If the guest adds a buffer to the virtio queue while another buffer
is still pending and hasn't been filled and returned by the rng
device, rng-random internally discards the pending request, which
leads to the second buffer getting stuck in the queue. For the guest
this manifests as delayed completion of reads from virtio-rng, i.e.
a read is completed only after another read is issued.
This patch adds an internal queue of requests, analogous to what
rng-egd uses, to make sure that requests and responses are balanced
and correctly ordered.
Signed-off-by: Ladi Prosek <lpro...@redhat.com>
---
backends/rng-random.c | 71 +++++++++++++++++++++++++++++++++++++++------------
1 file changed, 54 insertions(+), 17 deletions(-)
diff --git a/backends/rng-random.c b/backends/rng-random.c
index 4e51f46..3f1fd21 100644
--- a/backends/rng-random.c
+++ b/backends/rng-random.c
@@ -22,10 +22,16 @@ struct RndRandom
int fd;
char *filename;
+ GSList *requests;
+};
+
+typedef struct RngRequest
+{
EntropyReceiveFunc *receive_func;
void *opaque;
size_t size;
-};
+} RngRequest;
+
/**
* A simple and incomplete backend to request entropy from /dev/random.
@@ -37,19 +43,27 @@ struct RndRandom
static void entropy_available(void *opaque)
{
RndRandom *s = RNG_RANDOM(opaque);
- uint8_t buffer[s->size];
- ssize_t len;
- len = read(s->fd, buffer, s->size);
- if (len < 0 && errno == EAGAIN) {
- return;
- }
- g_assert(len != -1);
+ while (s->requests != NULL) {
+ RngRequest *req = s->requests->data;
+ uint8_t buffer[req->size];
+ ssize_t len;
+
+ len = read(s->fd, buffer, req->size);
+ if (len < 0 && errno == EAGAIN) {
+ return;
+ }
+ g_assert(len != -1);
- s->receive_func(s->opaque, buffer, len);
- s->receive_func = NULL;
+ req->receive_func(req->opaque, buffer, len);
- qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
+ s->requests = g_slist_remove_link(s->requests, s->requests);
+ g_free(req);
+ }
+
+ if (s->requests == NULL) {
+ qemu_set_fd_handler(s->fd, NULL, NULL, NULL);
+ }
}
static void rng_random_request_entropy(RngBackend *b, size_t size,
@@ -57,16 +71,36 @@ static void rng_random_request_entropy(RngBackend *b,
size_t size,
void *opaque)
{
RndRandom *s = RNG_RANDOM(b);
+ RngRequest *req;
- if (s->receive_func) {
- s->receive_func(s->opaque, NULL, 0);
+ req = g_malloc(sizeof(*req));
+
+ req->size = size;
+ req->receive_func = receive_entropy;
+ req->opaque = opaque;
+
+ s->requests = g_slist_append(s->requests, req);
+ if (s->requests->data == req) {
+ qemu_set_fd_handler(s->fd, entropy_available, NULL, s);
+ }
+}
+
+static void rng_random_free_requests(RndRandom *s)
+{
+ GSList *i;
+
+ for (i = s->requests; i; i = i->next) {
+ g_free(i->data);
}
- s->receive_func = receive_entropy;
- s->opaque = opaque;
- s->size = size;
+ g_slist_free(s->requests);
+ s->requests = NULL;
+}
- qemu_set_fd_handler(s->fd, entropy_available, NULL, s);
+static void rng_random_cancel_requests(RngBackend *b)
+{
+ RndRandom *s = RNG_RANDOM(b);
+ rng_random_free_requests(s);
}
static void rng_random_opened(RngBackend *b, Error **errp)
@@ -129,6 +163,8 @@ static void rng_random_finalize(Object *obj)
}
g_free(s->filename);
+
+ rng_random_free_requests(s);
}
static void rng_random_class_init(ObjectClass *klass, void *data)
@@ -136,6 +172,7 @@ static void rng_random_class_init(ObjectClass *klass, void
*data)
RngBackendClass *rbc = RNG_BACKEND_CLASS(klass);
rbc->request_entropy = rng_random_request_entropy;
+ rbc->cancel_requests = rng_random_cancel_requests;
rbc->opened = rng_random_opened;
}
--
2.5.0
