Add I/O priority

Signed-off-by: utam0k <k0ma@utam0k.jp>

libcontainer/process_linux.go

@@ -124,6 +124,13 @@ func (p *setnsProcess) signal(sig os.Signal) error {
 
 func (p *setnsProcess) start() (retErr error) {
 	defer p.comm.closeParent()
+
+	if p.process.IOPriority != nil {
+		if err := setIOPriority(p.process.IOPriority); err != nil {
+			return err
+		}
+	}
+
 	// get the "before" value of oom kill count
 	oom, _ := p.manager.OOMKillCount()
 	err := p.cmd.Start()
@@ -972,3 +979,21 @@ func initWaiter(r io.Reader) chan error {
 
 	return ch
 }
+
+func setIOPriority(ioprio *configs.IOPriority) error {
+	const ioprioWhoPgrp = 1
+
+	class, ok := configs.IOPrioClassMapping[ioprio.Class]
+	if !ok {
+		return fmt.Errorf("invalid io priority class: %s", ioprio.Class)
+	}
+
+	// Combine class and priority into a single value
+	// https://github.com/torvalds/linux/blob/v5.18/include/uapi/linux/ioprio.h#L5-L17
+	iop := (class << 13) | ioprio.Priority
+	_, _, errno := unix.RawSyscall(unix.SYS_IOPRIO_SET, ioprioWhoPgrp, 0, uintptr(iop))
+	if errno != 0 {
+		return fmt.Errorf("failed to set io priority: %w", errno)
+	}
+	return nil
+}