From 60253ed1e6ec6d8e5ef2efe7bf755f475dce9956 Mon Sep 17 00:00:00 2001

From: Ladi Prosek <lprosek@redhat.com>

Date: Thu, 3 Mar 2016 09:37:18 +0100

Subject: [PATCH] rng: add request queue support to rng-random

Requests are now created in the RngBackend parent class and the

code path is shared by both rng-egd and rng-random.

This commit fixes the rng-random implementation which processed

only one request at a time and simply discarded all but the most

recent one. In the guest this manifested as delayed completion

of reads from virtio-rng, i.e. a read was completed only after

another read was issued.

By switching rng-random to use the same request queue as rng-egd,

the unsafe stack-based allocation of the entropy buffer is

eliminated and replaced with g_malloc.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>

Reviewed-by: Amit Shah <amit.shah@redhat.com>

Message-Id: <1456994238-9585-5-git-send-email-lprosek@redhat.com>

Signed-off-by: Amit Shah <amit.shah@redhat.com>

---

 backends/rng-egd.c    |   16 ++--------------

 backends/rng-random.c |   43 +++++++++++++++++++------------------------

 backends/rng.c        |   13 ++++++++++++-

 include/sysemu/rng.h  |    3 +--

 4 files changed, 34 insertions(+), 41 deletions(-)

diff --git a/tools/qemu-xen/backends/rng-egd.c b/tools/qemu-xen/backends/rng-egd.c

index 8f2bd16..30332ed 100644

--- a/tools/qemu-xen/backends/rng-egd.c

+++ b/tools/qemu-xen/backends/rng-egd.c

@@ -27,20 +27,10 @@ typedef struct RngEgd

     char *chr_name;

 } RngEgd;

-static void rng_egd_request_entropy(RngBackend *b, size_t size,

-                                    EntropyReceiveFunc *receive_entropy,

-                                    void *opaque)

+static void rng_egd_request_entropy(RngBackend *b, RngRequest *req)

 {

     RngEgd *s = RNG_EGD(b);

-    RngRequest *req;

-

-    req = g_malloc(sizeof(*req));

-

-    req->offset = 0;

-    req->size = size;

-    req->receive_entropy = receive_entropy;

-    req->opaque = opaque;

-    req->data = g_malloc(req->size);

+    size_t size = req->size;

     while (size > 0) {

         uint8_t header[2];

@@ -54,8 +44,6 @@ static void rng_egd_request_entropy(RngBackend *b, size_t size,

         size -= len;

     }

-

-    s->parent.requests = g_slist_append(s->parent.requests, req);

 }

 static int rng_egd_chr_can_read(void *opaque)

diff --git a/tools/qemu-xen/backends/rng-random.c b/tools/qemu-xen/backends/rng-random.c

index 8cdad6a..a6cb385 100644

--- a/tools/qemu-xen/backends/rng-random.c

+++ b/tools/qemu-xen/backends/rng-random.c

@@ -22,10 +22,6 @@ struct RndRandom

     int fd;

     char *filename;

-

-    EntropyReceiveFunc *receive_func;

-    void *opaque;

-    size_t size;

 };

 /**

@@ -38,36 +34,35 @@ 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->parent.requests != NULL) {

+        RngRequest *req = s->parent.requests->data;

+        ssize_t len;

+

+        len = read(s->fd, req->data, 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_entropy(req->opaque, req->data, len);

+        rng_backend_finalize_request(&s->parent, req);

+    }

+

+    /* We've drained all requests, the fd handler can be reset. */

     qemu_set_fd_handler(s->fd, NULL, NULL, NULL);

 }

-static void rng_random_request_entropy(RngBackend *b, size_t size,

-                                        EntropyReceiveFunc *receive_entropy,

-                                        void *opaque)

+static void rng_random_request_entropy(RngBackend *b, RngRequest *req)

 {

     RndRandom *s = RNG_RANDOM(b);

-    if (s->receive_func) {

-        s->receive_func(s->opaque, NULL, 0);

+    if (s->parent.requests == NULL) {

+        /* If there are no pending requests yet, we need to

+         * install our fd handler. */

+        qemu_set_fd_handler(s->fd, entropy_available, NULL, s);

     }

-

-    s->receive_func = receive_entropy;

-    s->opaque = opaque;

-    s->size = size;

-

-    qemu_set_fd_handler(s->fd, entropy_available, NULL, s);

 }

 static void rng_random_opened(RngBackend *b, Error **errp)

diff --git a/tools/qemu-xen/backends/rng.c b/tools/qemu-xen/backends/rng.c

index 014cb9d..277a41b 100644

--- a/tools/qemu-xen/backends/rng.c

+++ b/tools/qemu-xen/backends/rng.c

@@ -20,9 +20,20 @@ void rng_backend_request_entropy(RngBackend *s, size_t size,

                                  void *opaque)

 {

     RngBackendClass *k = RNG_BACKEND_GET_CLASS(s);

+    RngRequest *req;

     if (k->request_entropy) {

-        k->request_entropy(s, size, receive_entropy, opaque);

+        req = g_malloc(sizeof(*req));

+

+        req->offset = 0;

+        req->size = size;

+        req->receive_entropy = receive_entropy;

+        req->opaque = opaque;

+        req->data = g_malloc(req->size);

+

+        k->request_entropy(s, req);

+

+        s->requests = g_slist_append(s->requests, req);

     }

 }

diff --git a/tools/qemu-xen/include/sysemu/rng.h b/tools/qemu-xen/include/sysemu/rng.h

index 08a2eda..4fffd68 100644

--- a/tools/qemu-xen/include/sysemu/rng.h

+++ b/tools/qemu-xen/include/sysemu/rng.h

@@ -45,8 +45,7 @@ struct RngBackendClass

 {

     ObjectClass parent_class;

-    void (*request_entropy)(RngBackend *s, size_t size,

-                            EntropyReceiveFunc *receive_entropy, void *opaque);

+    void (*request_entropy)(RngBackend *s, RngRequest *req);

     void (*opened)(RngBackend *s, Error **errp);

 };

-- 

1.7.0.4