[PATCH] virtio: sanity check on callback of virtio drivers

[Dawei Li <set_pte_at@outlook.com>]

This commit includes changes below:

1 Since register_virtio_driver doesn't force probe & remove
  to be mandatory callback, so it's caller's job to make the
  sanity check before invocation.

2 Replace sprintf with sysfs_emit or its variants for their
  built-in PAGE_SIZE awareness.

Signed-off-by: Dawei Li <set_pte_at@outlook.com>
---
 drivers/virtio/virtio.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 828ced060742..e391a8dff333 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -15,7 +15,7 @@ static ssize_t device_show(struct device *_d,
 			   struct device_attribute *attr, char *buf)
 {
 	struct virtio_device *dev = dev_to_virtio(_d);
-	return sprintf(buf, "0x%04x\n", dev->id.device);
+	return sysfs_emit(buf, "0x%04x\n", dev->id.device);
 }
 static DEVICE_ATTR_RO(device);
 
@@ -23,7 +23,7 @@ static ssize_t vendor_show(struct device *_d,
 			   struct device_attribute *attr, char *buf)
 {
 	struct virtio_device *dev = dev_to_virtio(_d);
-	return sprintf(buf, "0x%04x\n", dev->id.vendor);
+	return sysfs_emit(buf, "0x%04x\n", dev->id.vendor);
 }
 static DEVICE_ATTR_RO(vendor);
 
@@ -31,7 +31,7 @@ static ssize_t status_show(struct device *_d,
 			   struct device_attribute *attr, char *buf)
 {
 	struct virtio_device *dev = dev_to_virtio(_d);
-	return sprintf(buf, "0x%08x\n", dev->config->get_status(dev));
+	return sysfs_emit(buf, "0x%08x\n", dev->config->get_status(dev));
 }
 static DEVICE_ATTR_RO(status);
 
@@ -39,7 +39,7 @@ static ssize_t modalias_show(struct device *_d,
 			     struct device_attribute *attr, char *buf)
 {
 	struct virtio_device *dev = dev_to_virtio(_d);
-	return sprintf(buf, "virtio:d%08Xv%08X\n",
+	return sysfs_emit(buf, "virtio:d%08Xv%08X\n",
 		       dev->id.device, dev->id.vendor);
 }
 static DEVICE_ATTR_RO(modalias);
@@ -54,9 +54,9 @@ static ssize_t features_show(struct device *_d,
 	/* We actually represent this as a bitstring, as it could be
 	 * arbitrary length in future. */
 	for (i = 0; i < sizeof(dev->features)*8; i++)
-		len += sprintf(buf+len, "%c",
+		len += sysfs_emit_at(buf, len, "%c",
 			       __virtio_test_bit(dev, i) ? '1' : '0');
-	len += sprintf(buf+len, "\n");
+	len += sysfs_emit_at(buf, len, "\n");
 	return len;
 }
 static DEVICE_ATTR_RO(features);
@@ -302,9 +302,11 @@ static int virtio_dev_probe(struct device *_d)
 	if (err)
 		goto err;
 
-	err = drv->probe(dev);
-	if (err)
-		goto err;
+	if (drv->probe) {
+		err = drv->probe(dev);
+		if (err)
+			goto err;
+	}
 
 	/* If probe didn't do it, mark device DRIVER_OK ourselves. */
 	if (!(dev->config->get_status(dev) & VIRTIO_CONFIG_S_DRIVER_OK))
@@ -329,7 +331,8 @@ static void virtio_dev_remove(struct device *_d)
 
 	virtio_config_disable(dev);
 
-	drv->remove(dev);
+	if (drv->remove)
+		drv->remove(dev);
 
 	/* Driver should have reset device. */
 	WARN_ON_ONCE(dev->config->get_status(dev));
-- 
2.25.1