Re: [Qemu-devel] [PATCH v5 2/4] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()

[Laurent Vivier]

On 14/05/2019 18:27, Laurent Vivier wrote:
Add a new RNG backend using QEMU builtin getrandom function.
It can be created and used with something like:

     ... -object rng-builtin,id=rng0 -device virtio-rng,rng=rng0 ...

Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
Reviewed-by: Markus Armbruster <arm...@redhat.com>
Signed-off-by: Laurent Vivier <lviv...@redhat.com>
---
  backends/Makefile.objs |  2 +-
  backends/rng-builtin.c | 54 ++++++++++++++++++++++++++++++++++++++++++
  qemu-options.hx        |  7 ++++++
  3 files changed, 62 insertions(+), 1 deletion(-)
  create mode 100644 backends/rng-builtin.c

diff --git a/backends/Makefile.objs b/backends/Makefile.objs
index 981e8e122f2c..f0691116e86e 100644
--- a/backends/Makefile.objs
+++ b/backends/Makefile.objs
@@ -1,4 +1,4 @@
-common-obj-y += rng.o rng-egd.o
+common-obj-y += rng.o rng-egd.o rng-builtin.o
  common-obj-$(CONFIG_POSIX) += rng-random.o
  
  common-obj-$(CONFIG_TPM) += tpm.o
diff --git a/backends/rng-builtin.c b/backends/rng-builtin.c
new file mode 100644
index 000000000000..6b9543a7de87
--- /dev/null
+++ b/backends/rng-builtin.c
@@ -0,0 +1,54 @@
+/*
+ * QEMU Builtin Random Number Generator Backend
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "sysemu/rng.h"
+#include "qemu/main-loop.h"
+#include "qemu/guest-random.h"
+
+#define TYPE_RNG_BUILTIN "rng-builtin"
+#define RNG_BUILTIN(obj) OBJECT_CHECK(RngBuiltin, (obj), TYPE_RNG_BUILTIN)
+
+typedef struct RngBuiltin {
+    RngBackend parent;
+} RngBuiltin;
+
+static void rng_builtin_request_entropy(RngBackend *b, RngRequest *req)
+{
+    RngBuiltin *s = RNG_BUILTIN(b);
+
+    while (!QSIMPLEQ_EMPTY(&s->parent.requests)) {
+        RngRequest *req = QSIMPLEQ_FIRST(&s->parent.requests);
+
+        qemu_guest_getrandom_nofail(req->data, req->size);
+
+        req->receive_entropy(req->opaque, req->data, req->size);
+
+        rng_backend_finalize_request(&s->parent, req);


There is a problem here:

rng_backend_request_entropy() calls rng_builtin_request_entropy() and 
then add the request to the queue parent.requests, so receive_entropy() 
is called only on the next call of rng_backend_request_entropy() (and 
parameter req is unused).

Thanks,
Laurent