migration: Allow postcopy_ram_supported_by_host() to report err

Instead of print it to STDERR, bring the error upwards so that it can be
reported via QMP responses.

E.g.:

{ "execute": "migrate-set-capabilities" ,
  "arguments": { "capabilities":
  [ { "capability": "postcopy-ram", "state": true } ] } }

{ "error":
  { "class": "GenericError",
    "desc": "Postcopy is not supported: Host backend files need to be TMPFS
    or HUGETLBFS only" } }

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/migration/options.c b/migration/options.c
index fe7d7754c4..c6030587cf 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -302,6 +302,7 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
 {
     MigrationIncomingState *mis = migration_incoming_get_current();
 
+    ERRP_GUARD();
 #ifndef CONFIG_LIVE_BLOCK_MIGRATION
     if (new_caps[MIGRATION_CAPABILITY_BLOCK]) {
         error_setg(errp, "QEMU compiled without old-style (blk/-b, inc/-i) "
@@ -327,11 +328,8 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
          */
         if (!old_caps[MIGRATION_CAPABILITY_POSTCOPY_RAM] &&
             runstate_check(RUN_STATE_INMIGRATE) &&
-            !postcopy_ram_supported_by_host(mis)) {
-            /* postcopy_ram_supported_by_host will have emitted a more
-             * detailed message
-             */
-            error_setg(errp, "Postcopy is not supported");
+            !postcopy_ram_supported_by_host(mis, errp)) {
+            error_prepend(errp, "Postcopy is not supported: ");
             return false;
         }