Current File : //usr/local/go119/src/crypto/rand/rand_getrandom.go
// 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
package rand
import (
"internal/syscall/unix"
"runtime"
"syscall"
)
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 "freebsd", "dragonfly", "solaris", "illumos":
maxGetRandomRead = 1 << 8
default:
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
}
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