ext: move syscall wrappers from container

These are generally useful, and none of them are container-specific. Syscalls subtle to use and requiring container-specific setup remains in container.

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

ext/syscall.go

@@ -5,8 +5,62 @@ import (
 	"strconv"
 	"sync"
 	"syscall"
+	"unsafe"
 )
 
+// Prctl manipulates various aspects of the behavior of the calling thread or process.
+func Prctl(op, arg2, arg3 uintptr) error {
+	r, _, errno := syscall.Syscall(syscall.SYS_PRCTL, op, arg2, arg3)
+	if r < 0 {
+		return errno
+	}
+	return nil
+}
+
+// SetPtracer allows processes to ptrace(2) the calling process.
+func SetPtracer(pid uintptr) error {
+	return Prctl(syscall.PR_SET_PTRACER, pid, 0)
+}
+
+// linux/sched/coredump.h
+const (
+	SUID_DUMP_DISABLE = iota
+	SUID_DUMP_USER
+)
+
+// SetDumpable sets the "dumpable" attribute of the calling process.
+func SetDumpable(dumpable uintptr) error {
+	return Prctl(syscall.PR_SET_DUMPABLE, dumpable, 0)
+}
+
+// Isatty tests whether a file descriptor refers to a terminal.
+func Isatty(fd int) bool {
+	var buf [8]byte
+	r, _, _ := syscall.Syscall(
+		syscall.SYS_IOCTL,
+		uintptr(fd),
+		syscall.TIOCGWINSZ,
+		uintptr(unsafe.Pointer(&buf[0])),
+	)
+	return r == 0
+}
+
+// IgnoringEINTR makes a function call and repeats it if it returns an
+// EINTR error. This appears to be required even though we install all
+// signal handlers with SA_RESTART: see #22838, #38033, #38836, #40846.
+// Also #20400 and #36644 are issues in which a signal handler is
+// installed without setting SA_RESTART. None of these are the common case,
+// but there are enough of them that it seems that we can't avoid
+// an EINTR loop.
+func IgnoringEINTR(fn func() error) error {
+	for {
+		err := fn()
+		if err != syscall.EINTR {
+			return err
+		}
+	}
+}
+
 // include/uapi/linux/close_range.h
 const (
 	CLOSE_RANGE_UNSHARE = 1 << (iota + 1)