Hi Michael,

On Thu, Jun 04, 2020 at 03:05:23PM -0400, Michael S. Tsirkin wrote:

On Tue, May 26, 2020 at 07:58:09PM +0900, David Stevens wrote:

quoted

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 <redacted>

Is this just for graphics? If yes I'd rather we put it in the graphics
driver. We can always move it later ...

Wouldn't this be the API that audio virtualisation will have to use to share 
buffers between the host and any guests?

Thanks
Guennadi

quoted

---
 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));

This is the only part that gives me pause. Why do we need this hack?
What's wrong with just using dma_buf_export_info directly,
and if you want the virtio ops, just using container_off?

quoted

+
+	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

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