Re: [PATCH v4 --for 4.6 COLOPre 15/25] tools/libxl: check QEMU state before resume dm

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2015-07-15 at 14:00 +0100, Wei Liu wrote:
> On Wed, Jul 15, 2015 at 01:54:12PM +0100, Ian Campbell wrote:
> > On Wed, 2015-07-15 at 13:48 +0100, Ian Campbell wrote:
> > > >      switch (libxl__device_model_version_running(gc, domid)) {
> > > >      case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL: {
> > > > -        libxl__qemu_traditional_cmd(gc, domid, "continue");
> > > > -        libxl__wait_for_device_model_deprecated(gc, domid, "running", NULL, NULL, NULL);
> > > > +        uint32_t dm_domid = libxl_get_stubdom_id(CTX, domid);
> > > > +
> > > > +        path = libxl__device_model_xs_path(gc, dm_domid, domid, "/state");
> > > > +        state = libxl__xs_read(gc, XBT_NULL, path);
> > > > +        if (state != NULL && !strcmp(state, "paused")) {
> > > > +            libxl__qemu_traditional_cmd(gc, domid, "continue");
> > > 
> > > Please can you explain the apparent discrepancy between the use of
> > > dm_domid and domid here?
> > 
> > I see from the next patch that this pattern came from the existing
> > libxl_domain_unpause, which hopes to use this helper in the future.
> > 
> > Looking at git annotate:
> > 83cc69fa        (Ian Jackson    2012-06-28 18:43:28 +0100       1045)    if (type == LIBXL_DOMAIN_TYPE_HVM) {
> > 1fc3aeb3        (   Wei Liu     2015-04-09 19:49:25 +0100       1046)        uint32_t dm_domid = libxl_get_stubdom_id(ctx, domid);
> > 1fc3aeb3        (   Wei Liu     2015-04-09 19:49:25 +0100       1047)
> > 1fc3aeb3        (   Wei Liu     2015-04-09 19:49:25 +0100       1048)        path = libxl__device_model_xs_path(gc, dm_domid, domid, "/state");
> > bdf07e8e        (Ian Jackson    2011-12-12 17:48:42 +0000       1049)        state = libxl__xs_read(gc, XBT_NULL, path);
> > d1c7c3ef        (Keir Fraser    2009-11-30 10:53:39 +0000       1050)        if (state != NULL && !strcmp(state, "paused")) {
> > 0cb90b31        (Shriram Rajagopalan    2012-02-09 18:07:48 +0000       1051)            libxl__qemu_traditional_cmd(gc, domid, "continue");
> > 47cb2273        (Ian Jackson    2013-10-14 17:26:01 +0100       1052)            libxl__wait_for_device_model_deprecated(gc, domid, "running",
> > 3b6eaa3e        (Ian Campbell   2011-05-24 15:57:24 +0100       1053)                                         NULL, NULL, NULL);
> > d1c7c3ef        (Keir Fraser    2009-11-30 10:53:39 +0000       1054)        }
> > 
> > It seems this came from Wei in 1fc3aeb3aa26 "libxl: use new QEMU
> > xenstore protocol". I suspect it was a mistake. Wei?
> > 
> 
> No, it's not.
> 
> libxl__qemu_traditional_cmd accepts domid and then it calls
> libxl_get_stubdom_id to extract dm_domid.

How... exciting.

Some sort of helper to get the DM state would help to hide this sort of
wrinkle.

Anyway, I shall go see if this means I can ack the COLO patches which
moved this code.

Ian.