github.com/q45/go@v0.0.0-20151101211701-a4fb8c13db3f/src/internal/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  	"runtime"
     9  	"sync/atomic"
    10  	"syscall"
    11  	"unsafe"
    12  )
    13  
    14  var randomTrap = map[string]uintptr{
    15  	"386":     355,
    16  	"amd64":   318,
    17  	"arm":     384,
    18  	"ppc64":   359,
    19  	"ppc64le": 359,
    20  }[runtime.GOARCH]
    21  
    22  var randomUnsupported int32 // atomic
    23  
    24  // GetRandomFlag is a flag supported by the getrandom system call.
    25  type GetRandomFlag uintptr
    26  
    27  const (
    28  	// GRND_NONBLOCK means return EAGAIN rather than blocking.
    29  	GRND_NONBLOCK GetRandomFlag = 0x0001
    30  
    31  	// GRND_RANDOM means use the /dev/random pool instead of /dev/urandom.
    32  	GRND_RANDOM GetRandomFlag = 0x0002
    33  )
    34  
    35  // GetRandom calls the Linux getrandom system call.
    36  // See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6e9d6f38894798696f23c8084ca7edbf16ee895
    37  func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
    38  	if randomTrap == 0 {
    39  		return 0, syscall.ENOSYS
    40  	}
    41  	if len(p) == 0 {
    42  		return 0, nil
    43  	}
    44  	if atomic.LoadInt32(&randomUnsupported) != 0 {
    45  		return 0, syscall.ENOSYS
    46  	}
    47  	r1, _, errno := syscall.Syscall(randomTrap,
    48  		uintptr(unsafe.Pointer(&p[0])),
    49  		uintptr(len(p)),
    50  		uintptr(flags))
    51  	if errno != 0 {
    52  		if errno == syscall.ENOSYS {
    53  			atomic.StoreInt32(&randomUnsupported, 1)
    54  		}
    55  		return 0, errno
    56  	}
    57  	return int(r1), nil
    58  }