1 files changed, 108 insertions, 1 deletions

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 8d3cff42bdbb..e3d51a316316 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1802,6 +1802,26 @@ static ssize_t subchannel_id_show(struct vmbus_channel *channel,
 }
 static VMBUS_CHAN_ATTR_RO(subchannel_id);
 
+static int hv_mmap_ring_buffer_wrapper(struct file *filp, struct kobject *kobj,
+				       const struct bin_attribute *attr,
+				       struct vm_area_struct *vma)
+{
+	struct vmbus_channel *channel = container_of(kobj, struct vmbus_channel, kobj);
+
+	/*
+	 * hv_(create|remove)_ring_sysfs implementation ensures that mmap_ring_buffer
+	 * is not NULL.
+	 */
+	return channel->mmap_ring_buffer(channel, vma);
+}
+
+static struct bin_attribute chan_attr_ring_buffer = {
+	.attr = {
+		.name = "ring",
+		.mode = 0600,
+	},
+	.mmap = hv_mmap_ring_buffer_wrapper,
+};
 static struct attribute *vmbus_chan_attrs[] = {
 	&chan_attr_out_mask.attr,
 	&chan_attr_in_mask.attr,
@@ -1821,6 +1841,11 @@ static struct attribute *vmbus_chan_attrs[] = {
 	NULL
 };
 
+static struct bin_attribute *vmbus_chan_bin_attrs[] = {
+	&chan_attr_ring_buffer,
+	NULL
+};
+
 /*
  * Channel-level attribute_group callback function. Returns the permission for
  * each attribute, and returns 0 if an attribute is not visible.
@@ -1841,9 +1866,34 @@ static umode_t vmbus_chan_attr_is_visible(struct kobject *kobj,
 	return attr->mode;
 }
 
+static umode_t vmbus_chan_bin_attr_is_visible(struct kobject *kobj,
+					      const struct bin_attribute *attr, int idx)
+{
+	const struct vmbus_channel *channel =
+		container_of(kobj, struct vmbus_channel, kobj);
+
+	/* Hide ring attribute if channel's ring_sysfs_visible is set to false */
+	if (attr ==  &chan_attr_ring_buffer && !channel->ring_sysfs_visible)
+		return 0;
+
+	return attr->attr.mode;
+}
+
+static size_t vmbus_chan_bin_size(struct kobject *kobj,
+				  const struct bin_attribute *bin_attr, int a)
+{
+	const struct vmbus_channel *channel =
+		container_of(kobj, struct vmbus_channel, kobj);
+
+	return channel->ringbuffer_pagecount << PAGE_SHIFT;
+}
+
 static const struct attribute_group vmbus_chan_group = {
 	.attrs = vmbus_chan_attrs,
-	.is_visible = vmbus_chan_attr_is_visible
+	.bin_attrs = vmbus_chan_bin_attrs,
+	.is_visible = vmbus_chan_attr_is_visible,
+	.is_bin_visible = vmbus_chan_bin_attr_is_visible,
+	.bin_size = vmbus_chan_bin_size,
 };
 
 static const struct kobj_type vmbus_chan_ktype = {
@@ -1851,6 +1901,63 @@ static const struct kobj_type vmbus_chan_ktype = {
 	.release = vmbus_chan_release,
 };
 
+/**
+ * hv_create_ring_sysfs() - create "ring" sysfs entry corresponding to ring buffers for a channel.
+ * @channel: Pointer to vmbus_channel structure
+ * @hv_mmap_ring_buffer: function pointer for initializing the function to be called on mmap of
+ *                       channel's "ring" sysfs node, which is for the ring buffer of that channel.
+ *                       Function pointer is of below type:
+ *                       int (*hv_mmap_ring_buffer)(struct vmbus_channel *channel,
+ *                                                  struct vm_area_struct *vma))
+ *                       This has a pointer to the channel and a pointer to vm_area_struct,
+ *                       used for mmap, as arguments.
+ *
+ * Sysfs node for ring buffer of a channel is created along with other fields, however its
+ * visibility is disabled by default. Sysfs creation needs to be controlled when the use-case
+ * is running.
+ * For example, HV_NIC device is used either by uio_hv_generic or hv_netvsc at any given point of
+ * time, and "ring" sysfs is needed only when uio_hv_generic is bound to that device. To avoid
+ * exposing the ring buffer by default, this function is reponsible to enable visibility of
+ * ring for userspace to use.
+ * Note: Race conditions can happen with userspace and it is not encouraged to create new
+ * use-cases for this. This was added to maintain backward compatibility, while solving
+ * one of the race conditions in uio_hv_generic while creating sysfs.
+ *
+ * Returns 0 on success or error code on failure.
+ */
+int hv_create_ring_sysfs(struct vmbus_channel *channel,
+			 int (*hv_mmap_ring_buffer)(struct vmbus_channel *channel,
+						    struct vm_area_struct *vma))
+{
+	struct kobject *kobj = &channel->kobj;
+
+	channel->mmap_ring_buffer = hv_mmap_ring_buffer;
+	channel->ring_sysfs_visible = true;
+
+	return sysfs_update_group(kobj, &vmbus_chan_group);
+}
+EXPORT_SYMBOL_GPL(hv_create_ring_sysfs);
+
+/**
+ * hv_remove_ring_sysfs() - remove ring sysfs entry corresponding to ring buffers for a channel.
+ * @channel: Pointer to vmbus_channel structure
+ *
+ * Hide "ring" sysfs for a channel by changing its is_visible attribute and updating sysfs group.
+ *
+ * Returns 0 on success or error code on failure.
+ */
+int hv_remove_ring_sysfs(struct vmbus_channel *channel)
+{
+	struct kobject *kobj = &channel->kobj;
+	int ret;
+
+	channel->ring_sysfs_visible = false;
+	ret = sysfs_update_group(kobj, &vmbus_chan_group);
+	channel->mmap_ring_buffer = NULL;
+	return ret;
+}
+EXPORT_SYMBOL_GPL(hv_remove_ring_sysfs);
+
 /*
  * vmbus_add_channel_kobj - setup a sub-directory under device/channels
  */