On 6/3/25 11:52, wangtao wrote:
> First determine if dmabuf reads from or writes to the file.
> Then call exporter's rw_file callback function.
>
> Signed-off-by: wangtao <tao.wang...@honor.com>
> ---
> drivers/dma-buf/dma-buf.c | 32 ++++++++++++++++++++++++++++++++
> include/linux/dma-buf.h | 16 ++++++++++++++++
> 2 files changed, 48 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 5baa83b85515..fc9bf54c921a 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -523,7 +523,38 @@ static void dma_buf_show_fdinfo(struct seq_file *m,
> struct file *file)
> spin_unlock(&dmabuf->name_lock);
> }
>
> +static ssize_t dma_buf_rw_file(struct dma_buf *dmabuf, loff_t my_pos,
> + struct file *file, loff_t pos, size_t count, bool is_write)
> +{
> + if (!dmabuf->ops->rw_file)
> + return -EINVAL;
> +
> + if (my_pos >= dmabuf->size)
> + count = 0;
> + else
> + count = min_t(size_t, count, dmabuf->size - my_pos);
> + if (!count)
> + return 0;
> +
> + return dmabuf->ops->rw_file(dmabuf, my_pos, file, pos, count, is_write);
> +}
> +
> +static ssize_t dma_buf_copy_file_range(struct file *file_in, loff_t pos_in,
> + struct file *file_out, loff_t pos_out,
> + size_t count, unsigned int flags)
> +{
> + if (is_dma_buf_file(file_in) && file_out->f_op->write_iter)
> + return dma_buf_rw_file(file_in->private_data, pos_in,
> + file_out, pos_out, count, true);
> + else if (is_dma_buf_file(file_out) && file_in->f_op->read_iter)
> + return dma_buf_rw_file(file_out->private_data, pos_out,
> + file_in, pos_in, count, false);
> + else
> + return -EINVAL;
> +}
> +
> static const struct file_operations dma_buf_fops = {
> + .fop_flags = FOP_MEMORY_FILE,
> .release = dma_buf_file_release,
> .mmap = dma_buf_mmap_internal,
> .llseek = dma_buf_llseek,
> @@ -531,6 +562,7 @@ static const struct file_operations dma_buf_fops = {
> .unlocked_ioctl = dma_buf_ioctl,
> .compat_ioctl = compat_ptr_ioctl,
> .show_fdinfo = dma_buf_show_fdinfo,
> + .copy_file_range = dma_buf_copy_file_range,
> };
>
> /*
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 36216d28d8bd..d3636e985399 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 +286,21 @@ struct dma_buf_ops {
>
> int (*vmap)(struct dma_buf *dmabuf, struct iosys_map *map);
> void (*vunmap)(struct dma_buf *dmabuf, struct iosys_map *map);
> +
> + /**
> + * @rw_file:
> + *
> + * If an Exporter needs to support Direct I/O file operations, it can
> + * implement this optional callback. The exporter must verify that no
> + * other objects hold the sg_table, ensure exclusive access to the
> + * dmabuf's sg_table, and only then proceed with the I/O operation.
Explain why and not what. E.g. something like "Allows direct I/O between this
DMA-buf and the file".
Completely drop mentioning the sg_table, that is irrelevant. Exclusive access
depends on how the exporter implements the whole thing.
Regards,
Christian.
> + *
> + * Returns:
> + *
> + * 0 on success or a negative error code on failure.
> + */
> + ssize_t (*rw_file)(struct dma_buf *dmabuf, loff_t my_pos,
> + struct file *file, loff_t pos, size_t count, bool is_write);
> };
>
> /**
