Speed up Guid.NewGuid() on Linux

src/native/minipal/configure.cmake

@@ -11,6 +11,7 @@ check_function_exists(sysctlbyname HAVE_SYSCTLBYNAME)
 check_function_exists(fsync HAVE_FSYNC)
 
 check_symbol_exists(arc4random_buf "stdlib.h" HAVE_ARC4RANDOM_BUF)
+check_symbol_exists(getrandom "sys/random.h" HAVE_GETRANDOM)
 check_symbol_exists(O_CLOEXEC fcntl.h HAVE_O_CLOEXEC)
 check_symbol_exists(CLOCK_MONOTONIC time.h HAVE_CLOCK_MONOTONIC)
 check_symbol_exists(CLOCK_MONOTONIC_COARSE time.h HAVE_CLOCK_MONOTONIC_COARSE)

src/native/minipal/minipalconfig.h.in

@@ -2,6 +2,7 @@
 #define HAVE_MINIPAL_MINIPALCONFIG_H
 
 #cmakedefine01 HAVE_ARC4RANDOM_BUF
+#cmakedefine01 HAVE_GETRANDOM
 #cmakedefine01 HAVE_AUXV_HWCAP_H
 #cmakedefine01 HAVE_HWPROBE_H
 #cmakedefine01 HAVE_RESOURCE_H

src/native/minipal/random.c

@@ -16,6 +16,9 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
+#if HAVE_GETRANDOM
+#include <sys/random.h>
+#endif
 #endif
 #if defined(__APPLE__) && __APPLE__
 #include <CommonCrypto/CommonRandom.h>
@@ -100,6 +103,45 @@ int32_t minipal_get_cryptographically_secure_random_bytes(uint8_t* buffer, int32
     return BCRYPT_SUCCESS(status) ? 0 : -1;
 #else
 
+#if HAVE_GETRANDOM
+    // Try getrandom() first - it's faster than /dev/urandom as it avoids file descriptor overhead.
+    // getrandom() was added in Linux 3.17 (2014) and glibc 2.25 (2017).
+    static volatile bool sGetrandomUnavailable;
+
+    if (!sGetrandomUnavailable)
+    {
+        int32_t offset = 0;
+        while (offset != bufferLength)
+        {
+            ssize_t n = getrandom(buffer + offset, (size_t)(bufferLength - offset), 0);
+            if (n == -1)
+            {
+                if (errno == EINTR)
+                {
+                    continue;
+                }
+                // ENOSYS: syscall not available (old kernel or blocked by seccomp)
+                // EPERM: operation not permitted (some container environments)
+                // Fall back to /dev/urandom for these errors
+                if (errno == ENOSYS || errno == EPERM)
+                {
+                    sGetrandomUnavailable = true;
+                    break;
+                }
+                return -1;
+            }
+
+            offset += (int32_t)n;
+        }
+
+        if (offset == bufferLength)
+        {
+            return 0;
+        }
+    }
+#endif
+
+    // Fallback to /dev/urandom
     static volatile int rand_des = -1;
     static bool sMissingDevURandom;