Source file src/internal/syscall/unix/getrandom_freebsd.go

     1	// Copyright 2018 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package unix
     6	
     7	import (
     8		"sync/atomic"
     9		"syscall"
    10		"unsafe"
    11	)
    12	
    13	var randomUnsupported int32 // atomic
    14	
    15	// FreeBSD getrandom system call number.
    16	const randomTrap uintptr = 563
    17	
    18	// GetRandomFlag is a flag supported by the getrandom system call.
    19	type GetRandomFlag uintptr
    20	
    21	const (
    22		// GRND_NONBLOCK means return EAGAIN rather than blocking.
    23		GRND_NONBLOCK GetRandomFlag = 0x0001
    24	
    25		// GRND_RANDOM is only set for portability purpose, no-op on FreeBSD.
    26		GRND_RANDOM GetRandomFlag = 0x0002
    27	)
    28	
    29	// GetRandom calls the FreeBSD getrandom system call.
    30	func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
    31		if len(p) == 0 {
    32			return 0, nil
    33		}
    34		if atomic.LoadInt32(&randomUnsupported) != 0 {
    35			return 0, syscall.ENOSYS
    36		}
    37		r1, _, errno := syscall.Syscall(randomTrap,
    38			uintptr(unsafe.Pointer(&p[0])),
    39			uintptr(len(p)),
    40			uintptr(flags))
    41		if errno != 0 {
    42			if errno == syscall.ENOSYS {
    43				atomic.StoreInt32(&randomUnsupported, 1)
    44			}
    45			return 0, errno
    46		}
    47		return int(r1), nil
    48	}
    49	

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