github.com/sandwichdev/go-internals@v0.0.0-20210605002614-12311ac6b2c5/syscall/unix/getrandom_freebsd.go (about)

     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  }