lib/randutils: Do not block on getrandom()

In Endless we have hit a problem when using 'sfdisk' on the really first
boot to automatically expand the rootfs partition. On this platform
'sfdisk' is blocking on getrandom() because not enough random bytes are
available. This is an ARM platform without a hwrng.

We fix this passing GRND_NONBLOCK to getrandom(). 'sfdisk' will use the
best entropy it has available and fallback only as necessary.

Signed-off-by: Carlo Caione <carlo@endlessm.com>

diff --git a/lib/randutils.c b/lib/randutils.c
index e1c4059e19064463a98acdef1f5b91bb1111bd6e..02c3d9eb0d72b52aeaada6166006ce0153e21afb 100644 (file)
--- a/lib/randutils.c
+++ b/lib/randutils.c
@@ -36,6 +36,8 @@
 
 #if !defined(HAVE_GETRANDOM) && defined(SYS_getrandom)
 /* libc without function, but we have syscal */
+#define GRND_NONBLOCK 0x01
+#define GRND_RANDOM 0x02
 static int getrandom(void *buf, size_t buflen, unsigned int flags)
 {
        return (syscall(SYS_getrandom, buf, buflen, flags));
@@ -104,13 +106,15 @@ void random_get_bytes(void *buf, size_t nbytes)
                int x;
 
                errno = 0;
-               x = getrandom(cp, n, 0);
+               x = getrandom(cp, n, GRND_NONBLOCK);
                if (x > 0) {                    /* success */
                       n -= x;
                       cp += x;
                       lose_counter = 0;
                } else if (errno == ENOSYS)     /* kernel without getrandom() */
                        break;
+               else if (errno == EAGAIN)
+                       break;
                else if (lose_counter++ > 16)   /* entropy problem? */
                        break;
        }