[Qemu-devel] [PATCH 2/4] rng-urandom: add an RNG backend that uses /dev/urandom

[Anthony Liguori]

The filename can be overridden but it expects a non-blocking source of entropy.
A typical invocation would be:

qemu -object rng-urandom,id=rng0 -device virtio-rng-pci,rng=rng0

Signed-off-by: Anthony Liguori <address@hidden>
---
 backends/Makefile.objs |    2 +-
 backends/rng-urandom.c |  144 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 145 insertions(+), 1 deletions(-)
 create mode 100644 backends/rng-urandom.c

diff --git a/backends/Makefile.objs b/backends/Makefile.objs
index 06e08c7..423c9df 100644
--- a/backends/Makefile.objs
+++ b/backends/Makefile.objs
@@ -1 +1 @@
-common-obj-y += rng.o
+common-obj-y += rng.o rng-urandom.o
diff --git a/backends/rng-urandom.c b/backends/rng-urandom.c
new file mode 100644
index 0000000..7fbe886
--- /dev/null
+++ b/backends/rng-urandom.c
@@ -0,0 +1,144 @@
+/*
+ * QEMU Random Number Generator Backend
+ *
+ * Copyright IBM, Corp. 2012
+ *
+ * Authors:
+ *  Anthony Liguori   <address@hidden>
+ *
+ * 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/rng.h"
+#include "qerror.h"
+
+#define TYPE_RNG_URANDOM "rng-urandom"
+#define RNG_URANDOM(obj) OBJECT_CHECK(RndURandom, (obj), TYPE_RNG_URANDOM)
+
+typedef struct RndURandom
+{
+    RngBackend parent;
+
+    int fd;
+    char *filename;
+    GSList *pending_data;
+} RndURandom;
+
+/**
+ * A simple and incomplete backend to request entropy from /dev/urandom.
+ *
+ * This backend exposes an additional "filename" property that can be used to
+ * set the filename to use to open the backend.
+ */
+static void rng_urandom_request_entropy(RngBackend *b, size_t size,
+                                        EntropyReceiveFunc *receive_entropy,
+                                        void *opaque)
+{
+    RndURandom *s = RNG_URANDOM(b);
+    uint8_t data[size];
+    ssize_t ret;
+
+    g_assert(s->fd != -1);
+
+    do {
+        ret = read(s->fd, data, size);
+    } while (ret == -1 && errno == EINTR);
+
+    g_assert(ret != -1);
+
+    /* FIXME: needs to be done via a BH */
+    receive_entropy(opaque, data, ret);
+}
+
+static void rng_urandom_opened(RngBackend *b, Error **errp)
+{
+    RndURandom *s = RNG_URANDOM(b);
+
+    if (s->filename == NULL) {
+        error_set(errp, QERR_INVALID_PARAMETER_VALUE,
+                  "filename", "a valid filename");
+    } else {
+        s->fd = open(s->filename, O_RDONLY);
+
+        if (s->fd == -1) {
+            error_set(errp, QERR_OPEN_FILE_FAILED, s->filename);
+        }
+    }
+}
+
+static char *rng_urandom_get_filename(Object *obj, Error **errp)
+{
+    RndURandom *s = RNG_URANDOM(obj);
+
+    if (s->filename) {
+        return g_strdup(s->filename);
+    }
+
+    return NULL;
+}
+
+static void rng_urandom_set_filename(Object *obj, const char *filename,
+                                 Error **errp)
+{
+    RngBackend *b = RNG_BACKEND(obj);
+    RndURandom *s = RNG_URANDOM(obj);
+
+    if (b->opened) {
+        error_set(errp, QERR_PERMISSION_DENIED);
+        return;
+    }
+
+    if (s->filename) {
+        g_free(s->filename);
+    }
+
+    s->filename = g_strdup(filename);
+}
+
+static void rng_urandom_init(Object *obj)
+{
+    RndURandom *s = RNG_URANDOM(obj);
+
+    object_property_add_str(obj, "filename",
+                            rng_urandom_get_filename,
+                            rng_urandom_set_filename,
+                            NULL);
+
+    s->filename = g_strdup("/dev/urandom");
+}
+
+static void rng_urandom_finalize(Object *obj)
+{
+    RndURandom *s = RNG_URANDOM(obj);
+
+    if (s->fd != -1) {
+        close(s->fd);
+    }
+
+    g_free(s->filename);
+}
+
+static void rng_urandom_class_init(ObjectClass *klass, void *data)
+{
+    RngBackendClass *rbc = RNG_BACKEND_CLASS(klass);
+
+    rbc->request_entropy = rng_urandom_request_entropy;
+    rbc->opened = rng_urandom_opened;
+}
+
+static TypeInfo rng_urandom_info = {
+    .name = TYPE_RNG_URANDOM,
+    .parent = TYPE_RNG_BACKEND,
+    .instance_size = sizeof(RndURandom),
+    .class_init = rng_urandom_class_init,
+    .instance_init = rng_urandom_init,
+    .instance_finalize = rng_urandom_finalize,
+};
+
+static void register_types(void)
+{
+    type_register_static(&rng_urandom_info);
+}
+
+type_init(register_types);
-- 
1.7.5.4