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

     1  // Copyright 2014 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  // GetRandomFlag is a flag supported by the getrandom system call.
    16  type GetRandomFlag uintptr
    17  
    18  const (
    19  	// GRND_NONBLOCK means return EAGAIN rather than blocking.
    20  	GRND_NONBLOCK GetRandomFlag = 0x0001
    21  
    22  	// GRND_RANDOM means use the /dev/random pool instead of /dev/urandom.
    23  	GRND_RANDOM GetRandomFlag = 0x0002
    24  )
    25  
    26  // GetRandom calls the Linux getrandom system call.
    27  // See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6e9d6f38894798696f23c8084ca7edbf16ee895
    28  func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
    29  	if len(p) == 0 {
    30  		return 0, nil
    31  	}
    32  	if atomic.LoadInt32(&randomUnsupported) != 0 {
    33  		return 0, syscall.ENOSYS
    34  	}
    35  	r1, _, errno := syscall.Syscall(getrandomTrap,
    36  		uintptr(unsafe.Pointer(&p[0])),
    37  		uintptr(len(p)),
    38  		uintptr(flags))
    39  	if errno != 0 {
    40  		if errno == syscall.ENOSYS {
    41  			atomic.StoreInt32(&randomUnsupported, 1)
    42  		}
    43  		return 0, errno
    44  	}
    45  	return int(r1), nil
    46  }