getrandom(GRND_INSECURE) is the same as /dev/urandom, except:
- It won't leave a warning in dmesg if used at early boot time, which is
a common occurance;
- It won't introduce a tiny delay at early boot on newer kernels when
/dev/urandom tries to opportunistically create jitter entropy;
- It only requires 1 syscall, rather than 3.
Other than that, it returns the same "quality" of randomness as
/dev/urandom, and never blocks.
It's only available on kernels ≥5.6, so we try to use it, cache the
result of that attempt, and fall back to /dev/urandom if it didn't work
out.
---
lib/misc/lvm-wrappers.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/lib/misc/lvm-wrappers.c b/lib/misc/lvm-wrappers.c
index 2e0cfd514..1239f1085 100644
--- a/lib/misc/lvm-wrappers.c
+++ b/lib/misc/lvm-wrappers.c
@@ -16,6 +16,7 @@
#include <unistd.h>
#include <fcntl.h>
+#include <sys/random.h>
#ifdef UDEV_SYNC_SUPPORT
#include <libudev.h>
@@ -111,8 +112,17 @@ int lvm_getpagesize(void)
int read_urandom(void *buf, size_t len)
{
+ static int have_getrandom = -1;
int fd;
+ if (have_getrandom) {
+ bool success = getrandom(buf, len, GRND_INSECURE) == len;
+ if (have_getrandom == -1)
+ have_getrandom = success;
+ if (success)
+ return 1;
+ }
+
/* FIXME: we should stat here, and handle other cases */
/* FIXME: use common _io() routine's open/read/close */
if ((fd = open("/dev/urandom", O_RDONLY)) < 0) {
--
2.35.1
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