From nobody Thu Sep 19 01:11:26 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B286015CD60; Tue, 23 Jul 2024 18:12:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721758343; cv=none; b=G9dgZgmjo0Mc8JcHKhGLZFaEZiCkS/yJ6wP69VFHt6o/Rh67f6n9+ik66IMiTiqvcxxU/FWYyzZoz4MLSmq88r0xkFpOLwKDrwV27Vc/kFTvVgMT0FV1JQC1NGqTRDMYqBntdcQz5kbsfh+J1VhOE1GJoA0xjLLS4M9wxARPcU4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721758343; c=relaxed/simple; bh=ycTccZRzwhnWmuZYl2yN5kvt/i9Cmr0VW9EfC/7UA54=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JeYBZ2WWJ5vTOwPP0ubuv0WtFJ6SV1TKnwUy45qxjPqDszysVyzclp+gUHgfLbI6xRwux2LT8z5FV7e1v1eZ17m+KvM2U9HPcPr9Pa4r/Fpzu3JZM+gOqIbBIbR1v0+YmepYv+JxP1lcVy5hvkioooAjTfIPoR7ltcJLRuUZitA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=b6wl7t6V; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="b6wl7t6V" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65FCAC4AF0E; Tue, 23 Jul 2024 18:12:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721758343; bh=ycTccZRzwhnWmuZYl2yN5kvt/i9Cmr0VW9EfC/7UA54=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=b6wl7t6Vnx/yEyZvnuZI8xejX+EMDqYiC6oixtqi/wC6OK3zAe8IYO6hbfIV8Ma17 RLaPGrXo7rmTxgNQsHHTld9g3PEBCvQv37hOE6l4eGRycKf3zDA6Ds91DfzKciIRJa xrJISI+8CpDkcJvGGqsiv2f8NIOZoQaebEQGdV8TPKFui73DeJNhn/C0DdSKZD+W1N EWZuuocRtFqpv8tzGfD4nbDUCqzsDaPU0a8cpGlp1G6UQn08G1EvnJDiAkj/QNDeRa 4r+Y1p3whwd4s+LMBVGqd0ARazU1VyOY7jVc6P2Sel5BoUB+gK/Nn+ud9PeO7QF458 d5aCwheSsNJqw== From: Danilo Krummrich To: ojeda@kernel.org, alex.gaynor@gmail.com, wedsonaf@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, benno.lossin@proton.me, a.hindborg@samsung.com, aliceryhl@google.com, akpm@linux-foundation.org Cc: daniel.almeida@collabora.com, faith.ekstrand@collabora.com, boris.brezillon@collabora.com, lina@asahilina.net, mcanal@igalia.com, zhiw@nvidia.com, acurrid@nvidia.com, cjia@nvidia.com, jhubbard@nvidia.com, airlied@redhat.com, ajanulgu@redhat.com, lyude@redhat.com, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-mm@kvack.org, Danilo Krummrich Subject: [PATCH v2 16/23] rust: alloc: implement `collect` for `IntoIter` Date: Tue, 23 Jul 2024 20:10:05 +0200 Message-ID: <20240723181024.21168-17-dakr@kernel.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240723181024.21168-1-dakr@kernel.org> References: <20240723181024.21168-1-dakr@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently, we can't implement `FromIterator`. There are a couple of issues with this trait in the kernel, namely: - Rust's specialization feature is unstable. This prevents us to optimze for the special case where `I::IntoIter` equals `Vec`'s `IntoIter` type. - We also can't use `I::IntoIter`'s type ID either to work around this, since `FromIterator` doesn't require this type to be `'static`. - `FromIterator::from_iter` does return `Self` instead of `Result`, hence we can't properly handle allocation failures. - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle additional allocation flags. Instead, provide `IntoIter::collect`, such that we can at least convert `IntoIter` into a `Vec` again. Signed-off-by: Danilo Krummrich --- rust/kernel/alloc/kvec.rs | 80 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 79 insertions(+), 1 deletion(-) diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs index fbfb755b252d..5c317931e14c 100644 --- a/rust/kernel/alloc/kvec.rs +++ b/rust/kernel/alloc/kvec.rs @@ -2,7 +2,7 @@ =20 //! Implementation of [`Vec`]. =20 -use