From mboxrd@z Thu Jan 1 00:00:00 1970 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 773916A325; Wed, 24 Jul 2024 20:32:51 +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=1721853171; cv=none; b=GMqouoa+wB14jGYi5lBvplF9Drd8Cntg9XTYViWk4JNl+fvlsI6R42bIsN6JI5i8Ey34Tpt5Qeft95IXW/zg5TBNiSY8WgS1Qy0wNGbcacWFQnnB3PQEFAgMwIKk5L4L2rxXUUZYaWGT2N4ytbuzY9xCc3okSLEgz0AkPpJGxIE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721853171; c=relaxed/simple; bh=aMn98SjH3IZ9bjl+8IXsiVppV9Tm41peLtZlAfFNBk4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PTkgYpaC9dt2H14Kth3auMZlmC4BUcGrjtaZXFriYjAQ9rAlmfoTPy7+p0yT9Cg7ryyNcIKP1eVCAqAV/Ahx+G7hvBte6o6/OPnwmv1M6XnhxVPR9dJavRZWvpPi8UzydtZdYD9XhnDBX91QYHBPob/doxNThBN1pRMc5va1Oas= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NiJ6/9QS; 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="NiJ6/9QS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BCA8AC32781; Wed, 24 Jul 2024 20:32:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721853171; bh=aMn98SjH3IZ9bjl+8IXsiVppV9Tm41peLtZlAfFNBk4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=NiJ6/9QSMaxY8aTVfL+EY8OPRr9GHh5Pq767MwZ9SVpg3YHBkDmGmq2qWrjqEjbjJ 70q+61abPXwFFuqsbuW6On8V7ln+4QeqVPz/F71uS+vTq8a111e+5I2AFN8l+atgdA OBZF3Qse3vU5ajFzLJx3U8zIUQqOktqnev5MPaA7YLa21BaW8Ywxi3ZK2MG+rVcvMp j7o6AZPPBX9x4afSw5bpvhevG9Grpin1G6PbII6/W4G7SdCAUvCDaRMtA7cxWCHw5Q XbbynSDoShB2iAqrgu/VSQcemu9RXjAfoeSQG5wM/PcO/XxIl3o6cMIWvecL3l6lWP RAolo696nW11Q== Date: Wed, 24 Jul 2024 22:32:41 +0200 From: Danilo Krummrich To: Heghedus Razvan Cc: 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, 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 Subject: Re: [PATCH v2 16/23] rust: alloc: implement `collect` for `IntoIter` Message-ID: References: <20240723181024.21168-1-dakr@kernel.org> <20240723181024.21168-17-dakr@kernel.org> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jul 24, 2024 at 02:35:46PM +0000, Heghedus Razvan wrote: > On Tue Jul 23, 2024 at 9:10 PM EEST, Danilo Krummrich wrote: > > 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. > Well that's a shame, so I guess collecting a Filter or Map is not possible. Not with the Rust's `FromIterator` trait, unfortunately. However, once we have other collectable data structures in place, we can come up with a kernel compatible version of the `FromIterator` trait and implement against it. > > > > > 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 @@ > > > > //! Implementation of [`Vec`]. > > > > -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 = ManuallyDrop::new(self); > > + let ptr = me.ptr; > > + let buf = me.buf; > > + let len = me.len; > > + let cap = 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 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 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 count of elements. > > + /// > > + /// # Examples > > + /// > > + /// ``` > > + /// let v = kernel::kvec![1, 2, 3]?; > > + /// let mut it = v.into_iter(); > > + /// > > + /// assert_eq!(it.next(), Some(1)); > > + /// > > + /// let v = it.collect(); > > + /// assert_eq!(v, [2, 3]); > > + /// > > + /// # Ok::<(), Error>(()) > > + /// ``` > > + pub fn collect(self) -> Vec { > > + let (mut ptr, buf, len, mut cap) = self.into_raw_parts(); > > + let has_advanced = ptr != buf.as_ptr(); > > + > > + if has_advanced { > > + // SAFETY: Copy the contents we have advanced to at the beginning 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 = buf.as_ptr(); > > + } > > + > > + // This can never fail, `len` is guaranteed to be smaller than `cap`. > > + let layout = core::alloc::Layout::array::(len).unwrap(); > > + > > + // SAFETY: `buf` points to the start of the backing buffer and `len` is guaranteed to be > > + // smaller than `cap`. Depending on `alloc` this operation may shrink the buffer or leaves > > + // it as it is. > > + ptr = match unsafe { A::realloc(Some(buf.cast()), layout, GFP_KERNEL) } { > Here you use `GFP_KERNEL` flag directly. Shouldn't this be an argument of `collect` function? Even though we only ever ask the allocator to shrink the buffer (or keep it as it is), it should be, good catch! > > > + // If we fail to shrink, which likely can't even happen, continue with the existing > > + // buffer. > > + Err(_) => ptr, > > + Ok(ptr) => { > > + cap = len; > > + ptr.as_ptr().cast() > > + } > > + }; > > + > > + // SAFETY: If the iterator has been advanced, the advanced elements have been copied to > > + // the beginning of the buffer and `len` has been adjusted accordingly. `ptr` is guaranteed > > + // to point to the start of the backing buffer. `cap` is either the original capacity or, > > + // after shrinking the buffer, equal to `len`. `alloc` is guaranteed to be unchanged since > > + // `into_iter` has been called on the original `Vec`. > > + unsafe { Vec::from_raw_parts(ptr, len, cap) } > > + } > > } > > > > impl Iterator for IntoIter > > -- > > 2.45.2 > >