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// Copyright 2021 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"
)
//extern getrandom
func libc_getrandom(*byte, uintptr, uint32) uintptr
var getrandomUnsupported 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 getrandom system call.
func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
if len(p) == 0 {
return 0, nil
}
if atomic.LoadInt32(&getrandomUnsupported) != 0 {
return 0, syscall.ENOSYS
}
syscall.Entersyscall()
r1 := libc_getrandom(&p[0], uintptr(len(p)), uint32(flags))
syscall.Exitsyscall()
if r1 == 0 {
errno := syscall.GetErrno()
if errno == syscall.ENOSYS {
atomic.StoreInt32(&getrandomUnsupported, 1)
}
return 0, errno
}
return int(r1), nil
}
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