Re: [Qemu-devel] [Qemu PATCH v2] add a boot option to do strict boot

[Amos Kong]

On Wed, Jan 09, 2013 at 08:14:07AM -0700, Eric Blake wrote:
> On 01/09/2013 01:39 AM, Amos Kong wrote:
> > Current seabios will try to boot from selected devices first,
> > if they are all failed, seabios will also try to boot from
> > un-selected devices.
> > 
> > We need to make it configurable. I already posted a seabios
> > patch to add a new device type to halt booting. Qemu can add
> > "HALT" at the end of bootindex string, then seabios will halt
> > booting after trying to boot from selected devices.
> > 
> > This option only effects when boot priority is changed by
> > bootindex options, the old style(-boot order=..) will still
> > try to boot from un-selected devices.
> > 
> > v2: add HALT entry in get_boot_devices_list()
> >     define boot_strict to bool
> > 
> > Signed-off-by: Amos Kong <address@hidden>
> > ---
> 
> Libvirt will need to expose an attribute that lets the user control
> whether to use this new option; how do we probe via QMP whether the new
> -boot strict=on command-line option is available?


Old style to adjust boot priority by order parameter:
-boot order=n,strict=on (BAD, unselected devices will be tried)

New style to adjust boot priority by bootindex:
-device virtio-net-pci,...,bootindex=1 -boot strict=on (OK)

We only want strict option to support new style.

(those two styles are implemented in two different way insider
seabios, the latest simple patch only changed the bootindex way)
 
> > +++ b/qemu-options.hx
> > @@ -376,14 +376,14 @@ ETEXI
> >  
> >  DEF("boot", HAS_ARG, QEMU_OPTION_boot,
> >      "-boot [order=drives][,once=drives][,menu=on|off]\n"
> > -    "      
> > [,splash=sp_name][,splash-time=sp_time][,reboot-timeout=rb_time]\n"
> > +    "      
> > [,splash=sp_name][,splash-time=sp_time][,reboot-timeout=rb_time][,strict=on|off]\n"
> >      "                'drives': floppy (a), hard disk (c), CD-ROM (d), 
> > network (n)\n"
> >      "                'sp_name': the file's name that would be passed to 
> > bios as logo picture, if menu=on\n"
> >      "                'sp_time': the period that splash picture last if 
> > menu=on, unit is ms\n"
> >      "                'rb_timeout': the timeout before guest reboot when 
> > boot failed, unit is ms\n",
> 
> So if I understand correctly, -boot order=... is incompatible with -boot
> strict=on; even though you have listed both options under a single -boot
> entry in the -help. We've already declared that -help output is no
> longer guaranteed stable, so this doesn't really impact libvirt, but
> would it make any more sense to list this as two orthogonal entries, to
> make it clear that they don't mix?
> 
> -boot order=drivers[,once=drives]...
> -boot strict=on|off[,menu=on|off]...
> 
> But this is all bikeshedding, so it's not worth a v3 if you disagree.
> 
> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>