[PATCH 3/4] binder: Add flags to relinquish ownership of fds

[Hillf Danton]

On 9 Jan 2023 21:38:06 +0000 T.J. Mercier <tjmercier at google.com>
>  
> @@ -2275,6 +2276,26 @@ static int binder_translate_fd(u32 fd, binder_size_t fd_offset,
>  		goto err_security;
>  	}
>  
> +	if (IS_ENABLED(CONFIG_MEMCG) && (flags & BINDER_FD_FLAG_XFER_CHARGE)) {
> +		struct dma_buf *dmabuf;
> +
> +		if (unlikely(!is_dma_buf_file(file))) {
> +			binder_user_error(
> +				"%d:%d got transaction with XFER_CHARGE for non-dmabuf fd, %d\n",
> +				proc->pid, thread->pid, fd);
> +			ret = -EINVAL;
> +			goto err_dmabuf;
> +		}

It barely makes sense to expose is_dma_buf_file() only for this.
> +
> +		dmabuf = file->private_data;
> +		ret = dma_buf_transfer_charge(dmabuf, target_proc->tsk);
> +		if (ret) {
> +			pr_warn("%d:%d Unable to transfer DMA-BUF fd charge to %d\n",
> +				proc->pid, thread->pid, target_proc->pid);
> +			goto err_xfer;
> +		}
> +	}
> +

This whole hunk should go to dma-buf instead by adding change to
dma_buf_transfer_charge() for instance.