Re: [PATCH 1/2] dmabuf: add DMA_BUF_IOCTL_RW_FILE

["Christian König" <christian.koenig@amd.com>]

On 5/13/25 11:27, wangtao wrote:
> Add DMA_BUF_IOCTL_RW_FILE to save/restore data from/to a dma-buf.

Similar approach where rejected before in favor of using udmabuf.

Is there any reason you can't use that approach as well?

Regards,
Christian. 

> 
> Signed-off-by: wangtao <tao.wangtao@honor.com>
> ---
>  drivers/dma-buf/dma-buf.c    |  8 ++++++++
>  include/linux/dma-buf.h      |  3 +++
>  include/uapi/linux/dma-buf.h | 29 +++++++++++++++++++++++++++++
>  3 files changed, 40 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 5baa83b85515..95d8b0158ffd 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -460,6 +460,7 @@ static long dma_buf_ioctl(struct file *file,
>  	struct dma_buf *dmabuf;
>  	struct dma_buf_sync sync;
>  	enum dma_data_direction direction;
> +	struct dma_buf_rw_file kfile;
>  	int ret;
>  
>  	dmabuf = file->private_data;
> @@ -504,6 +505,13 @@ static long dma_buf_ioctl(struct file *file,
>  		return dma_buf_import_sync_file(dmabuf, (const void __user *)arg);
>  #endif
>  
> +	case DMA_BUF_IOCTL_RW_FILE:
> +		if (copy_from_user(&kfile, (void __user *) arg, sizeof(kfile)))
> +			return -EFAULT;
> +		if (!dmabuf->ops->rw_file)
> +			return -EINVAL;
> +		return dmabuf->ops->rw_file(dmabuf, &kfile);
> +
>  	default:
>  		return -ENOTTY;
>  	}
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 36216d28d8bd..de236ba2094b 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -22,6 +22,7 @@
>  #include <linux/fs.h>
>  #include <linux/dma-fence.h>
>  #include <linux/wait.h>
> +#include <uapi/linux/dma-buf.h>
>  
>  struct device;
>  struct dma_buf;
> @@ -285,6 +286,8 @@ struct dma_buf_ops {
>  
>  	int (*vmap)(struct dma_buf *dmabuf, struct iosys_map *map);
>  	void (*vunmap)(struct dma_buf *dmabuf, struct iosys_map *map);
> +
> +	int (*rw_file)(struct dma_buf *dmabuf, struct dma_buf_rw_file *file);
>  };
>  
>  /**
> diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
> index 5a6fda66d9ad..ec9164b7b753 100644
> --- a/include/uapi/linux/dma-buf.h
> +++ b/include/uapi/linux/dma-buf.h
> @@ -167,6 +167,29 @@ struct dma_buf_import_sync_file {
>  	__s32 fd;
>  };
>  
> +/**
> + * struct dma_buf_rw_file - read/write file associated with a dma-buf
> + *
> + * Userspace can performs a DMA_BUF_IOCTL_BACK to save data from a dma-buf or
> + * restore data to a dma-buf.
> + */
> +struct dma_buf_rw_file {
> +
> +	/** @flags: Flags indicating read/write for this dma-buf. */
> +	__u32 flags;
> +	/** @fd: File descriptor of the file associated with this dma-buf. */
> +	__s32 fd;
> +	/** @file_offset: Offset within the file where this dma-buf starts.
> +	 *
> +	 *  Offset and Length must be page-aligned for direct I/O.
> +	 */
> +	__u64 file_offset;
> +	/** @buf_offset: Offset within this dma-buf where the read/write starts. */
> +	__u64 buf_offset;
> +	/** @buf_len: Length of this dma-buf read/write. */
> +	__u64 buf_len;
> +};
> +
>  #define DMA_BUF_BASE		'b'
>  #define DMA_BUF_IOCTL_SYNC	_IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
>  
> @@ -179,4 +202,10 @@ struct dma_buf_import_sync_file {
>  #define DMA_BUF_IOCTL_EXPORT_SYNC_FILE	_IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
>  #define DMA_BUF_IOCTL_IMPORT_SYNC_FILE	_IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file)
>  
> +#define DMA_BUF_RW_FLAGS_OP_MASK (0xFF << 0)
> +#define DMA_BUF_RW_FLAGS_READ (1 << 0) /* Restore dma-buf data */
> +#define DMA_BUF_RW_FLAGS_WRITE (2 << 0) /* Save dma-buf data */
> +#define DMA_BUF_RW_FLAGS_DIRECT (1u << 31) /* Direct read/write file */
> +#define DMA_BUF_IOCTL_RW_FILE	_IOW(DMA_BUF_BASE, 4, struct dma_buf_rw_file)
> +
>  #endif