Re: [RFC 3/5] io_uring: add infra and support for IORING_OP_URING_CMD

[Pavel Begunkov <asml.silence@gmail.com>]

On 4/4/22 08:16, Christoph Hellwig wrote:
[...]
>> +static void io_uring_cmd_work(struct io_kiocb *req, bool *locked)
>> +{
>> +	req->uring_cmd.driver_cb(&req->uring_cmd);
>> +}
>> +
>> +void io_uring_cmd_complete_in_task(struct io_uring_cmd *ioucmd,
>> +			void (*driver_cb)(struct io_uring_cmd *))
>> +{
>> +	struct io_kiocb *req = container_of(ioucmd, struct io_kiocb, uring_cmd);
>> +
>> +	req->uring_cmd.driver_cb = driver_cb;
>> +	req->io_task_work.func = io_uring_cmd_work;
>> +	io_req_task_work_add(req, !!(req->ctx->flags & IORING_SETUP_SQPOLL));
>> +}
>> +EXPORT_SYMBOL_GPL(io_uring_cmd_complete_in_task);
> 
> I'm still not a fund of the double indirect call here.  I don't really
> have a good idea yet, but I plan to look into it.

I haven't familiarised myself with the series properly, but if it's about
driver_cb, we can expose struct io_kiocb and io_req_task_work_add() so
the lower layers can implement their own io_task_work.func. Hopefully, it
won't be inventively abused...


# io_uring.h

static inline struct io_uring_cmd *io_req_to_ucmd(struct io_kiocb *req)
{
	return container_of();
}

typedef void (*io_tw_cb_t)(struct io_kiocb *req, bool *locked);

static inline void io_cmd_tw_add(struct io_uring_cmd *ioucmd, io_tw_cb_t foo)
{
	struct io_kiocb *req = container_of(ioucmb...);

	req->io_task_work.func = foo;
	io_req_task_work_add();
}

>>   static void io_req_task_queue_fail(struct io_kiocb *req, int ret)
> 
> Also it would be great to not add it between io_req_task_queue_fail and
> the callback set by it.
> 
>> +void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret)
>> +{
>> +	struct io_kiocb *req = container_of(ioucmd, struct io_kiocb, uring_cmd);
>> +
>> +	if (ret < 0)
>> +		req_set_fail(req);
>> +	io_req_complete(req, ret);
>> +}
>> +EXPORT_SYMBOL_GPL(io_uring_cmd_done);
> 
> It seems like all callers of io_req_complete actually call req_set_fail
> on failure.  So maybe it would be nice pre-cleanup to handle the
> req_set_fail call from ĩo_req_complete?

Interpretation of the result is different, e.g. io_tee(), that was the
reason it was left in the callers.

[...]
>> @@ -60,7 +62,10 @@ struct io_uring_sqe {
>>   		__s32	splice_fd_in;
>>   		__u32	file_index;
>>   	};
>> -	__u64	__pad2[2];
>> +	union {
>> +		__u64	__pad2[2];
>> +		__u64	cmd;
>> +	};
> 
> Can someone explain these changes to me a little more?

not required indeed, just

-	__u64	__pad2[2];
+	__u64	cmd;
+	__u64	__pad2;

-- 
Pavel Begunkov