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Source file src/internal/syscall/unix/getrandom_linux.go

Documentation: internal/syscall/unix

  // Copyright 2014 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package unix
  
  import (
  	"sync/atomic"
  	"syscall"
  	"unsafe"
  )
  
  var randomUnsupported int32 // atomic
  
  // GetRandomFlag is a flag supported by the getrandom system call.
  type GetRandomFlag uintptr
  
  const (
  	// GRND_NONBLOCK means return EAGAIN rather than blocking.
  	GRND_NONBLOCK GetRandomFlag = 0x0001
  
  	// GRND_RANDOM means use the /dev/random pool instead of /dev/urandom.
  	GRND_RANDOM GetRandomFlag = 0x0002
  )
  
  // GetRandom calls the Linux getrandom system call.
  // See https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6e9d6f38894798696f23c8084ca7edbf16ee895
  func GetRandom(p []byte, flags GetRandomFlag) (n int, err error) {
  	if randomTrap == 0 {
  		return 0, syscall.ENOSYS
  	}
  	if len(p) == 0 {
  		return 0, nil
  	}
  	if atomic.LoadInt32(&randomUnsupported) != 0 {
  		return 0, syscall.ENOSYS
  	}
  	r1, _, errno := syscall.Syscall(randomTrap,
  		uintptr(unsafe.Pointer(&p[0])),
  		uintptr(len(p)),
  		uintptr(flags))
  	if errno != 0 {
  		if errno == syscall.ENOSYS {
  			atomic.StoreInt32(&randomUnsupported, 1)
  		}
  		return 0, errno
  	}
  	return int(r1), nil
  }
  

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