linux-kernel - Re: [PATCH 1/7] rust: file: add Rust abstraction for `struct file`

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Message-ID: <25TYokAJ6urAw9GygDDgCcp2mDZT42AF6l8v_u5y-0XZONnHa9kr4Tz_zh30URNuaT-8Q0JnTXgZqeAiinxPEZqzS8StBKyjizZ9e5mysS8=@proton.me>
Date:   Thu, 30 Nov 2023 16:12:14 +0000
From:   Benno Lossin <benno.lossin@...ton.me>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/7] rust: file: add Rust abstraction for `struct file`

On 11/30/23 16:58, Theodore Ts'o wrote:
> On Thu, Nov 30, 2023 at 03:46:55PM +0000, Benno Lossin wrote:
>>>>> +    pub const O_APPEND: u32 = bindings::O_APPEND;
>>>>
>>>> Why do all of these constants begin with `O_`?
>>>
>>> Because that is how they are defined in the kernel in the C code.  Why
>>> would they not be the same here?
>>
>> Then why does the C side name them that way? Is it because `O_*` is
>> supposed to mean something, or is it done due to namespacing?
> 
> It's because these sets of constants were flags passed to the open(2)
> system call, and so they are dictated by the POSIX specification.  So
> O_ means that they are a set of integer values which are used by
> open(2), and they are defined when userspace #include's the fcntl.h
> header file.  One could consider it be namespacing --- we need to
> distinguish these from other constants: MAY_APPEND, RWF_APPEND,
> ESCAPE_APPEND, STATX_ATTR_APPEND, BTRFS_INODE_APPEND.
> 
> But it's also a convention that dates back for ***decades*** and if we
> want code to be understandable by kernel programmers, we need to obey
> standard kernel naming conventions.

I see, that makes a lot of sense. Thanks for the explanation.

>> In Rust we have namespacing, so we generally drop common prefixes.
> 
> I don't know about Rust namespacing, but in other languages, how you
> have to especify namespaces tend to be ***far*** more verbose than
> just adding an O_ prefix.

In this case we already have the `flags` namespace, so I thought about
just dropping the `O_` prefix altogether.

-- 
Cheers,
Benno