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// 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.
package unix
import (
"sync/atomic"
"syscall"
"unsafe"
)
var randomUnsupported int32 // atomic
// GetRandomFlag is a flag supported by the getrandom system call.
type GetRandomFlag uintptr
const (
// GRND_NONBLOCK means return EAGAIN rather than blocking.
GRND_NONBLOCK GetRandomFlag = 0x0001
// GRND_RANDOM means use the /dev/random pool instead of /dev/urandom.
GRND_RANDOM GetRandomFlag = 0x0002
)
// GetRandom calls the Linux getrandom system call.
// See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6e9d6f38894798696f23c8084ca7edbf16ee895
func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
if randomTrap == 0 {
return 0, syscall.ENOSYS
}
if len(p) == 0 {
return 0, nil
}
if atomic.LoadInt32(&randomUnsupported) != 0 {
return 0, syscall.ENOSYS
}
r1, _, errno := syscall.Syscall(randomTrap,
uintptr(unsafe.Pointer(&p[0])),
uintptr(len(p)),
uintptr(flags))
if errno != 0 {
if errno == syscall.ENOSYS {
atomic.StoreInt32(&randomUnsupported, 1)
}
return 0, errno
}
return int(r1), nil
}
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