portability: add getrandom

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>

portability/getrandom.c

+#include <sys/random.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+ssize_t getrandom(void *buf, size_t buflen, unsigned int flags)
+{
+	int fd;
+	ssize_t ret;
+
+	fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC);
+	if (fd < 0)
+		return -1;
+
+	ret = read(fd, buf, buflen);
+	close(fd);
+	return ret;
+}
+

portability/meson.build

@@ -3,6 +3,7 @@ cc = meson.get_compiler('c')
 libportability_src = []
 
 check_symbols = [
+	['getrandom', 'getrandom.c', 'NEED_GETRANDOM', 'sys/random.h'],
 	['memrchr', 'memrchr.c', 'NEED_MEMRCHR', 'string.h'],
 	['mknodat', 'mknodat.c', 'NEED_MKNODAT', 'sys/stat.h'],
 	['pipe2', 'pipe2.c', 'NEED_PIPE2', 'unistd.h'],

portability/sys/random.h

+#include_next <sys/random.h>
+#include <sys/types.h>
+
+#ifdef NEED_GETRANDOM
+ssize_t getrandom(void *buf, size_t buflen, unsigned int flags);
+#endif