RE: [PATCH 2/4] io_uring/cmd: add per-op data to struct io_uring_cmd_data

[lizetao <lizetao1@huawei.com>]

Hi,

> -----Original Message-----
> From: Mark Harmstone <maharmstone@fb.com>
> Sent: Friday, January 3, 2025 11:02 PM
> To: linux-btrfs@vger.kernel.org; io-uring@vger.kernel.org
> Cc: Jens Axboe <axboe@kernel.dk>
> Subject: [PATCH 2/4] io_uring/cmd: add per-op data to struct
> io_uring_cmd_data
> 
> From: Jens Axboe <axboe@kernel.dk>
> 
> In case an op handler for ->uring_cmd() needs stable storage for user data, it
> can allocate io_uring_cmd_data->op_data and use it for the duration of the
> request. When the request gets cleaned up, uring_cmd will free it
> automatically.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  include/linux/io_uring/cmd.h |  1 +
>  io_uring/uring_cmd.c         | 13 +++++++++++--
>  2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h index
> 61f97a398e9d..a65c7043078f 100644
> --- a/include/linux/io_uring/cmd.h
> +++ b/include/linux/io_uring/cmd.h
> @@ -20,6 +20,7 @@ struct io_uring_cmd {
> 
>  struct io_uring_cmd_data {
>  	struct io_uring_sqe	sqes[2];
> +	void			*op_data;
>  };
> 
>  static inline const void *io_uring_sqe_cmd(const struct io_uring_sqe *sqe) diff
> --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c index
> 629cb4266da6..ce7726a04883 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -23,12 +23,16 @@ static struct io_uring_cmd_data
> *io_uring_async_get(struct io_kiocb *req)
> 
>  	cache = io_alloc_cache_get(&ctx->uring_cache);
>  	if (cache) {
> +		cache->op_data = NULL;

Why is op_data set to NULL here? If you are worried about some omissions, would it be
better to use WARN_ON to assert that op_data is a null pointer? This will also make it easier
to analyze the cause of the problem.

---
Li Zetao