1 files changed, 48 insertions, 0 deletions
diff --git a/src/crypto/rand/rand_getrandom.go b/src/crypto/rand/rand_getrandom.go
new file mode 100644
index 0000000..46c4133
--- /dev/null
+++ b/src/crypto/rand/rand_getrandom.go
@@ -0,0 +1,48 @@
+// 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.
+
+//go:build dragonfly || freebsd || linux || netbsd || solaris
+
+package rand
+
+import (
+	"internal/syscall/unix"
+	"runtime"
+	"syscall"
+)
+
+func init() {
+	var maxGetRandomRead int
+	switch runtime.GOOS {
+	case "linux", "android":
+		// Per the manpage:
+		//     When reading from the urandom source, a maximum of 33554431 bytes
+		//     is returned by a single call to getrandom() on systems where int
+		//     has a size of 32 bits.
+		maxGetRandomRead = (1 << 25) - 1
+	case "dragonfly", "freebsd", "illumos", "netbsd", "solaris":
+		maxGetRandomRead = 1 << 8
+	default:
+		panic("no maximum specified for GetRandom")
+	}
+	altGetRandom = batched(getRandom, maxGetRandomRead)
+}
+
+// If the kernel is too old to support the getrandom syscall(),
+// unix.GetRandom will immediately return ENOSYS and we will then fall back to
+// reading from /dev/urandom in rand_unix.go. unix.GetRandom caches the ENOSYS
+// result so we only suffer the syscall overhead once in this case.
+// If the kernel supports the getrandom() syscall, unix.GetRandom will block
+// until the kernel has sufficient randomness (as we don't use GRND_NONBLOCK).
+// In this case, unix.GetRandom will not return an error.
+func getRandom(p []byte) error {
+	n, err := unix.GetRandom(p, 0)
+	if err != nil {
+		return err
+	}
+	if n != len(p) {
+		return syscall.EIO
+	}
+	return nil
+}