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

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Message-ID: <20231201011615.GB509422@mit.edu>
Date:   Thu, 30 Nov 2023 20:16:15 -0500
From:   "Theodore Ts'o" <tytso@....edu>
To:     Benno Lossin <benno.lossin@...ton.me>
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 Thu, Nov 30, 2023 at 04:12:14PM +0000, Benno Lossin wrote:
> > 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.

Note that in C code, the flags are known to be an integer, and there
are times when we assume that it's possible to take the bitfield, and
then either (a) or'ing in bitfields from some other "namespace",
because it's known that the open flags only use a certain number of
the low bits of the integer, or even that O_RDONLY, O_WRONLY, and
O_RDWR are 0, 1, and 2, repsectively, and so you can do something like
((flags & 0x03) + 1) such that 1 means "read access", 2 means "write
access", and 3 (1|2) is read and write.

This may make a programmer used to a type-strict language feel a
little dirty, but again, this is a convention going back deckades,
back when a PDP-11 had only 32k of words in its address space....

Cheers,


     	    	       	    	- Ted