| // 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 linux || freebsd || dragonfly || solaris |
| // +build linux freebsd dragonfly solaris |
| |
| package rand |
| |
| import ( |
| "errors" |
| "internal/syscall/unix" |
| ) |
| |
| // maxGetRandomRead is platform dependent. |
| func init() { |
| altGetRandom = batched(getRandomBatch, 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 getRandomBatch(p []byte) error { |
| n, err := unix.GetRandom(p, 0) |
| if n != len(p) { |
| return errors.New("short read") |
| } |
| return err |
| } |