spapr: Simplify ovec diff

spapr_ovec_diff(ov, old, new) has somewhat complex semantics.  ov is set
to those bits which are in new but not old, and it returns as a boolean
whether or not there are any bits in old but not new.

It turns out that both callers only care about the second, not the first.
This is basically equivalent to a bitmap subset operation, which is easier
to understand and implement.  So replace spapr_ovec_diff() with
spapr_ovec_subset().

Cc: Mike Roth <mdroth@linux.vnet.ibm.com>

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cedric Le Goater <clg@fr.ibm.com>

1 files changed, 3 insertions, 11 deletions

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 3dedb41..f11422f 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1840,8 +1840,6 @@ static bool spapr_ov5_cas_needed(void *opaque)
 {
     SpaprMachineState *spapr = opaque;
     SpaprOptionVector *ov5_mask = spapr_ovec_new();
-    SpaprOptionVector *ov5_legacy = spapr_ovec_new();
-    SpaprOptionVector *ov5_removed = spapr_ovec_new();
     bool cas_needed;
 
     /* Prior to the introduction of SpaprOptionVector, we had two option
@@ -1873,17 +1871,11 @@ static bool spapr_ov5_cas_needed(void *opaque)
     spapr_ovec_set(ov5_mask, OV5_DRCONF_MEMORY);
     spapr_ovec_set(ov5_mask, OV5_DRMEM_V2);
 
-    /* spapr_ovec_diff returns true if bits were removed. we avoid using
-     * the mask itself since in the future it's possible "legacy" bits may be
-     * removed via machine options, which could generate a false positive
-     * that breaks migration.
-     */
-    spapr_ovec_intersect(ov5_legacy, spapr->ov5, ov5_mask);
-    cas_needed = spapr_ovec_diff(ov5_removed, spapr->ov5, ov5_legacy);
+    /* We need extra information if we have any bits outside the mask
+     * defined above */
+    cas_needed = !spapr_ovec_subset(spapr->ov5, ov5_mask);
 
     spapr_ovec_cleanup(ov5_mask);
-    spapr_ovec_cleanup(ov5_legacy);
-    spapr_ovec_cleanup(ov5_removed);
 
     return cas_needed;
 }