Re: [RFC PATCH v3 1/3] io_uring: add helper for uring_cmd completion in submitter-task

[Christoph Hellwig <hch@lst.de>]

On Thu, Mar 18, 2021 at 10:55:55AM +0530, Kanchan Joshi wrote:
> I started with that, but the problem was implementing the driver callback .
> The callbacks receive only one argument which is "struct callback_head
> *", and the driver needs to extract "io_uring_cmd *" out of it.
> This part -
> +static void uring_cmd_work(struct callback_head *cb)
> +{
> +     struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
> +     struct io_uring_cmd *cmd = &req->uring_cmd;
> 
> If the callback has to move to the driver (nvme), the driver needs
> visibility to "struct io_kiocb" which is uring-local.
> Do you see a better way to handle this?

Can't you just add a helper in io_uring.c that does something like this:

struct io_uring_cmd *callback_to_io_uring_cmd(struct callback_head *cb)
{
	return &container_of(cb, struct io_kiocb, task_work)->uring_cmd;
}
EXPORT_SYMBOL_GPL(callback_to_io_uring_cmd);