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

From: Christoph Hellwig <hch@lst.de>
To: Kanchan Joshi <joshiiitr@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>, Kanchan Joshi <joshi.k@samsung.com>,
	Christoph Hellwig <hch@lst.de>, Keith Busch <kbusch@kernel.org>,
	Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>,
	io-uring@vger.kernel.org, linux-nvme@lists.infradead.org,
	anuj20.g@samsung.com, Javier Gonzalez <javier.gonz@samsung.com>,
	Nitesh Shetty <nj.shetty@samsung.com>,
	Selvakumar S <selvakuma.s1@samsung.com>
Subject: Re: [RFC PATCH v3 1/3] io_uring: add helper for uring_cmd completion in submitter-task
Date: Thu, 18 Mar 2021 06:48:07 +0100	[thread overview]
Message-ID: <20210318054807.GA28576@lst.de> (raw)
In-Reply-To: <CA+1E3r+Mt7KKeFeYf7WY3CoKwnkXT-jE2EgJSTE6zaAfJX0dzQ@mail.gmail.com>

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);