container: sched policy string representation

This also uses priority obtained via sched_get_priority_min, and improves bounds checking.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/container.go

@@ -40,7 +40,7 @@ type (
 		AllowOrphan bool
 		// Scheduling policy to set via sched_setscheduler(2). The zero value
 		// skips this call. Supported policies are [SCHED_BATCH], [SCHED_IDLE].
-		SchedPolicy int
+		SchedPolicy SchedPolicy
 		// Cgroup fd, nil to disable.
 		Cgroup *int
 		// ExtraFiles passed through to initial process in the container, with
@@ -373,12 +373,23 @@ func (p *Container) Start() error {
 
 			// sched_setscheduler: thread-directed but acts on all processes
 			// created from the calling thread
-			if p.SchedPolicy > 0 {
+			if p.SchedPolicy > 0 && p.SchedPolicy <= _SCHED_LAST {
+				var param schedParam
+				if priority, err := p.SchedPolicy.GetPriorityMin(); err != nil {
+					return &StartError{
+						Fatal: true,
+						Step:  "get minimum priority",
+						Err:   err,
+					}
+				} else {
+					param.priority = priority
+				}
+
 				p.msg.Verbosef("setting scheduling policy %d", p.SchedPolicy)
 				if err := schedSetscheduler(
 					0, // calling thread
 					p.SchedPolicy,
-					&schedParam{0},
+					&param,
 				); err != nil {
 					return &StartError{
 						Fatal: true,