Re: [PATCH 4/8] io_uring: add support for IORING_OP_URING_CMD

[Jens Axboe <axboe@kernel.dk>]

On 3/17/21 11:42 PM, Christoph Hellwig wrote:
> On Wed, Mar 17, 2021 at 04:10:23PM -0600, Jens Axboe wrote:
>> +/*
>> + * Called by consumers of io_uring_cmd, if they originally returned
>> + * -EIOCBQUEUED upon receiving the command.
>> + */
>> +void io_uring_cmd_done(struct io_uring_cmd *cmd, ssize_t ret)
>> +{
>> +	struct io_kiocb *req = container_of(cmd, struct io_kiocb, uring_cmd);
>> +
>> +	if (ret < 0)
>> +		req_set_fail_links(req);
>> +	io_req_complete(req, ret);
>> +}
>> +EXPORT_SYMBOL(io_uring_cmd_done);
> 
> This really should be EXPORT_SYMBOL_GPL. But more importantly I'm not

Did make that change in my tree yesterday.

> sure it is an all that useful interface.  All useful non-trivial ioctls
> tend to access user memory, so something that queues up work in the task
> context like in Joshis patch should really be part of the documented
> interface.

Agree, and I made some comments on that patch to how to make that situation
better. Should go in with this part, to have in-task completions for
finishing it up.

>> +static int io_uring_cmd_prep(struct io_kiocb *req,
>> +			     const struct io_uring_sqe *sqe)
>> +{
>> +	const struct io_uring_cmd_sqe *csqe = (const void *) sqe;
> 
> We really should not need this casting.  The struct io_uring_sqe
> usage in io_uring.c needs to be replaced with a union or some other
> properly type safe way to handle this.
> 
>> +	ret = file->f_op->uring_cmd(&req->uring_cmd, issue_flags);
>> +	/* queued async, consumer will call io_uring_cmd_done() when complete */
>> +	if (ret == -EIOCBQUEUED)
>> +		return 0;
>> +	io_uring_cmd_done(&req->uring_cmd, ret);
>> +	return 0;
> 
> This can be simplified to:
> 
> 	if (ret != -EIOCBQUEUED)
> 		io_uring_cmd_done(&req->uring_cmd, ret);
> 	return 0;

Good point, will do that.

>> + * Note that the first member here must be a struct file, as the
>> + * io_uring command layout depends on that.
>> + */
>> +struct io_uring_cmd {
>> +	struct file	*file;
>> +	__u16		op;
>> +	__u16		unused;
>> +	__u32		len;
>> +	__u64		pdu[5];	/* 40 bytes available inline for free use */
>> +};
> 
> I am a little worried about exposting this internal structure to random
> drivers.  OTOH we need something that eventually allows a container_of
> to io_kiocb for the completion, so I can't think of anything better
> at the moment either.
> 


-- 
Jens Axboe