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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"
"unsafe"
)
//go:cgo_import_dynamic libc_getrandom getrandom "libc.so"
//go:linkname procGetrandom libc_getrandom
var procGetrandom 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
}
r1, _, errno := syscall6(uintptr(unsafe.Pointer(&procGetrandom)),
3,
uintptr(unsafe.Pointer(&p[0])),
uintptr(len(p)),
uintptr(flags),
0, 0, 0)
if errno != 0 {
if errno == syscall.ENOSYS {
atomic.StoreInt32(&getrandomUnsupported, 1)
}
return 0, errno
}
return int(r1), nil
}
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