From nobody Thu Sep 19 15:58:15 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 373C51AC8A6; Fri, 16 Aug 2024 00:13:44 +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=1723767225; cv=none; b=CrrSkvzil9whnAA6/zjl5jTupNltcNhG8uPlXsAynHsEqqxUvCTUwlVN8d0AznKJoodBKvyaU+SrF+fwa49xgjt2d9ey8jCioYk0s3jxh6ldDZQ/huVXU8EXL1JwlXRYA2/EQcUw1N2qKbCZpuksOqPw6DwL3NOw5BLjUBcyHyc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723767225; c=relaxed/simple; bh=I6cUolcDKGiOxN2jlE3/L4Zfc5m68bEHs0e/qmkx1fA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ddZKTcDYZ8y24IZCjM1f47m0VE40hokIy4JnTQHemD30incO4R09pthFfRiZD/PAe2z8qOfNL6Re92SRtMbPWgl37OKVfuPepE/icOaKhYOXaLAn3SlxDf/b/prXJQ3OB8/wLSbNEXoFkXEjjBaqAX7hFq6OTQ+pVPpD5aPJC7c= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YN169jcj; 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="YN169jcj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8C35C4AF09; Fri, 16 Aug 2024 00:13:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1723767224; bh=I6cUolcDKGiOxN2jlE3/L4Zfc5m68bEHs0e/qmkx1fA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YN169jcjN81Cmi6OKpdlT7HPyJDRt6/wiY2aKNkcvQL4eo/KLCVl8/ZBlAuASgG7W 5igkBN3w9Dr1JcrgOrglgcb7FhUOPrn6KPAkgLoMT8Mf+m6qWrvzEkdxOfRrsg5x6D HlpqJH2geyzU4Rb7k4tkg8op+ExRtO4eqi8Yh9DXUs+RGy9kVnGHqUq5N0m8t67CkK YAPnH/iKSYdpk59cNGm5lAZR2tSRqRL7PEaReigmEtyCOuvmiwHE30XEgEebteZkII 1GZXiOyJNWR0VwcgYig+oFSYY6nYQjsRvnXw7d4Kn4Bwv11UFuTLqooJbqLsK61760 3ymAtnrv26/0g== 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 v6 15/26] rust: alloc: implement `collect` for `IntoIter` Date: Fri, 16 Aug 2024 02:10:57 +0200 Message-ID: <20240816001216.26575-16-dakr@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240816001216.26575-1-dakr@kernel.org> References: <20240816001216.26575-1-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 | 78 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs index 3b79f977b65e..ad96f4c3af9e 100644 --- a/rust/kernel/alloc/kvec.rs +++ b/rust/kernel/alloc/kvec.rs @@ -681,6 +681,84 @@ 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(GFP_KERNEL); + /// assert_eq!(v, [2, 3]); + /// + /// # Ok::<(), Error>(()) + /// ``` + 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 { + // 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, 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 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 2.46.0