github.com/zebozhuang/go@v0.0.0-20200207033046-f8a98f6f5c5d/src/crypto/rand/rand_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 rand
     6  
     7  import (
     8  	"internal/syscall/unix"
     9  )
    10  
    11  func init() {
    12  	altGetRandom = getRandomLinux
    13  }
    14  
    15  // If the kernel is too old (before 3.17) to support the getrandom syscall(),
    16  // unix.GetRandom will immediately return ENOSYS and we will then fall back to
    17  // reading from /dev/urandom in rand_unix.go. unix.GetRandom caches the ENOSYS
    18  // result so we only suffer the syscall overhead once in this case.
    19  // If the kernel supports the getrandom() syscall, unix.GetRandom will block
    20  // until the kernel has sufficient randomness (as we don't use GRND_NONBLOCK).
    21  // In this case, unix.GetRandom will not return an error.
    22  func getRandomLinux(p []byte) (ok bool) {
    23  	n, err := unix.GetRandom(p, 0)
    24  	return n == len(p) && err == nil
    25  }