linux-kernel - Re: [PATCH v4 0/3] io_uring: add splice(2) support

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Message-ID: <e2fe9083-d5bf-001d-0821-04e265cb85cb@gmail.com>
Date:   Tue, 25 Feb 2020 01:51:47 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Stefan Metzmacher <metze@...ba.org>, io-uring@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/3] io_uring: add splice(2) support

On 25/02/2020 01:34, Jens Axboe wrote:
> On 2/24/20 8:35 AM, Jens Axboe wrote:
>> On 2/24/20 1:32 AM, Pavel Begunkov wrote:
>>> *on top of for-5.6 + async patches*
>>>
>>> Not the fastets implementation, but I'd need to stir up/duplicate
>>> splice.c bits to do it more efficiently.
>>>
>>> note: rebase on top of the recent inflight patchset.
>>
>> Let's get this queued up, looks good to go to me. Do you have a few
>> liburing test cases we can add for this?
> 
> Seems to me like we have an address space issue for the off_in and

Is that a problem? From the old fixing thread loop_rw_iter() it appeared
to me, that it's ok to pass a kernel address as a user one.
f_op->write of some implemented through the same copy_to_user().


> off_out parameters. Why aren't we passing in pointers to these
> and making them work like regular splice?

That's one extra copy_to_user() + copy_from_user(), which I hope to remove
in the future. And I'm not really a fan of such API, and would prefer to give
away such tracking to the userspace.

> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 792ef01a521c..b0cfd68be8c9 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -448,8 +448,8 @@ struct io_epoll {
>  struct io_splice {
>  	struct file			*file_out;
>  	struct file			*file_in;
> -	loff_t				off_out;
> -	loff_t				off_in;
> +	loff_t __user			*off_out;
> +	loff_t __user			*off_in;
>  	u64				len;
>  	unsigned int			flags;
>  };
> @@ -2578,8 +2578,8 @@ static int io_splice_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  		return 0;
>  
>  	sp->file_in = NULL;
> -	sp->off_in = READ_ONCE(sqe->splice_off_in);
> -	sp->off_out = READ_ONCE(sqe->off);
> +	sp->off_in = u64_to_user_ptr(READ_ONCE(sqe->splice_off_in));
> +	sp->off_out = u64_to_user_ptr(READ_ONCE(sqe->off));
>  	sp->len = READ_ONCE(sqe->len);
>  	sp->flags = READ_ONCE(sqe->splice_flags);
>  
> @@ -2614,7 +2614,6 @@ static int io_splice(struct io_kiocb *req, struct io_kiocb **nxt,
>  	struct file *in = sp->file_in;
>  	struct file *out = sp->file_out;
>  	unsigned int flags = sp->flags & ~SPLICE_F_FD_IN_FIXED;
> -	loff_t *poff_in, *poff_out;
>  	long ret;
>  
>  	if (force_nonblock) {
> @@ -2623,9 +2622,7 @@ static int io_splice(struct io_kiocb *req, struct io_kiocb **nxt,
>  		flags |= SPLICE_F_NONBLOCK;
>  	}
>  
> -	poff_in = (sp->off_in == -1) ? NULL : &sp->off_in;
> -	poff_out = (sp->off_out == -1) ? NULL : &sp->off_out;
> -	ret = do_splice(in, poff_in, out, poff_out, sp->len, flags);
> +	ret = do_splice(in, sp->off_in, out, sp->off_out, sp->len, flags);
>  	if (force_nonblock && ret == -EAGAIN)
>  		return -EAGAIN;
>  
> 

-- 
Pavel Begunkov



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