[Qemu-devel] [PATCH v4 2/3] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()

[Laurent Vivier <lvivier@redhat.com>]

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.henderson@linaro.org>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 backends/Makefile.objs |  2 +-
 backends/rng-builtin.c | 56 ++++++++++++++++++++++++++++++++++++++++++
 qemu-options.hx        | 10 +++++++-
 3 files changed, 66 insertions(+), 2 deletions(-)
 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..b1264b745407
--- /dev/null
+++ b/backends/rng-builtin.c
@@ -0,0 +1,56 @@
+/*
+ * 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 "qapi/error.h"
+#include "qapi/qmp/qerror.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);
+    }
+}
+
+static void rng_builtin_class_init(ObjectClass *klass, void *data)
+{
+    RngBackendClass *rbc = RNG_BACKEND_CLASS(klass);
+
+    rbc->request_entropy = rng_builtin_request_entropy;
+}
+
+static const TypeInfo rng_builtin_info = {
+    .name = TYPE_RNG_BUILTIN,
+    .parent = TYPE_RNG_BACKEND,
+    .instance_size = sizeof(RngBuiltin),
+    .class_init = rng_builtin_class_init,
+};
+
+static void register_types(void)
+{
+    type_register_static(&rng_builtin_info);
+}
+
+type_init(register_types);
diff --git a/qemu-options.hx b/qemu-options.hx
index 4df0ea3aed5c..6ab920f12be4 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4280,13 +4280,21 @@ other options.
 
 The @option{share} boolean option is @var{on} by default with memfd.
 
+@item -object rng-builtin,id=@var{id}
+
+Creates a random number generator backend which obtains entropy from
+QEMU builtin functions. The @option{id} parameter is a unique ID that
+will be used to reference this entropy backend from the @option{virtio-rng}
+device.
+
 @item -object rng-random,id=@var{id},filename=@var{/dev/random}
 
 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/urandom}.
+entropy from and if omitted defaults to @option{/dev/urandom}. By default,
+the @option{virtio-rng} device uses this RNG backend.
 
 @item -object rng-egd,id=@var{id},chardev=@var{chardevid}
 
-- 
2.20.1