hst: expose scheduling policy

This is primarily useful for poorly written music players for now.

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

hst/config.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"hakurei.app/container/check"
+	"hakurei.app/container/std"
 )
 
 // Config configures an application container.
@@ -103,6 +104,10 @@ type Config struct {
 	// Init user namespace supplementary groups inherited by all container processes.
 	Groups []string `json:"groups"`
 
+	// Scheduling policy to set for the container. The zero value retains the
+	// current scheduling policy.
+	SchedPolicy std.SchedPolicy `json:"sched_policy,omitempty"`
+
 	// High level configuration applied to the underlying [container].
 	Container *ContainerConfig `json:"container"`
 }
@@ -116,6 +121,10 @@ var (
 	// [Config.Identity] value.
 	ErrIdentityBounds = errors.New("identity out of bounds")
 
+	// ErrSchedPolicyBounds is returned by [Config.Validate] for an out of bounds
+	// [Config.SchedPolicy] value.
+	ErrSchedPolicyBounds = errors.New("scheduling policy out of bounds")
+
 	// ErrEnviron is returned by [Config.Validate] if an environment variable
 	// name contains '=' or NUL.
 	ErrEnviron = errors.New("invalid environment variable name")
@@ -138,6 +147,13 @@ func (config *Config) Validate() error {
 			Msg: "identity " + strconv.Itoa(config.Identity) + " out of range"}
 	}
 
+	if config.SchedPolicy < 0 || config.SchedPolicy > std.SCHED_LAST {
+		return &AppError{Step: "validate configuration", Err: ErrSchedPolicyBounds,
+			Msg: "scheduling policy " +
+				strconv.Itoa(int(config.SchedPolicy)) +
+				" out of range"}
+	}
+
 	if err := config.SessionBus.CheckInterfaces("session"); err != nil {
 		return err
 	}