Re: [Qemu-devel] [PATCH v2 33/41] postcopy: introduce -postcopy and -postcopy-flags option

[Isaku Yamahata <yamahata@valinux.co.jp>]

On Fri, Jun 08, 2012 at 12:52:54PM +0200, Juan Quintela wrote:
> Isaku Yamahata <yamahata@valinux.co.jp> wrote:
> > This patch prepares for postcopy livemigration.
> > It introduces -postcopy option and its internal flag, migration_postcopy.
> > It introduces -postcopy-flags for chaging the behavior of incoming postcopy
> > mainly for benchmark/debug.
> 
> Why do we need postcopy flag?  -incoming should be enough to detect that
> we are doing postcopy.
> 
>     QLIST_HEAD(, LoadStateEntry) loadvm_handlers =
>         QLIST_HEAD_INITIALIZER(loadvm_handlers);
>     LoadStateEntry *le, *new_le;
>     uint8_t section_type;
>     unsigned int v;
>     int ret;
> 
>     if (qemu_savevm_state_blocked(NULL)) {
>         return -EINVAL;
>     }
> 
>     v = qemu_get_be32(f);
>     if (v != QEMU_VM_FILE_MAGIC)
>         return -EINVAL;
> 
>     v = qemu_get_be32(f);
>     if (v == QEMU_VM_FILE_VERSION_COMPAT) {
>         fprintf(stderr, "SaveVM v2 format is obsolete and don't work anymore\n");
>         return -ENOTSUP;
>     }
>     if (v != QEMU_VM_FILE_VERSION)
>         return -ENOTSUP;
> 
> Shouldn't we be able to change some version field here and make the
> "recognition of postcopy automatic"?  Having to hack around a new
> command line option for each page is not going to be nice.  And about
> postcopy flags, if they are for "incoming side", please consider just
> sent that flags on the stream as a first field?

Yes, you are right.
If bumping version is allowed, -postcopy can be dropped with auto detection.
-postcopy-flags can be dropped because it is used only for benchmark purpose
to change incoming side behavior independent of outgoing side.
-- 
yamahata