From: Alice Ryhl <aliceryhl@google.com>
To: brauner@kernel.org
Cc: a.hindborg@samsung.com, alex.gaynor@gmail.com,
aliceryhl@google.com, arve@android.com, benno.lossin@proton.me,
bjorn3_gh@protonmail.com, boqun.feng@gmail.com,
cmllamas@google.com, dan.j.williams@intel.com, dxu@dxuuu.xyz,
gary@garyguo.net, gregkh@linuxfoundation.org,
joel@joelfernandes.org, keescook@chromium.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
maco@android.com, ojeda@kernel.org, peterz@infradead.org,
rust-for-linux@vger.kernel.org, surenb@google.com,
tglx@linutronix.de, tkjos@android.com, viro@zeniv.linux.org.uk,
wedsonaf@gmail.com, willy@infradead.org
Subject: Re: [PATCH 4/7] rust: file: add `FileDescriptorReservation`
Date: Thu, 30 Nov 2023 09:23:22 +0000 [thread overview]
Message-ID: <20231130092322.110837-1-aliceryhl@google.com> (raw)
In-Reply-To: <20231130-neuwagen-balkon-aa1b34055fec@brauner>
Christian Brauner <brauner@kernel.org> writes:
> On Wed, Nov 29, 2023 at 06:14:24PM +0100, Alice Ryhl wrote:
> > On Wed, Nov 29, 2023 at 5:55 PM Alice Ryhl <aliceryhl@google.com> wrote:
> >
> > > >> + pub fn commit(self, file: ARef<File>) {
> > > >> + // SAFETY: `self.fd` was previously returned by `get_unused_fd_flags`, and `file.ptr` is
> > > >> + // guaranteed to have an owned ref count by its type invariants.
> > > >> + unsafe { bindings::fd_install(self.fd, file.0.get()) };
> > > >
> > > > Why file.0.get()? Where did that come from?
> > >
> > > This gets a raw pointer to the C type.
> > >
> > > The `.0` part is a field access. `ARef` struct is a tuple struct, so its
> > > fields are unnamed. However, the fields can still be accessed by index.
> >
> > Oh, sorry, this is wrong. Let me try again:
> >
> > This gets a raw pointer to the C type. The `.0` part accesses the
> > field of type `Opaque<bindings::file>` in the Rust wrapper. Recall
> > that File is defined like this:
> >
> > pub struct File(Opaque<bindings::file>);
> >
> > The above syntax defines a tuple struct, which means that the fields
> > are unnamed. The `.0` syntax accesses the first field of a tuple
> > struct [1].
> >
> > The `.get()` method is from the `Opaque` struct, which returns a raw
> > pointer to the C type being wrapped.
>
> It'd be nice if this could be written in a more obvious/elegant way. And
> if not a comment would help. I know there'll be more text then code but
> until this is second nature to read I personally won't mind... Because
> searching for this specific syntax isn't really possible.
Adding a comment to every instance of this is probably not realisitic.
This kind of code will be very common in abstraction code. However,
there are two other options that I think are reasonable:
1. I can change the definition of `File` so that the field has a name:
struct File {
inner: Opaque<bindings::file>,
}
Then, it would say `file.inner.get()`.
2. Alternatively, I can add a method to file:
impl File {
#[inline]
pub fn as_ptr(&self) -> *mut bindings::file {
self.0.get()
}
}
And then write `file.as_ptr()` whenever I want a pointer.
