[libvirt] [Xen-devel] [PATCH] libxl: initialize vfb defbools in libxlMakeVfb

Ian Campbell ian.campbell at citrix.com
Mon Apr 20 09:43:30 UTC 2015

On Mon, 2015-04-20 at 11:32 +0200, Olaf Hering wrote:
> On Mon, Apr 20, Ian Campbell wrote:
> > On Fri, 2015-04-17 at 13:40 -0600, Jim Fehlig wrote:
> > > On 04/17/2015 11:19 AM, Olaf Hering wrote:
> > > > If the domU configu has sdl enabled libvirtd crashes:
> > > > libvirtd[5158]: libvirtd: libxl.c:343: libxl_defbool_val: Assertion `!libxl_defbool_is_default(db)' failed.
> > > 
> > > The assertion seems harsh considering the offense...
> > 
> > libxl should be setting a default for this value if the application
> > hasn't, by calling libxl__device_vfb_setdefault at some correct point.
> This is an internal function. Its up to the caller of
> libxl_device_vfb_init to initialize the defbool members.

No, it isn't. It's up to libxl to call libxl__device_vfb_setdefault
somewhere on the code path between entering the library and actually
using this defbool. (Possibly indirectly via the containing struct in
this case)

We normally do this as close to entry into the library as we can, e.g.
in the libxl_device_FOO_add or e.g. in libxl_domain_create.

It is always a libxl bug if a defbool gets used without having had a
defaulted value applied by the library first, hence the assert.

If what you said were true then an assert would be a rather harsh
overreaction to an application coding error.


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