[PATCH v4 1/3] virtio: add dma-buf support for exported objects

[David Stevens]

This change adds a new flavor of dma-bufs that can be used by virtio
drivers to share exported objects. A virtio dma-buf can be queried by
virtio drivers to obtain the UUID which identifies the underlying
exported object.

Signed-off-by: David Stevens <stevensd@xxxxxxxxxxxx>
---
 drivers/virtio/Makefile         |  2 +-
 drivers/virtio/virtio.c         |  6 +++
 drivers/virtio/virtio_dma_buf.c | 89 +++++++++++++++++++++++++++++++++
 include/linux/virtio.h          |  1 +
 include/linux/virtio_dma_buf.h  | 58 +++++++++++++++++++++
 5 files changed, 155 insertions(+), 1 deletion(-)
 create mode 100644 drivers/virtio/virtio_dma_buf.c
 create mode 100644 include/linux/virtio_dma_buf.h

diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 29a1386ecc03..ecdae5b596de 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_VIRTIO) += virtio.o virtio_ring.o
+obj-$(CONFIG_VIRTIO) += virtio.o virtio_ring.o virtio_dma_buf.o
 obj-$(CONFIG_VIRTIO_MMIO) += virtio_mmio.o
 obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
 virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index a977e32a88f2..5d46f0ded92d 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -357,6 +357,12 @@ int register_virtio_device(struct virtio_device *dev)
 }
 EXPORT_SYMBOL_GPL(register_virtio_device);
 
+bool is_virtio_device(struct device *dev)
+{
+	return dev->bus == &virtio_bus;
+}
+EXPORT_SYMBOL_GPL(is_virtio_device);
+
 void unregister_virtio_device(struct virtio_device *dev)
 {
 	int index = dev->index; /* save for after device release */
diff --git a/drivers/virtio/virtio_dma_buf.c b/drivers/virtio/virtio_dma_buf.c
new file mode 100644
index 000000000000..23e3399b11ed
--- /dev/null
+++ b/drivers/virtio/virtio_dma_buf.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * dma-bufs for virtio exported objects
+ *
+ * Copyright (C) 2020 Google, Inc.
+ */
+
+#include <linux/virtio_dma_buf.h>
+
+/**
+ * virtio_dma_buf_export - Creates a new dma-buf for a virtio exported object
+ *
+ * This wraps dma_buf_export() to allow virtio drivers to create a dma-buf
+ * for an virtio exported object that can be queried by other virtio drivers
+ * for the object's UUID.
+ */
+struct dma_buf *virtio_dma_buf_export(
+		const struct virtio_dma_buf_export_info *virtio_exp_info)
+{
+	struct dma_buf_export_info exp_info;
+
+	if (!virtio_exp_info->ops
+		|| virtio_exp_info->ops->ops.attach != &virtio_dma_buf_attach
+		|| !virtio_exp_info->ops->get_uuid) {
+		return ERR_PTR(-EINVAL);
+	}
+
+	exp_info.exp_name = virtio_exp_info->exp_name;
+	exp_info.owner = virtio_exp_info->owner;
+	exp_info.ops = &virtio_exp_info->ops->ops;
+	exp_info.size = virtio_exp_info->size;
+	exp_info.flags = virtio_exp_info->flags;
+	exp_info.resv = virtio_exp_info->resv;
+	exp_info.priv = virtio_exp_info->priv;
+	BUILD_BUG_ON(sizeof(struct virtio_dma_buf_export_info)
+		     != sizeof(struct dma_buf_export_info));
+
+	return dma_buf_export(&exp_info);
+}
+EXPORT_SYMBOL(virtio_dma_buf_export);
+
+/**
+ * virtio_dma_buf_attach - mandatory attach callback for virtio dma-bufs
+ */
+int virtio_dma_buf_attach(struct dma_buf *dma_buf,
+			  struct dma_buf_attachment *attach)
+{
+	int ret;
+	const struct virtio_dma_buf_ops *ops = container_of(
+			dma_buf->ops, const struct virtio_dma_buf_ops, ops);
+
+	if (ops->device_attach) {
+		ret = ops->device_attach(dma_buf, attach);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(virtio_dma_buf_attach);
+
+/**
+ * is_virtio_dma_buf - returns true if the given dma-buf is a virtio dma-buf
+ * @dma_buf: buffer to query
+ */
+bool is_virtio_dma_buf(struct dma_buf *dma_buf)
+{
+	return dma_buf->ops->attach == &virtio_dma_buf_attach;
+}
+EXPORT_SYMBOL(is_virtio_dma_buf);
+
+/**
+ * virtio_dma_buf_get_uuid - gets the uuid of the virtio dma-buf's exported object
+ * @dma_buf: [in] buffer to query
+ * @uuid: [out] the uuid
+ *
+ * Returns: 0 on success, negative on failure.
+ */
+int virtio_dma_buf_get_uuid(struct dma_buf *dma_buf,
+			    uuid_t *uuid)
+{
+	const struct virtio_dma_buf_ops *ops = container_of(
+			dma_buf->ops, const struct virtio_dma_buf_ops, ops);
+
+	if (!is_virtio_dma_buf(dma_buf))
+		return -EINVAL;
+
+	return ops->get_uuid(dma_buf, uuid);
+}
+EXPORT_SYMBOL(virtio_dma_buf_get_uuid);
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 15f906e4a748..9397e25616c4 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -128,6 +128,7 @@ static inline struct virtio_device *dev_to_virtio(struct device *_dev)
 void virtio_add_status(struct virtio_device *dev, unsigned int status);
 int register_virtio_device(struct virtio_device *dev);
 void unregister_virtio_device(struct virtio_device *dev);
+bool is_virtio_device(struct device *dev);
 
