[RFC 08/12] io_uring: add basic dmabuf helpers

[Pavel Begunkov <asml.silence@gmail.com>]

Add basic dmabuf helpers and structures for io_uring, which will be used
for dmabuf buffer registration. That can also be reused in other places
in io_uring, which is ommited from the series.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/Makefile |  1 +
 io_uring/dmabuf.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++
 io_uring/dmabuf.h | 34 +++++++++++++++++++++++++++
 3 files changed, 95 insertions(+)
 create mode 100644 io_uring/dmabuf.c
 create mode 100644 io_uring/dmabuf.h

diff --git a/io_uring/Makefile b/io_uring/Makefile
index d97c6b51d584..0f5a7ec38452 100644
--- a/io_uring/Makefile
+++ b/io_uring/Makefile
@@ -21,3 +21,4 @@ obj-$(CONFIG_EPOLL)		+= epoll.o
 obj-$(CONFIG_NET_RX_BUSY_POLL)	+= napi.o
 obj-$(CONFIG_NET) += net.o cmd_net.o
 obj-$(CONFIG_PROC_FS) += fdinfo.o
+obj-$(CONFIG_DMA_SHARED_BUFFER) += dmabuf.o
diff --git a/io_uring/dmabuf.c b/io_uring/dmabuf.c
new file mode 100644
index 000000000000..cb9d8bb5d5b3
--- /dev/null
+++ b/io_uring/dmabuf.c
@@ -0,0 +1,60 @@
+#include "dmabuf.h"
+
+void io_dmabuf_release(struct io_dmabuf *buf)
+{
+	if (buf->sgt)
+		dma_buf_unmap_attachment_unlocked(buf->attach, buf->sgt,
+						  buf->dir);
+	if (buf->attach)
+		dma_buf_detach(buf->dmabuf, buf->attach);
+	if (buf->dmabuf)
+		dma_buf_put(buf->dmabuf);
+	if (buf->dev)
+		put_device(buf->dev);
+
+	memset(buf, 0, sizeof(*buf));
+}
+
+int io_dmabuf_import(struct io_dmabuf *buf, int dmabuf_fd,
+		     struct device *dev, enum dma_data_direction dir)
+{
+	unsigned long total_size = 0;
+	struct scatterlist *sg;
+	int i, ret;
+
+	if (WARN_ON_ONCE(!dev))
+		return -EFAULT;
+
+	buf->dir = dir;
+	buf->dmabuf = dma_buf_get(dmabuf_fd);
+	if (IS_ERR(buf->dmabuf)) {
+		ret = PTR_ERR(buf->dmabuf);
+		buf->dmabuf = NULL;
+		goto err;
+	}
+
+	buf->attach = dma_buf_attach(buf->dmabuf, dev);
+	if (IS_ERR(buf->attach)) {
+		ret = PTR_ERR(buf->attach);
+		buf->attach = NULL;
+		goto err;
+	}
+
+	buf->sgt = dma_buf_map_attachment_unlocked(buf->attach, dir);
+	if (IS_ERR(buf->sgt)) {
+		ret = PTR_ERR(buf->sgt);
+		buf->sgt = NULL;
+		goto err;
+	}
+
+	for_each_sgtable_dma_sg(buf->sgt, sg, i)
+		total_size += sg_dma_len(sg);
+
+	buf->dir = dir;
+	buf->dev = get_device(dev);
+	buf->len = total_size;
+	return 0;
+err:
+	io_dmabuf_release(buf);
+	return ret;
+}
diff --git a/io_uring/dmabuf.h b/io_uring/dmabuf.h
new file mode 100644
index 000000000000..c785ccfe0b9e
--- /dev/null
+++ b/io_uring/dmabuf.h
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef IOU_DMABUF_H
+#define IOU_DMABUF_H
+
+#include <linux/io_uring_types.h>
+#include <linux/dma-buf.h>
+
+struct io_dmabuf {
+	size_t				len;
+	struct dma_buf_attachment	*attach;
+	struct dma_buf			*dmabuf;
+	struct sg_table			*sgt;
+	struct device			*dev;
+	enum dma_data_direction		dir;
+};
+
+#ifdef CONFIG_DMA_SHARED_BUFFER
+void io_dmabuf_release(struct io_dmabuf *buf);
+int io_dmabuf_import(struct io_dmabuf *buf, int dmabuf_fd,
+		     struct device *dev, enum dma_data_direction dir);
+
+#else
+static inline void io_dmabuf_release(struct io_dmabuf *buf)
+{
+}
+
+static inline int io_dmabuf_import(struct io_dmabuf *buf, int dmabuf_fd,
+		     struct device *dev, enum dma_data_direction dir)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
+#endif
-- 
2.49.0