super::{AllocError, Allocator, Flags}; +use super::{flags::*, AllocError, Allocator, Flags}; use crate::types::Unique; use core::{ fmt, @@ -633,6 +633,84 @@ impl IntoIter fn as_raw_mut_slice(&mut self) -> *mut [T] { ptr::slice_from_raw_parts_mut(self.ptr, self.len) } + + fn into_raw_parts(self) -> (*mut T, NonNull, usize, usize) { + let me =3D ManuallyDrop::new(self); + let ptr =3D me.ptr; + let buf =3D me.buf; + let len =3D me.len; + let cap =3D me.cap; + (ptr, buf, len, cap) + } + + /// Same as `Iterator::collect` but specialized for `Vec`'s `IntoIter`. + /// + /// Currently, we can't implement `FromIterator`. There are a couple o= f issues with this trait + /// in the kernel, namely: + /// + /// - Rust's specialization feature is unstable. This prevents us to o= ptimze for the special + /// case where `I::IntoIter` equals `Vec`'s `IntoIter` type. + /// - We also can't use `I::IntoIter`'s type ID either to work around = this, since `FromIterator` + /// doesn't require this type to be `'static`. + /// - `FromIterator::from_iter` does return `Self` instead of `Result<= Self, AllocError>`, hence + /// we can't properly handle allocation failures. + /// - Neither `Iterator::collect` nor `FromIterator::from_iter` can ha= ndle additional allocation + /// flags. + /// + /// Instead, provide `IntoIter::collect`, such that we can at least co= nvert a `IntoIter` into a + /// `Vec` again. + /// + /// Note that `IntoIter::collect` doesn't require `Flags`, since it re= -uses the existing backing + /// buffer. However, this backing buffer may be shrunk to the actual c= ount of elements. + /// + /// # Examples + /// + /// ``` + /// let v =3D kernel::kvec![1, 2, 3]?; + /// let mut it =3D v.into_iter(); + /// + /// assert_eq!(it.next(), Some(1)); + /// + /// let v =3D it.collect(); + /// assert_eq!(v, [2, 3]); + /// + /// # Ok::<(), Error>(()) + /// ``` + pub fn collect(self) -> Vec { + let (mut ptr, buf, len, mut cap) =3D self.into_raw_parts(); + let has_advanced =3D ptr !=3D buf.as_ptr(); + + if has_advanced { + // SAFETY: Copy the contents we have advanced to at the beginn= ing of the buffer. + // `ptr` is guaranteed to be between `buf` and `buf.add(cap)` = and `ptr.add(len)` is + // guaranteed to be smaller than `buf.add(cap)`. + unsafe { ptr::copy(ptr, buf.as_ptr(), len) }; + ptr =3D buf.as_ptr(); + } + + // This can never fail, `len` is guaranteed to be smaller than `ca= p`. + let layout =3D core::alloc::Layout::array::(len).unwrap(); + + // SAFETY: `buf` points to the start of the backing buffer and `le= n` is guaranteed to be + // smaller than `cap`. Depending on `alloc` this operation may shr= ink the buffer or leaves + // it as it is. + ptr =3D match unsafe { A::realloc(Some(buf.cast()), layout, GFP_KE= RNEL) } { + // If we fail to shrink, which likely can't even happen, conti= nue with the existing + // buffer. + Err(_) =3D> ptr, + Ok(ptr) =3D> { + cap =3D len; + ptr.as_ptr().cast() + } + }; + + // SAFETY: If the iterator has been advanced, the advanced element= s have been copied to + // the beginning of the buffer and `len` has been adjusted accordi= ngly. `ptr` is guaranteed + // to point to the start of the backing buffer. `cap` is either th= e original capacity or, + // after shrinking the buffer, equal to `len`. `alloc` is guarante= ed to be unchanged since + // `into_iter` has been called on the original `Vec`. + unsafe { Vec::from_raw_parts(ptr, len, cap) } + } } =20 impl Iterator for IntoIter --=20 2.45.2