virtio: expose features in sysfs

Each device negotiates feature bits; expose these in sysfs to help
diagnostics and debugging.

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

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 3f52c76..bd07452 100644 (file)
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -31,11 +31,27 @@ static ssize_t modalias_show(struct device *_d,
        return sprintf(buf, "virtio:d%08Xv%08X\n",
                       dev->id.device, dev->id.vendor);
 }
+static ssize_t features_show(struct device *_d,
+                            struct device_attribute *attr, char *buf)
+{
+       struct virtio_device *dev = container_of(_d, struct virtio_device, dev);
+       unsigned int i;
+       ssize_t len = 0;
+
+       /* We actually represent this as a bitstring, as it could be
+        * arbitrary length in future. */
+       for (i = 0; i < ARRAY_SIZE(dev->features)*BITS_PER_LONG; i++)
+               len += sprintf(buf+len, "%c",
+                              test_bit(i, dev->features) ? '1' : '0');
+       len += sprintf(buf+len, "\n");
+       return len;
+}
 static struct device_attribute virtio_dev_attrs[] = {
        __ATTR_RO(device),
        __ATTR_RO(vendor),
        __ATTR_RO(status),
        __ATTR_RO(modalias),
+       __ATTR_RO(features),
        __ATTR_NULL
 };