboots if you add or remove disks on the controller, or add or remove
HBA.

Fam