blob: 46c4133a73b2ebd94b32af895407c3fbe0c4dc33 [file] [log] [blame]
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build dragonfly || freebsd || linux || netbsd || solaris
package rand
import (
func init() {
var maxGetRandomRead int
switch runtime.GOOS {
case "linux", "android":
// Per the manpage:
// When reading from the urandom source, a maximum of 33554431 bytes
// is returned by a single call to getrandom() on systems where int
// has a size of 32 bits.
maxGetRandomRead = (1 << 25) - 1
case "dragonfly", "freebsd", "illumos", "netbsd", "solaris":
maxGetRandomRead = 1 << 8
panic("no maximum specified for GetRandom")
altGetRandom = batched(getRandom, maxGetRandomRead)
// If the kernel is too old to support the getrandom syscall(),
// unix.GetRandom will immediately return ENOSYS and we will then fall back to
// reading from /dev/urandom in rand_unix.go. unix.GetRandom caches the ENOSYS
// result so we only suffer the syscall overhead once in this case.
// If the kernel supports the getrandom() syscall, unix.GetRandom will block
// until the kernel has sufficient randomness (as we don't use GRND_NONBLOCK).
// In this case, unix.GetRandom will not return an error.
func getRandom(p []byte) error {
n, err := unix.GetRandom(p, 0)
if err != nil {
return err
if n != len(p) {
return syscall.EIO
return nil