getrandom.go

     1  // Copyright 2021 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  //go:build dragonfly || freebsd || linux
     6  
     7  package unix
     8  
     9  import (
    10  	"sync/atomic"
    11  	"syscall"
    12  	"unsafe"
    13  )
    14  
    15  var getrandomUnsupported atomic.Bool
    16  
    17  // GetRandomFlag is a flag supported by the getrandom system call.
    18  type GetRandomFlag uintptr
    19  
    20  // GetRandom calls the getrandom system call.
    21  func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
    22  	if len(p) == 0 {
    23  		return 0, nil
    24  	}
    25  	if getrandomUnsupported.Load() {
    26  		return 0, syscall.ENOSYS
    27  	}
    28  	r1, _, errno := syscall.Syscall(getrandomTrap,
    29  		uintptr(unsafe.Pointer(&p[0])),
    30  		uintptr(len(p)),
    31  		uintptr(flags))
    32  	if errno != 0 {
    33  		if errno == syscall.ENOSYS {
    34  			getrandomUnsupported.Store(true)
    35  		}
    36  		return 0, errno
    37  	}
    38  	return int(r1), nil
    39  }
    40
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