lguest: virtio-rng support

This is a simple patch to add support for the virtio "hardware random
generator" to lguest.  It gets about 1.2 MB/sec reading from /dev/hwrng
in the guest.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 90 insertions, 0 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 684d61191be..a1fca9db788 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -41,6 +41,7 @@
 #include "linux/virtio_net.h"
 #include "linux/virtio_blk.h"
 #include "linux/virtio_console.h"
+#include "linux/virtio_rng.h"
 #include "linux/virtio_ring.h"
 #include "asm-x86/bootparam.h"
 /*L:110 We can ignore the 39 include files we need for this program, but I do
@@ -199,6 +200,33 @@ static void *_convert(struct iovec *iov, size_t size, size_t align,
 #define le32_to_cpu(v32) (v32)
 #define le64_to_cpu(v64) (v64)
 
+/* Is this iovec empty? */
+static bool iov_empty(const struct iovec iov[], unsigned int num_iov)
+{
+        unsigned int i;
+
+        for (i = 0; i < num_iov; i++)
+                if (iov[i].iov_len)
+                        return false;
+        return true;
+}
+
+/* Take len bytes from the front of this iovec. */
+static void iov_consume(struct iovec iov[], unsigned num_iov, unsigned len)
+{
+        unsigned int i;
+
+        for (i = 0; i < num_iov; i++) {
+                unsigned int used;
+
+                used = iov[i].iov_len < len ? iov[i].iov_len : len;
+                iov[i].iov_base += used;
+                iov[i].iov_len -= used;
+                len -= used;
+        }
+        assert(len == 0);
+}
+
 /* The device virtqueue descriptors are followed by feature bitmasks. */
 static u8 *get_feature_bits(struct device *dev)
 {
@@ -1678,6 +1706,64 @@ static void setup_block_file(const char *filename)
         verbose("device %u: virtblock %llu sectors\n",
                 devices.device_num, le64_to_cpu(conf.capacity));
 }
+
+/* Our random number generator device reads from /dev/random into the Guest's
+ * input buffers.  The usual case is that the Guest doesn't want random numbers
+ * and so has no buffers although /dev/random is still readable, whereas
+ * console is the reverse.
+ *
+ * The same logic applies, however. */
+static bool handle_rng_input(int fd, struct device *dev)
+{
+        int len;
+        unsigned int head, in_num, out_num, totlen = 0;
+        struct iovec iov[dev->vq->vring.num];
+
+        /* First we need a buffer from the Guests's virtqueue. */
+        head = get_vq_desc(dev->vq, iov, &out_num, &in_num);
+
+        /* If they're not ready for input, stop listening to this file
+         * descriptor.  We'll start again once they add an input buffer. */
+        if (head == dev->vq->vring.num)
+                return false;
+
+        if (out_num)
+                errx(1, "Output buffers in rng?");
+
+        /* This is why we convert to iovecs: the readv() call uses them, and so
+         * it reads straight into the Guest's buffer.  We loop to make sure we
+         * fill it. */
+        while (!iov_empty(iov, in_num)) {
+                len = readv(dev->fd, iov, in_num);
+                if (len <= 0)
+                        err(1, "Read from /dev/random gave %i", len);
+                iov_consume(iov, in_num, len);
+                totlen += len;
+        }
+
+        /* Tell the Guest about the new input. */
+        add_used_and_trigger(fd, dev->vq, head, totlen);
+
+        /* Everything went OK! */
+        return true;
+}
+
+/* And this creates a "hardware" random number device for the Guest. */
+static void setup_rng(void)
+{
+        struct device *dev;
+        int fd;
+
+        fd = open_or_die("/dev/random", O_RDONLY);
+
+        /* The device responds to return from I/O thread. */
+        dev = new_device("rng", VIRTIO_ID_RNG, fd, handle_rng_input);
+
+        /* The device has one virtqueue, where the Guest places inbufs. */
+        add_virtqueue(dev, VIRTQUEUE_NUM, enable_fd);
+
+        verbose("device %u: rng\n", devices.device_num++);
+}
 /* That's the end of device setup. */
 
 /*L:230 Reboot is pretty easy: clean up and exec() the Launcher afresh. */
@@ -1748,6 +1834,7 @@ static struct option opts[] = {
         { "verbose", 0, NULL, 'v' },
         { "tunnet", 1, NULL, 't' },
         { "block", 1, NULL, 'b' },
+        { "rng", 0, NULL, 'r' },
         { "initrd", 1, NULL, 'i' },
         { NULL },
 };
@@ -1822,6 +1909,9 @@ int main(int argc, char *argv[])
                 case 'b':
                         setup_block_file(optarg);
                         break;
+                case 'r':
+                        setup_rng();
+                        break;
                 case 'i':
                         initrd_name = optarg;
                         break;