[libvirt] [PATCH] Fix scheduler support check

[Martin Kletzander]

Commit 94cc577807ba tried fixing build on systems that did not have
SCHED_BATCH or SCHED_IDLE defined.  But instead of changing it to
conditional support, it rather completely disabled the support for
setting any scheduler.  Since then, such old systems are not
supported, but rather than reverting that commit, let's change that to
the conditional support.  That way any addition to the list of
schedulers can follow the same style so that we're consistent in the
future.

Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
---

Notes:
    Of course there are various ways how to address that, I went with
    case.  Also defining undefined SCHED_* to -1 makes some gnulib
    syntax-check go haywire.

 src/util/virprocess.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/util/virprocess.c b/src/util/virprocess.c
index 718c4a2664e1..39d6b30c40f2 100644
--- a/src/util/virprocess.c
+++ b/src/util/virprocess.c
@@ -1183,7 +1183,7 @@ virProcessExitWithStatus(int status)
     exit(value);
 }

-#if HAVE_SCHED_SETSCHEDULER && defined(SCHED_BATCH) && defined(SCHED_IDLE)
+#if HAVE_SCHED_SETSCHEDULER

 static int
 virProcessSchedTranslatePolicy(virProcessSchedPolicy policy)
@@ -1196,10 +1196,18 @@ virProcessSchedTranslatePolicy(virProcessSchedPolicy policy)
         return SCHED_BATCH;

     case VIR_PROC_POLICY_IDLE:
+# ifdef SCHED_IDLE
         return SCHED_IDLE;
+# else
+        return -1;
+# endif

     case VIR_PROC_POLICY_FIFO:
+# ifdef SCHED_FIFO
         return SCHED_FIFO;
+# else
+        return -1;
+# endif

     case VIR_PROC_POLICY_RR:
         return SCHED_RR;
@@ -1225,6 +1233,13 @@ virProcessSetScheduler(pid_t pid,
     if (!policy)
         return 0;

+    if (pol < 0) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Scheduler '%s' is not supported on this platform"),
+                       virProcessSchedPolicyTypeToString(policy));
+        return -1;
+    }
+
     if (pol == SCHED_FIFO || pol == SCHED_RR) {
         int min = 0;
         int max = 0;
-- 
2.10.2