Re: [Xen-devel] [PATCH 3/8] kexec: add public interface for improved load/unload sub-ops

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Fri, Mar 08, 2013 at 11:52:21AM +0000, David Vrabel wrote:
> On 08/03/13 10:50, Daniel Kiper wrote:
> > On Thu, Feb 21, 2013 at 05:48:09PM +0000, David Vrabel wrote:
> >> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> >>
> >> Add replacement KEXEC_CMD_load and KEXEC_CMD_unload sub-ops to the
> >> kexec hypercall.  These new sub-ops allow a priviledged guest to
> >> provide the image data to be loaded into Xen memory or the crash
> >> region instead of guests loading the image data themselves and
> >> providing the relocation code and metadata.
> >>
> >> The old interface is provided to guests requesting an interface
> >> version prior to 4.3.
> >>
> >> Signed-off: David Vrabel <david.vrabel@xxxxxxxxxx>
> >
> > [...]
> >
> >> diff --git a/xen/include/public/kexec.h b/xen/include/public/kexec.h
> >> index 61a8d7d..5259446 100644
> >> --- a/xen/include/public/kexec.h
> >> +++ b/xen/include/public/kexec.h
> >> @@ -116,12 +116,12 @@ typedef struct xen_kexec_exec {
> >>   * type  == KEXEC_TYPE_DEFAULT or KEXEC_TYPE_CRASH [in]
> >>   * image == relocation information for kexec (ignored for unload) [in]
> >>   */
> >> -#define KEXEC_CMD_kexec_load            1
> >> -#define KEXEC_CMD_kexec_unload          2
> >> -typedef struct xen_kexec_load {
> >> +#define KEXEC_CMD_kexec_load_v1         1 /* obsolete since 0x00040300 */
> >> +#define KEXEC_CMD_kexec_unload_v1       2 /* obsolete since 0x00040300 */
> >> +typedef struct xen_kexec_load_v1 {
> >>      int type;
> >>      xen_kexec_image_t image;
> >> -} xen_kexec_load_t;
> >> +} xen_kexec_load_v1_t;
> >
> > I think that this is not good idea to redefine meaning of constants,
> > types, structures, etc. IMO it is comparable to redefining meaning
> > of words in any laguage (e.g. English). It will be very confusing
> > and may easily lead to stupid bugs. I think that old interface should
> > stay as is (with its bad behavior). New interface should be introduced
> > with "_v2" suffix, e.g. KEXEC_CMD_kexec_load_v2, ...
> > This would not confuse our descendants.
>
> This is something that was requested (by Ian C) as the Xen way of doing it.

Yes, I remember but still do not agree with that idea in general.
Maybe discussion on kexec interface is good point to change
that Xen community behavior? Ian?

Daniel

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