Re: [PATCH v2] io_uring: let IORING_OP_FILES_UPDATE support to choose fixed file slots

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

On 5/30/22 14:15, Xiaoguang Wang wrote:
> One big issue with file registration feature is that it needs user
> space apps to maintain free slot info about io_uring's fixed file
> table, which really is a burden for development. Now since io_uring
> starts to choose free file slot for user space apps by using
> IORING_FILE_INDEX_ALLOC flag in accept or open operations, but they
> need app to uses direct accept or direct open, which as far as I know,
> some apps are not prepared to use direct accept or open yet.
> 
> To support apps, who still need real fds, use registration feature
> easier, let IORING_OP_FILES_UPDATE support to choose fixed file slots,
> which will store picked fixed files slots in fd array and let cqe return
> the number of slots allocated.

Why close bits are piggybacked in this patch without any mention
in the commit message? What is error semantics of
IORING_CLOSE_FD_AND_FILE_SLOT. Fail if any errored or both? How
can it be reliably used? Why we do two separate things in one
request with not clear semantics?

There is already one fix pending. Another problem on the surface
is that it may call io_close() twice and the second will fail, e.g.

-> io_close()
---> close_fixed()
---> if (file->flush) return -EAGAIN
-> io_close()
---> close_fixed() // fails


I do think we need to revert the close change, and then remake
properly and only if someone can describe sane semantics for it.



> Suggested-by: Hao Xu <howeyxu@tencent.com>
> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
> ---
> V2:
>    Add illegal flags check in io_close_prep().
> ---
>   fs/io_uring.c                 | 75 +++++++++++++++++++++++++++++++++++++------
>   include/uapi/linux/io_uring.h |  1 +
>   2 files changed, 66 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 6d91148e9679..18a7459fb6e7 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -574,6 +574,7 @@ struct io_close {
>   	struct file			*file;
>   	int				fd;
>   	u32				file_slot;
> +	u32				flags;
>   };
>   
>   struct io_timeout_data {
> @@ -1366,7 +1367,9 @@ static int io_req_prep_async(struct io_kiocb *req);
>   
>   static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
>   				 unsigned int issue_flags, u32 slot_index);
> -static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags);
> +static int __io_close_fixed(struct io_kiocb *req, unsigned int issue_flags,
> +			    unsigned int offset);
> +static inline int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags);
>   
>   static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer);
>   static void io_eventfd_signal(struct io_ring_ctx *ctx);
> @@ -5945,16 +5948,22 @@ static int io_statx(struct io_kiocb *req, unsigned int issue_flags)
>   	return 0;
>   }
>   
> +#define IORING_CLOSE_FD_AND_FILE_SLOT 1
> +
>   static int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>   {
> -	if (sqe->off || sqe->addr || sqe->len || sqe->rw_flags || sqe->buf_index)
> +	if (sqe->off || sqe->addr || sqe->len || sqe->buf_index)
>   		return -EINVAL;
>   	if (req->flags & REQ_F_FIXED_FILE)
>   		return -EBADF;
>   
>   	req->close.fd = READ_ONCE(sqe->fd);
>   	req->close.file_slot = READ_ONCE(sqe->file_index);
> -	if (req->close.file_slot && req->close.fd)
> +	req->close.flags = READ_ONCE(sqe->close_flags);
> +	if (req->close.flags & ~IORING_CLOSE_FD_AND_FILE_SLOT)
> +		return -EINVAL;
> +	if (!(req->close.flags & IORING_CLOSE_FD_AND_FILE_SLOT) &&
> +	    req->close.file_slot && req->close.fd)
>   		return -EINVAL;
>   
>   	return 0;
> @@ -5970,7 +5979,8 @@ static int io_close(struct io_kiocb *req, unsigned int issue_flags)
>   
>   	if (req->close.file_slot) {
>   		ret = io_close_fixed(req, issue_flags);
> -		goto err;
> +		if (ret || !(req->close.flags & IORING_CLOSE_FD_AND_FILE_SLOT))
> +			goto err;
>   	}
>   
>   	spin_lock(&files->file_lock);
> @@ -8003,6 +8013,42 @@ static int io_files_update_prep(struct io_kiocb *req,
>   	return 0;
>   }
>   
> +static int io_files_update_with_index_alloc(struct io_kiocb *req,
> +					    unsigned int issue_flags)
> +{
> +	__s32 __user *fds = u64_to_user_ptr(req->rsrc_update.arg);
> +	struct file *file;
> +	unsigned int done, nr_fds = req->rsrc_update.nr_args;
> +	int ret, fd;
> +
> +	for (done = 0; done < nr_fds; done++) {
> +		if (copy_from_user(&fd, &fds[done], sizeof(fd))) {
> +			ret = -EFAULT;
> +			break;
> +		}
> +
> +		file = fget(fd);
> +		if (!file) {
> +			ret = -EBADF;
> +			goto out;
> +		}
> +		ret = io_fixed_fd_install(req, issue_flags, file,
> +					  IORING_FILE_INDEX_ALLOC);
> +		if (ret < 0)
> +			goto out;
> +		if (copy_to_user(&fds[done], &ret, sizeof(ret))) {
> +			ret = -EFAULT;
> +			__io_close_fixed(req, issue_flags, ret);
> +			break;
> +		}
> +	}
> +
> +out:
> +	if (done)
> +		return done;
> +	return ret;
> +}
> +
>   static int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
>   {
>   	struct io_ring_ctx *ctx = req->ctx;
> @@ -8016,10 +8062,14 @@ static int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
>   	up.resv = 0;
>   	up.resv2 = 0;
>   
> -	io_ring_submit_lock(ctx, issue_flags);
> -	ret = __io_register_rsrc_update(ctx, IORING_RSRC_FILE,
> -					&up, req->rsrc_update.nr_args);
> -	io_ring_submit_unlock(ctx, issue_flags);
> +	if (req->rsrc_update.offset == IORING_FILE_INDEX_ALLOC) {
> +		ret = io_files_update_with_index_alloc(req, issue_flags);
> +	} else {
> +		io_ring_submit_lock(ctx, issue_flags);
> +		ret = __io_register_rsrc_update(ctx, IORING_RSRC_FILE,
> +				&up, req->rsrc_update.nr_args);
> +		io_ring_submit_unlock(ctx, issue_flags);
> +	}
>   
>   	if (ret < 0)
>   		req_set_fail(req);
> @@ -10183,9 +10233,9 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
>   	return ret;
>   }
>   
> -static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags)
> +static int __io_close_fixed(struct io_kiocb *req, unsigned int issue_flags,
> +			    unsigned int offset)
>   {
> -	unsigned int offset = req->close.file_slot - 1;
>   	struct io_ring_ctx *ctx = req->ctx;
>   	struct io_fixed_file *file_slot;
>   	struct file *file;
> @@ -10222,6 +10272,11 @@ static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags)
>   	return ret;
>   }
>   
> +static inline int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags)
> +{
> +	return __io_close_fixed(req, issue_flags, req->close.file_slot - 1);
> +}
> +
>   static int __io_sqe_files_update(struct io_ring_ctx *ctx,
>   				 struct io_uring_rsrc_update2 *up,
>   				 unsigned nr_args)
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 53e7dae92e42..e347b3fea4e4 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -47,6 +47,7 @@ struct io_uring_sqe {
>   		__u32		unlink_flags;
>   		__u32		hardlink_flags;
>   		__u32		xattr_flags;
> +		__u32		close_flags;
>   	};
>   	__u64	user_data;	/* data to be passed back at completion time */
>   	/* pack this to avoid bogus arm OABI complaints */

-- 
Pavel Begunkov