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

[Benno Lossin]

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