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Date: Thu, 30 Nov 2023 16:40:08 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: 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>,
Greg Kroah-Hartman <gregkh@...uxfoundation.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 4/7] rust: file: add `FileDescriptorReservation`
On 11/29/23 14:11, Alice Ryhl wrote:
> +impl FileDescriptorReservation {
> + /// Creates a new file descriptor reservation.
> + pub fn new(flags: u32) -> Result<Self> {
> + // SAFETY: FFI call, there are no safety requirements on `flags`.
> + let fd: i32 = unsafe { bindings::get_unused_fd_flags(flags) };
> + if fd < 0 {
> + return Err(Error::from_errno(fd));
> + }
I think here we could also use the modified `to_result` function that
returns a `u32` if the value is non-negative.
> + Ok(Self {
> + fd: fd as _,
> + _not_send_sync: PhantomData,
> + })
> + }
> +
> + /// Returns the file descriptor number that was reserved.
> + pub fn reserved_fd(&self) -> u32 {
> + self.fd
> + }
> +
> + /// Commits the reservation.
> + ///
> + /// The previously reserved file descriptor is bound to `file`. This method consumes the
> + /// [`FileDescriptorReservation`], so it will not be usable after this call.
> + 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()) };
> +
> + // `fd_install` consumes both the file descriptor and the file reference, so we cannot run
> + // the destructors.
> + core::mem::forget(self);
> + core::mem::forget(file);
Would be useful to have an `ARef::into_raw` function that would do
the `forget` for us.
--
Cheers,
Benno
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