Re: [Qemu-devel] [PATCH 03/10] S390: Check Bootdevice Type

[Dominik Dingel]

On Fri, 26 Apr 2013 17:48:37 +0200
Alexander Graf <address@hidden> wrote:

> 
> On 26.04.2013, at 17:42, Christian Borntraeger wrote:
> 
> > On 26/04/13 17:22, Alexander Graf wrote:
> >> 
> >> On 26.04.2013, at 14:12, Dominik Dingel wrote:
> >> 
> >>> Check for a kernel IPL entry and load kernel image if one was
> >>> specified.
> >>> If no kernel image was supplied and the first boot device
> >>> is not a virtio-ccw-blk device, print error message and exit.
> >>> 
> >>> In case it is a virtio-ccw-blk device store the dev_no in reg[7]
> >> 
> >> I thought we want a boot order, not a singular device to boot off of?
> >> 
> >> Alex
> > 
> > First of all we want to be able to choose a boot device as a first step.
> > With this patch the user is able to use libvirt and friends to choose the
> > disk to boot from.
> > 
> > The nice approach with this bios/ipl device is that we can update both
> > in lock-step so this reg7 interface is not an ABI.
> > 
> > So in a future version we actually could:
> > a: implement diag 308 subcode 5/6, which would enable 
> > /sys/devices/firmware/[ipl|reipl]
> > just like on z/VM or LPAR (this allows to reboot from a different device).
> > b: implement a list.
> > 
> > b looks  nice, but I actually prefer a for two reasons:
> > 1. be closer to the real hw
> > 2. predictability
> > but we can certainly discuss this.
> > 
> > So I suggest to go with this patch and implement later on what we
> > agree upon?
> 
> I don't see how having "first device we find" is any better than a rushed 
> interface we need to agree on right before 1.5 hard freeze. Let's just 
> release 1.5 with the very simple one and then go for something awesome in the 
> next version.
> 
> 
> Alex

Okay, I like more the evolution over the revolution kind of approach. So this 
patchset does include a few improvements over the :"boot the first blk device 
we see" system. 
We can specify explicitly with the boot index the device to boot and with 
loadparm even the boot entry. 

And I also see it like Christian that this is not really an interface, as it 
should be never exposed to the outside. We only enable the outside to use boot 
index, which is clearly stated in docs/bootindex.txt and in a later addition we 
will enable fallbacks.

Dominik

Dominik