Alice
next prev parent reply other threads:[~2023-11-30 9:23 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-29 12:51 [PATCH 0/7] File abstractions needed by Rust Binder Alice Ryhl
2023-11-29 12:51 ` [PATCH 1/7] rust: file: add Rust abstraction for `struct file` Alice Ryhl
2023-11-29 15:13 ` Matthew Wilcox
2023-11-29 15:23 ` Peter Zijlstra
2023-11-29 17:08 ` Boqun Feng
2023-11-30 10:42 ` Peter Zijlstra
2023-11-30 15:25 ` Boqun Feng
2023-12-01 8:53 ` Peter Zijlstra
2023-12-01 9:19 ` Boqun Feng
2023-12-01 9:40 ` Peter Zijlstra
2023-12-01 10:36 ` Boqun Feng
2023-12-01 11:05 ` Peter Zijlstra
2023-12-01 9:00 ` Peter Zijlstra
2023-12-01 9:52 ` Boqun Feng
2023-11-29 16:42 ` Alice Ryhl
2023-11-29 16:45 ` Peter Zijlstra
2023-11-30 15:02 ` Benno Lossin
2023-11-29 17:06 ` Christian Brauner
2023-11-29 21:27 ` Alice Ryhl
2023-11-29 23:17 ` Benno Lossin
2023-11-30 10:48 ` Christian Brauner
2023-11-30 12:10 ` Alice Ryhl
2023-11-30 12:36 ` Christian Brauner
2023-11-30 14:53 ` Benno Lossin
2023-11-30 14:59 ` Greg Kroah-Hartman
2023-11-30 15:46 ` Benno Lossin
2023-11-30 15:56 ` Greg Kroah-Hartman
2023-11-30 15:58 ` Theodore Ts'o
2023-11-30 16:12 ` Benno Lossin
2023-12-01 1:16 ` Theodore Ts'o
2023-12-01 12:11 ` David Laight
2023-12-01 12:27 ` Alice Ryhl
2023-12-01 15:04 ` Theodore Ts'o
2023-12-01 15:14 ` Benno Lossin
2023-12-01 17:25 ` David Laight
2023-12-01 17:37 ` Benno Lossin
2023-11-29 12:51 ` [PATCH 2/7] rust: cred: add Rust abstraction for `struct cred` Alice Ryhl
2023-11-30 16:17 ` Benno Lossin
2023-12-01 9:06 ` Alice Ryhl
2023-12-01 10:27 ` Christian Brauner
2023-12-04 15:42 ` Alice Ryhl
2023-11-29 13:11 ` [PATCH 3/7] rust: security: add abstraction for secctx Alice Ryhl
2023-11-30 16:26 ` Benno Lossin
2023-12-01 10:48 ` Alice Ryhl
2023-12-02 10:03 ` Benno Lossin
2023-11-29 13:11 ` [PATCH 4/7] rust: file: add `FileDescriptorReservation` Alice Ryhl
2023-11-29 16:14 ` Christian Brauner
2023-11-29 16:55 ` Alice Ryhl
2023-11-29 17:14 ` Alice Ryhl
2023-11-30 9:12 ` Christian Brauner
2023-11-30 9:23 ` Alice Ryhl [this message]
2023-11-30 9:09 ` Christian Brauner
2023-11-30 9:17 ` Alice Ryhl
2023-11-30 10:51 ` Christian Brauner
2023-11-30 11:54 ` Alice Ryhl
2023-11-30 12:17 ` Benno Lossin
2023-11-30 12:33 ` Christian Brauner
2023-11-30 16:40 ` Benno Lossin
2023-12-01 11:32 ` Alice Ryhl
2023-11-29 13:12 ` [PATCH 5/7] rust: file: add `Kuid` wrapper Alice Ryhl
2023-11-29 16:28 ` Christian Brauner
2023-11-29 16:48 ` Peter Zijlstra
2023-11-30 12:46 ` Christian Brauner
2023-12-06 19:59 ` Kent Overstreet
2023-12-08 16:26 ` Peter Zijlstra
2023-12-08 19:58 ` Kent Overstreet
2023-12-08 5:28 ` comex
2023-12-08 16:19 ` Miguel Ojeda
2023-12-08 17:08 ` Nick Desaulniers
2023-12-08 17:37 ` Miguel Ojeda
2023-12-08 17:43 ` Boqun Feng
2023-12-08 20:43 ` Matthew Wilcox
2023-12-09 7:24 ` comex
2023-11-30 9:36 ` Alice Ryhl
2023-11-30 10:52 ` Christian Brauner
2023-11-30 10:36 ` Peter Zijlstra
2023-12-06 20:02 ` Kent Overstreet
2023-12-07 7:18 ` Greg Kroah-Hartman
2023-12-07 7:46 ` Kent Overstreet
2023-11-30 16:48 ` Benno Lossin
2023-11-29 13:12 ` [PATCH 6/7] rust: file: add `DeferredFdCloser` Alice Ryhl
2023-11-30 17:12 ` Benno Lossin
2023-12-01 11:35 ` Alice Ryhl
2023-12-02 10:16 ` Benno Lossin
2023-12-05 14:43 ` Alice Ryhl
2023-12-05 18:16 ` Alice Ryhl
2023-11-29 13:12 ` [PATCH 7/7] rust: file: add abstraction for `poll_table` Alice Ryhl
2023-11-30 17:42 ` Benno Lossin
2023-12-01 11:47 ` Alice Ryhl
2023-11-30 22:39 ` Boqun Feng
2023-12-01 11:50 ` Alice Ryhl
2023-11-30 22:50 ` Boqun Feng
2023-11-29 16:31 ` [PATCH 0/7] File abstractions needed by Rust Binder Christian Brauner
2023-11-29 16:48 ` Miguel Ojeda
2023-12-06 20:05 ` Kent Overstreet
2023-12-08 16:59 ` Miguel Ojeda
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