add getentropy(), fix return value of getrandom()HEADmaster

Signed-off-by: Thorsten Glaser <tg@debian.org>

1 files changed, 43 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/common/getentropy.c b/libc/sysdeps/linux/common/getentropy.c
new file mode 100644
index 000000000..971674c4f
--- /dev/null
+++ b/libc/sysdeps/linux/common/getentropy.c
@@ -0,0 +1,43 @@
+/*
+ * getentropy() by wrapping getrandom(), for µClibc-ng
+ *
+ * © 2025 mirabilos Ⓕ CC0 or MirBSD or GNU LGPLv2
+ *
+ * Note: may be a thread cancellation point, unlike the
+ * implementations in glibc and musl libc. Should this
+ * ever become a concern, it will need patching.
+ */
+
+#define _DEFAULT_SOURCE
+#include <errno.h>
+#include <unistd.h>
+#include <sys/random.h>
+
+int
+getentropy(void *__buf, size_t __len)
+{
+	ssize_t n;
+
+	if (__len > 256U) {
+		errno = EIO;
+		return (-1);
+	}
+
+ again:
+	if ((n = getrandom(__buf, __len, 0)) == -1)
+		switch (errno) {
+		case EAGAIN: /* should not happen but better safe than sorry */
+		case EINTR:
+			goto again;
+		default:
+			errno = EIO;
+			/* FALLTHROUGH */
+		case EFAULT:
+		case ENOSYS:
+			return (-1);
+		}
+	if ((size_t)n != __len)
+		/* also shouldn’t happen (safety net) */
+		goto again;
+	return (0);
+}