 void virtio_break_device(struct virtio_device *dev);
 
diff --git a/include/linux/virtio_dma_buf.h b/include/linux/virtio_dma_buf.h
new file mode 100644
index 000000000000..29fee167afbd
--- /dev/null
+++ b/include/linux/virtio_dma_buf.h
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * dma-bufs for virtio exported objects
+ *
+ * Copyright (C) 2020 Google, Inc.
+ */
+
+#ifndef _LINUX_VIRTIO_DMA_BUF_H
+#define _LINUX_VIRTIO_DMA_BUF_H
+
+#include <linux/dma-buf.h>
+#include <linux/uuid.h>
+#include <linux/virtio.h>
+
+/**
+ * struct virtio_dma_buf_ops - operations possible on exported object dma-buf
+ * @ops: the base dma_buf_ops. ops.attach MUST be virtio_dma_buf_attach.
+ * @device_attach: [optional] callback invoked by virtio_dma_buf_attach during
+ *		   all attach operations.
+ * @get_uid: [required] callback to get the uuid of the exported object.
+ */
+struct virtio_dma_buf_ops {
+	struct dma_buf_ops ops;
+	int (*device_attach)(struct dma_buf *dma_buf,
+			     struct dma_buf_attachment *attach);
+	int (*get_uuid)(struct dma_buf *dma_buf, uuid_t *uuid);
+};
+
+/**
+ * struct virtio_dma_buf_export_info - see struct dma_buf_export_info
+ */
+struct virtio_dma_buf_export_info {
+	const char *exp_name;
+	struct module *owner;
+	const struct virtio_dma_buf_ops *ops;
+	size_t size;
+	int flags;
+	struct dma_resv *resv;
+	void *priv;
+};
+
+/**
+ * DEFINE_VIRTIO_DMA_BUF_EXPORT_INFO - helper macro for exporters
+ */
+#define DEFINE_VIRTIO_DMA_BUF_EXPORT_INFO(name)	\
+	struct virtio_dma_buf_export_info name = { \
+		.exp_name = KBUILD_MODNAME, \
+		.owner = THIS_MODULE }
+
+int virtio_dma_buf_attach(struct dma_buf *dma_buf,
+			  struct dma_buf_attachment *attach);
+
+struct dma_buf *virtio_dma_buf_export(
+		const struct virtio_dma_buf_export_info *virtio_exp_info);
+bool is_virtio_dma_buf(struct dma_buf *dma_buf);
+int virtio_dma_buf_get_uuid(struct dma_buf *dma_buf, uuid_t *uuid);
+
+#endif /* _LINUX_VIRTIO_DMA_BUF_H */
-- 
2.27.0.rc0.183.gde8f92d652-goog