From nobody Thu Sep 19 21:58:51 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 C9D561BCA0F; Wed, 11 Sep 2024 22:56:20 +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=1726095380; cv=none; b=I8SXTQw4h7mUT2GzbRX9IenPg3st+FnJ2HBOUpVjrn6qP3USVdX/o8FtzX96nSltl0oLjEL/j1BWfffw2JP2F7z0/lvXIcxDU9w+5iPjIEmbcEFLbw5/twfVfMN3Hjdb5Tw3AArtWFbSlSgAB4ibTGRSVVGqiXkXQyxW6IHHsq0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726095380; c=relaxed/simple; bh=d0GTO9ovdr9mLJZ1kH3EJFt21UVQxchmojeAlHWWgj8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=IvIBGzhixKX4lNCeqWcarwrN0pow+tIYiQkVmDNnY0+iy4T9s7/8MC9dXiceYC6ENu1pz3FwmxyT3tZHiQQFX9UDJ0RmzfjvRNqpWQb9cI0Cgh1/qIw93+dmS36CWw4axxVq43Cy9iA6Pe7fBDJF2AZSTDD3RM7XKCjdGglkxMA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HNs5tm92; 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="HNs5tm92" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CD080C4CEC0; Wed, 11 Sep 2024 22:56:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1726095380; bh=d0GTO9ovdr9mLJZ1kH3EJFt21UVQxchmojeAlHWWgj8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HNs5tm92QKne4wWPulUe3fcINVeehDTsWYP7OKbBuDAFJioQkoDs4xtPbMxWiphQb PZ2Xb2cE86reASaruvlmCSipU1rMPqObS0eRNUwsW3pQIH8bTigMxzP0QNorxbtwi8 hKr2oRBWsQAcxalCvk4SXGAdIuxQQwKJ55ChGFBQ9wdJEpSw8/TByF2JJfW8LlU+vH CAmR/f1U71SlL4T+Om9uVQWQFDPHSwlZ/trHlxvTVa6bmYEB2DMK7/UVMEpjm0Vexc Svc8EMpnLgkW2ZbarbI+b/qasorJz8jaeNpZWcGpm/AUYy3l9X/e/y/DOhuqfGCJKZ t8uAn5K+Ub5pQ== 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, 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 v7 15/26] rust: alloc: implement `collect` for `IntoIter` Date: Thu, 12 Sep 2024 00:52:51 +0200 Message-ID: <20240911225449.152928-16-dakr@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240911225449.152928-1-dakr@kernel.org> References: <20240911225449.152928-1-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. Reviewed-by: Alice Ryhl Signed-off-by: Danilo Krummrich --- rust/kernel/alloc/kvec.rs | 86 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs index e91761c5c52d..686e969463f8 100644 --- a/rust/kernel/alloc/kvec.rs +++ b/rust/kernel/alloc/kvec.rs @@ -690,6 +690,92 @@ 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`. + /// + /// # 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(GFP_KERNEL); + /// assert_eq!(v, [2, 3]); + /// + /// # Ok::<(), Error>(()) + /// ``` + /// # Implementation Details + /// + /// 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. + pub fn collect(self, flags: Flags) -> 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 { + // Copy the contents we have advanced to at the beginning of t= he buffer. + // + // SAFETY: + // - `ptr` is valid for reads of `len * size_of::()` bytes, + // - `buf.as_ptr()` is valid for writes of `len * size_of::= ()` bytes, + // - `ptr` and `buf.as_ptr()` are not be subject to aliasing r= estrictions relative to + // each other, + // - both `ptr` and `buf.ptr()` are properly aligned. + 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, flags)= } { + // 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 buff= er. + // - `cap` is either the original capacity or, after shrinking the= buffer, equal to `len`. + // - `alloc` is guaranteed to be unchanged since `into_iter` has b= een called on the original + // `Vec`. + unsafe { Vec::from_raw_parts(ptr, len, cap) } + } } =20 impl Iterator for IntoIter --=20 2.46.0