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>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 3f52c767dfe9..bd0745250fd9 100644
--- 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
 };