Re: [PATCH v11 11/11] (lib)xl: soft reset support

[Wei Liu <wei.liu2@citrix.com>]

On Mon, Sep 14, 2015 at 06:54:51PM +0200, Vitaly Kuznetsov wrote:
> Wei Liu <wei.liu2@citrix.com> writes:
> 
> > Sorry for the delay.
> >
> > FYI all other patches of this series were applied by Jan. You only need
> > to resend this one.
> 
> Cool, I will.
> 
> >
> > See below for a few comments.
> >
> > On Fri, Sep 04, 2015 at 03:39:51PM +0200, Vitaly Kuznetsov wrote:
> >> Use existing create/restore path to perform 'soft reset' for HVM
> >> domains. Tear everything down, e.g. destroy domain's device model,
> >> remove the domain from xenstore, save toolstack record and start
> >> over.
> >> 
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> >> ---
> >> Changes since v10:
> >> - Adapt to 'migration v2' changes.
> >> - Use LIBXL_DEVICE_MODEL_SAVE_FILE as Qemu save file (and rename it to
> >>   LIBXL_DEVICE_MODEL_RESTORE_FILE later) to support stubdom case (as
> >>   we connect consoles to both files on create.
> >> - Fix coding style, minor description change in xl.cfg.pod.5 [Wei Liu]
> >> 
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> >> ---
> >>  docs/man/xl.cfg.pod.5        |   8 +-
> >>  tools/libxl/libxl.c          |  22 ++++-
> >>  tools/libxl/libxl.h          |  15 ++++
> >>  tools/libxl/libxl_create.c   | 192 ++++++++++++++++++++++++++++++++++++++-----
> >>  tools/libxl/libxl_internal.h |   4 +
> >>  tools/libxl/libxl_types.idl  |   2 +
> >>  tools/libxl/xl.h             |   1 +
> >>  tools/libxl/xl_cmdimpl.c     |  25 +++++-
> >>  8 files changed, 242 insertions(+), 27 deletions(-)
> >> 
> >> diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
> >> index c6345b8..d8c4186 100644
> >> --- a/docs/man/xl.cfg.pod.5
> >> +++ b/docs/man/xl.cfg.pod.5
> >> @@ -349,6 +349,12 @@ destroy the domain.
> >>  write a "coredump" of the domain to F</var/lib/xen/dump/NAME> and then
> >>  restart the domain.
> >>  
> >> +=item B<soft-reset>
> >> +
> >> +Reset all Xen specific interfaces for the Xen-aware HVM domain allowing
> >> +it to reestablish these interfaces and continue executing the domain. PV
> >> +guest is not supported.
> >> +
> >
> > And "non-Xen-aware HVM will crash" ?
> 
> Sorry, I should have replied to that suggestion earlier. Non-Xen-aware
> HVM guest can't really trigger this action and (in theory) is capable of
> doing kexec without any assistance.
> 
> > If there is no definite answer to
> > guest state maybe just saying "PV guest and non-Xen-aware HVM guests are
> > not supported" ?
> 
> This sounds correct.
> 
> >
> > It's important to let user know about the consequence because libxl
> > doesn't actually stop you from soft-resetting a HVM guest that is not
> > Xen-aware.
> 
> The question is who (and when/how) is going to trigger this action? In
> case someone does that while HVM domain (doesn't really matter if it is
> Xen-aware or not) does not expect this action it will crash.
> 
> *In theory* nothing bad is going to happen to a non-Xen-aware HVM guest
> if someone else will trigger this action for it (e.g. on 'reset'
> signal), it will just get an assistance it doesn't need.
> 

OK then. We should still make it clear it is unsupported for
non-Xen-aware HVM guest even if it happens to work.

Wei.

> [...]
> 
> -- 
>   Vitaly