linux-kernel - Re: [RFC PATCH v2 2/4] rust: io_uring: introduce rust abstraction for io-uring cmd

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Message-ID: <aJoDTDwkoj50eKBX@sidongui-MacBookPro.local>
Date: Mon, 11 Aug 2025 23:50:52 +0900
From: Sidong Yang <sidong.yang@...iosa.ai>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Benno Lossin <lossin@...nel.org>,
	Caleb Sander Mateos <csander@...estorage.com>,
	Miguel Ojeda <ojeda@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Jens Axboe <axboe@...nel.dk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	io-uring@...r.kernel.org
Subject: Re: [RFC PATCH v2 2/4] rust: io_uring: introduce rust abstraction
 for io-uring cmd

On Mon, Aug 11, 2025 at 09:44:22AM -0300, Daniel Almeida wrote:
> 
> > 
> > There is `uring_cmd` callback in `file_operation` at c side. `Pin<&mut IoUringCmd>`
> > would be create in the callback function. But the callback function could be
> > called repeatedly with same `io_uring_cmd` instance as far as I know.
> > 
> > But in c side, there is initialization step `io_uring_cmd_prep()`.
> > How about fill zero pdu in `io_uring_cmd_prep()`? And we could assign a byte
> > as flag in pdu for checking initialized also we should provide 31 bytes except
> > a byte for the flag.
> > 
> 
> That was a follow-up question of mine. Can´t we enforce zero-initialization
> in C to get rid of this MaybeUninit? Uninitialized data is just bad in general.
> 
> Hopefully this can be done as you've described above, but I don't want to over
> extend my opinion on something I know nothing about.

I need to add a commit that initialize pdu in prep step in next version. 
I'd like to get a comment from io_uring maintainer Jens. Thanks.

If we could initialize (filling zero) in prep step, How about casting issue?
Driver still needs to cast array to its private struct in unsafe?

Thanks,
Sidong

> 
> - Daniel