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b=ID+VTQPgxM4/fo/86PhXM8wRLmUNRAGD0AtIR9PtyYSxsVsHuIDvWngmOC+r+/vdl cIN5C0KpCslxLORbqND66Zfvihy6aQlgFRHQSOk+wpPpD6no4Yud3FS3rT5/CDIs+Q BXWO+4zgoIp3+nxfgwueV/3Up8duKjAUksUMzqgF9+qdt+ovvcXwaop8+MVbGixguk J37SZmf69xbVFHxg4sKet5BDZPN8wgDPz2zaed4SF2pBsXmPcOIYsKi3/lRW5i0dhD GYikD+tDejphoiiin0o0ZiQI8f3sVZyMcYBKWRWvI1mrEHnXAvU4qMpi8FZ/YZw/ab ZS9nCCDnFf1ig== 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 v4 17/28] rust: alloc: implement `collect` for `IntoIter` Date: Mon, 5 Aug 2024 17:19:36 +0200 Message-ID: <20240805152004.5039-18-dakr@kernel.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240805152004.5039-1-dakr@kernel.org> References: <20240805152004.5039-1-dakr@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 7DA4E10001A X-Stat-Signature: nzz75p1979q81cxbjkgncemh8rmqpxmn X-Rspam-User: X-HE-Tag: 1722871311-538663 X-HE-Meta: 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 N65qx1PV +aDoOz93Sw0eYLKnIbgqTS2uZH7UQka9P2l82GH8w1Jqh56UZ0Yk1SUWnBJtWyfvzfE9FQ5grjAg7NCcQFvB5Wmd4aFMkX1kcwKVKxfXTqnSmBRLpnOM2jXhmIru8r92XalNp4CH+K7tGf1VgMDrtpf1W/fq5iEZuoV8LNf14lbjc1svEWOXjRnxipW0ESktq3ajYtacOhee/Bq/y0XJPr9gLaPb0b9Gwizu4XCcVzzxMN/os9G5BGfweVR5naawJOMj9rG9enwGUiUy1In/aHvRkPjUgV24AzwHWR6zUeMXNOKL3Vx9kCOXFQurPP0iqQ0f3YVxXYMxpnrw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 51426e0b28e0..160c6b3868fe 100644 --- a/rust/kernel/alloc/kvec.rs +++ b/rust/kernel/alloc/kvec.rs @@ -644,6 +644,84 @@ 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(GFP_KERNEL); + /// assert_eq!(v, [2, 3]); + /// + /// # Ok::<(), Error>(()) + /// ``` + pub fn collect(self, flags: Flags) -> 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, flags) } { + // 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