Re: Xen/Xentools 3.3 Domain-Unnamed

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On Tuesday 19 August 2008 13:47:46 Manuel Bouyer wrote:
> On Tue, Aug 19, 2008 at 01:41:17PM +0200, Christoph Egger wrote:
> > This is what I got from XenSource:
> >
> > -------------------------------------------------------------------------
> >------------- You'll need to do errno remapping at the bottom of
> > libxenctrl/libxenguest, or within your equivalent of Linux's privcmd
> > kernel driver.
> >
> > Either is easy -- even in libxc there's one shared macro or function that
> > provides access to the actual hypercall interface, I'm pretty sure.
> > -------------------------------------------------------------------------
> >-------------
>
> I think the right way to do this would be to use the Xen's E* macros
> in the userland code where it's appropriate, and change the interface
> to return the hypervisor's errors though a different channel
> (as they don't have the same semantic as the errors from the local OS).
> But whatever

That is a lot of work. First, you have to prefix Xen's E* macros and change
all C code to use them in order to not interfer with <sys/errno.h>.

Second, you have to maintain a copy as a python module since
python's  errno  is used.

Third, this is almost the opposite what XenSource said and therefore
I don't believe in accepting those patches (and I'm not going to maintain
patches in pkgsrc I don't get upstream).

So this is not the way to go. Sorry.

> > I first tried to fix this in the xentools as suggested by XenSource.
> > But then I noticed this had an impact to *all* Dom0 privcmd ioctl's,
> > which made things worse.
> >
> > Reason: Only IOCTL_PRIVCMD_HYPERCALL is a passthrough from
> > userspace into the hypervisor and back. All others also perform
> > hypercalls into the hypervisor, but the return code from them
> > is never passed back into userspace.
> >
> > Therefore, the easiest fix (and with minimal effort) is to do
> > the error code remapping in sys/arch/xen/xen/privcmd.c after the
> > hypercall returned in IOCTL_PRIVCMD_HYPERCALL.
> >
> > Attached patch is doing this and works fine.
> > With it, there are no longer any phantom domains named
> > "Domain-Unnamed" left.
>
> Are EDEADLK/EAGAIN the only error codes that need translation ?

I can think of EWOULDBLOCK but this is an alias to EAGAIN. So yes,
nothing else has bitten us so far.

Christoph