Re: [Xen-devel] [PATCH 4/4] kexec/xen: directly load images images into Xen

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Mon, Oct 07, 2013 at 10:36:19AM +0100, David Vrabel wrote:
> On 04/10/13 22:33, Daniel Kiper wrote:
> > On Fri, Sep 20, 2013 at 02:16:38PM +0100, David Vrabel wrote:
> >> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> >>
> >> Xen 4.4 has an improvided kexec hypercall ABI that allows images to be
> >> loaded and executed without any kernel involvement.  Use the API
> >> provided by libxc to load images when running in a Xen guest.
> >>
> >> Support for loading images via the kexec_load syscall in non-upstream
> >> ("classic") Xen kernels is no longer supported.
> >>
> >> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> >
> > [...]
> >
> >> --- /dev/null
> >> +++ b/kexec/kexec-xen.c
> [...]
> >> +int xen_kexec_unload(uint64_t kexec_flags)
> >> +{
> >> +  xc_interface *xch;
> >> +  uint8_t type;
> >> +  int ret;
> >> +
> >> +  xch = xc_interface_open(NULL, NULL, 0);
> >> +  if (!xch)
> >> +          return -1;
> >> +
> >> +  type = kexec_flags & KEXEC_TYPE_CRASH;
> >
> > Why? Could not we unload normal kexec images?
>
> This is correct but could be
>
>   type = kexec_flags & KEXEC_TYPE_CRASH ? KEXEC_TYPE_CRASH
>           : KEXEC_TYPE_DEFAULT
>
> for clarity.

OK, thanks.

> >> @@ -928,6 +938,10 @@ static int kexec_loaded(void)
> >>    char *p;
> >>    char line[3];
> >>
> >> +  /* No way to tell if an image is loaded under Xen, assume it is. */
> >> +  if (xen_present())
> >> +          return 1;
> >> +
> >
> > Why? I think that we should have relevant machanism to do that.
>
> Because it's not needed.  There's no point in checking if an image a
> loaded before trying to exec it because you can just try the exec and
> have that fail.

OK, it makes sens.

> I'm not going to add a sub-op for this just because one particular tool
> mistakenly thinks it needs to check in advance.

However, I think that it is worth to have mechanism to discover which
image is loaded. Even here it does not make sens. It could be useful
for others.

Daniel

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