[PATCH v5 08/16] block: add dma-buf support for raw bdev

[Pavel Begunkov]

Add a simple proxy implementation of init_dma_buf_io_ctx() forwarding
the call to a new struct block_device_operations operation. Also reject
dma-buf backed iterators for buffered IO.

Reviewed-by: Christoph Hellwig <hch at lst.de>
[pavel: reject dma-buf without O_DIRECT]
Signed-off-by: Pavel Begunkov <asml.silence at gmail.com>
---
 block/fops.c           | 19 +++++++++++++++++++
 include/linux/blkdev.h |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/block/fops.c b/block/fops.c
index 56bbacf6e317..3c403afb0f64 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -767,6 +767,9 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			ret = direct_write_fallback(iocb, from, ret,
 					blkdev_buffered_write(iocb, from));
 	} else {
+		if (unlikely(iov_iter_is_dmabuf_map(from)))
+			return -EOPNOTSUPP;
+
 		/*
 		 * Take i_rwsem and invalidate_lock to avoid racing with
 		 * set_blocksize changing i_blkbits/folio order and punching
@@ -821,6 +824,8 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 		if (ret < 0 || !count)
 			goto reexpand;
 	}
+	if (unlikely(iov_iter_is_dmabuf_map(to)))
+		return -EOPNOTSUPP;
 
 	/*
 	 * Take i_rwsem and invalidate_lock to avoid racing with set_blocksize
@@ -924,6 +929,19 @@ static int blkdev_mmap_prepare(struct vm_area_desc *desc)
 	return generic_file_mmap_prepare(desc);
 }
 
+static int blkdev_init_dma_buf_io_ctx(struct file *file,
+				      struct dma_buf_io_ctx *ctx)
+{
+	struct block_device *bdev = file_bdev(file);
+	struct gendisk *disk = bdev->bd_disk;
+
+	if (!(file->f_flags & O_DIRECT))
+		return -EINVAL;
+	if (!disk->fops->init_dma_buf_io_ctx)
+		return -EINVAL;
+	return disk->fops->init_dma_buf_io_ctx(bdev, ctx);
+}
+
 const struct file_operations def_blk_fops = {
 	.open		= blkdev_open,
 	.release	= blkdev_release,
@@ -942,6 +960,7 @@ const struct file_operations def_blk_fops = {
 	.fallocate	= blkdev_fallocate,
 	.uring_cmd	= blkdev_uring_cmd,
 	.fop_flags	= FOP_BUFFER_RASYNC | FOP_DONTCACHE,
+	.init_dma_buf_io_ctx = blkdev_init_dma_buf_io_ctx,
 };
 
 static __init int blkdev_init(void)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 9213a5716f95..9f4c92e51dc9 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1682,6 +1682,8 @@ struct block_device_operations {
 	/* returns the length of the identifier or a negative errno: */
 	int (*get_unique_id)(struct gendisk *disk, u8 id[16],
 			enum blk_unique_id id_type);
+	int (*init_dma_buf_io_ctx)(struct block_device *,
+				   struct dma_buf_io_ctx *);
 	struct module *owner;
 	const struct pr_ops *pr_ops;
 
-- 
2.54.0