ext: wrap close_range syscall

This is useful for container when called with CLOSE_RANGE_CLOEXEC.

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

ext/syscall.go

@@ -7,6 +7,26 @@ import (
 	"syscall"
 )
 
+// include/uapi/linux/close_range.h
+const (
+	CLOSE_RANGE_UNSHARE = 1 << (iota + 1)
+	CLOSE_RANGE_CLOEXEC
+)
+
+// CloseRange close all file descriptors in a given range.
+func CloseRange(first, last Uint, flags Int) error {
+	_, _, errno := syscall.Syscall(
+		SYS_CLOSE_RANGE,
+		uintptr(first),
+		uintptr(last),
+		uintptr(flags),
+	)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
+
 // SchedPolicy denotes a scheduling policy defined in include/uapi/linux/sched.h.
 type SchedPolicy int