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, 2 insertions, 1 deletions

diff --git a/migration/savevm.c b/migration/savevm.c
index 9671211339..211eff3a8b 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1753,7 +1753,8 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis,
         return -EINVAL;
     }
 
-    if (!postcopy_ram_supported_by_host(mis)) {
+    if (!postcopy_ram_supported_by_host(mis, &local_err)) {
+        error_report_err(local_err);
         postcopy_state_set(POSTCOPY_INCOMING_NONE);
         return -1;
     }