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

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Message-ID: <20231201150442.GC509422@mit.edu>
Date:   Fri, 1 Dec 2023 10:04:42 -0500
From:   "Theodore Ts'o" <tytso@....edu>
To:     Alice Ryhl <aliceryhl@...gle.com>
Cc:     david.laight@...lab.com, a.hindborg@...sung.com,
        alex.gaynor@...il.com, arve@...roid.com, benno.lossin@...ton.me,
        bjorn3_gh@...tonmail.com, boqun.feng@...il.com, brauner@...nel.org,
        cmllamas@...gle.com, dan.j.williams@...el.com, dxu@...uu.xyz,
        gary@...yguo.net, gregkh@...uxfoundation.org,
        joel@...lfernandes.org, keescook@...omium.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        maco@...roid.com, ojeda@...nel.org, peterz@...radead.org,
        rust-for-linux@...r.kernel.org, surenb@...gle.com,
        tglx@...utronix.de, tkjos@...roid.com, viro@...iv.linux.org.uk,
        wedsonaf@...il.com, willy@...radead.org
Subject: Re: [PATCH 1/7] rust: file: add Rust abstraction for `struct file`

On Fri, Dec 01, 2023 at 12:27:40PM +0000, Alice Ryhl wrote:
> 
> You can import it with a use statement. For example:
> 
> use kernel::file::flags::O_RDONLY;
> // use as O_RDONLY

That's good to hear, but it still means that we have to use the XYZ_*
prefix, because otherwise, after something like

use kernel::file::flags::RDONLY;
use kernel::uapi::rwf::RDONLY;

that will blow up.  So that has to be

use kernel::file::flags::O_RDONLY;
use kernel::uapi::rwf::RWF_RDONLY;

Which is a bit more verbose, at least things won't blow up
spectacularly when you need to use both namespaces in the same
codepath.

Also note how we do things like this:

#define IOCB_APPEND          (__force int) RWF_APPEND

In other words, the IOCB_* namespace and the RWF_* namespace partially
share code points, and so they *have* to be assigned to the same value
--- and note that since RWF_APPEND is defined as part of the UAPI, it
might not even be the same across different architectures....

Cheers,

						- Ted