[Qemu-devel] [PATCH] VirtIO-RNG: Update default entropy source to `/dev/urandom`

[Kashyap Chamarthy <kchamart@redhat.com>]

When QEMU exposes a VirtIO-RNG device to the guest, that device needs a
source of entropy, and that source needs to be "non-blocking", like
`/dev/urandom`.  However, currently QEMU defaults to the problematic
`/dev/random`, which is "blocking" (as in, it waits until sufficient
entropy is available).

So change the entropy source to the recommended `/dev/urandom`.

Related discussion in these[1][2] past threads.

[1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html
    -- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?"
[2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html
    -- "[RFC] Virtio RNG: Consider changing the default entropy source to
       /dev/urandom"

Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
---
 backends/rng-random.c | 2 +-
 qemu-options.hx       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/backends/rng-random.c b/backends/rng-random.c
index e2a49b0571d79eab335d5a74841d92c50a727b6a..eff36ef14084bccaad1eabe952e2cf6ffa9a2529 100644
--- a/backends/rng-random.c
+++ b/backends/rng-random.c
@@ -112,7 +112,7 @@ static void rng_random_init(Object *obj)
                             rng_random_set_filename,
                             NULL);
 
-    s->filename = g_strdup("/dev/random");
+    s->filename = g_strdup("/dev/urandom");
     s->fd = -1;
 }
 
diff --git a/qemu-options.hx b/qemu-options.hx
index 51802cbb266a208d70989c4f0ab3317a76edc1ea..a525609149e4d0e4bb60959f029a1a16eb36900d 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4276,7 +4276,7 @@ Creates a random number generator backend which obtains entropy from
 a device on the host. The @option{id} parameter is a unique ID that
 will be used to reference this entropy backend from the @option{virtio-rng}
 device. The @option{filename} parameter specifies which file to obtain
-entropy from and if omitted defaults to @option{/dev/random}.
+entropy from and if omitted defaults to @option{/dev/urandom}.
 
 @item -object rng-egd,id=@var{id},chardev=@var{chardevid}
 
-- 
2.17.2