github.com/shijuvar/go@v0.0.0-20141209052335-e8f13700b70c/src/internal/syscall/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 syscall
     6  
     7  import (
     8  	"runtime"
     9  	"sync/atomic"
    10  	stdsyscall "syscall"
    11  	"unsafe"
    12  )
    13  
    14  var randomTrap = map[string]uintptr{
    15  	"386":   355,
    16  	"amd64": 318,
    17  	"arm":   384,
    18  }[runtime.GOARCH]
    19  
    20  var randomUnsupported int32 // atomic
    21  
    22  // GetRandomFlag is a flag supported by the getrandom system call.
    23  type GetRandomFlag uintptr
    24  
    25  const (
    26  	// GRND_NONBLOCK means return EAGAIN rather than blocking.
    27  	GRND_NONBLOCK GetRandomFlag = 0x0001
    28  
    29  	// GRND_RANDOM means use the /dev/random pool instead of /dev/urandom.
    30  	GRND_RANDOM GetRandomFlag = 0x0002
    31  )
    32  
    33  // GetRandom calls the Linux getrandom system call.
    34  // See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6e9d6f38894798696f23c8084ca7edbf16ee895
    35  func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
    36  	if randomTrap == 0 {
    37  		return 0, stdsyscall.ENOSYS
    38  	}
    39  	if len(p) == 0 {
    40  		return 0, nil
    41  	}
    42  	if atomic.LoadInt32(&randomUnsupported) != 0 {
    43  		return 0, stdsyscall.ENOSYS
    44  	}
    45  	r1, _, errno := stdsyscall.Syscall(randomTrap,
    46  		uintptr(unsafe.Pointer(&p[0])),
    47  		uintptr(len(p)),
    48  		uintptr(flags))
    49  	if errno != 0 {
    50  		if errno == stdsyscall.ENOSYS {
    51  			atomic.StoreInt32(&randomUnsupported, 1)
    52  		}
    53  		return 0, errno
    54  	}
    55  	return int(r1), nil
    56  }