Re: [PATCH] tools/libxc: Disable CONFIG_MIGRATE in stubdom environments

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 27/01/15 17:01, Ian Campbell wrote:
> On Tue, 2015-01-27 at 16:58 +0000, Andrew Cooper wrote:
>> The legacy save/restore infrastructure requires several function pointers from
>> the toolstack (libxl or Xend in the past) in order to work, and for HVM guests
>> also need to be able to play around in dom0's filesystem to move the device
>> model save record.
>>
>> Migration v2 changes some of this, but is similarly dependent on
>> toolstack-provided function pointers.
>>
>> Someone who wishes to re-architect the interaction of moving parts for running
>> a domain might be in a position to re-enabled this, but for now, explicitly
>> fail with ENOSYS (from xc_nomigrate.c) rather than failing with an error about
>> a missing function pointer (or indeed falling over a NULL pointer on certain
>> paths).
> You are talking about a toolstack which is itself running in a stubdom
> here, right?

The patch here prevents libxenguest, when compiled as part of a minios
stub environment, from offering migration capability to the sub environment.

One would need to construct a stub environment with libxl and
libxl-save-helper to have a decent stab at making migration of PV guests
from a stub environment work.

>
> As opposed to e.g. an HVM domain using a qemu-stubdom, but being
> migrated by a normal toolstack in domain 0 (or at least, not in a
> mini-os based stubdom).

A qemu-stubdom equally cant participate in migrate of its domain
(because of the issues in passing the qemu save record), but that is a
separate issue.

~Andrew

>
> Ian.
>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> CC: Ian Campbell <Ian.Campbell@citrix.com>
>> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
>> CC: Wei Liu <wei.liu2@citrix.com>
>> ---
>>  tools/libxc/Makefile |    5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/tools/libxc/Makefile b/tools/libxc/Makefile
>> index bd2ca6c..735afdb 100644
>> --- a/tools/libxc/Makefile
>> +++ b/tools/libxc/Makefile
>> @@ -4,6 +4,11 @@ include $(XEN_ROOT)/tools/Rules.mk
>>  MAJOR    = 4.5
>>  MINOR    = 0
>>  
>> +ifeq ($(CONFIG_LIBXC_MINIOS),y)
>> +# Save/restore of a domain is currently incompatible with a stubdom environment
>> +override CONFIG_MIGRATE := n
>> +endif
>> +
>>  CTRL_SRCS-y       :=
>>  CTRL_SRCS-y       += xc_core.c
>>  CTRL_SRCS-$(CONFIG_X86) += xc_core_x86.c
>